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

Scientific Events

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MPIE Colloquium

10304 1518609265

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

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]

MPIE Colloquium

10352 1498039052

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

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

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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

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Phase Transformations under Rapid Heating in Metallic Micro- and Nanolaminates

[more]

Phase-transformation effects on residual stress development in welding

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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 Microscopy

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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

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]

9995 1518609196

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]

 
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