Symposium at MSE 2020: C02: "Advanced Transmission Electron Microscopy for Materials Science C02: Advanced Transmission Electron Microscopy for Materials Science"

Symposium at MSE 2020: C02: Advanced Transmission Electron Microscopy for Materials Science
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7th International Symposium on Computational Mechanics of Polycrystals, CMCn 2020 and DAMASK User Meeting

7th International Symposium on Computational Mechanics of Polycrystals, CMcn 2020
CMCn2020 The Max-Planck-Institut für Eisenforschung in Düsseldorf is organizing the 7th International Symposium on Computational Mechanics of Polycrystals and we would like to invite you and your research colleagues to participate in this event. This symposium is part of a biannual series of symposia that originated with the establishment of the first joint research group formed between the Max Planck Society and the Fraunhofer Society and investigating Computational Mechanics of Polycrystals. This year the symposium is again combined with the DAMASK User Meeting. DAMASK is the multi-physics simulation software developed at MPIE. The symposium will take place on September 14th and 15th, 2020 in the Max-Planck-Institut für Eisenforschung at Max-Planck-Straße 1, 40237 Düsseldorf, Germany.The DAMASK User Meeting will be held on the following two days, September 16th and 17th at the same location.

BiGmax Online Workshop 2020 on Big-Data-Driven Materials Science

BiGmax Online Workshop 2020 on Big-Data-Driven Materials Science
We are happy to announce and welcome you this year to an online seminar in place for the BiGmax workshop on Big-Data-Driven Materials Science. We were enlightened by your interest in the workshop back then in April. With the global Covid19 pandemic now, the online workshop will be slightly shorter. Currently, two topical sessions are planned with a half-day online seminar for each. One session will be on machine learning and image processing for materials science data. The other session will be on machine learning for and on the development of ab-initio methods. Each session will contain live talks and posters presentations. Aligned with the mission of BiGmax, the workshop will connect materials scientists with physicists, and experts for machine learning, scientific computing, and data science.We will contact all participants who had originally planned to join and contribute to the workshop. We will send an email invitation to every single one of you with the program and the details on how to participate. With that we hope to reconvene online this year and are very much looking forward to hearing, discussing, and learning from your contributions. [more]

Sustainable Metallurgy

MPIE Seminar
Metallic materials which have enabled progress over thousands of years and are produced in huge quantities (e.g. 1.8 billion tons of steels per year), are now facing severe and in part abrupt limits set by sustainability constraints and the associated legislative measures. Accelerated demand for structural alloys in key areas such as energy, construction, infrastructure, safety, mobile communication and transportation creates growth rates of up to 200% until 2050. Yet, most of these materials are energy, greenhouse gas and pollution intense when extracted, produced and manufactured. The lecture provides an introduction to this field and reviews approaches to improve the sustainability of and through structural metallic alloys. It reports about progress in direct sustainability for different steps along the value chain including CO2-reduced primary production; recycling; scrap-compatible alloy design; contaminant tolerance of alloys; and improved alloy longevity through corrosion protection, damage tolerance and repairability for longer product use. It is also shown how structural materials enable improved energy efficiency through reduced weight, higher thermal stability, and better mechanical properties. The respective leverage effects of the individual measures on rendering structural alloys more sustainable are described. [more]

Nanobrücken 2020: A Nanomechanical Testing Conference

Nanobrücken 2020: Nanomechanical Testing Conference & Bruker User Meeting
The Max-Planck-Institut für Eisenforschung GmbH (MPIE) and Bruker are pleased to announce Nanobrücken 2020: Nanomechanical Testing Conference & Bruker User Meeting, which will take place February 4–6 at MPIE located in Düsseldorf, Germany. Please save the date in your calendar and register to secure your seat at Nanobrücken 2020. [more]

Non-monotonic rheology of a magnetic liquid crystal system in an external fieldNon-monotonic rheology of a magnetic liquid crystal system in an external field

MPIE Seminar
Utilizing molecular dynamics simulations, we report a non-monotonic dependence of the shear stress on the strength of an external magnetic eld (H) in a liquid-crystalline mixture of magnetic and non-magnetic anisotropic particles.This non-monotonic behavior is in sharp contrast with the well-studied monotonic H-dependency of the shear stress in conventional ferro uids, where the shear stress increases with H until it reaches a saturation value. We relatethe origin of this non-monotonicity to the competing eects of particle alignment along the shear-induced direction, on the one hand, and the magnetic eld direction on the other hand. To isolate the role of these competing eects,we consider a two-component mixture composed of particles with eectively identical steric interactions, where the orientations of a small fraction, i.e. the magnetic ones, are coupled to the external magnetic eld. By increasing Hfrom zero, the orientations of the magnetic particles show a Freederickz-like transition and eventually start deviating from the shear-induced orientation, leading to an increase in shear stress. Upon further increase of H, a demixingof the magnetic particles, from the non-magnetic ones, occurs which leads to a drop in shear stress, hence creating a non-monotonic response to H. Unlike the equilibrium demixing phenomena reported in previous studies, the demixingobserved here is neither due to size-polydispersity nor due to a wall-induced nematic transition. Based on a simplied Onsager analysis, we rather argue that it occurs solely due to packing entropy of particles with dierent shear- or magnetic-eld-induced orientations. [more]

5th NRW-APT User Meeting

The Max-Planck-Institut für Eisenforschung GmbH in Düsseldorf is organizing the 5th NRW-APT user meeting on November the 07th 2019 and we would like to invite you and your research colleagues to participate in this event. This meeting will bring together scientists from North Rhine-Westphalia dealing with APT technique or correlating APT with other techniques. We want to discuss problems and share knowledge regarding sample preparation, measurement conditions, data reconstruction & analysis, etc..If you and your colleagues would like to attend this event, then please register before October 18th 2019. There are limited places only. We are looking forward to see you in Düsseldorf! [more]

International Workshop on Advanced and In-situ Microscopies of Functional Nanomaterials and Devices, IAMNano 2019

The workshop aims to provide a forum for researchers who are interested in applying advanced imaging and spectroscopy methods of electron microscopy, including aberration-corrected, in situ, environmental and low-voltage electron microscopy, to topical issues in materials science and engineering, in nanoscience, in soft matter research, in interface and surface science, and in biomaterials research. As these methods are of fundamental importance in virtually all technological fields, contributions are invited that address the broad spectrum of current materials research. Novel methodological developments will be discussed as well as topical areas of research on thin films, bulk materials, surfaces, materials at the nanoscale and at the interface between the physical and life sciences, for understanding structure‐property relationships of materials, as well as for metrology. Selected topics will be introduced by invited keynote speakers during the plenary sessions. A poster session provides room for the presentation and discussion of current research. [more]

Pushing the boundaries of micro and nanomechanics

Pushing the boundaries of micro and nanomechanics
Current level of miniaturization in everyday devices indicates that micro and nano architectures have become functional elements in electronics and diminutive mechanical-based systems. Yet, the potential of such multiscale functional elements is not fully realized due to incomplete understanding of their deformation mechanisms in application relevant loading conditions such as high strain rates (mimicking drops and impacts) and high/cryo temperatures. Even the state-of-the-art micro/nano mechanical testers are currently incapable of conducting experiments in such harsh loading environments. Thus, the mechanical properties of micro and nano scale materials are largely unknown at strain rates beyond 0.1/s and temperatures beyond 250°C or below room temperature. This premise forms the motivation of my research vision: “To investigate the small scale plasticity and failure mechanisms under extreme conditions, using novel micro/nano mechanical experimental platforms”. In this presentation, I will highlight three aspects from my previous research: i) Instrumentation and protocols for conducting extreme micro and nanomechanical testing, ii) Case studies of micro/nano scale metals and amorphous materials tested at high strain rates and high temperature combinations and iii) Sample manufacturing techniques for high through-put micro/nanomechanical testing. Specifically, I will present the work on in situ nanomechanical testing at high strain rates enabled by a custom-built hybrid piezo and microelectromechanical systems (MEMS) based testing system and the case-study on silver nanowires tested at strain rates upto ~200/s. Further, the instrumentation and protocols for micromechanical testing at combinations of high strain rates and extreme temperatures will be explained, with a case study on fused silica and silicon micropillar compression at strain rates upto 1000/s and temperatures upto 400°C. The final part of the talk will focus on my recent work with unique manufacturing methods: two-photon lithography/electrodeposition combination and localized electrodeposition, which are capable of manufacturing ideal damage-free test-beds of metallic micro/nano architectures including arrays of micropillars, microsprings and complex microlattices. [more]

Manipulation of individual defects in 2D and layered Materials

Manipulation of individual defects in 2D and layered Materials
Defects decisively influence the properties of virtually any material. It is therefore desirable to control the occurrence and properties of defects down to the atomic scale. While many methods have been successfully developed to influence defects in an indirect way (e.g. heat treatments, ion implantation, etc...), the direct interaction and control over individual defects is still in its infancy. This method of direct control promises to greatly deepen our understanding of the properties of single defects and may even lead to the discovery of novel physical phenomena. In this work, we demonstrate ways of directly controlling and testing individual defects in the form of dislocations and grain boundaries. Bilayer graphene, being the thinnest material to host extended dislocations, serves as the perfect model material for dislocation manipulation. Using a precisely controlled micromanipulator it is possible to directly interact with individual line defects in situ in scanning electron microscopy1. Besides showcasing fundamental properties of dislocations such as line tension and interaction with free edges, a novel switching reaction at threading dislocations was observed. For the manipulation further developments were made in the form of a mechanical cleaning approach as well as a setup for diffraction in SEM2. Furthermore, using a layered crystal (VSe2) the sliding behavior of twist grain boundaries is analyzed. By cutting and compressing inclined micropillars made from a single-crystalline specimen, twist grain boundaries can be created. After compression, grain boundary sliding can be tested using micromanipulation combined with spring-table based force measurement. Ultra-low sliding friction and self-retraction is observed for twist grain boundaries. Finally, an experimental pathway towards the analysis of the atomic-scale grain-boundary sliding mechanisms in layered systems will be demonstrated. 1. Schweizer, P., Dolle, C. & Spiecker, E. In situ manipulation and switching of dislocations in bilayer graphene. Sci. Adv. 4, (2018). 2. Schweizer, P., Denninger, P., Dolle, C., Rechberger, S. & Spiecker, E. Low Energy Nano Diffraction (LEND) – Bringing true Diffraction to SEM. Microsc. Microanal. 25, 450–451 (2019). [more]

Multi-scale design and analyses of advanced materials: Experimental approaches

Multi-scale design and analyses of advanced materials: Experimental approaches
When a 100-tonne steel forging die fails during industrial processing; the root causes are often localised to small length scales. Advanced materials therefore need to be designed at the characteristic material length scales; incorporating environmental considerations such as local defects or temperature, amongst many others. This talk highlights two recent examples of project work led by Dr. Best with industrial partners. The first focuses on the bottom-up design of ceramic thin-film coatings using nano- and micro-mechanical approaches, where high-temperature fracture toughness measurements were primarily utilised to design multi-layered protective coatings with improved lifetimes for steel forging dies. The second addresses the top-down analysis of a 3D-printed bulk metallic glass, where the connection between bulk toughness and local short range order was linked through in-situ micro-pillar compression. In both examples, the interplay between structure-property relations at multiple length scales is emphasised. [more]

Close Packed Phases in Nickel-Based Superalloys - Investigation by Diffusion Multiples

Close Packed Phases in Nickel-Based Superalloys - Investigation by Diffusion Multiples
Precipitation of close-packed phases is a common problem of modern nickel-based superalloys, containing refractory or higher melting point elements such as Re, Ru, Cr, Mo and W. Thus, a fundamental understanding of phase stabilities of close-packed phases governed by these elements is of high relevance regarding the improvement of databases for nickel-based superalloys and the development of next generation superalloys. Diffusion multiples have been used to investigate the ternary systems Ni-Mo-Cr, Ni-Mo-Re and Ni-Mo-Ru at 1100°C and 1250°C. A novel manufacturing technique for diffusion multiples based on a two-step casting process will be presented. EDS and EBSD measurements lead to isothermal sections of phase diagrams. Additionally investigations of certain quaternary systems will be shown. Solubility limits of sigma-, P-, delta- and hcp-phase were determined. Adaptation of the MatCalc database to the experimental results by project partners in Vienna lead to significant improvements in predictions for multicomponent alloys. [more]

Lessons learned from nano scale specimens tested by MEMS based apparatus

Lessons learned from nano scale specimens tested by MEMS based apparatus
Materials at small scale behave differently from their bulk counterparts. This deviation originates from the abundance of interfaces at small scale. Quantifying the properties and revealing the underlying mechanisms requires experiments with small samples in situ in analytical chambers. However, small size poses the challenge of sample handling, but offers the opportunity of in situ inspection of mechanism during testing in analytical chambers. In order to overcome the challenge and take advantage of the opportunity, we developed a MEMS based micro scale testing stage where the sample and the stage are co-fabricated. The stage suppresses any misalignment error in loading by five orders of magnitude. The stage allows in situ inspection of samples during testing in SEM and TEM. We employed the stage in two scenarios. (1) Exploring the effect of microstructural heterogeneity, such as grain size and orientation, on the deformation mechanisms in nano grained polycrystalline metals. Here the test specimens are free standing thin films subjected to uniaxial tension. We found that heterogeneity introduces two apparently dissimilar, but fundamentally linked, anomalous behaviors. The samples undergo plastic deformation during unloading, i.e., exhibit Bauschinger type phenomenon. Upon unloading, they recover a significant part of plastic deformation with time. The underlying mechanism, verified by in situ TEM inspection, is as follows: during loading, the relatively larger grains undergo plastic deformation and relax by employing dislocations, while the smaller grains remain elastically deformed. During unloading, the smaller grains apply reverse stress on the larger grains causing reverse plasticity resulting in a deviation from linear stress-strain response. Upon complete unloading, the residual stress of the elastically strained small grains continue to apply reverse stress on the larger grains resulting in biased jumps of dislocation in the larger grains and strain recovery. (2) Exploring the effect of size on brittle to ductile transition (BDT) temperature (540C) in single crystal silicon. Here the sample is a micro scale single crystal silicon beam subjected to bending which limits the high stress region to a small volume in the sample, and minimizes the probability of premature failure from random flaws. We found that silicon indeed deforms plastically at small scale at temperatures much lower than 540C. Ductility is achieved through a competition between fracture stress and the stress needed to nucleate dislocations from the surface. Our combined SEM, TEM and AFM analysis reveals that as a threshold stress is approached, multiple dislocation nucleation sites appear simultaneously from the high stressed surface of the beam with a uniform spacing of about 200 nm between them. Dislocations then emanate from these sites with time lowering the stress while bending the beam plastically. This process continues until the effective shear stress drops and dislocation activities stop. A simple mechanistic model is presented to relate dislocation nucleation with plasticity in silicon. [more]

Molecular dynamics simulations and beyond for plasticity and wear of metals

Molecular dynamics simulations and beyond for plasticity and wear of metals
While the general principles underlying the plastic response of metals are mostly understood—especially for the crystalline state—advanced tailoring of their properties and the development of novel, high-performance materials requires detailed insights into the mechanisms at the atomic scale. This talk will discuss how computer models and simulations can be the tools of choice to discover such mechanisms in the context of our work on amorphous metals and wear. I will first introduce some concepts of molecular dynamics computer simulations and how we used them to investigate the plastic deformation of metallic crystal/glass composites, where localized and collective shear transformations govern the macroscopic behavior. In particular, I will address the questions of when and how precipitates can enhance the mechanical properties of metallic glasses and what the difference between a nanocomposite and a nanocrystal is. In the second part, I will discuss our current work on wear of materials and what to do when the time and length scale limitations of molecular dynamics become a problem. When surfaces in contact slide relative to each other, they are in fact only in contact in some small areas due to their roughness. At this length scale, we employ molecular dynamics with different model materials in order to elucidate how detachment of matter occurs in the form of individual particles, which in the end comes down to the details of nanoscale plasticity and fracture processes. In order to gain insights on relevant figures of merit for applications, though, we have to collect statistics of wear particle formation at the meso to macroscale, using continuum methods. Since some of this work is in its early stages, I will finish the talk with a preview of promising future research directions and methods, such as taking the microstructure evolution of the material into account. [more]

Using analytical electron microscopy to study microstructural evolution and its effect on structural & functional properties

Using analytical electron microscopy to study microstructural evolution and its effect on structural & functional properties
Analytical electron microscopy is applied to study elementary processes which govern micro- and nanostructural evolution and their effect on structural and functional properties in two-phase material systems. Modern computational alloy design for application relevant blade materials operating at high temperatures require reliable diffusion data, which consider the realistic superalloy condition. A new method will be presented to study diffusion kinetics in compositionally complex superalloys using intrinsic nano-diffusion-couples that are exposed to in situ and ex situ annealing experiments. Magnetic two-phase Heusler compounds are fascinating because they enable to study the influence of misfit induced strain gradients at interfaces on magnetic texture formation. Micro-engineering of misfit induced strains into a functional magnetic composite represents a novel approach which may well pave the way towards a new era of exploiting flexomagnetism, an area which has yet to be explored experimentally. [more]

MPIE-Kolloquium: Sustainable Molten Salt Route for Electro-extraction & Electro-refining of Low-grade Ores to Yield High Purity Titanium

Sustainable Molten Salt Route for Electro-extraction & Electro-refining of Low-grade Ores to Yield High Purity Titanium
Titanium is the fourth most abundant engineering material in the Earth’s crust. Although it has many beneficial properties, the cost of extraction remains a challenge and over 90% of high grade titanium is derived from the expensive and time-consuming Kroll Process. Electro-refining methods show promise but present their own special challenges. We present an overview and update of a novel molten salt process to extract and refine low-grade ores to produce high-grade powder titanium. Titanium oxycarbide produced by carbothermic reduction is electro-refined in a molten eutectic bath of NaCl:KCl salt. Anodic dissolution causes the Ti product to be plated out in the form of a dendritic product which collects on the cathode while impurities are retained in the anode. A gentle introduction to the process will be given and recent studies to apply the method to include the effect of using ilmenite and ilmenite/rutile blends as a feedstock, as well as the applicability of the process to other metals, specifically niobium (Nb) and vanadium-baring minerals presented. [more]

