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Yasmin Ahmed Salem
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Scientific Events

Scientific Events

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4th International Conference on Medium and High Manganese Steels

6th International Symposium on Computational Mechanics of Polycrystals, CMCn 2018

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

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 1st 2018. We emphasize that registration is mandatory and that there are limited places only. Many thanks, we hope to see you in Düsseldorf! [more]

MPIE Colloquium

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Martensitic Microstructure: Modern Art or Science?

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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]

MPIE Colloquium

13920 1525694664

Quantum Chemistry in Position Space and Chemical Bonding in Intermetallic Compounds

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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]

MPIE Colloquium

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High Temperature Materials - Recent Developments for Future Challenges

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]

 
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