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Yasmin Ahmed Salem, M.A.
Yasmin Ahmed Salem, M.A.
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Scientific Events

Scientific Events

Month:

MPIE Seminar

23527 1579009239

Sustainable Metallurgy

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]

MPIE Seminar

23526 1579012896

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

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]

Molecular dynamics on the diffusive time scale

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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]

MPIE Workshop: Mechanisms of White Etching Matter Formation

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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]

Topological Optimization and Textile Manufacturing of 3D Lattice Materials

15524 1537856221

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]

Additive Manufacturing, 3D Printing, Porosity and Synchrotron Experiments

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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]

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

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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]

 
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