Exploring the Solar System: From the Nano to Astronomical Scale

MPIE Colloquium
Microscopy, by definition, is the science of using a microscope to observe objects that are unseen by the naked eye. However, astronomical objects such as planets, moons and comets or asteroids are easily identifiable in the night sky, yet scientists are increasingly relying on microscopic methods to investigate their composition, structure, and determine their origins. Whether this is via extra-terrestrial exploration with satellites, landers or rovers, or by studying returned astromaterials in the laboratory itself, the use of microscopy within the diverse field of planetary science is quickly becoming the norm. Correlating multiple microscopic and spectroscopic methods within the scanning electron microscope (SEM) when studying meteorites allows us to extend the spectrum from nano or micro-scale imaging at one end, all the way up to the astronomical scale at the other. For example, the Mars Science Laboratory (MSL) rover, Curiosity, landed in Gale Crater; a region that had been heavily investigated using satellite data from previous mission Mars Odyssey. Using similar infrared microscopic methods in the laboratory, we can distinguish the same compositions within Martian meteorites as those directly observed on the Martian surface.Recent studies (e.g. Stephen et al. 2014; King et al. 2018) have combined traditional SEM imaging and analysis (energy-dispersive spectroscopy - EDS, electron-backscatter diffraction – EBSD, wavelength-dispersive spectroscopy – WDS) with micro Fourier transform infrared (μFT-IR) to inform the varied geological histories of meteorite parent bodies, including aqueous alteration on both asteroids and planets. Further studies combine SEM & TEM imaging with other X-ray techniques at varying scales, i.e. X-ray microscopy (XRM) or X-ray tomography (XRT), to help classify new meteorites and examine potential parent bodies throughout the Solar System (MacArthur et al. 2019).Non-destructive, microscopic methods allow for detailed investigation through multiple volumes that would otherwise be inaccessible without damaging the specimens themselves; a crucial consideration when working with limited material from an extra-terrestrial source. Correlating microscopy techniques across instruments, scales and disciplines is perhaps one of the best approaches to studying these astromaterials, and fully unravelling their geological history, as well as their journey to Earth.References:King et al. (2018) Investigating the history of volatiles in the solar system using synchrotron infrared micro-spectroscopy' Infrared Physics and Technology 94, 244-249.MacArthur et al. (2019) Mineralogical constraints on the thermal history of Martian regolith breccia Northwest Africa 8114, Geochimica et Cosmochimica Acta 246, 267-298.Stephen et al. (2014) Mid-IR mapping of Martian meteorites with 8-micron spatial resolution, Meteoritics and Planetary Science, pp A381. [more]

Micromechanics of bone: fundamental research and clinical applications

Micromechanics of bone: fundamental research and clinical applications
In this talk, the work within the Biomechanics Research Team at the Laboratory for Mechanics of Materials and Nanostructures of Empa on micromechanics of bone will be presented. Fundamental research on the failure mechanisms of bone on the microscale as a function of loading mode will be discussed. Nanostructural characterization is combined with micromechanical experimentation and mechanical modeling to allow identifying structure-property relationships in this complex nanocomposite. Recent technical developments allowing experiments with well defined boundary and environmental conditions in a broad strain rate range are employed to investigate the effect of water on the strain rate dependence of bone on the microscale. Furthermore, direct clinical applications of this fundamental research for assessing bone quality of patients in clinical studies will be discussed. [more]

Deformation mechanisms in metals under a tribological load

In 1950, Bowden and Tabor pointed out that in metallic tribological contacts the majority of the dissipated energy is spend to change the contacting materials’ microstructures. This – in part – explains why most metals show a highly dynamic subsurface microstructure under the shear load imposed by a sliding contact. In order to understand these processes, the elementary mechanisms accommodating the shear strain and acting in the material need to be revealed and understood. In this presentation, three examples of research avenues following this hypothesis will be given. During the very early stages of sliding, dislocations show an interesting self-organization phenomenon. How these structures interfere with twin boundaries and what might be learned about the dislocation motion under the slider will be the first part of the talk. Second, we will address how the high entropy alloy (HEA) CoCrFeMnNi reacts to a tribological load and whether there is evidence for mechanisms specific to HEAs. Third, we will focus our attention at tribo-chemically activated oxidation process studied for high-purity copper. [more]

Joint MPIE / ER-C workshop on recent advances and frontiers of atomic scale characterization

Joint MPIE / ER-C workshop on recent advances and frontiers of atomic scale characterization
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Aberration-corrected STEM and ultra-high energy resolution EELS

Aberration-corrected STEM and ultra-high energy resolution EELS
Electron microscopy has advanced very significantly in the last two decades. Electron-optical correction of aberrations, which we introduced for the scanning transmission electron microscope (STEM) in 1997, has allowed STEMs to reach sub-Å resolution from 2002 on. It has led to new STEM capabilities, such as atomic-resolution elemental mapping, and determining the type of single atoms by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDXS). More recently, we have focused on Ultra-High Energy Resolution EELS (UHERE). We have developed a monochromator and a spectrometer that use multipolar optics similar to the optics of aberration correctors, plus several stabilization methods, and we have reached <5 meV energy resolution at 30 keV primary energy. This has opened up a new field: vibrational spectroscopy in the electron microscope. When collecting large-angle scattering events, vibrational spectroscopy can lead to sub-nm spatial resolution, and when collecting small-angle scattering angle events, it can produce EEL spectra with the electron beam positioned tens of nm away from the probed area. The second geometry has led to a powerful new technique: aloof vibrational analysis of materials, which avoids significant radiation damage. Even more recently, we have focused on combining the analytical techniques with in-situ sample treatment. Our progress includes cooling the sample to liquid N2 temperature in a side-entry holder capable of reaching better than 1 Å resolution. My talk will review these developments, and illustrate them by application examples. [more]

Making quantum transport visible in thermoelectric Bi2Te3 nanoparticles

Bi2Te3, Sb2Te3, and Bi2Se3, well established thermoelectric materials, are also three-dimensional (3D) topological insulators (TI) exhibiting a bulk bandgap and highly conductive, robust, gapless surface states. While the transport properties of 3D TIs are of utmost importance for potential applications, they are difficult to characterize. The reason is that transport in those materials is always dominated by bulk carriers. Still, the signature of the nontrivial electronic band structure on the thermoelectric transport properties can be evidenced in transport experiments using nanostructures with a high surface-to-volume ratio. Using a nanoparticle-based materials’ design, the highly porous macroscopic sample features a carrier density of the surface states in a comparable order of magnitude as the bulk carrier density. Further, the sintered nanoparticles impose energetic barriers for the transport of bulk carriers (hopping transport), while the connected surfaces of the nanoparticles provide a 3D percolation path for surface carriers. Within this work, I will discuss the nanoparticle processing as well as the transport properties of these combined thermoelectric and 3D TI samples. [more]

Nanoindentation based investigations of PLC-type plastic instability

Nanoindentation based investigations of PLC-type plastic instability
Portevin Le-Chatelier (PLC) effect is a type of plastic instability that results in severe strain localization, reduction in ductility and formation of surface striations during forming operations. Understanding the underlying microscopic mechanism(s) that govern it requires detailed experimental investigations of the relationships between the phenomenon and local microstructural constituents. Most current models of PLC, both phenomenological and theoretical, are based on descriptions of mesoscopic observations and global responses observed in stress-strain curves. More predictive (or physically based) models will require investigations at the microstructural length-scales. In this talk, it will be shown that the gap in understanding of the microscopic origins and macroscopic manifestations of PLC can be bridged by nanoindentation testing. Specifically, it will be shown that by exploiting the high resolution of force and displacement measurements and the site-specific capabilities of the nanoindenter, coupled with complimentary microstructural characterization techniques, we are able to gain new insight into critical aspects of the PLC effect, including its anisotropy, underlying governing mechanisms and associated activation parameters. [more]

The Heusler System (For Thermoelectric Application): How You Can Use the periodic table As A Lego Box To Build The States You Are Interested In

The Heusler System (For Thermoelectric Application): How You Can Use the periodic table As A Lego Box To Build The States You Are Interested In
The periodic table becomes one hundred years old just this year. The family of Heusler compounds uses nearly all the elements in the Periodic Table to allow for the design of materials with all sorts of properties. These include: hard and soft magnets, shape memory and magnetocaloric metals, thermoelectric semiconductors, topological insulators, and Weyl semimetals. These are just a few examples of more than 1000 known members of this remarkable class of materials that can display such a wide range of extraordinary multifunctional and tunable properties. Many more remain to be discovered! Just like a box of Lego bricks we can put together certain atoms (valence electrons), arranged in a particular symmetry, to achieve a desired electronic energy band structure. A necessary precondition for such a straightforward approach is a single particle picture: this allows for the prediction of many properties in this versatile class of materials, and equally enables “inverse design”. In my talk I will discuss the simple rules that we have learned to date and what the future might portend for further additions to the large and ever-growing Heusler family. [more]

HEA symposium "High entropy and compositionally complex alloys" at DPG Spring Meeting 2019 in Regensburg

HEA symposium "High entropy and compositionally complex alloys" at DPG Spring Meeting 2019 in Regensburg
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4th International Conference on Medium and High Manganese Steels

4th International Conference on Medium and High Manganese Steels
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TEM Studies on Materials with a Negative Poisson’s Ratio

TEM Studies on Materials with a Negative Poisson’s Ratio
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Computational Modeling of Moving Boundary Problems

MPIE Seminar
The focus of this presentation is on computational methods for moving boundary/interface problems and its applications including fracture, fluid structure interaction, inverse analysis and topology optimization. First, two computational methods for dynamic fracture will be presented, i.e. the cracking particles method (CPM) and dual-horizon peridynamics (DH-PD). These methods do neither require a representation of the crack surface and associated complex crack tracking algorithms nor criteria for crack branching and crack interactions. They also do not need to distinguish between crack nucleation and crack propagation. Complex discrete fracture patterns are the natural outcome of the simulation. The performance of these methods will be demonstrated by several benchmark problems for non-linear quasi-brittle dynamic fracture and adiabatic shear bands. Subsequently, a local partition of unity-enriched meshfree method for non-linear fracture in thin shells -- based on Kirchhoff-Love theory -- exploiting the higher order continuity of the meshfree approximation will be presented. The method does not require rotational degrees of freedom and the discretization of the director field. This also drastically simplifies the enrichment strategy accounting for the crack kinematics. Based on the meshfree thin shell formulation, an immersed particle method (IPM) for modeling fracturing thin-structures due to fluid-structure interaction is proposed. The key feature of this method is that it does not require any modifications when the structure fails and allows fluid to flow through the openings between crack surfaces naturally.The last part of the presentation focuses on inverse analysis and topology optimization with focus on computational materials design of piezoelectric/flexoelectric nanostructures and topological insulators. In the first application of piezo/flexoelectricity, we use isogeometric basis functions (NURBS or RHT-splines) in combination with level sets since C1 continuity is required for the numerical solution of the flexoelectric problem. Hence, only the electric potential and the displacement field is discretized avoiding the need of a complex mixed formulation. The level set method will be used to implicitly describe the topology of the structure. In order to update the level set function, a stabilized Hamilton-Jacobi equation is solved and an adjoint method is employed in order to determine the velocity normal to the interface of the voids/inclusions, which is related to the sensitivity of the objective function to variations in the material properties over the domain. The formulation will be presented for continua though results will also be shown for thin plates. The method will be extended to composites consisting of flexible inclusions with poor flexoelectric constants. Nonetheless, it will be shown that adding these flexible inclusions will result in a drastic increase in the energy conversion factor of the optimized flexoelectric nanostructures. In the second application, we propose a computational methodology to perform inverse design of quantum spin hall effect (QSHE)-based phononic topological insulators. We first obtain two-fold degeneracy, or a Dirac cone, in the bandstructure using a level set- based topology optimization approach. Subsequently, four-fold degeneracy, or a double Dirac cone, is obtained by using zone folding, after breaking of translational symmetry, which mimics the effect of strong spin-orbit coupling and which breaks the four-fold degeneracy resulting in a bandgap, is applied. We use the approach to perform inverse design of hexagonal unit cells of C6 and C3 symmetry. The numerical examples show that a topological domain wall with two variations of the designed metamaterials exhibit topologically protected interfacial wave propagation, and also demonstrate that larger topologically- protected bandgaps may be obtained with unit cells based on C3 symmetry. [more]

Nanoscale thermodynamics at complex oxide surfaces and interfaces for application in electronics, sensing, and energy conversion

Perovskite oxides exhibit a plethora of fascinating electronic material properties covering an exceptionally wide range of phenomena in solid state and surface physics. This has led to tremendous efforts to functionalize these materials in applications for energy technology, gas sensing, and electronics. Layered in an atomically defined epitaxial heterostructures and superlattices, diverse properties of perovskites can be combined on the nanoscale level. In such structures, even new functionality can arise at interfaces of layered materials, exhibiting properties that are absent in the bare bulk materials. In our approach, we utilize atomically-defined layer growth to obtain desired material properties. However, on top of that, we employ thermodynamic engineering of crystal defects as a unique approach to functionalize material properties at surfaces and interfaces: Even at material synthesis conditions close to perfection, device properties are often determined by imperfection, hence, by lattice disorder and crystal defects. As we discuss, we can intentionally control defect structure in nanoscale devices, by developing and utilizing thermodynamic routes to trigger surface and interface reactions in confined systems. While historically defects were seen as something to be avoided, a change of paradigm is required in the field of complex oxides today: In these materials, we can promote functionality, such as metallicity in nominally insulating compounds, by atomic defect-management. Therefore, rather than avoiding defect formation, it is an essential necessity to control and to utilize defect formation in oxides on the nanoscale. Here, we discuss fundamental aspects of lattice disorder effects in bulk oxides, and elaborate the special character of defect formation in thin films, surfaces and interfaces. Focusing on SrTiO3 as a perovskite model system, we will crosslink fundamental perspectives on lattice disorder to actual applications, addressing different examples, such as resistive switching memories, high-mobility electron gases and induced magnetism, oxygen sensors, and electro-catalysts. [more]

Opportunities for bcc refractory-metal superalloys

Reinforcement with ordered intermetallic precipitates is a potent strategy for the development of strength alongside damage tolerance and is central to the success of fcc nickel-based superalloys. Such a strategy is equally of interest within bcc-based systems for their increased melting point and acceptable cost. However, only limited studies have been made on refractory metal (RM) or titanium based alloys strengthened by ordered-bcc precipitates (e.g. B2 or L21). Are such “bcc superalloys” possible? Do they offer useful properties? In this talk, opportunities for refractory-metal-based superalloys systems will be discussed, including a review of Cr-Ni2AlTi, Mo-NiAl, Ta-(Ti,Zr)2Al(Mo,Nb) and Nb-Pd2HfAl systems together with newly developed alloys. These alloys exploit an extensive two-phase field that exists between A2 (RM,Ti) and B2 TiFe to produce nanoscale precipitate reinforced microstructures that increase strength by over 500 MPa. This work was supported through EUROfusion Researcher Grant & EPSRC Doctoral Prize Fellowships, EPSRC ‘DARE’ (darealloys.org) EP/L025213/1 and Rolls-Royce/EPSRC Strategic Partnership EP/H022309/1 and EP/H500375/1. [more]

Phase Transitions in Non-Equilibrium Metallic Systems

Seminar Talk
Nearly all classes of materials show non-equilibrium phase transitions and the first technological use of quenching metals for designing properties is documented as ~800 BC. However, the decomposition towards equilibrium is still difficult to understand due to the strong non-equilibrium kinetics. Two examples are discussed: First the decomposition of a quenched super saturated solid solution and second the decomposition of a quenched metallic melt. In the first example the technological important AlMgSi alloys are addressed. Low temperature solute clustering, its implications on aging and the effect of trace elements are discussed. Moreover, it is shown which physical pre-requisites need to be fulfilled to modify diffusion by orders of magnitude and to examine a “diffusion on demand” concept. In the second example the first solid–solid transition via melting in a metal, detected upon the decomposition of a metallic glass, is demonstrated. The transformation path is discussed under its thermodynamic and kinetic prerequisites. Moreover, the capabilities of the applied novel technique of fast scanning calorimetry is addressed. Finally, it is outlined how this technique links the two examples via its potential for in-situ measuring the non-equilibrium vacancy evolution. [more]

Dislocation-based Functionality in Oxides

MPIE Colloquium
Dislocations in oxides are typically heavily charged and are surrounded by compensating electric charges. As such they are kinetically more stable than chemical dopants. Adepalli et al. termed dislocations a means for “one-dimensional doping” [1]. As they are often introduced by mechanical methods, they may also be termed “mechanical doping” or “self-doping”, as the charges derive from local concentration of the matrix elements. In the literature dislocations have been demonstrated to enhance oxygen conductivity [1] and improve the figure of merit of thermoelectrics by reducing thermal conductivity through phonon scattering by dislocations [2]. Dislocations have been suggested to improve interfacial reaction kinetics and have been theoretically predicted to pin domain walls in ferroelectrics. In Darmstadt we have so far focused on establishing a set of techniques to introduce dislocations into single crystals at room temperature or enhanced temperature and to study (dislocation) creep. Structural investigations have been performed by dark-field X-ray diffraction, rocking curve analysis [3], TEM, NMR and EPR techniques. The first property evaluations have been done with respect to electrical and thermal conductivity and domain wall pinning. All this has to be seen with the perspective of a just developing field, with many opportunities, many obstacles and a lot of exciting uncertainty. Select examples will be provided on dislocation structures, electrical and thermal conductivity in SrTiO3 and our first attempts on dislocation creep in BaTiO3. Time provided, I will show 4 slides on the small brother field: “Elastic-deformation tuned conductivity in piezoelectric ZnO." [1] Adepalli, K. K., Kelsch, M., Merkle, R., and Maier, J., "Enhanced ionic conductivity in polycrystalline TiO2 by "one-dimensional doping''," Phys. Chem.Chem. Phys., 16[10] 4942-51 (2014). [2] S. Il Kim, K. H. Lee, H. A. Mun, S. H. Kim, S. W. Hwang, J. W. Roh, D. J. Yang, W. H. Shin, X. S. Li, Y. H. Lee, G. J. Snyder, S. W. Kim, “Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics“, Science, 348, 109-114 (2015). [3] E.A. Patterson, M. Major, W. Donner, K. Durst, K.G. Webber and J. Rödel, „Temperature dependent deformation and dislocation density in SrTiO3 single crystals”, J. Amer. Ceram. Soc., 99, 3411-120 (2016). [more]

Recent Advances in Heat-resistant Structural Material Development with Laves Phases at Oak Ridge National Laboratory

MPIE Colloquium
This presentation provides an overview of recent developmental efforts at Oak Ridge National Laboratory (ORNL) on heat-resistant ferrous materials with Laves-phase strengthening for fossil-fired energy conversion systems. Laves phases are attractive as second-phase strengtheners in Fe-base alloys, including ferritic and austenitic stainless steels, since most of the Fe-rich Laves phases (Fe2M intermetallic compounds, M: Nb, Mo, W, Zr, Ti, etc.) are thermodynamically equilibrated with BCC- or FCC-Fe solid solution. Because of the characteristics, relatively easy control of second-phase dispersion is expected through a traditional “solution-and-annealing” process combined with proper alloying additions. The thermal stability of the Laves phase precipitates at elevated temperature was found to be controlled and improved through combinations of multiple Laves-phase forming elements, which guides the alloy design and provides effective strengthening of high-temperature structural materials for the extended periods of time. Laves-phase precipitation in Fe-base matrix can be expected in relatively large composition/temperature ranges, which also allows designing the alloys with proper surface protections, such as chromia- or alumina-scale formation on the surface. This leads to proposing and designing new high-temperature structural materials to be used in extreme environments such as Advanced USC or supercritical CO2 cycle applications. The presentation will also introduce various developmental efforts in Fe-base, Cr-base, and Cu-base alloys with Laves-phase strengthening at ORNL in the last decades. Research supported by the U.S. Department of Energy, Office of Fossil Energy, the Crosscutting Research Program. [more]

