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Yasmin Ahmed Salem, M.A.
Yasmin Ahmed Salem
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Phone: +49 211 6792 722
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Scientific Events

Scientific Events

Month:

19135 1563788138

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]

18024 1552645836

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]

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

20499 1568363883

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

20262 1568021684

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

20120 1566837630

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

20121 1566837933

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]

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

19015 1560759446

MPIE-Kolloquium: 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]

 
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