International Workshop on Laves Phases

International Workshop on Laves Phases
Laves phases constitute the largest class of intermetallic phases. Within the inter-institutional research initiative “The Nature of Laves Phases” of the Max Planck Society (2006-2011) fundamental aspects of Laves phases have been investigated. Since then, advances in high resolution analytical methods and modelling gave new insight. Simultaneously interest in development and application of alloys strengthened by Laves phases has considerably increased. The workshop is devoted to summarise our current understanding of Laves phases and to identify topics for future research.The workshop is jointly organised by Forschungszentrum Jülich, Max-Planck-Institut für Chemische Physik fester Stoffe (Dresden), Tokyo Institute of Technology and Max-Planck Institut für Eisenforschung GmbH (Düsseldorf). [more]

3D Nano-Architected Metamaterials

MPIE Colloquium
Advances in 3D additive manufacturing techniques have enabled the fabrication of nanostructures with remarkable mechanical properties. Using the latest 3D printing techniques, novel material structures with specific architectures, often referred to as metamaterials, can be produced. They can exhibit superior mechanical and physical properties at extremely low mass densities and, thus, expand the current limits of the yet stiff and strong architectures, architectures with high mechanical resilience or with negative Poisson’s ratio. Mechanical size effects were shown to result in extraordinary strength values of different specific architectures. Understanding the underlying characteristics of these complex new materials, such as the deformation and failure mechanisms, and how they impact behavior of the structure, is critical and increasingly challenging. In this presentation, the principles underlying ultra-strong yet light 3D nano-architected metamaterials as well as strategies to tailor their properties will be discussed. [more]

Molecular dynamics on the diffusive time scale

Molecular dynamics on the diffusive time scale
We formulate a theory of non-equilibrium statistical thermodynamics for ensembles of atoms or molecules. The theory is an application of Jayne's maximum entropy principle, which allows the statistical treatment of systems away from equilibrium. In particular, neither temperature nor atomic fractions are required to be uniform but instead are allowed to take different values from particle to particle. In addition, following the Coleman-Noll method of continuum thermodynamics we derive a dissipation inequality expressed in terms of discrete thermodynamic fluxes and forces. This discrete dissipation inequality effectively sets the structure for discrete kinetic potentials that couple the microscopic field rates to the corresponding driving forces, thus resulting in a closed set of equations governing the evolution of the system. We complement the general theory with a variational meanfield theory that provides a basis for the formulation of computationally tractable approximations. We present several validation cases, concerned with equilibrium properties of alloys, heat conduction in silicon nanowires, hydrogen desorption from palladium thin films and segregation/precipitation in alloys, that demonstrate the range and scope of the method and assess its fidelity and predictiveness. These validation cases are characterized by the need or desirability to account for atomic-level properties while simultaneously entailing time scales much longer than those accessible to direct molecular dynamics. The ability of simple meanfield models and discrete kinetic laws to reproduce equilibrium properties and long-term behavior of complex systems is remarkable. [more]

Hydrogen storage in single metal nanocrystals

MPIE Colloquium
[more]

10th European APT Workshop

10th European APT Workshop
In the European atom probe tomography workshop we aim to foster the exchange of new ideas in atom probe tomography and field ion microscopy community, especially those aspects not regularly covered in scientific publications. We therefore put special emphasis on peer-to-peer discussions around poster presentations and provide a choice of tutorials given by renown experts for the advanced atom probe user/scientist. We also aim to integrate scientists that are interested in applying atom probe tomography in an emerging field into the community. This will foster knowledge transfer between new applicatons and fundamental reserach in the physics of APT. We specially invite poster contributions. Details about the scientific and training program will be announced shortly. Registraton deadline is the 26th of October 2018. [more]

Opening Symposium for Advanced S/TEM and APT Facilities

Opening Symposium for Advanced S/TEM and APT Facilities
The Max-Planck-Institut für Eisenforschung GmbH (MPIE) is happy to announce the opening symposium for advanced S/TEM and APT facilities, scheduled on 5th - 6th November 2018. We are pleased to celebrate this inauguration by a stimulating scientific colloquium with renowned experts and friends from all over the world. Topics of the symposium will include:• Development of advanced APT and (S)TEM techniques• New horizons in correlative (S)TEM and APT• Application to catalysis and energy materials• Interface science. We look forward to greeting you in Düsseldorf! [more]

MPIE Workshop: Mechanisms of White Etching Matter Formation

MPIE Workshop: Mechanisms of White Etching Matter Formation
The Max-Planck-Insititut für Eisenforschung in Düsseldorf cordially invites academic and industrial researchers to the workshop on WEM formation, taking place on October 23nd 2018. This workshop will focus on the fundamental materials scientific processes behind this phenomenon. For this we have invited a number of speakers from complementary fields that are crucial for understanding the phenomenon. Topics will range from WEM formation mechanisms in bearings and rails, over WEM generation by heat, surface machining and high pressure torsion, and the role of hydrogen and electric current, to the remarkable resistance of high nitrogen steels to WEC failure. Participants must register till September 30th. The event is financed by the BMBF through grant 03SF0535 and is free of charge. [more]

Atomic Electron Tomography Using Coherent and Incoherent Imaging in (Scanning) Transmission Electron Microscopy

Atomic Electron Tomography Using Coherent and Incoherent Imaging in (Scanning) Transmission Electron Microscopy
[more]

Metal and Alloy Nanoparticles from Ultrafast, Scalable, Continuous Synthesis and their Downstream Integration in Catalysis and Additive Manufacturing

Metal and Alloy Nanoparticles from Ultrafast, Scalable, Continuous Synthesis and their Downstream Integration in Catalysis and Additive Manufacturing
[more]

Symposium "Experiments and Simulations Towards Understanding Tribology Across Length-Scales" at the MSE (Materials Science Engineering)

Symposium "Experiments and Simulations Towards Understanding Tribology Across Length-Scales" at the MSE (Materials Science Engineering)

Exploring Surface Interactions at the Molecular Scale in Tribological Applications Exploring Surface Interactions at the Molecular Scale in Tribological Applications

In this talk the contribution of molecular simulations and in particular non-equilibrium molecular dynamics (NEMD) modelling techniques providing unique insights into the nanoscale behaviour of lubricants is discussed. NEMD has progressed from a tool to corroborate theories of the liquid state to an instrument that can directly evaluate important fluid properties, and is now moving towards a potential design tool in tribology. The key methodological advances which have allowed this evolution will be highlighted. This will be followed by a summary of bulk and confined NEMD simulations of liquid lubricants and lubricant additives, as they have progressed from simple atomic fluids to ever more complex, realistic molecules. Confined NEMD simulations have revolutionised our fundamental understanding of the behaviour of very thin lubricant films between solid surfaces. This includes the density and viscosity inhomogeneities in confined films, as well as important tribological phenomena such as stick-slip and boundary slip. It is also being increasingly employed to study shear localisation behaviour in thicker films subjected to high pressures.The inclusion of chemical reactivity for additives and their adsorption to metal surfaces and oxides will be also discussed with examples given of how Density Functional Theory (DFT) calculations can be used to provide further insight when the focus is on the physics and chemistry that governs film formation. Coupling between molecular and continuum simulation methods for large systems will also be briefly discussed. [more]

Topological Optimization and Textile Manufacturing of 3D Lattice Materials

Topological Optimization and Textile Manufacturing of 3D Lattice Materials
Recent advances in topological optimization methodologies for design of internal material architecture, coupled with the emergence of micro- and nanoscale fabrication processes, 3D imaging, and micron scale testing methodologies, now make it possible to design, fabricate, and characterize lattice materials with unprecedented control. This talk will describe a collaborative effort that employs scalable 3D textile manufacturing, location specific joining, and vapor phase alloying to produce metallic lattices with a wide range of internal architectures, alloy compositions, and mechanical and functional properties. The project involves three length scales. The highest level (component scale) spans centimeters to meters and encompasses gradients in unit cell architecture, porosity, and the creation of sandwich structures. The second level (architectural unit cells) spans tens of microns to millimeters and employs architectural optimization to design the geometry of the braided/woven structure. The smallest level (microstructure) spans nanometers to tens of microns focuses on vapor phase alloying of the wires after textile manufacturing. Topology optimization allows properties to be decoupled and tailored for specific applications. Dramatic enhancements in permeability have been balanced with modest reductions in stiffness and are being used to develop heat exchanger materials with high thermal transport, low impedance, low thermal gradients and high temperature strength. In a parallel effort, architectural designs to maximize both structural resonance and inter-wire friction are also being employed to develop metallic lattices capable of mechanical damping at elevated temperatures. These examples will be used to highlight the benefits to be gained by development of metallic lattice materials with a wide range of tailorable properties. [more]

6th International Symposium on Computational Mechanics of Polycrystals, CMCn 2018 and DAMASK User Meeting

6th International Symposium on Computational Mechanics of Polycrystals, CMCn 2018
CMCn2018 The Max-Planck-Institut für Eisenforschung in Düsseldorf is organizing the 6th International Symposium on Computational Mechanics of Polycrystals and we would like to invite you and your research colleagues to participate in this event. This symposium is part of a biannual series of symposia that originated with the establishment of the first joint research group formed between the Max Planck Society and the Fraunhofer Society and investigating Computational Mechanics of Polycrystals. This year the symposium is again combined with the DAMASK User Meeting. DAMASK is the multi-physics simulation software developed at MPIE. The symposium will take place on September 17th and 18th, 2018 in the Max-Planck-Institut für Eisenforschung at Max-Planck-Straße 1, 40237 Düsseldorf, Germany. The DAMASK User Meeting will be held on the following day, September 19th at the same location. If you and your colleagues would like to attend this event, then please register before July 15th 2018. We emphasize that registration is mandatory and that there are limited places only. Many thanks, we hope to see you in Düsseldorf! [more]

Thermoelectric energy conversion - From waste heat to sustainable energy

Thermoelectric materials can convert waste heat into electricity, which is of significant technological and environmental interest. In my talk I will give a short introduction into the field of thermoelectrics including the measurement of the thermoelectric properties of bulk materials at low and elevated temperatures. I will introduce a selection of general concepts, which allow to improve and optimize thermoelectric materials and I will briefly talk about a selection of new directions in the field, where some of them (will) heavily rely on and benefit from the fields of metallurgy and atom probe tomography (e.g. phase boundary mapping and antiphase boundaries as a new route towards low thermal conductivities). [more]

Use of computational and physical simulation on arc welding heat affected zone microstructure evolution studies

Use of computational and physical simulation on arc welding heat affected zone microstructure evolution studies
The heat affected zone (HAZ) is most commonly the critical part of welding joint and the comprehension of the thermal cycle it suffers during welding and its effects on the final microstructure is fundamental to predict and reduce the properties degradation on that zone. The traditional approach to study the HAZ involves several welding tests varying the principal parameters (voltage, current and welding speed) with subsequent mechanical testing. These welding trials could be very time, material and cost demanding; could not replicate the plant/field true welding conditions (need for small scale/plant no available for research tests) and still may not provide a profound insight on the mechanisms in play as the thermal history would not be evaluated. In this context, it is very interesting to use simulation techniques that have evolve significantly in the last two decades to optimize the research effort. In one side, we have the material computational simulation development, with the use of finite element methods and double ellipsoid heat source model to describe the process (thermometallurgic – mechanical coupling) and methods like CALPHAD, Phase Field and Cellular Automata to describe the microstructure evolution in details. One the other side, there are equipment (Gleeble) capable of applying very rapid and controlled thermo-mechanical cycles (acquired in the computational simulation) to a sample, so to produce physical simulated specimen that represents the HAZ region of interest, enabling more detailed characterization and some mechanical testing in isolated microstructures. This permits some validation of the computational simulation too. Seizing these techniques potential, LNTSold have been developing a series of studies in welding simulation to characterize the HAZ of different steels for oil and gas industry applications. For the X100M API 5L steel pipe, it was simulated on FEA software (Sysweld) the welding process of the pipe (SAW) and the field pipeline assembly (GMAW). The main concern for this steel is the toughness reduction it may be subject to in the HAZ, with possible formation of local brittle zones due to the evolution of very sensible constituents as the martensita-austenite (MA) constituent. From the bibliography reference, the two HAZ critical regions are the coarse grain region and the intercritically re-heated coarse grain region, so it was studied the thermal cycle of these regions with heat input variation in the FEA software. The thermal cycle was then reproduced in Gleeble samples to produce specimens for microscopy (focus on the MA constituent morphology and quantity analysis) and for Charpy impact test, to assess the toughness losses. The results indicate that the MA morphology depends very much on the peak temperature and that its quantity does not seem to control directly the impact resistance. For an AISI 4130 steel connector, it was performed a study with FEA software (Sysweld) and CALPHAD software (JMatPro) of the coarse grain HAZ region of the last welding passes, focusing in the hardness prediction and considering the post-weld heat treatment. A simulated CCT diagram and an experimental one were developed to include phase and hardness prediction in the FEA modelling. Then some heat treatment conditions (temperature x time) were evaluated using CALPHAD, trying to optimize the production time. All welding and the best heat treatment conditions were physically reproduced in Gleeble. The simulated CCT showed initially a good correlation with the experimental one, but the FEA hardness prediction was more precise using the experimental CCT. It was possible to achieve the hardness requirements and even increase the impact resistance with a faster heat treatment with close relation to simulation results. Finally, the welding of a 9% Ni steel pipe with Ni 625 alloy filler metal was also simulated in the FEA software and the different HAZ regions reproduced in Gleeble with dilatometry analysis to study the reversion and retention of austenite, which plays an important role in this steel tenacity. The goal it is also to isolate the microstructure and study its hydrogen embrittlement susceptibility. [more]

Quantification and simulation of slip transfer across grain boundaries in near-cube oriented aluminum and meso-scale elastic strain heterogeneity in titanium

Heterogeneous deformation in metallic polycrystals arises from several factors, including anisotropy in elastic properties and plastic slip. The ability to accurately simulate heterogeneous deformation requires physically based models of slip that includes grain boundary properties, as grain boundaries are usually barriers to slip. As slip transfer across boundaries occurs in some boundaries, grain boundary properties have been installed in a dislocation density based crystal plasticity model to enable slip transfer, and used to examine idealized bicrystal tensile samples. This code will be used to simulate deformation of annealed pure aluminum foil multicrystal experiments, in order to examine thresholds for slip transfer. An analysis of slip transfer events indicates that for near-cube oriented grains, the threshold is higher than observed in hexagonal materials, and potential reasons for this will be discussed. Secondly, as computational simulations of polycrystals normally assume a zero-stress initial condition, this assumption is questionable in non-cubic metals where the coefficient of thermal expansion (CTE) is anisotropic. To assess the effect of the anisotropic CTE on initial stress states, two pure titanium samples with different textures were examined using in-situ high energy x-ray diffraction microscopy to measure the evolution of the internal stresses in each grain during heating and cooling. These data show a significant change in expansion rates in the <a> and <c> directions at about 700 C. A simulation of this experiment shows good agreement with experimentally measured data, indicating that it is possible to start a simulation with a good estimate of the internal stress state arising from the anisotropic CTE. This work was supported by grants from US DOE/BES and the Community of Madrid [more]

Iron Nitrides and Carbides: Phase Equilibria, Crystallography, and Phase Transformations

MPIE Colloquium
[more]

Heterogeneous Catalysis: Not Always Supported Metallic Nanoparticles

MPIE Colloquium
[more]

Gordon Research Conference “Thin Film and Small Scale Mechanical Behavior”

Gordon Research Conference “Thin Film and Small Scale Mechanical Behavior”

Predicting phase behavior of grain boundaries with evolutionary algorithms and machine learning

[more]

Mini‐symposium “Experimental Micromechanics and Nanomechanics” at the “10th edition of the European Solids Mechanics Conference”

Mini‐symposium “Experimental Micromechanics and Nanomechanics” at the “10th edition of the European Solids Mechanics Conference”

Martensitic Microstructure: Modern Art or Science?

MPIE Colloquium
[more]

Additive Manufacturing, 3D Printing, Porosity and Synchrotron Experiments

Additive Manufacturing, 3D Printing, Porosity and Synchrotron Experiments
3D printing of metals has advanced rapidly in the past decade and is used across a wide range of industry. Many aspects of the technology are considered to be well understood in the sense that validated computer simulations are available. At the microscopic scale, however, more work is required to quantify and understand defect structures, which affect fatigue resistance, for example. Synchrotron-based 3D X-ray computed microtomography (µXCT) was performed at the Advanced Photon Source on a variety of AM samples using both laser (SLM) and electron beam (EBM) powder bed; this showed systematic trends in porosity. Optical and SEM characterization of powders used in additively manufacturing (AM) reveals a variety of morphologies and size distributions. Computer vision (CV), as a subset of machine learning, has been successfully applied to classify different microstructures, including powders. The power of CV is further demonstrated by application to detecting and classifying defects in the spreading in powder bed machines, where the defects often correspond to deficiencies in the printed part. In addition to the printed material, a wide range of powders were measured and invariably exhibited porosity to varying degrees. Outside of incomplete melting and keyholing, porosity in printed parts is inherited from pores or bubbles in the powder. This explanation is reinforced by evidence from simulation and from dynamic x-ray radiography (DXR), also conducted at the APS. DXR has revealed a wide range of phenomena, including void entrapment (from powder particles), keyholes (i.e., vapor holes) and hot cracking. Keyhole depth is linearly related to the excess power over a vaporization threshold. Concurrent diffraction provides information on solidification and phase transformation in, e.g., Ti-6Al-4V and stainless steel. High Energy (x-ray) Diffraction Microscopy (HEDM) experiments are also described that provide data on 3D microstructure and local elastic strain in 3D printed materials, including Ti-6Al-4V and Ti-7Al. The reconstruction of 3D microstructure in Ti-6Al-4V is challenging because of the fine, two-phase lamellar microstructure and the residual stress in the as-built condition. Both the majority hexagonal phase and the minority bcc phase were reconstructed. [more]

Quantum Chemistry in Position Space and Chemical Bonding in Intermetallic Compounds

MPIE Colloquium
[more]

Symposium “Mechanical Properties and Adhesion 45th ICMCTF (International Conference on Metallurgical Coatings and Thin Films)

Symposium “Mechanical Properties and Adhesion 45th ICMCTF (International Conference on Metallurgical Coatings and Thin Films)

In Situ Investigation of the Dynamic Evolution of Materials and Interfaces in Energy Storage Systems

Abstract: In energy storage devices, materials evolve from their initial state due to electrochemical reactions and interfacial instabilities at interfaces. To develop batteries with improved safety, energy density, and lifetime, it is critical to understand transformation mechanisms and degradation processes within these devices. In my research group, multiscale in situ techniques are used to reveal reaction mechanisms and interfacial transformations to guide the development of better batteries and other devices. Our recent work has used in situ transmission electron microscopy (TEM) to reveal phase transformation pathways and mechanical degradation/fracture when sulfide nanocrystals react with different alkali ions (lithium, sodium, and potassium). Surprisingly, mechanical fracture was found to occur only during reaction with lithium, despite larger volume changes during reaction with sodium and potassium. Since fracture is a known capacity decay mechanism in batteries, this result indicates that these materials are useful for the development of novel, high-energy sodium and potassium batteries. In a different study, operando synchrotron X-ray diffraction methods were used to precisely measure crystallographic strain evolution in battery electrode materials; this technique enables measurements beyond what is possible with TEM. In the final portion of the presentation, in situ X-ray photoelectron spectroscopy (XPS) experiments that reveal chemical evolution of solid-state interfaces in energy storage and electronic materials will be presented. Overall, this research demonstrates how fundamental understanding of dynamic processes can be used to guide the design and engineering of new materials and devices with high energy density and long lifetime. [more]

High Temperature Materials - Recent Developments for Future Challenges

MPIE Colloquium
The introduction of the talk provides an overview on materials research in IEK-2 (Institute for Energy and Climate Research, Materials Characterization) in Forschungszentrum Jülich. Selected examples of metallic and ceramic high performance materials for applications in energy conversion and storage systems are introduced, e.g. new materials for membranes, coatings or turbine blades. The main part of the presentation focuses on recent developments of novel high temperature Mo‑Si‑B materials, which are potential candidates to substitute Ni-base superalloys in power plants or aircraft turbines. Such alloys include a Mo solid solution phase as well as silicides, which are creep and oxidation resistant, but very brittle phases. The challenge is to balance the properties at ambient temperatures and high temperatures to tailor these multi-phase alloys for the use in a wide temperature range up to 1200°C and various mechanical loads. Concepts of material design, i.e. alloying strategy and process-microstructure-properties relationships are presented in terms of improved mechanical properties and oxidation resistance. The effect of additional elements on the mechanical properties, like fracture toughness, ductile-brittle-transition and creep resistance will be described. The presentation also includes the formation of isotropic and anisotropic microstructures by powder metallurgy, directional solidification and additive manufacturing. The latter process is quite challenging due to ultra-high melting temperatures of >2000°C and corresponding difficulties during melting and rapid cooling. [more]

Topic day “Novel materials and alloy design - microstructure property relationship” at the Metallkundekolloquium/Arlbergkolloquium

Topic day “Novel materials and alloy design - microstructure property relationship” at the Metallkundekolloquium/Arlbergkolloquium

“Experimental Nanomechanics” at the “16th European Mechanics of Materials Conference”

“Experimental Nanomechanics” at the “16th European Mechanics of Materials Conference”

Topical session “Mechanical Properties at Small Scales” at the DPG-Spring Meeting 2018

Topical session “Mechanical Properties at Small Scales” at the DPG-Spring Meeting 2018

Nanoindentation for Investigating Dynamics of Shear Bands in Metallic Glasses

MPIE Colloquium
Deformation in metallic glasses occurs by initiation and propagation of multiple thin shear bands. This mode is rather difficult to analyse since generally, a single band soon propagates to a large extent in the specimen leading to a catastrophic failure. Exceptions are for example in creep tests under very low stress and moderate temperature or in confined deformation tests. We used instrumented nano-indentations to perform series of independent experiments at room temperature on a Mg65Cu12.5Ni12.5(Ce75La25)10 metallic glass. Loading part of the curves shows serrations which size and duration were measured using an automatic procedure. To make analyses consistent, data were considered only in the domain with similar strain rates, in the range of 1 to 0.3 s-1. Times between successive serrations follow a normal distribution characterizing a random occurrence of deformation burst in the glass. It was then conjectured, first that serration occurs through activation of appropriate zone in the glass that should naturally scale with a multiple of an elementary domain size characterizing the deformation mechanism. Second, as activated zones leading to serration are very few in the glass, the model should be described by the Poisson statistics. Data analyses reveals that serration size are well fitted by a Poisson distribution. The model predict an elementary size which scale with that of the activation volume of 3 atoms, measured from creep test at constant load in the same series of experiments. Eventually, energy dissipated during serration is analyzed as to define shear bands dynamics characteristics.Depending on time, I shall present the use of nano-indention for investigating dynamics of nanoporous metallic materials deformation. N. Thurieau, L. Perriere, M. Laurent-Brocq, Y. Champion, J. Appl. Phys., 118 (2015) 204302. [more]

Topic day “Dislocation based plasticity – experiment vs. simulation” at “The Schöntal Symposium Dislocation-based Plasticity” of the DFG Forschergruppe FOR 1650

Topic day “Dislocation based plasticity – experiment vs. simulation” at “The Schöntal Symposium Dislocation-based Plasticity” of the DFG Forschergruppe FOR 1650

Mechanism of Enhanced Ductility in Mg Alloys

Mechanism of Enhanced Ductility in Mg Alloys
Pure Mg has low ductility due to strong plastic anisotropy and due to a transition of <c+a> pyramidaldislocations to a sessile basal-oriented structure [1]. Alloying generally improves ductility; for instance, Mg-3wt.%RE (RE=Y, Tb, Dy, Ho, Er) alloys show relatively high ductility [2], and typically larger than mostcommercial Mg-Al-Zn alloys at similar grain sizes. Possible concepts for ductility in alloys include thereduction of plastic anisotropy due to solute strengthening of basal slip, the nucleation of <c+a> from basal I1stacking faults, the prevention of the detrimental <c+a> transformation to sessile structures, and the weakeningof strong basal texture by some solute/particle mechanisms. Here, we introduce a new mechanism ofpyramidal cross-slip from the lower-energy Pyr. II plane to the higher energy Pyr. I plane as the key toductility in Mg and alloys [3]. Certain alloying elements reduce the energy difference between Pyr. I and IIscrew dislocations, accelerating cross-slip that then leads to rapid dislocation multiplication and alleviates theeffects of the undesirable pyramidal-to-basal dissocation. A theory for the cross-slip energy barrier ispresented, and first-principles density functional theory (DFT) calculations, following methods in [4], are usedto compute the necessary pyramidal stacking fault energies as a function of solute type for many solutes in thedilute concentration limit. Predictions of the theory then demonstrate why Rare Earth solutes are highlyeffective at very low concentrations, and generally capture the trends in ductility and texture evolution acrossthe full range of Mg alloys studied to date. The new mechanism then points in directions for achievingenhanced ductility across a range of non-RE alloys.[1] Z. Wu, W.A. Curtin, Nature 526 (2015) 62-67[2] S. Sandlobes, et al., Acta Materialia 59 (2011) 429-439; Acta Materialia 70 (2014) 92–104[3] Z. Wu, R. Ahmad, B. Yin, S. Sandlobes, and W. A. Curtin, Science 359, 447-452 (2018).[4] B. Yin, Z. Wu, and W. A. Curtin, Acta Materialia 136 (2017) 249-261. [more]

Early stages of high temperature oxidation and sulphidation studied by synchrotron X-ray diffraction and spectroscopy

Early stages of high temperature oxidation and sulphidation studied by synchrotron X-ray diffraction and spectroscopy
Ferritic high temperature alloys are widely used as boiler tube and heat exchanger materials in thermal power plants. All technologies have in common that the applied materials are exposed to different temperatures, process pressures and reactive atmospheres which lead to a change of the material properties and a further degradation of the material. Material changes caused by ageing in highly corrosive and toxic gases such as SO2 are mainly studied ex situ after the reaction is finished.The presentation will focus on a novel approach to study high temperature oxidation and sulphidation of alloys aged in a strongly corrosive environment in real time by energy dispersive X-ray diffraction (EDXRD). A special designed corrosion reactor was used to combine high temperature gas corrosion experiments with the collection of diffraction pattern. For this technique high energetic white X-ray radiation (10-100 keV) was used instead of conventional monochromatic radiation. It enables us to study crystallization procedures on short and medium time scales (1 min < t < 24 h) as a function of process time.X-ray diffraction is not phase sensitive for structural very similar oxide phases such as Fe2O3 and Cr2O3. To enlighten the formation mechanism of protective Cr2O3 at high temperature in corrosive atmosphere for different ferritic alloys an experimental setup for X-ray absorption near edge structure spectroscopy (XANES) in corrosive environment was developed and put into operation. The presentation will provide an overview of the possibilities of high temperature corrosion analysis using synchrotron-based X-ray diffraction and spectroscopy techniques. [more]

"Mechanics meets Energy VI” symposium at Kloster Steinfeld/Eifel

"Fundamentals of mechanical response" at the Conference on Electronic and Advanced Materials

Fundamentals of mechanical response

Atomistic modeling of grain boundary segregation in transition metals

Atomistic modeling of grain boundary segregation in transition metals
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4th NRW-APT User Meeting

The Max-Planck-Institut für Eisenforschung GmbH in Düsseldorf is organizing the 4th NRW-APT user meeting on November the 23rd 2017 and we would like to invite you and your research colleagues to participate in this event. This meeting will bring together scientists from North Rhine-Westphalia dealing with APT technique or correlating APT with other techniques. We want to discuss problems and share knowledge regarding sample preparation, measurement conditions, data reconstruction & analysis, etc. If you and your colleagues would like to attend this event, then please register before November 6th 2017. There are limited places only. We are looking forward to see you in Düsseldorf! [more]

Synthesis and characterization of tungsten-based composites for high-temperature applications

Synthesis and characterization of tungsten-based composites for high-temperature applications
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Insights into the Role of Mechanics on Diffusion-Controlled Phase Transformations using Phase Field Models

MPIE Colloquium
The role played by the microstructures ensuing from phase transformations on the mechanical properties is now very well documented and thoroughly studied, in particular in metallic alloys. Although there is also a large number of works devoted to the reverse, i.e. the influence of mechanics on the microstructure formation and evolution, a general picture is still lacking, in particular when the phase transformations are diffusion-controlled. Indeed, drawing such a general picture requires to address at the same time the issues related to both mechanical behavior and phase transformations, as well as to address new issues arising from the tight coupling between evolving interfaces and evolving strain/stress fields.Besides the well-known modification of two-phase thermodynamic equilibrium by elasticity, as explored by Larché and Cahn (e.g. [10]) and Voorhees and Johnson (e.g. [9]), the trends are less obvious concerning the morphological evolutions when the chemical and mechanical driving forces are competing to reduce the overall free energy of the materials.In this contribution, an attempt will be made to draw some trends by examining several situations in different types of alloys where the different contributions that mechanics encompasses are decoupled. For that purpose, we will resort to extensive calculations with phase field models that have been specifically developed [1,7].First we will discuss the role of elasticity on the shape selection of precipitates, beyond the classical results of hard precipitates in a soft matrix against soft precipitates in a hard matrix, that are relevant only for isotropic elasticity.Indeed, we will show how the anisotropy of the elastic energy arising from either the moduli or the eigenstrain is crucial for the shape selection, even for diffusion-controlled transformation at high temperatures where it is usually believed that elasticity is totally relaxed by plasticity. The examples supporting our analysis will concern cuboidal ordered precipitates in Ni-base superalloys [6] and acicular structures in alloys exhibiting allotropic transformation such as Ti alloys, steels or brass [3].In a second part, we will show that in many cases, plasticity does not relax totally the elastic strain associated with the phase transformations [4]. As a direct consequence, plasticity may not change qualitatively the shape evolutions driven by elasticity, as it will be illustrated on the rafting of the ordered precipitates in Ni-base superalloys [5] and on the acicular structures [4], although it can change the kinetics of the processes. However, we will show that in some cases, plasticity may induce shape bifurcations [5,8] that are difficult to infer with simplified qualitative arguments, as usually done in the literature on diffusion-controlled phase transformations.We will conclude with a few open questions that we have been able to identify thanks to our phase field calculations, such as the inheritance of plastic strain by the growing phases [2].[1] K. Ammar, B. Appolaire, G. Cailletaud, and S. Forest. Combining phase field approach and homogenization methods for modelling phase transformation in elastoplastic media. European Journal of Computational Mechanics, 18(5-6):485–523, 2009.[2] K. Ammar, B. Appolaire, S. Forest, M. Cottura, Y. Le Bouar, and A. Finel. Modelling inheritance of plastic deformation during migration of phase boundaries using a phase field method. Meccanica, 49:2699–2717, 2014.[3] M. Cottura, B. Appolaire, A. Finel, and Y. Le Bouar. Phase field study of acicular growth: Role of elasticity in Widmanstätten structure. Acta Materialia, 72:200–210, 2014.[4] M. Cottura, B. Appolaire, A. Finel, and Y. Le Bouar. Plastic relaxation during diffusion-controlled growth of Widmanstätten plates. Scripta Materialia, 108:117–121, 2015.[5] M. Cottura, B. Appolaire, A. Finel, and Y. Le Bouar. Coupling the phase field method for diffusive transformations with dislocation density-based crystal plasticity: Application to Ni-based superalloys. Journal of the Mechanics and Physics of Solids, 94:473–489, 2016.[6] M. Cottura, Y. Le Bouar, B. Appolaire, and A. Finel. Rôle of elastic inhomogeneity in the development of cuboidal microstructures in Ni-based superalloys. Acta Materialia, 94:15–25, 2015.[7] M. Cottura, Y. Le Bouar, A. Finel, B. Appolaire, K. Ammar, and S. Forest. A phase field model incorporating strain gradient viscoplasticity: Application to rafting in Ni-base superalloys. Journal of the Mechanics and Physics of Solids, 60:1243–1256, 2012.[8] V. de Rancourt, K. Ammar, B. Appolaire, and S. Forest. Homogenization of viscoplastic constitutive laws within a phase field approach. Journal of the Mechanics and Physics of Solids, 88:291–319, 2016.[9] W.C. Johnson and P.W. Voorhees. Interfacial stress, interfacial energy, and phase equilibria in binary alloys. Journal of Statistical Physics, 95(5-6):1281– 1309, 1999.[10] F. Larché and J.W. Cahn. Thermochemical equilibrium of multiphase solids under stress. Acta Metallurgica, 26(10):1579–1589, 1978. [more]

Application of Scientific Principles to Aluminium Automotive Sheet

Abstract Aluminium has been used in the manufacture of automobiles for more than 100 years and current usage averages more than 150kg per vehicle. Recent demands for higher fuel economy, improved vehicle performance, and lower CO2 emissions are currently driving a dramatic increase in the usage of specially designed aluminium alloys in the automotive industry. Aluminium flat-rolled sheet products are currently seeing wide-spread application for many components previously produced from steel. The technical requirements for aluminium sheet include high levels of formability, high strength, corrosion resistance, surface appearance, and long term reliability of joints. While these requirements are often in direct conflict, improved understanding of microstructure and surface has enabled the economical production of sheet that can meet the necessary customer demands. Three key developments in metallurgy and surface science that have made aluminium automotive sheet possible are reviewed: control of precipitate morphology for high strength, surface microstructure for bond durability, and crystallographic texture for surface appearance after forming. [more]

Shear bands in metallic glasses: what are they, how to find them?

The plastic deformation in metallic glasses proceeds through the activation and sliding of shear bands (SBs). A better plasticity in metallic glasses can be achieved through the enhancement of SB stability and proliferation. Therefore, efforts have been made to understand the true nature of SBs in metallic glasses. However, direct measurements on SBs are limited due to the small width of a shear band (few tenths of nanometers) and the lack of resolution at the atomic scale. In this context, atom probe tomography could bring some missing information about SBs.In the first part of the talk, I present the current state of knowledge on shear bands in metallic glasses. I give information concerning the commonly accepted formation, nature and location of shear bands. In the second part of the talk, I present my own results with Pd- and Pt-based bulk metallic glasses (BMGs) samples deformed by High-Pressure Torsion. HR-TEM and DSC measurements indicate some changes in the short-range order of the samples. The importance of pre-existing SB spacing on the mechanical response during nanoindentation measurements is also presented. The influence of residual stresses on SB proliferation around indenter imprint is shown. Finally, we show the possibility of a phase separation in amorphous Au-based metallic glass thin films and Zr-based BMGs. Atom probe tomography could also be used to confirm the presence of multiple amorphous phases. [more]

Diffusion and segregation of solutes in grain boundaries: from pure metals to high-entropy alloys

Diffusion and segregation of solutes in grain boundaries: from pure metals to high-entropy alloys
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Phase-field Modeling of Polycrystalline Structures: From Needle Crystals to Spherulites Phase-field Modeling of Polycrystalline Structures: From Needle Crystals to Spherulites

MPIE Colloquium
Results in modeling complex polycrystalline structures by phase-field models that monitor the local crystallographic by scalar or vector orientation fields will be reviewed. The applied models incorporate homogeneous and heterogeneous nucleation of growth centers, and several mechanisms to form new grains at the perimeter of growing crystals, a phenomenon termed growth front nucleation. Examples for PF modeling of such complex polycrystalline structures are shown as impinging symmetric dendrites, polycrystalline growth forms (ranging from disordered dendrites to spherulitic patterns), and various eutectic structures, including spiraling two-phase dendrites. Simulations exploring possible control of solidification patterns in thin films via external fields, confined geometry, particle additives, scratching/piercing the films, etc. are also displayed. Advantages, problems, and possible solutions associated with quantitative PF simulations are discussed briefly. [more]

Variational Methods in Material Modeling: Applications of Hamilton’s Principle

The aim of modern material modeling is the realistic prediction of the behavior of materials and construction parts by numerical simulation. Experimental investigations prove that the microstructure and thus the mechanical properties may vary under loads. It is thus essential to describe the load-dependent microstructure in these cases by material models to close the system of fundamental physical equations. One elegant way for the derivation of such material models is given by the Hamilton principle which belongs to the class of variational, energy-based modeling strategies. The talk starts with fundamental investigations for modeling the simple harmonic oscillator. Afterwards, the presented modeling concept is generalized to the Hamilton principle which is also applicable to deformable solids with evolving microstructure. As first example for such materials, phase transformations in solids are modeled. The numerical results are compared to experimental observations and an industrially relevant application is presented. In the last part of the talk, the universal character of the Hamilton principle is demonstrated by solving the inverse problem of topology optimization. To this end, a growth approach as observed in biological processes is presented which computes component structures with minimal weight at maximum stiffness. [more]

International conference “Intermetallics 2017”

International conference “Intermetallics 2017”

Complex multicomponent alloys: coupled structural and mechanical study of a bcc model alloy, and possible improvement path

A lot of research effort has now been dedicated to the study of complex multicomponent alloys (more commonly called High Entropy Alloys HEA). This family of materials introduced in 2004 breaks with the traditional alloying concept, since they explore the domain of concentrated solid solution(s) of +5 elements. Several studies sprovide fundamental understanding on the structure and the mechanical properties of some of these alloys, mostly fcc [1–3]. If the results are promising, as for example the incredible fracture toughness of FeCoCrMnNi at low temperatures [4], recent papers suggest that equiatomic fcc alloys with less than 5 elements, or non-equiatomic fcc concentrated alloys also display great, or even greater mechanical properties [2,5,6]. The sub-family of bcc complex multicomponent alloys has been less investigated. Therefore, a multi-scale characterization of a model bcc multicomponent alloy with composition Ti20Zr20Hf20Nb20Ta20 is performed. After optimization of the microstructure, investigated by SEM (EBSD), TEM and EXAFS, the mechanical properties of the alloy are studied during both tensile/relaxations tests and shear tests. Deformation mechanisms are discussed in terms of activation volume and flow stress partitioning, interpreted with the help of microstructural investigations by transmission electron microscopy. Finally, the “HEA” concept is coupled with the chemical design based on electronic parameters Bo and Md used in Ti-alloys. This concept, first introduced by Morigana was successfully used to help predicting the structure stability, and hence the mechanical behavior – dislocation glide, twinning induced plasticity (TWIP) or transformation induced plasticity (TRIP) – of Ti-rich alloys [7,8]. The studied composition Ti35Zr27.5Hf27.5Nb5Ta5 displays a large ductility of 20% and an increased work-hardening [9]. It confirms that extending the concept of “HEAs” to non-equiatomic compositions can be highly beneficial and that the design strategy developed for Ti-alloys can be used with great results in concentrated alloys. [1] F. Otto, A. Dlouhý, C. Somsen, H. Bei, G. Eggeler, E.P. George, The influences of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy, Acta Mater. 61 (2013) 5743–5755. doi:http://dx.doi.org/10.1016/j.actamat.2013.06.018. [2] Z. Wu, H. Bei, G.M. Pharr, E.P. George, Temperature dependence of the mechanical properties of equiatomic solid solution alloys with face-centered cubic crystal structures, Acta Mater. 81 (2014) 428–441. doi:http://dx.doi.org/10.1016/j.actamat.2014.08.026. [3] C. Varvenne, A. Luque, W.A. Curtin, Theory of strengthening in fcc high entropy alloys, Acta Mater. 118 (2016) 164–176. doi:http://dx.doi.org/10.1016/j.actamat.2016.07.040. [4] B. Gludovatz, A. Hohenwarter, D. Catoor, E.H. Chang, E.P. George, R.O. Ritchie, A fracture-resistant high-entropy alloy for cryogenic applications, Science. 345 (2014) 1153–1158. doi:10.1126/science.1254581. [5] Y. Deng, C.C. Tasan, K.G. Pradeep, H. Springer, A. Kostka, D. Raabe, Design of a twinning-induced plasticity high entropy alloy, Acta Mater. 94 (2015) 124–133. doi:10.1016/j.actamat.2015.04.014. [6] Z. Li, K.G. Pradeep, Y. Deng, D. Raabe, C.C. Tasan, Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off, Nature. advance online publication (2016). http://dx.doi.org/10.1038/nature17981. [7] M. Abdel-Hady, K. Hinoshita, M. Morinaga, General approach to phase stability and elastic properties of β-type Ti-alloys using electronic parameters, Scr. Mater. 55 (2006) 477–480. doi:http://dx.doi.org/10.1016/j.scriptamat.2006.04.022. [8] M. Marteleur, F. Sun, T. Gloriant, P. Vermaut, P.J. Jacques, F. Prima, On the design of new β-metastable titanium alloys with improved work hardening rate thanks to simultaneous TRIP and TWIP effects, Scr. Mater. 66 (2012) 749–752. doi:http://dx.doi.org/10.1016/j.scriptamat.2012.01.049. [9] L. Lilensten, J.-P. Couzinié, J. Bourgon, L. Perrière, G. Dirras, F. Prima, I. Guillot, Design and tensile properties of a bcc Ti-rich high-entropy alloy with transformation-induced plasticity, Mater. Res. Lett. 5 (2017) 110–116. doi:10.1080/21663831.2016.1221861. [more]

Spatially Resolved Texture and Microstructure Evolution of Additively Manufactured and Gas Gun Deformed 304L Stainless Steel; Investigated by Neutron Diffraction and Electron Backscatter Diffraction

Spatially Resolved Texture and Microstructure Evolution of Additively Manufactured and Gas Gun Deformed 304L Stainless Steel; Investigated by Neutron Diffraction and Electron Backscatter Diffraction
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Nitride coatings based on high-entropy alloys

Nitride coatings based on high-entropy alloys
The new alloying concept, known as high-entropy alloys (HEAs) or multi-principal elements alloys (MPEAs) are a new emerging class of perspective materials that possess a wide range of unique properties. Since the appearance of the first studies of HEAs, more than 1000 scientific works were published. It was investigated relationship between microstructure of new alloys, which can include SS (with BCC, FCC and HCP structures), IM and even amorphous state and their physical properties. It was shown that the HEAs possess different outstanding functional properties, like superconductivity with transition temperature Tc = 7.3 K, high level electrical resistivity, high saturated magnetization, high corrosion resistance, good hydrogen storage properties, as a template for graphene production. For achievement superior mechanical behavior and thermal stability it was designed and produced protective coatings based on HEAs. However, the research of nitride coatings based on HEA are still very limited. Clearly, the understanding of features of microstructure such non-homogeneous complex systems is essential in order to move in the improvement of the physical properties of high-entropy thin films with different intrinsic architecture. [more]

Summer School on Experimental Nano- and Micromechanics

Summer School on Experimental Nano- and Micromechanics
The size dependent mechanical response of materials has attracted strong attention during the past decade. While past research focused mainly on single crystalline behavior, today´s investigations target the mechanical response and underlying deformation mechanisms of heterogeneous microstructures. The summer school is aimed at providing a comprehensive overview on experimental nano- and micromechanical testing methods. Focus thereby is put on material properties which can be reliably extracted from in situ micromechanical experiments. - Which properties can we experimentally explore? - Where are the limits and pitfalls of our methods? - Where do we need support of simulation techniques? - What are future challenges in the field? The school will deal with nanoindentation as well as methods to explore the plastic and fracture properties of materials and interfaces, frequently used characterization techniques with in situ capabilities and, finally, simulation techniques. [more]

AAMS17

Alloys for Additive Manufacturing Symposium 2017
As Additive Manufacturing technologies are being adopted in more and more industries, the focus of research and development is shifting to the materials in use. Additionally, an increasing number of researchers in academia and industry realise the potential of Additive Manufacturing to produce materials that were heretofore inaccessible by conventional manufacturing techniques or not economically feasible. The Alloys for Additive Manufacturing Symposium aims to be a venue for the discussion of these issues by researchers in academia and application. All materials scientific issues pertaining to the additive manufacturing of metals, alloys and composites including a metallic phase fall under the scope of this conference. [more]

Introducing high temperature intermetallic eutectic as potential structural materials

Introducing high temperature intermetallic eutectic as potential structural materials
Intermetallic fascinated high temperature materials community for the last five decades. Starting with gamma TiAl, both Ti based and Ni based single phase intermetallics have been subject of extensive investigation. It took five decades for actual application in latest generation GE engine. However, very little attention has been given to multiphase multicomponent intermetallics. These, in particular eutectics, are abundant in the central regions of phase diagrams of ternary and higher components. With a hypothesis that they represent exciting opportunity, this talk will present the outline of our fairly extensive efforts in developing high temperature intermetallic composites based on a novel design of materials through microstructural engineering of intermetallics at nano scale. We shall concentrate on the Ni-Al-Zr system and show that unique complex multiphase microstructures could be developed containing intermetallics of Ni3Al, Ni5Zr, Ni7Zr2 and NiAl. The microstructures contain single or multiple coupled eutectics that are distributed seamlessly along the entire samples. For example, for an alloy Ni-12At%Al-11at%Zr, two intermetallic phases (Ni3Al and Ni5Zr) are seamlessly distributed along the entire sample with two different length scales and morphologies. Often these microstructures can be visualised by a 3D analysis that shows variations of connectivity among phases. Many of these alloys show strength in excess of 2GPa This architecture exhibits excellent high temperature microstructural stability, exceptional high strength with reasonable tensile ductility at high temperature. We show that this can be derived from an approach designed to exploit eutectic reactions that combine Intermetallics in a microstructural scale that restricts slip lengths to obtain both strength and ductility. Some of these alloys also have exceptional oxidation resistance that is retained up to a temperature of 973K. Finally we shall present some results of creep strength of these alloy that hints at the stress induced transformation. [more]

Symposium: 3D materials characterization at all length scales and its applications to iron and steel

3D materials characterization at all length scales and its applications to iron and steel
The atomic and micro-scale structures of most materials are 3D, but a lack of tools for experimental 3D investigation of materials has limited most published research, including simulation and modelling, to 2D datasets. In the 21st century this situation has changed significantly. New 3D characterization and modelling methods are generating powerful insights into materials properties and microstructure formation on all length scales. [more]

Symposium “Environmental, in-situ and time-resolved microscopy” at MC 2017 (Microscopy Conference 2017)

Symposium “Environmental, in-situ and time-resolved microscopy” at MC 2017 (Microscopy Conference 2017)

Workshop: Status and Future Challenges in Characterisation of Interfaces for Electrochemical Applications

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Size Effects in Metals: On the Role of Internal Boundaries across the Scales

MPIE Colloquium
Size effects are a key ingredient to control and improve the mechanical behaviour of metallic microstructures and miniaturized components. The analysis of size effects in metals has received continuous attention in the past two decades, both experimentally and numerically. This lecture focuses on the role of grain and phase boundaries in restricting dislocation motion, giving rise to size effects. Some essential features of a thermodynamically consistent model for a grain boundary are presented, which accounts for the grain boundary energy and defect structure and evolution. The role of a phase boundary is investigated with a dislocation transport driven crystal plasticity model, revealing the explicit role of the plastic phase contrast and phase boundary resistance. Interesting size effects are thereby recovered. Size effects can also be eliminated or inhibited by other microstructural mechanisms. Two cases are addressed to illustrate this. The first case reveals the role of dislocation climb and its effectiveness in dissolving dislocation pile-ups. The second case concerns a very thin austenitic film in martensite, whereby the particular structure of the phase and its interface give rise to preferential sliding mechanisms that circumvent the common dislocation driven size effects.This lecture addresses the strengthening role of internal boundaries, constituting a major con- tribution to size effects in metals. It is shown that besides dislocation pile-ups, other mechanisms may be essential. For grain boundaries, the defect absorption and redistribution matters. For phase boundaries, phase contrast in dislocation transport alone already contributes to size effects. Moreover, dislocation-pile ups can be dissolved through climb at higher temperatures or circum- vented by other particular micromechanisms. This analysis effectively illustrates that predicting size effects in metals quantitatively remains a major challenge. References [1] van Beers P.R.M., Kouznetsova V.G., Geers M.G.D.: Defect redistribution within a continuum grain boundary plasticity model. J. Mech. Phys. Solids 83:243-262, 2015.[2] Dogge M.M.W., Peerlings R.H.J., Geers M.G.D.: Interface modeling in continuum dislocation transport. Me- chanics of Materials. 88:30-43, 2015.[3] Geers M.G.D., Cottura M., Appolaire B., Busso E.P., Forest S.,Villani A.: Coupled glide-climb diffusion- enhanced crystal plasticity. J. Mech. Phys. Solids. 70:136-153, 2014.[4] Maresca F., Kouznetsova V.G., Geers M.G.D.: Subgrain lath martensite mechanics: a numerical-experimental analysis. J. Mech. Phys. Solids. 73:69-83, 2014.[5] Maresca F., Kouznetsova V.G., Geers M.G.D.: Deformation behaviour of lath martensite in multi-phase steels. Scripta Materialia 110:74-77, 2016.[6] Maresca F., Kouznetsova V.G., Geers M.G.D.: Predictive modeling of interfacial damage in substructured steels: application to martensitic microstructures. Mod. Sim. Mat. Sc. Engng. 24(2):025006, 2016.[7] Du C., Hoefnagels J.P.M, Vaes R., Geers M.G.D.: Block and sub-block boundary strengthening in lath marten- site, Scripta Materialia,116:117-121, 2016.[8] Du C., Hoefnagels J.P.M, Vaes R., Geers M.G.D.: Plasticity of lath martensite by sliding of substructure boundaries, Scripta Materialia 120:37-40, 2016. [more]

Some Methods and Applications of Data-driven Inference in Materials Science Some Methods and Applications of Data-driven Inference in Materials Science

MPIE Colloquium
Experiments and simulations in materials science and engineering often generate prodigious quantities of data. Extracting information from this data turns out to be more challenging than may at first appear, prompting efforts to create innovative ways of analyzing “big data.” I will provide an overview of my own adventure in data-driven materials research and focus in on a few methods and example applications that have proven to be especially productive. The first deals with the inference of failure criteria for individual microstructure features from databases of individual failure events. The second concerns mining and analysis of image data from the open literature to gain new insight into materials without performing any new experiments or simulations. I will conclude with some thoughts about the future of data-based methods in materials science and engineering. [more]

New concepts in electrochemistry – from magnetic structuring of macroscopic layers to single nanoparticle analysis

New concepts in electrochemistry – from magnetic structuring of macroscopic layers to single nanoparticle analysis
Electrochemistry is a well-established technique for the electrodeposition of thin films for corrosion protection or of 3D structures for integrated circuits. It is also key to most approaches for sustainable energy conversion and storage and it is widely utilized in sensors for the detection and quantification of ions and biomolecules. In this presentation novel concepts adopting classical electrochemical methods for the fabrication and characterization of magnetic materials at the micro- and nanoscale will be presented.First the influence of magnetic fields on electrochemical deposition will be discussed using the magnetic-field assisted fabrication of structured electrodeposits in the milli- and micrometer range as an example. The relevant magnetic forces and their effect on local mass transport control will be discussed.[1,2]Electrochemistry will then be highlighted as a powerful tool for the characterization of magnetic nanoparticles beyond conventional imaging methods. For superparamagnetic Fe3O4 core Au shell nanoparticles electrochemical analysis of the particle coating quality will be shown.[3] Advancing from this, single nanoparticle electrochemistry will be presented as a new method that provides hitherto inaccessible insights into magnetic field effects on single nanoparticles in suspensions. Thus, magnetic field enhanced particle agglomeration and altered particle corrosion dynamics can be detected on a single particle level.[4]Fig. 1: Magnetic field assisted structuring of electrodeposits (left) and electrochemical characterization of magnetic core shell nanoparticles (right).References:[1] K. Tschulik, C. Cierpka, A. Gebert, L. Schultz, C.J. Kähler, M. Uhlemann, , Anal. Chem. 2011, 83, 3275–3281.[2] K. Ngamchuea, K. Tschulik, R. G. Compton, Nano Res. 2015, 8, 3293–3306.[3] K. Tschulik, K. Ngamchuea, C. Ziegler, M. G. Beier, C. Damm, A. Eychmueller, R. G. Compton, Adv. Funct. Mater. 2015, 25, 5149–5158.[4] K. Tschulik, R. G. Compton, Phys. Chem. Chem. Phys. 2014, 16, 13909–13913. [more]

Phase Transformations under Rapid Heating in Metallic Micro- and Nanolaminates

Phase Transformations under Rapid Heating in Metallic Micro- and Nanolaminates
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Phase-transformation effects on residual stress development in welding

Phase-transformation effects on residual stress development in welding
This presentation provides an overview of research that has been (and is being) carried out at The University of Manchester, with a focus on the role that phase transformations play in the development of stress in steel welds. There are several motivations for this research. Residual stresses play a significant role in affecting the long-term structural performance of safety-critical components in many power plants. They can also contribute to the driving force for crack growth and, in nuclear environments, they can activate material degradation mechanisms such as creep and stress-corrosion cracking even in the absence of operating stresses. This is significant because many safety-critical components in a nuclear plant undergo welding during manufacture, and welding is known introduce substantial levels of residual stress. Solid-state phase transformations affect the development of stresses in steels because these transformations have associated strains, which in turn affect the development of stress upon heating and cooling. Residual stresses also tend to be limited by the yield stress of the material, so the mechanical properties of transformation products will have a direct bearing on the development of stress. Some of the topics that will be covered in this presentation include the development and assessment of low-transformation-temperature filler materials for the mitigation of residual stresses, assessments of the effects of particular welding processes on the development of stresses, work towards understanding the mechanisms contributing to the development of transformation strains, and the incorporation of phase transformation effects into finite-element models for the prediction of residual stresses in steel welds. [more]

The Dynamics of Active Metal Catalysts Revealed by In Situ Electron MicroscopyThe Dynamics of Active Metal Catalysts Revealed by In Situ Electron Microscopy The Dynamics of Active Metal Catalysts Revealed by In Situ Electron Microscopy

The Dynamics of Active Metal Catalysts Revealed by In Situ Electron Microscopy
Conventional high-resolution imaging by electron microscopy plays an important role in the structural and compositional analysis of catalysts. However, since the observations are generally performed under vacuum and close to room temperature, the obtained atomistic details concern an equilibrium state that is of limited value when the active state of a catalyst is in the focus of the investigation. Since the early attempts of Ruska in 1942 [1], in situ microscopy has demonstrated its potential and, with the recent availability of commercial tools and instruments, led to a shift of the focus from ultimate spatial resolution towards observation of relevant dynamics. During the last couple of years we have implemented commercially available sample holders for in situ studies of catalysts in their reactive state inside a transmission electron microscope. In order to relate local processes that occur on the nanometer scale with collective processes that involve fast movement of large numbers of atoms, we have adapted an environmental scanning electron microscope (ESEM) for the investigation of surface dynamics on active catalysts. Using these two instruments, we are now able to cover a pressure range from 10-4 to 103 mbar and a spatial resolution ranging from the mm to the sub-nm scale. Presently we are investigating metal catalyzed CVD growth of graphene [2,3], as well as structural dynamics during oscillatory red-ox reactions on metal catalysts. The observations are performed in real-time and under conditions in which the active state of the catalyst can be monitored. The latter is of upmost importance, since the key requirement is to observe relevant processes and dynamics that are related to catalytic function. The ability to directly image the active catalyst and associated morphological changes at high spatial resolution enables us to refine the interpretation of spatially averaged spectroscopic data that was obtained under otherwise similar reaction conditions, for example during near-ambient-pressure in situ XPS measurements [4]. It will be shown that the ability of observing the adaption of an active surface to changes in the chemical potential of the surrounding gas phase in real-time potentially offers new and direct ways of optimizing catalysts and applied reaction conditions. References[1] E. Ruska, Kolloid-Zeitschrift, 100 (1942) 212-219[2] Z.-J. Wang et al., ACS Nano, 9 (2015) 1506–1519[3] Z.-J. Wang et al., Nat. Commun. 7 (2016) DOI:10.1038/ncomms13256[4] R. Blume et al., PhysChemChemPhys, 16 (2014) 25989 [more]

Publishing in Material Science - and how to Maximize your success

Publishing your research results is an integral – if not the most important – part of your research. In this talk, some insight in the publishing process at the inhouse editorial offices of the successful journal family of Advanced Materials will be given. I will clarify the workflow at a publishing house from the moment the manuscript arrives until it is published and emphasize the role of the editor in that process. In the second part, I concentrate specifically on the requirements for successful publication in our high-impact journals and explain our requirements for acceptable manuscripts in our journals – and which pit falls authors should avoid in the preparation and submission process. [more]

3rd NRW-APT User Meeting

The Max-Planck-Institut für Eisenforschung GmbH in Düsseldorf is organizing the 3rd NRW-APT user meeting on May 16th 2017 and we would like to invite you and your research colleagues to participate in this event. This meeting will bring together scientists from North Rhine-Westphalia dealing with APT technique or correlating APT with other techniques. We want to discuss problems and share knowledge regarding sample preparation, measurement conditions, data reconstruction & analysis, etc. If you and your colleagues would like to attend this event, then please register before May 2nd 2017. There are limited places only. We are looking forward to see you in Düsseldorf! [more]

Symposium “Mechanical Properties and Adhesion 44th ICMCTF (International Conference on Metallurgical Coatings and Thin Films)

Symposium “Mechanical Properties and Adhesion 44th ICMCTF (International Conference on Metallurgical Coatings and Thin Films)

Topic day “Lokale Charakterisierungsmethoden in der Werkstoffforschung” at the Metallkundekolloquium/Arlbergkolloquium

Topic day “Lokale Charakterisierungsmethoden in der Werkstoffforschung” at the Metallkundekolloquium/Arlbergkolloquium

Hydrogen Interaction in Metals

Hydrogen interaction in metals
The workshop is part of our series of one-day workshops "Frontiers in Material Science & Engineering", where we bring together leading experts from academia and industry in a workshop format that allows in-depth discussions of fundamental and applied research in this area. Places are limited to 50 participants. The workshop participation is free-of-charge and is sponsored by the MPIE. [more]

Workshop "Frontiers in Material Science & Engineering: Hydrogen Interaction in Metals"

Workshop "Frontiers in Material Science & Engineering: Hydrogen Interaction in Metals"

MPIE-Colloquium: Complex nanostructures and nanocomposites for plasmonic and photonic applications

MPIE-Colloquium: Complex nanostructures and nanocomposites for plasmonic and photonic applications
Nanoparticles, nanowires, and many other nanostructures are produced and investigated for applications for quite some time. The desired functionality is not easy to achieve in a reproducible way. Various methods will be presented how such structures can be produced in a well defined arrangement and well defined functionality. Nanoporous gold nanosponges will be presented and it will be shown how disorder can be used to obtain a robust and reproducible functionality, i.e. disorder can be used for precision.In addition, nanoporous nanostructures can be easily tuned for applications by advancing them to nanocomposites with desired functionality, which can be used in medicine, energy storage and conversion, photocatalysis and further applications. [more]

MULTICOMPONENT AND HIGH-ENTROPY ALLOYS

Conventional strategy for developing metallurgical alloys is to select the main component based on a primary property requirement, and to use alloying additions to confer secondary properties. This strategy has led to the development of many successful alloys based on a single main component with a mix of different alloying additions to provide a balance of required in-service properties. Typical examples include high temperature Ni superalloys, wrought Al alloys and corrosion resistant stainless steels. However, conventional alloy development strategy leads to an enormous amount of knowledge about alloys based on one component, but little or no knowledge about alloys containing several main components in approximately equal proportions. Theories for the occurrence, structure and properties of crystalline phases are similarly restricted to alloys based on one or two main components. Information and understanding is highly developed about alloys close to the corners and edges of a multicomponent phase diagram, with much less known about alloys in the centre of the diagram. This talk describes a range of other multicomponent alloying strategies and gives a number of examples of high-entropy and other multicomponent alloys. [more]

MPIE Colloquium: Computing Mass Transport in Crystals: Theory, Computation, and Applications

MPIE Colloquium: Computing Mass Transport in Crystals: Theory, Computation, and Applications
The processing of materials as well as their technologically important properties are controlled by a combination of thermodynamics--which determines equilibrium--and kinetics--how a material evolves. Mass transport in solids, where different chemical species diffuse in a material due to random motion with or without a driving force, is a fundamental kinetic process for a wide variety of materials problems: growth of precipitates in nearly every advanced structural alloy from steels to superalloys, fusing of powders to make advanced ceramics, degradation of materials from irradiation, permanent changes in shape of materials over long times at high temperatures, corrosion of materials in different chemical environments, charge/discharge cycles in batteries, migration of atoms in electric fields, and more. Mass transport is a fundamentally multiscale phenomenon driven by crystalline defects, where many individual defect displacements sum up to produce chemical distributions at larger length and time scales. State-of-the-art first principles methods make the computation of defect energies and transitions routine for crystalline systems, and upscaling from activation barriers to mesoscale mobilities requires the solution of the master equation for diffusivity. For all but the simplest cases of interstitial diffusivity, and particular approximations with vacancy-mediated diffusion on simple lattices, calculating diffusivity directly is a challenge. This leaves two choices: uncontrolled approximations to map the problem onto a simpler (solved) problem, or a stochastic method like kinetic Monte Carlo, which can be difficult to converge for cases of strong correlations. I will describe and demonstrate our new developments for direct and automated Green function solutions for transport that take full advantage of crystal symmetry. This approach has provided new predictions for light element diffusion in magnesium, "pipe diffusion" of hydrogen along dislocations cores in palladium, and the evolution of vacancies and silicon near a dislocation in nickel. I will also show our latest results for technologically relevant magnesium alloys with containing Al, Zn, and rare earth elements (Gd, Y, Nd, Ce and La), where prior theoretical models to predict diffusivity from atomic jump frequencies make uncontrolled approximations that impact their accuracy. The underlying automation also makes the extension of first-principles transport databases significantly more practical and eliminate uncontrolled approximations in the transport model. [more]

Hydrogen Storage Technology at the Helmholtz Zentrum Geesthacht

The use of fossil fuels as energy supply is growing increasingly problematic both from the point of view of environmental emissions and energy sustainability. As an alternative to fossil fuels, hydrogen is widely regarded as a key element for a potential energy solution. In this respect, hydrogen storage technologies are considered a key roadblock towards the use of H2 as energy carrier. Among the methods available to store hydrogen, solid-state storage appears to be a very interesting alternative, showing for example the highest volumetric storage densities and high safety. Within the Helmholtz “Advanced Engineering Materials” Programme, the Department of Nanotechnology focusses on the development of both nanostructured hydrogen storage materials and hydrogen storage systems. A detailed account of the actual and future research activities in the field of hydrogen technology at the Helmholtz-Zentrum Geesthacht will be presented. [more]

Solar cells, defects and recombination – news from CIGS

Solar cells, defects and recombination – news from CIGS
After a short introduction to thin film solar cells, I will review what we know about defects in Cu(InGa)Se2 (CIGS), where we found significant differences between Cu-rich and Cu-poor material. By photoluminescence we recently found fundamental differences between pure CIS and Ga containing CIGS: with Ga the recombination is higher in Cu-rich material. And high Ga content CIGS shows a deep defect which gets more and more shallow when we decrease the Ga content. Finally, I will show that we can use photoluminescence to characterise the tails states in kesterite. [more]

Plasticity in Magnesium: Twinning and Slip Transmission

Plasticity in Magnesium: Twinning and Slip Transmission
Although magnesium is the lightest structural metal and has a great potential to be utilized in lightweight constructions, e.g. in automotive engineering, the use of wrought magnesium alloys is limited due to, inter alia, a high mechanical anisotropy and poor room temperature formability. Against this background, understanding the underlying physical mechanisms and microstructural changes in the material during processing is crucial in order to overcome the difficulties associated with the limited ductility by innovative processing, microstructure and alloy design. In order to isolate and access specific mechanisms of plasticity, model experiments on single crystal provide an invaluable tool, as they permit a much clearer and forthright analysis compared to conventional polycrystal studies. Specifically oriented single crystals of various orientations were subjected to channel-die plane strain compression at room and elevated temperatures. The microstructure and texture evolution were characterized experimentally with respect to the deformation behavior. Pure Mg crystals of ‘hard’ orientations that were compressed along the c-axis displayed limited room temperature ductility, although pyramidal 〈c+a〉 slip was readily activated, and fractured along crystallographic {112 ̅4} planes as a result of highly localized shear. A two stage work hardening behavior was observed in ‘soft’ Mg crystals aligned for single or coplanar basal slip. The higher work hardening in the second stage was correlated with the occurrence of anomalous extension twinning that formed as a result of deformation heterogeneity and constituted obstacles for dislocation glide. The interaction between slip and twinning was further investigated by performing in-situ simple shear experiments on Mg bicrystals. It was shown that slip transmission takes place across different twin boundaries with basal slip being readily transmitted through a whole twin, which contradicts a classical Hall-Petch type hardening. The amount of twinning shear for {101 ̅2} twins in Mg was measured experimentally and discussed in terms of the shear-coupled grain boundary migration by considering the formal dislocation content of the respective twin boundaries. The coupling factor that equals the amount of twinning shear was found to result from a combination of two elementary coupling modes, i.e. the correct formal description of the twin boundary comprises two arrays of dislocations with 〈101 ̅0〉 and [0001] type Burgers vectors. [more]

NANO-HITEN - Development of High Strength Hot-rolled Sheet Steel Consisting of Ferrite and Nanometer-sized Carbides

NANO-HITEN - Development of High Strength Hot-rolled Sheet Steel Consisting of Ferrite and Nanometer-sized Carbides
A ferritic steel precipitation-strengthened by nanometer-sized carbides was developed to obtain a high strength hot-rolled sheet steel having tensile strength of 780 MPa grade with excellent stretch flange formability. Manganese in a content of 1.5 % and molybdenum in a content of 0.2 % were added to 0.04 % carbon Ti- bearing steel in order to lower austenite–ferrite transformation temperature for fine carbides and to retard generating of pearlite and large cementites, respectively. Tensile strength of hot-rolled sheet steel increased with titanium content and it was achieved to 800 MPa in a 0.09 % Ti steel. Microstructure of the 0.09 %Ti steel was ferrite without pearlite and large cementites. Fine carbides of 3 nm in diameter were observed in rows in the ferrite matrix of the 0.09 % Ti steel with transmission electron microscope. The characteristic arrangement of the nanometer-sized carbides indicates that the carbides were formed at austenite–ferrite interfaces during transformation. By energy dispersive X-ray spectroscopy, the carbides were found to con- tain molybdenum in the same atomic concentration as titanium. Crystal structure of the nanometer-sized carbides was determined to be NaCl-type by X-ray diffractometry. The calculated amount of precipitation- strengthening by the carbides was approximately 300 MPa. This is two or three times higher than that of conventional Ti-bearing high strength hot-rolled sheet steels. Based on the results obtained in the laboratory investigation, mill trial was carried out. The developed hot- rolled high strength sheet steel exhibited excellent stretch flange formability. [more]

"Mechanics meets Energy V” symposium at castle Ringberg

The Search For Charge Density Based Structure-Property Relationships

The Search For Charge Density Based Structure-Property Relationships
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Workshop: Status and Future Challenges in Characterisation of Interfaces for Electrochemical Applications

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Unraveling the mysteries of faculty applications (in the US)

Unraveling the mysteries of faculty applications (in the US)
The application process for tenure-track university faculty positions in the US is often opaque and unclear. Job listings can be broad and vague and are sometimes difficult to find; clear guidelines for cover letters, research statements, and CVs are non-existent; interview formats vary drastically between departments, even in the same university or college. But fear not! All of these obstacles are surmountable, with sufficient preparation, of course. This talk will attempt to elucidate many of the aspects of the application process. Topics that will be covered include: a brief overview of the American university structure, job responsibilities of a tenure-track professor, how to find job listings, how to determine which universities and departments to apply to, and tips for applying, interviewing, and negotiating. [more]

Investigation of Nanostructural Materials by means of X-Ray Powder Diffraction

Investigation of Nanostructural Materials by means of X-Ray Powder Diffraction
Nanostructured materials represent a well-established part of nanoscience today due to their tunable electrical, optical, magnetic and catalytic properties, and their potential in nanomedicine. There are some common techniques used for the investigation of nanomaterials, e.g. light scattering (DLS and NTA), scanning and transmission electron microscopy (SEM and TEM), fluorescence and IR spectroscopy and many others. X-ray powder diffraction (PXRD) with different geometrical setups is a complementary non-destructive technique for the determination of crystallographic and size-related properties of nanostructured materials. Here, some examples of PXRD measurements in different applications with the use of Rietveld analysis, including size-specific data obtained from colloid-chemical analysis, transmission and scanning electron microscopy will be presented. Several scientific questions will be addressed, like: - How can crystallite size, residual stress and texture be determined for nanostructured materials? - How is it possible to investigate a thin coating of nanomaterials? - Which advantages does a characterization of samples in temperature chamber offer? It will be shown that the non-destructive X-ray method is well suited to describe not only the crystallographic properties of nanostructural materials, but also their size, shape and inner structure with a possible atomic substitution as well as their “nano”-orientation on the surface. All these scientific answers can be received by the use of different X-ray diffractometers such Bruker D8 Advance and Panalytical Empyrean available at the facility for X-ray Diffraction of the University of Duisburg-Essen. [more]

Predicting solute segregation kinetics and properties in binary alloys from a dynamical variational gaussian model

Predicting solute segregation kinetics and properties in binary alloys from a dynamical variational gaussian model
The thermodynamics and kinetics of solute segregation in crystals is important for controlling microstructure and properties. Prime examples are the effects of solute drag on interface migration and of static strain aging on the yield stress. A fully quantitative prediction of solute segregation is difficult, however, due to the spatially varying solute-defect binding energies that are atomic in origin. Moreover, as solute segregation enhances (locally) the solute concentration, dilute approximations for the underlying thermodynamics and kinetics become questionable. We present a dynamical version of the variational gaussian method for binary alloys [1] and illustrate its potential for select problems involving solute segregation including static strain aging in Al-Mg alloys [2]. Our model adapts the recently proposed Diffusive Molecular Dynamics (DMD) model for vacancy diffusion in crystals where a phonon- free description of solids is coupled with statistical averaging over various configurations to allow for the efficient calculation of free energies. In the alloy version of the model, the free energy is minimized by optimizing the atomic positions and vibrational amplitudes while relaxational dynamics are used to evolve the solute concentration field based on the local energy landscape. We show that this model successfully describes solute redistribution over diffusive timescales. In contrast to traditional continuum diffusion treatments, atomistic effects are automatically accounted for, and full kinetic pathways of the evolution of material properties are revealed in addition to the equilibrium properties. [1] E. Dontsova, J. Rottler, C. W. Sinclair, Phys. Rev. B 90, 174102 (2014) [2] E. Dontsova, J. Rottler, C. W. Sinclair, Phys. Rev. B 91, 224103 (2015) [more]

Doping Induced Properties of Nanocrystalline CVD Diamond Films and Particles

MPIE Colloquium
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Microstructures and Mechanical Behavior of FeNiMnAl(Cr) Alloys

FeNiMnAl alloys show a wide range of microstructures and mechanical properties, but have been little explored. Studies on four different types of microstructures in this alloy system will beoutlined: 1) ultrafine microstructures (5-50 nm), present in Fe30Ni20Mn20Al30,Fe25Ni25Mn20Al30 and Fe35Ni15Mn25Al25,which consist of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler) phases, and in Fe30Ni20Mn25Al25,which consist of (Ni, Al)-rich B2 and (Fe, Mn)-rich b.c.c. phases, with the phases aligned along <100>; 2) fine microstructures (50-70 nm), present in Fe30Ni20Mn30Al20, Fe25Ni25Mn30Al20, and Fe28Ni18Mn33Al21, which consist of alternating (Fe,Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered plates with an orientation relationship close to f.c.c.(002)//B2(002); f.c.c.(011)//B2(001); 3) coarser (0.5-1.5µm) lamellar microstructures observed in alloys with a lower aluminum content, such as Fe30Ni20Mn35Al15, that consistof alternating (Fe,Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered phases with a Kurdjumov-Sachs orientation relationship between the phases; and 4) high-entropy Fe40.4Ni11.3Mn34.8Al7.5Cr6alloys. The microstructures and mechanical properties in these alloys have been determined as a function of annealing time, testing temperature and strainrate.  Some of the unusual mechanical behavior that has been observed will be emphasized. This research was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences (grant DE-FG02-07ER46392). [more]

Linking Microstructural Evolution and Tribology in Metallic Contacts

Linking Microstructural Evolution and Tribology in Metallic Contacts
The tribology community presently relies on phenomenological models to describe the various seemingly disjointed steady-state regimes of metal wear. Pure metals such as gold -- frequently used in electrical contacts - exhibit high friction and wear. In contrast, nanocrystalline metals, such as hard gold, often show much lower friction and correspondingly low wear. The engineering community has generally used a phenomenological connection between hardness and friction/wear to explain this macroscale response, and thus to guide designs. We present results of recent simulations and experiments that demonstrate a general framework for connecting materials properties (i.e. microstructural evolution) to tribological response. We present evidence that the competition between grain refinement (from cold working), grain coarsening (from stress-induced grain growth), and wear (delamination and plowing) can be used to describe transient and steady state tribological behavior of metals, alloys and composites. We will explore the seemingly disjointed steady-state friction regimes of metals and alloys, with a goal of elucidating the structure-property relationships, allowing for the engineering of tribological materials and contacts based on the kinetics of grain boundary motion. [more]

Symposium "Tribology across length-scales: Experiments and simulations" at the MSE (Materials Science Engineering)

Symposium "Tribology across length-scales: Experiments and simulations" at the MSE (Materials Science Engineering)

High-throughput with Particle Technology

High-throughput screening is a well-established method for scientific experimentation in chemistry and biology. Examples are heterogeneous catalysts, drug developments and nanoparticle toxicology. These methods involve the synthesis of small sample volumes often in form of particles that are quickly tested. These tests are designed to quickly obtain easily accessible data (called descriptors) that are related with a predictor function to the desired properties. The descriptor-predictor-relation is found through mathematical modelling and calibration. One particle based high-throughput concept for the evaluation of potential toxicological hazards will be presented in more detail. Furthermore, a new concept is presented which transfers high-throughput screening to the exploration of new structural metals. The method comprises the synthesis of many small alloy samples in form of particles. These samples obtain a defined microstructure by fast or parallel thermal and mechanical treatments and are subsequently subjected to novel fast descriptor tests while a mathematical algorithm develops the predictor function. The method presented here is a collaborative approach among many researchers and also involves sample routing and automation considerations as well as process modelling. [more]

5th International Symposium on Computational Mechanics of Polycrystals, CMCn 2016 and first DAMASK User Meeting

5th International Symposium on Computational Mechanics of Polycrystals, CMCn 2016 and first DAMASK User Meeting
The Max-Planck-Institut für Eisenforschung in Düsseldorf is organizing the 5th International Symposium on Computational Mechanics of Polycrystals and we would like to invite you and your research colleagues to participate in this event. This symposium is part of a biannual series of symposia that originated from the first joint research group established between the Max Planck Society and the Fraunhofer Society on the Computational Mechanics of Polycrystals. This year the symposium is combined with the first DAMASK User Meeting. DAMASK is the multi-physics simulation software developed at MPIE. If you and your colleagues would like to attend this event, then please register online before July 1st 2016. We emphasize that registration is mandatory and that there are limited places only. Many thanks and hope to see you in Düsseldorf! [more]

MPIE-Colloquium: Tuning Materials Properties Through Extreme Chemical Complexity

MPIE-Colloquium: Tuning Materials Properties Through Extreme Chemical Complexity
The development of metallic alloys is arguably one of the oldest of sciences, dating back at least 3,000 years. It is therefore very surprising when a new class of metallic alloys is discovered. High Entropy Alloys (HEA) appear to be such a class furthermore, one that is receiving a great deal of attention in terms of the underlying physics responsible for their formation as well as unusual physical,mechanical and radiation resistance properties that make them candidates for technological applications. The term HEA typically refers to alloys that are comprised of 5, 6, 7… elements, each in in equal proportion, that condense onto simple underlying crystalline lattices but where the different atomic species are distributed randomly on the different sites -face centered cubic (fcc) Cr0.2Mn0.2Fe0.2Co0.2Ni0.2 and body-centered-cubic (bcc) V0.2Nb0.2Mo0.2Ta0.2W0.2 being textbook examples. The naming of these alloys originates from an early conjecture that these unusual systems are stabilized as disordered solid solutions alloys by the high entropy of mixing associated with the large number of components  - a conjecture that has since proved insufficient. In the first part of the presentation I will describe a model that allows us to predict which combinations of N elements taken from the periodic table are most likely to yield a HEA that is based on the results of modern high-throughput ab initio electronic structure computations. In the second part I will broaden the discussion to a wider class of equiatomic fcc concentrated solid solution alloys that is based on the 3d- and 4d-transition metal elements Cr, Mn, Fe, Co, Ni, Pd that range from simple binary alloys, such as Ni0.5Co0.5 and Ni0.5Fe0.5, to the quinary high entropy alloys Cr0.2Mn0.2Fe0.2Co0.2Ni0.2 and Cr0.2Pd0.2Fe0.2Co0.2Ni0.2 themselves. Here I will discuss the role that increasing chemical complexity and disorder has on the underlying electronic structure and the magnetic and transport properties. Finally, I will argue that the manipulation of chemical complexity may offer a new design principle for more radiation tolerant structural materials for energy applications. [more]

A pull-to-bend testing technique for testing Single crystal Silicon

A pull-to-bend testing technique for testing Single crystal Silicon
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MagneticMaterial Modeling for Numerical Simulation of Electrical Machines

Magnetic Material Modeling for Numerical Simulation of Electrical Machines
The development of energy efficient electrical machines requires accurate knowledge of the magnetic material behavior, i.e., iron loss components  and magnetizability, already in the design stage. In addition, knowledge on the magnetic property deterioration due to induced  residual  stresses occurring during the manufacturing as well as due to applied mechanical  stresses during the operation of the electrical machine is indispensable for the contemporary machine-design.In general, the modeling can be approached at different length scales, i.e., from quantum mechanics at the atomic level and micromagnetics at the sub-micrometer length scale to continuum modeling at the ultra-millimeter scale. The difficulty to apply micromag- netic approaches in the numerical simulation of electrical machines is given both, by the tremendous  need of computational effort as well as the difficulty to consider the inter- action with effects present at the macroscale such as, e.g., residual  stresses or non-local eddy currents.A more modern view of such aspects is to regard materials  as multilevel structures, where structural features at all length scales play a significant role. Multiscale modeling is the field of solving such problems that have important features at multiple spatial and/or temporal scales.  It allows calculating material properties on one level using information or models from other levels. In the light of this, this presentation will give an overview on the current modeling  approaches applied at the Institute of Electrical Machines (IEM) for soft magnetic materials in the simulation of rotating electrical machines.  Particular attention will be paid to the effect of residual  as well as applied  mechanical stress on the magnetic behavior occurring at the various steps of machine manufacturing and during machine operation.Selected References[1] N. Leuning, S. Steentjes, M. Schulte, W. Bleck, and K. Hameyer, ”Effect of elastic and plastic tensile mechanical loading on the magnetic properties of NGO elec- trical steel,” Journal of Magnetism and Magnetic Materials, vol.  417, pp.  42-48, November 2016.[2] S. Elfgen,  S. Steentjes, S. B¨ohmer, D. Franck, and K. Hameyer, ”Continuous Local Material Model for Cut Edge Effects in Soft Magnetic Materials,” IEEE Transac- tions on Magnetics, vol. 52, no. 5, pp. 1-4, May 2016.[3] N. Leuning, S. Steentjes, M. Schulte, W. Bleck, and K. Hameyer, ”Effect of Mate- rial Processing and Imposed Mechanical  Stress on the Magnetic, Mechanical, and Microstructural Properties of High-Silicon Electrical Steel,” steel research interna-tional, to appear, 2016.  [more]

Composite voxels fornonlinear mechanical problems

Composite voxels for nonlinear mechanical problems
Two-scale simulations of components classically  rely upon finite element simulations  on boundary- and interface-fitted  meshes on both the macro and the micro scale. For complex microstructures fast and memory-efficient  solvers posed on regular voxels grids, in particular the FFT-based homogenization method [1], provide a powerful  alternative to FE simulations on unstructured  meshes and can be used to replace the micro-solver [2, 3]. Since representative volume elements of the microstructure  consist of up to 80003  voxels, even this micro-solver reaches its limits for nonlinear elastic computations.This talk focuses on the composite voxel technique [4], where sub-voxels  are merged into bigger voxels to which an effective material law based on laminates is assigned. Due to the down-sampled grid, both the memory requirements and the computational effort are severely reduced. We discuss the extensions of linear elastic ideas [4, 5] to the physically non-linear setting  and assess the accuracy  of reconstructed solution fields by comparing them to direct full-resolution computations.References[1] H. Moulinec and P. Suquet. A numerical method for computing the overall response of nonlinear composites with complex microstructure.Computer Methods in Applied Mechanics and Engineering, 157(1-2):69–94, 1998. [2] J. Spahn, H. Andra, M. Kabel, and R. Mueller.A multiscale approach for modeling pro- gressive damage of composite materials using fast Fourier transforms. Computer Methods in Applied Mechanics and Engineering, 268(0):871 – 883, 2014. [3] J. Kochmann,  S. Wulfinghoff, S. Reese, J. R. Mianroodi,  and B. Svendsen.  Two-scale FEFFT- and phase-field-based computational modeling of bulk microstructural evolution and macroscopic material behavior. Computer Methods in Applied Mechanics and Engi- neering, 305:89 – 110, 2016. [4] M. Kabel, D. Merkert, and M. Schneider. Use of composite voxels in FFT-based homog- enization. Computer Methods in Applied Mechanics and Engineering, 294(0):168–188,2015. [5] L. Gelebart and F. Ouaki. Filtering Material Properties to Improve FFT-based Methodsfor Numerical Homogenization.  J. Comput. Phys., 294(C):90–95, 2015. [more]

In situ HR-EBSD characterization during micro-mechanical testing

In situ HR-EBSD characterization during micro-mechanical testing
Quantification of the mechanical properties of crystalline materials at micro and nano length-scales is as important as it is challenging. In situ mechanical testing inside the SEM using a micro-indenter offers the great advantage of a direct observation of the progressive deformation in materials and has been applied for many years to assess the deformation mechanisms at small scale. This is now reinforced by the capability of doing in situ EBSD and HR-EBSD in order to map the evolution of the microstructure, the stress field and the GNDs distribution in the materials at several steps during progressive deformation. We apply this technique to estimate the size of the plastic zone underneath the crack tip during micro-cantilever bending in tungsten and NiAl intermetallic for fracture toughness determination. HR-EBSD is used to map the evolution of the stress field around the notch tip and to estimate the GNDs in the plastically deformed zone. In situ EBSD has been also applied to micropillar compression in alpha Titanium in order to study the formation and evolution of compressive twins during the deformation. The results show dislocation driven twin formation and twin propagation and thickening according to the local resolve shear stress. [more]

Deformationmechanisms of TWIP steel: from micro-pillars to bulk samples

Deformation mechanisms of TWIP steel: from micro-pillars to bulk samples
  • Date: Jul 6, 2016
  • Time: 13:30 - 15:00
  • Speaker: Prof. Mingxin HUANG
  • Department of Mechanical Engineering, The University of Hong Kong, Hong KongShort biography of the speaker Dr. Mingxin HUANG is currently an Associate Professor at The University of Hong Kong, Hong Kong. His research interests focus on two areas: (1) fundamentals of microstructure-property relationship and phase transformation of advanced steels, and (2) development of lightweight materials for automotive applications. Both experimental and modelling works are involved in his research. His research projects have been well funded by government funding agents as well as industries from Europe and China (e.g. ArcelorMittal France, General Motors, Ansteel, Baosteel). Dr. Huang received his Bachelor as well as Master degrees from Shanghai Jiao Tong University (SJTU) in 2002 and 2004, respectively, and his PhD in 2008 from Delft University of Technology (TU Delft), The Netherlands. From 2008 to 2010, he worked as a research engineer at ArcelorMittal R&D centre in Maizieres-les-Metz, France. His research work in ArcelorMittal focused on the development of new advanced steels for automotive applications. Dr. Huang joined University of Hong Kong in 2010 as an Assistant Professor and was promoted to Associate Professor with tenure in 2016. Dr. Huang has published 50+ journal papers on major international journals in his field such as Acta Materialia and Scripta Materialia. Dr. Huang is an editorial board member of Materials Science and Technology, the Key Reader for Metallurgical and Materials Transactions A and has received twice “Outstanding Reviewer of Scripta Materialia” awards.
  • Location: Max-Planck-Institut für Eisenforschung GmbH
  • Room: Seminarraum 1
  • Host: Prof. Dierk Raabe
Twinning-induced plasticity (TWIP) steels have excellent combinationof strength and ductility and are potential lightweight materials forautomotive applications. Understanding the deformation mechanisms in TWIPsteels is essential for the successful application of TWIP steels. The firstpart of this work is to employ micron-sized single crystalline pillars toinvestigate the nucleation and growth mechanism of deformation twins. It isfound that the nucleation and growth of deformation twins are due to emissionand glide of successive partial dislocations. A physical model is proposed tosimulate the nucleation and growth of deformation twins. The second part of thepresentation discusses the deformationmechanism of bulk samples. Deformation mechanism of bulk samples at high strainrates will be discussed firstly. By synchrotron X-raydiffraction experiments, the present work demonstrates that a higher strainrate leads to a lower dislocation density and a lower twinning probability,which is opposite to other fcc metals. Furthermore, it has been demonstratedthat the contribution of twins to the flow stress is very limited. Instead,dislocations strengthening via forest hardening accounts for up to 90% of theflow stress. In other words, the contribution of twins to flow stress of TWIPsteels may have been overestimated in the existing literature. Finally, thepresent talk will discuss a nanotwinned steelwhich is manufactured by a simple thermomechanical treatment consisting of coldrolling and recovery annealing and possesses a high yield strength (1450 MPa)and considerable uniform tensile elongation (20%).   [more]

Alloys for Additive Manufacturing Workshop 2016

Additive Manufacturing is a technology on the verge of widespread adoption. In some fields such as dental implants, the tooling or the aerospace industry, it is rapidly becoming state of the art for the production of highly complex and/or individualised parts. Research is currently focussing on improvement of the processes in terms of reliability and productivity. At the same time, many researchers and users come to the conclusion that a renewed effort in understanding materials behaviour during the AM processes is a key requirement to pushing AM closer to application. [more]

MPIE-Colloquium: Phase Transformations: Atom-Probe Tomography versus Modeling

MPIE-Colloquium: Phase Transformations: Atom-Probe Tomography versus Modeling
The design of Atom probe tomography (APT) at Oxford and Rouen universities for 25 years ago has been an outstanding breakthrough in the microscopy world. APT is the only analytical microscope able to provide 3D images of a material at the atomic scale [1]. Because of its ultimate spatial resolution (0.1 nm in depth, a few tenths of a nm at the sample surface), combined with its quantitativity of composition measurements, APT has played a major role in the investigation of the early stages of phase separation in solids. APT has also been the first instrument to show Cottrell atmospheres (tiny clouds of impurity atoms around dislocations in crystals) at the atomic-scale in the three dimensions of space [2]. A new breakthrough has been achieved ten years ago with the implementation of ultrafast pulsed laser (duration < 1ps) to atom probe tomography [3]. This new generation of laser-enhanced atom probe tomograph, designed in our lab and at Madison, USA, has opened the instrument to semi-conductors and oxides that are key materials in micro-electronics and nanosciences [4,5]. Correlative approaches combining TEM with APT has been shown to be crucial for more accurate APT reconstructions of microelectronics devices [6]. A key force of APT is that 3D reconstructions can be confronted at the same scale to kinetic Monte-Carlo simulations conducted on rigid lattice. This dual approach has been recently applied to phase separation in self-organised GeMn magnetic thin films [5]. In this talk, APT results will be confronted to simulations but also to analytical models dealing with precipitation kinetics (non-classical nucleation [7], coarsening in ternary systems, influence of precipitate size on their composition [8]). A recently developed analytical model dealing with nucleation, growth and coarsening in ternary systems including diffusion coupling between chemical species has revealed that the kinetic pathway does not necessarily follow the tie lines of phase diagram in agreement with APT experiments on model nickel base superalloys [9]. [1] D. Blavette, A. Bostel, J.M. Sarrau, B. Deconihout and A. Menand, 1993, Nature 363, 432 [2] D. Blavette, E. Cadel, A. Fraczkiewicz, A. Menand, 1999, Science 17, 2317 [3] B. Gault, F. Vurpillot, A. Vella, M. Gilbert, A. Menand, D. Blavette, B., 2006, Rev. Sci. Instr. 77, 043705 [4] S. Duguay, T. Philippe, F. Cristiano, D. Blavette, Applied Physics Letter (2010) 97, 242104 [5] I. Mouton, R, Larde, E. Talbot, C. Pareige, D. Blavette, JAP 115, 053515 (2014) [6] A. Grenier, R. Serra, G. Audoit, Jp Barnes, S. Duguay, D. Blavette, N. Rolland, F. Vurpillot, P. Morin, P. Gouraud, Applied Physics Letters 106, 213102 (2015) [7] T. Philippe, D. Blavette, Journal Of Chemical Physics, 135, 134508 1-3 (2011) [8] M. Bonvalet, T. Philippe, X. Sauvage, D. Blavette, Phil. Mag Vol. 94, N°26, 2956-2966 (2014) [9] M. Bonvalet, T. Philippe, X. Sauvage, D. Blavette, Acta Materialia 100 (2015) 169-177 [more]

Driving Forces and Challenges of Interfacing Functional Oxide Perovskites

Driving Forces and Challenges of Interfacing Functional Oxide Perovskites
Perovskite (ABO3) oxides are by no exaggeration an extremely versatile class of materials, exhibiting a broad spectrum of fascinating physical properties: superconductivity, ferromagnetism, ferroelectricity, multiferroic behavior. Scaling down from bulk single crystals to thin and ultrathin (few unit cell thick) epitaxial films the first question is to what extent we are capable to preserve the properties of the bulk and understand the role played by epitaxial growth in changing the physical properties. Another degree of freedom and of complexity as well arises when we interface coherently thin films of two or more chemically and physically different oxides. On one hand, the interfacing poses challenges in terms of finding the fabrication conditions that satisfy the needs of all partners. On the other hand, new physical properties may arise at the interfaces: these are the driving forces for heterostructures and superlattices of perovskite oxides, with a boom of efforts in the last decades, supported by the progress in molecular beam epitaxy and pulsed-laser deposition of complex oxides. Simultaneously the advances of high resolution and scanning transmission electron microscopy with analytical accessoires (EELS, EDX) have been of tremendous help in investigating such heterostructures with unprecedented spatial resolution, contributing directly to the understanding of the physical properties at a unit cell level. In order to underline these statements, I shall give example of the physical properties of heterostructures and superlattices of ferromagnetic and ferroelectric perovskites from my work. [more]

MPIE-Colloquium: Atomic Resolution Observations of Step Structure and Dynamics in Grain Boundaries

MPIE-Colloquium: Atomic Resolution Observations of Step Structure and Dynamics in Grain Boundaries
The development of aberration correction for electron microscopy has greatly increased our ability to characterize materials at the atomic scale. The technological advances that have extended the resolution limit to 0.5Å have also made it possible to record images with better signal-to-noise and at faster rates. In this work, atomic resolution images of moving steps in grain boundaries in gold bicrystals were obtained from extended HR(S)TEM time series by averaging between structural events. The resulting precision of atomic displacements and the small volume of material involved in the observed structures allowed a direct atom-by-atom comparison with MD simulations, revealing details of the transition beyond the temporal resolution of experimental techniques. Specifically, simulations uncovered a transition pathway that involves constriction and expansion of a characteristic stacking fault often associated with grain boundaries in face-centered cubic materials. This analysis is part of a broader study of grain boundary behavior during deformation and capillary shrinkage of island grains. Dynamic observations show that the rate of shrinkage is non-parabolic, and the mechanism is controlled by step motion. Finally, some current developments in electron microscopy will be outlined with a view toward future research on interfaces in materials. [more]

MPIE-Colloquium: Structural Defects and Local Interfacial Chemistry of Complex Oxide Heterointerfaces

MPIE-Colloquium: Structural Defects and Local Interfacial Chemistry of Complex Oxide Heterointerfaces
Transition metal oxide superlattices have been widely investigated during recent years as they are one of the largest material groups where physical and chemical properties such as ferroelectricity, magnetism, ionic and electronic conductivity are closely coupled to structural parameters. Cation sub¬sti¬tution in complex oxides is an effective way to develop the functionalities through carrier doping, band engineering, or application of chemical pressure. For example, the coupling between charge and spin degrees of freedom across the interfaces and the local charge carrier concentration profiles have profound influences on the occurrence of superconductivity in low dimensional systems. Super-conductivity arises when a parent insulator compound is doped beyond some critical con-centration. Furthermore, the magnetic behaviour and conductivity of complex oxide superlattices can be tuned by controlling the layer thickness and by selecting appropriate intervening layer materials. Various methods for growing controlled superlattice structures exist, a favourite has been pulsed laser deposition (PLD), but molecular beam epitaxy (MBE) is now also popular because of the controlled deposition rate and the flexibility allowed by the use of individual element sources. In theory, this allows composition control to the level of individual atomic layers. The PLD process requires higher temperatures and pressures than MBE. It also involves significantly higher energies for the impinging particles, which has potential implications for the interface roughness. In this presentation, I will discuss mapping of the local structure and interfacial chemistry of various complex oxide hetero-interfaces through advanced scanning transmission electron microscopy (STEM) in combination with energy-dispersive x-ray (EDX) analysis and electron energy-loss spectroscopy (EELS).1 EELS allows for local probing of chemical composition and bonding, as well as electronic and magnetic structure, making the combination of STEM and EELS ideal for discovery of structure-property correlations at the atomic scale.2,3 References 1 F. Baiutti et al., Nature Comm. (2015), DOI: 10.1038/ncomms9586, in press. A.V. Boris et al., Science 332 (2011) 937-940. E. Detemple et al., Appl. Phys. Lett. 99 (2011) 211903. E. Detemple et al., J. Appl. Phys. 112 (2012) 013509. A. Frano et al., Adv. Mater. 26 (2014) 258-262. F. Wrobel et al., submitted (2015). K. Song et al., APL Materials 2 (2014) 032104. D. Zhou et al., APL Materials 2 (2014) 127301. D. Zhou et al., Adv. Mater. Interfaces 2 (2015) 1500377. D. Zhou et al., Ultra¬micro¬sco¬py 160 (2016) 110–117. 2 PAvA gratefully acknowledges the intense collaboration with the following people without their contributions this work wouldn’t have been possible: F. Baiutti, E. Benckiser, C. Bernhard, A.V. Boris, M. Castro-Colin, G. Cristiani, E. Detemple, K. Du, A. Frano, E. Gilardi, G. Gregori, H.-U. Habermeier, V. Hinkov, B. Keimer, M. Kelsch, F.F. Krause, G. Logvenov, Y. Lu, J. Maier, V.K. Malik, A.F. Mark, Y. Matiks, M. Morenzoni, K. Müller-Caspary, E. Okunishi, P. Popovich, T. Prokscha, Q.M. Ramasse, M. Reehuis, A. Rosenauer, Z. Salman, H. Schmid, W. Sigle, K. Song, V. Srot, A. Suter, Y. Wang, P. Wochner, F. Wrobel, M. Wu, D. Zhou. 3 The research leading to these results has received funding from the European Union Seventh Framework Program [FP/2007/2013] under grant agreement no 312483 (ESTEEM2). [more]

Role of orientation and grain interactions on the deformation of Ti64

Role of orientation and grain interactions on the deformation of Ti64
  • Date: May 23, 2016
  • Time: 13:30 - 14:00
  • Speaker: Prof Prita Pant
  • Department of Metallurgical Engineering and Materials Science, IIT-Bombay, Mumbai, India Speaker Bio: Prof Prita Pant graduated with a Ph.D from Cornell University in 2004 and is currently an Associate Professor at the Indian Institute of Technology Bombay. Her research interests focus on correlating deformation response of metals and alloys with microstructure. Her group has been using both bulk and micro-deformation techniques along with microscopy to investigate the evolution in microstructure with deformation and quantify the effect of dominant microstructural features on mechanical behavior. They also carry out both Molecular Dynamics (MD) and Dislocation Dynamics (DD) simulations to investigate deformation behavior.
  • Location: Max-Planck-Institut für Eisenforschung GmbH
  • Room: Room 1034 Hall 9
  • Host: Prof. Gerhard Dehm / Dr. Nagamani Jaya Balila
  • Contact: stein@mpie.de
Titanium and its alloys are extensively used for aerospace and biomedical applications due to their high specific strength – even at elevated temperature, and excellent corrosion resistance. Due to its hexagonal crystal structure, alpha titanium is highly anisotropic. Hence it is essential to understand the role of crystallographic orientation and texture in deformation. In this poster, we will present results from bulk deformation and nanoindentation experiments, where we have investigated the role of orientation and of grain interaction on deformation. We show that both orientation and near neighbor interactions play an equally important role in the deformation of polycrystals. We further show that boundaries between hard and soft grains are significantly harder than boundaries between soft grains due to greater incompatibility in deformation between hard and soft grains. In the last five minutes of my talk, she will present some results from her ongoing Dislocation Dynamics simulation studies of deformation of the ferrite phase during wire drawing of pearlitic steel.. [more]

Softening Non-Metallic Crystals by Inhomogeneous Elasticity

Softening Non-Metallic Crystals by Inhomogeneous Elasticity
Materials with more non-metallic bonding are brittle, but are widely used, for instance as protective coatings. These often fail by cracking, so if their fracture resistance were increased, by making plastic flow easier, their lifetime could be extended. Some non-metallic materials deform readily, on a limited number of crystal planes, such as the ternary carbide Ti3SiC2 as well as Nb2Co7, W2B5 and Ta4C3. However, at present the understanding of how to design crystal structures for easy plastic flow is guided only by desirable ratios of elastic constants. Here, it is shown that flow is predicted to become very much easier if there are electronegativity differences within a crystal's unit cell, which cause non-uniform elastic deformation. Very substantial changes in flow behavior appear possible, suggesting this is a first step in developing a simple way of controlling plastic flow in non-metallic crystals. [more]

Re-thinking Rare Earth Magnets for Energy Applications: Demand, Sustainability and the Reality of Alternatives

Re-thinking Rare Earth Magnets for Energy Applications: Demand, Sustainability and the Reality of Alternatives
Due to their ubiquity, magnetic materials play an important role in improving the efficiency and performance of devices in electric power generation, conversion and transportation 1. Permanent magnets are essential components in motors and generators of hybrid and electric cars, wind turbines, etc. Magnetocaloric materials could be the basis for a new solid state energy efficient cooling technique alternative to compressor based refrigeration 2. The talk focuses on rare earth and rare earth free permanent magnets 3 and magnetocaloric materials, with an emphasis on their optimization for energy and resource efficiency in terms critical element utilization. The concept of criticality of strategic metals is explained by looking at demand, sustainability 4 and the reality of alternatives of rare earths. Modelling, synthesis, characterization, and property evaluation of the materials will be discussed considering their micromagnetic length scales, hysteresis and phase transition characteristics. Specifically I will give examples for how to (a) reduce Dy needs by grain boundary diffusion processes, (b) utilize excess Ce in (Nd,Ce)Fe14B balance magnets, (c) tailor anisotropy by 5d elements in (Fe1−xCox)2B alloys and (d) assess magnetic moments in iron nitrides 5-7. 1 Magnetic Materials and Devices for the 21st Century: Stronger, Lighter, and More Energy Efficient, Adv. Mat. 23 (2011) 821. 2 Giant magnetocaloric effect driven by structural transition, Nature Mat. 11 (2012) 620. 3 Towards high-performance permanent magnets without rare earths, J. Phys.: Condens. Matter 26 (2014) 064205. 4Recycling Used Nd-Fe-B Sintered Magnets via a Hydrogen-Based Route to Produce Anisotropic, Resin Bonded Magnets, Advanced Energy Materials 3 (2013) 151. 5Temperature dependent Dy diffusion processes in Nd-Fe-B permanent magnets, Acta Mat. 83 (2015) 248 6Effect of doping by 5d elements on magnetic properties of (Fe1−xCox)2B alloys, Phys. Rev. B 92 (2015) 174413. 7Increased magnetic moment induced by lattice expansion from α-Fe to α′-Fe8N, J. Appl. Phys. 117 (2015) 173911. [more]

Rasterkraftmikroskopie und nanomechanische Methoden - Schwerpunkt Hochtemperatur Mikromechanik

Rasterkraftmikroskopie und nanomechanische Methoden
Schwerpunkt des diesjährigen Arbeitskreistreffens ist die Hochtemperatur Mikromechanik. Als externer Vortragender konnte Dr. David E.J. Armstrong von der Universität Oxford gewonnen werden. Dr. Armstrong gilt als einer der Pioniere auf dem Gebiet der Hochtemperatur‐ Bruchmechanik von Reaktorwerkstoffen in kleinen Dimensionen und wird gezielt über Probleme bei der Implementierung einer Heizung in mikromechanische Prüfapparaturen berichten. [more]

Symposium ”In-situ Microscopy with Electrons, X-Rays and Scanning Probes in Materials Science“

Symposium ”In-situ Microscopy with Electrons, X-Rays and Scanning Probes in Materials Science“

Grain boundary, triple junction and quadruple point mobility controlled normal grain growth

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Atomic-Scale Tomography: An Achievable Vision

This presentation will explore the concept of Atomic-scale tomography (AST), introduce available pathways for achieving AST and discuss how AST will facilitates integration with computational materials engineering. Dr. Thomas F. Kelly, then a professor at the University of Wisconsin – Madison, founded Imago Scientific Instruments in 1998. In September, 2001 Imago completed its first LEAP Microscope and began analyzing specimens. The LEAP has revolutionized the field of atom probe tomography. Imago was subsequently acquired by Ametek and integrated within Cameca. Dr Kelly is now the VP for innovation for Cameca Instruments. [more]

"Mechanics meets Energy IV” symposium at Akademie Biggesee

Strain-induced room temperature grain coarsening: side effect or major energy dissipation mechanism?

In this talk an overview of the room temperature grain coarsening effect in polymer-supported thin gold and copper films under cyclic mechanical loading will be presented. Detailed EBSD analysis, as the major characterization method, allows to capture extensive statistical data about the evolution of thousands of grains with the cycle number but also to observe the motion and elimination of single grain boundaries. It will be shown that very strong and homogeneous grain coarsening occurs in 500 nm gold films where the average grain size grows from 200 nm to approximately 2 µm during cyclic loading. In contrast, 500 nm thick copper films with bi-modal grain size distribution exhibit rather moderate grain coarsening which leads to the reduction of the fraction of ultra-fine grained areas. The correlation between the grain coarsening and the development of fatigue damage will be discussed along with background mechanisms of motion and elimination of grain boundaries. [more]

Mathematical and physical simulation of a funnel thin slab continuous casting machine of a Mexican plant

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Measurement of fracture toughness by nanoindentation methods: recent advances and future challenges

The analysis of deformation and failure mechanisms in small-scale devices and thin films is a critical issue, not yet solved. In this presentation, we describe recent advances and developments for the measurement of fracture toughness at small scales by the use of nanoindentation-based methods including techniques based on micro-cantilever, beam bending and micro-pillar splitting. A critical comparison of the techniques is made by testing a selected group of bulk and thin film materials. For pillar splitting, cohesive finite element simulations are used for analysis and development of a simple relationship between the critical load at failure, pillar radius, and fracture toughness for a given material. The minimum pillar diameter required for nucleation and growth of a crack during indentation is also estimated. An analysis of pillar splitting for a film on a dissimilar substrate material shows that the critical load for splitting is relatively insensitive to the substrate compliance for a large range of material properties. Micro-pillars are then produced by Focused Ion Beam (FIB) ring milling, being the pillar diameter approximately equal to its length; this ensures full relaxation of pre-existing residual stress in the upper portion of the specimen. Nanoindentation splitting tests are performed in-situ and the deformation mechanisms corresponding to each class of materials have been investigated. Experimental results from a selected group of materials show good agreement between single cantilever and pillar splitting methods, while a discrepancy of ~25% is found between the pillar splitting technique and double-cantilever testing. The limitations of the method are finally discussed. In particular, a minimum pillar’s diameter for the nucleation and growth of a crack during indentation is identified and quantified for a wide range of materials properties. It is concluded that both the micro-cantilever and pillar splitting techniques are valuable methods for micro-scale assessment of fracture toughness of brittle ceramics, provided the underlying assumptions can be validated. Although the pillar splitting method has some advantages because of the simplicity of sample preparation and testing, it is not applicable to most metals because their higher toughness prevents splitting, and in this case, micro-cantilever bend testing is preferred. [more]

Atomistic Studies on Dislocation – Interface Interactions:

Interfaces play a decisive role in the deformation of any polycrystalline metal or precipitate-strengthened alloy. Perhaps best known is the role of grain boundaries (GBs) as obstacle to dislocation motion as evidenced by the Hall-Petch strengthening. However, GBs can also serve as initiation sites for fracture and provide easy pathways for crack propagation. When the grain size is reduced below 100 nm, GBs become furthermore the dominant sources and sinks for dislocations, and pinning of dislocations at GBs becomes an important hardening mechanism. At very small grain sizes below about 10 nm, the contribution of grain boundary glide and grain rotation becomes significant. All these processes take place at the atomic scale. Consequently, atomistic simulations have played a key role in studying grain- and interphase boundaries (IPBs), and their interactions with dislocations. However, most of the detailed studies on dislocation – interface interactions were performed on quasi-two dimensional simulation setups with straight dislocation lines interacting with perfectly planar interfaces. Similarly, the deformation of nanocrystalline metals is commonly studied using artificial structures generated by means of the Voronoi tessellation. This procedure creates planar GBs and non-equilibrium triple junction topologies, as well as unrealistic numbers of neighboring grains and distributions of triple line lengths. Here we give an overview on our recent atomistic studies on dislocation – interface interactions, with the focus on non-planar boundaries and more realistic GB topologies. Simulations on twinned nanoparticles and nanowires are used to demonstrate that the presence of twin boundaries can change the deformation mechanism, thereby explaining experimentally observed dislocation structures. Controlled studies on dislocations interacting with various high-angle GBs in a bicrystal setup allow to quantify changes in the stress field and energy of absorbed dislocations and show the importance of GB curvature on slip transmission through GBs. We then compare the processes taking place in various nanocrystalline samples with different degrees of GB curvature as well as different GB network topologies. Here, a statistical analysis shows clear differences in terms of stress states and contributions of dislocation glide versus GB-mediated processes, however the distribution of critical stresses for dislocation nucleation and dislocation depinning from GB as well as on the distribution of plastic strain caused by individual slip events remains unaffected by the GB topology. Finally, we report on simulations on atom probe tomography – informed superalloy samples, which reveal the importance of interface curvature and chemical composition on the misfit dislocation network and subsequent interactions with matrix dislocations. [more]

Career Talk: BASF Coatings GmbH

Career Talk
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Understanding fatigue crack initiation in Ni superalloys: a study with HR-EBSD, HR-DIC and CP-FEA

The lifetime of aerospace engineering components is often limited by fatigue. Traditional management strategies presuppose an existing defect length and estimate time to failure through short crack growth and propagation methods, using empirical approaches such as fitting of a Paris’ law. New advances in material processing and production render this argument insufficient to exploit tackle the next generation clean and well-engineered materials, as these growth based empirical studies are too conservative for effective engine management. In this talk, I will outline our recent work focussing on exploiting the next generation of characterisation tools, such as high (angular) resolution electron backscatter diffraction, high (spatial) resolution digital image correlation, combined with geometrically faithful and relatively simple (i.e. limited free parameters) lengthscale based crystal plasticity approaches. These have been brought to bear on a experimental and modelling campaign that focusses on tracking deformation and damage accumulation in single, directionally solidified, polycrystalline and polycrystalline Ni-superalloys with inclusions. In this talk I will outline some highlights from this body work which include: a comparison of ability of HR-DIC and HR-EBSD to recover components of the deformation tensor; understanding accumulated damage and the onset of cracking near non-metallic inclusions; and predicting and understanding accumulated slip in fatigue. [more]

Nanostructure of wet-chemically prepared, polymer-stabilized silver–gold nanoalloys (6 nm) over the entire composition range

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Design and characterization of novel TiAl alloys and metal-diamond composites for beam-based additive manufacturing

Metal additive manufacturing (AM) techniques are powder-based, layer by layer methods which can directly build 3D structures onto substrates with complex geometries. They offer a unique ability to dynamically mix materials during the deposition process and produce functionally graded structures, new composite microstructures and perhaps even new material classes. Some of the challenging issues related to the energy beam based process are the very high heating and cooling rates, leading to non-equilibrium microstructures, which are usually harder, less ductile, and often exhibit high residual stresses; the strongly textured, anisotropic microstructures inherited from the solidification conditions; or the pronounced residual stresses resulting from the large thermal gradients in the AM fabricated parts. However, the very rapid consolidation of the material in a small material volume and the achieved high solidification rates allow for the manufacture of components containing meta-stable materials. In this talk some relevant results of the AM related research at Empa will be presented. The first part of the presentation deals with the development and characterization of a novel oxide dispersion strengthened (ODS) titanium aluminide alloy (Ti-45Al-3Nb ODS) for beam-based AM processes. The alloy design and selection process was supported by computational thermodynamics based on the CALPHAD approach, taking into account requirements for processing as well as long term alloy behavior under service conditions. Besides, an in situ method to study the behavior of alloys during rapid heating and cooling combining laser heating with synchrotron micro X-ray diffraction (microXRD) and high-speed imaging was developed. In the second part, the feasibility of producing metal-diamond composites by SLM was studied. A Cu-Sn-Ti alloy powder was mixed with 10-20 vol.% artificial, mono-crystalline diamonds. The influence of the processing parameters on the density and microstructure of the composites as well as on the stability of the diamonds was studied. It was shown that stable specimens containing intact diamonds could be produced. [more]

Properties of CuCdTeO films: from solid solutions to composites

Properties of CuCdTeO films: from solid solutions to composites
[more]

Career Talk: McKinsey & Company

Career Talk
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Tailoring Metastable Metallic Materials for Engineering Applications

Tailoring Metastable Metallic Materials for Engineering Applications
In modern society, metallic materials are crucially important (e.g. for applications related to energy, safety, infrastructure, transportation, health, medicine, life sciences, IT). Contemporary examples with inherent challenges to be overcome are the design of ultrahigh specific strength materials. There is a critical need for successful developments in this area in particular for reduced energy consumption, reduction of pollutant emissions and passenger safety. Also, the ageing society makes biomedical materials for implant and stent design crucially important. A drawback of nearly all current high strength metallic materials is that they lack ductility (i.e. are brittle and hard to form) - or on the opposite side, they may be highly ductile but lack strength. Hence, it is mandatory to develop new routes for creation of tailored metallic materials based on hierarchical hybrid structures enabling property as well as function optimization. One starting point along these lines is the design of monolithic amorphous materials or bulk micro-, ultrafine- or nano-structured composite structures with intrinsic length-scale modulation and phase transformation under highly non-equilibrium conditions. This can include the incorporation of dispersed phases which are close to or beyond their thermodynamic and mechanical stability limit thus forming hierarchically structured hybrid and ductile/tough alloys. Alternatively, the material itself can be designed in a manner such that it is at the verge of its thermodynamic/mechanical stability. This talk will present recent results obtained for metallic glass-based hybrid structures with transformation effects at different length-scales and microcrystalline-grained hybrid structures based on elastic instabilities and modulated length-scale. The deformation behaviour and possible phase transitions during deformation will be related to the intrinsic properties of the phases as well as the microstructure of the material including heterogeneities and length-scale modulation in order to derive guidelines for the design of macroscopically ductile high-strength materials. Finally, the results will be critically assessed from the viewpoint of possible scaling-up for technological applications and the use of simple and cost effective processing technologies. [more]

New insights into interfaces of metals, oxides and nanoparticles via APT

New insights into interfaces of metals, oxides and nanoparticles via APT
In many materials, internal interfaces and surfaces are governing their properties. Due to the inherently atomic scale of interfaces, they have notoriously been elusive to structural and chemical analysis, limiting our current understanding about their behavior. Atom probe tomography, as a single atom sensitive mass spectrometry method with atomic resolution achievable, can significantly add to the understanding of interfaces. In this talk, I will present results on the analysis of local chemistry at grain boundaries in metals and oxides and the challenges associated with the data interpretation. This will also include nanomaterials such as nanoparticles and nanowires, where surface distributions of the chemical elements can be investigated and correlated with the particle’s properties. [more]
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