Scientific Events

Properties of materials are sensitively influenced by the microstructure inherited from their synthesis and processing. In response to high stress, temperature and composition gradients microstructures evolve in a complex way that involves nucleation of new phases, interface migration and mass redistribution that lead to complex morphological evolution on the mesoscale. Understanding this evolution and the ways it influences properties can be key to optimizing materials for targeted applications. Due to their importance related to grain structure evolution and properties of polycrystals, significant effort has been devoted to calculation of free energies and mobilities of isolated grain boundaries using atomistic simulations. It is commonly assumed that interface properties are continuous functions of temperature, pressure and chemical composition. On the other hand there is accumulating evidence suggesting that interfaces are capable of first order structural transitions, in which case the properties like segregation, excess volume, mobility, cohesive strength and sliding resistance may change discontinuously. This talk will review the results of recent atomistic computer simulations, investigating the nature of structural phase transitions in metallic grain boundaries, induced by changes in temperature and composition. We start by reviewing changes in the structure of elemental boundaries that are observed when these interfaces are exposed to very high homologous temperatures, and the nature of the qualitatively different types of structural disordering that can arise. The transitions involve changes in atomic density in the grain-boundary plane, which was discovered only when new simulation methodologies were developed that permit such variations. We show that interfaces can absorb large number of point defects through a first order phase transition, which may play important role in recovery of materials from radiation damage. Our simulations demonstrated strong effect of the transitions on self and impurity diffusion as well as grain boundary migration and shear strength. [more]

The processing regime relevant to superplasticity in the Ti-6Al-4V alloy is identifed. The effect is found to be potent in the range 850 to 900 deg ?C at strain rates between 0.001/s and 0.0001/s. Within this regime, mechanical behaviour is characterised by steady-state grain size and negligible cavity formation; electron backscatter diffraction studies confirm a random texture, leaving grain boundary sliding as the overarching deformation mechanism. Outside of the superplastic regime, grain size refinement involving recrystallisation and the formation of voids and cavities cause macroscopic softening; low ductility results. Stress hardening is correlated to grain growth and accumulation of dislocations. The findings are used to construct a processing map, on which the dominant deformation mechanisms are identified. Physically-based constitutive equations are presented which are faithful to the observed deformation mechanisms. Internal state variables are used to represent the evolution of grain size, dislocation density and void fraction. Material constants are determined using genetic-algorithm optimisation techniques. Finally, the deformation behaviour of this material in an industrially relevant problem is simulated: the deformation of diffusion-bonded material for the manufacture of hollow, lightweight structures, e.g. those used for fan blades of aeroengines. [more]

In this talk, I will give an overview of our attempts to design various solid catalysts for industrially important chemical conversions. These reactions include conversion of biomass derived platform chemicals to other value-added chemicals, lower alkane activation and CO2 activation. We try to understand how the structural aspects of catalysts affect the reactivity, which is crucial in developing better catalysts. For this purpose, we try to make use of various characterization techniques. Recent results from our work in this direction will be described, taking a few examples. [more]

The Max-Planck-Institut für Eisenforschung in Düsseldorf is organizing a workshop on Hydrogen Embrittlement and Sour Gas Corrosion in Oil and Gas Industry on 27th and 28th January 2015 and we would like to invite you and your research colleagues to participate in this event. The intention is to 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. In the upcoming workshop, a broad variety of topics concerning hydrogen embrittlement and sour gas corrosion in oil and gas industry, with a focus on corrosion resistant alloys, will be presented. We also invite all interested participants to contribute with poster presentations on hydrogen embrittlement and sour gas corrosion related discussions during coffee and lunch breaks. Note that there are no restrictions on the poster lay-outs. If you and your colleagues would like to attend this event, then please register online before 10th December 2014. We emphasize that registration is mandatory and that there are limited places only. A participation fee of 100 Euros applies. [more]

The Max-Planck-Institut für Eisenforschung in Düsseldorf is organizing the 4th 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. Scope Plastic deformation of polycrystals is the result of a complex interplay of deformation mechanisms in individual grains and grain interactions. The mechanims mediating plastic deformation, e.g. dislocation glide, mechanical twinning, or displacive phase transformations, occur on the atomic scale. However, the macroscopic response of polycrystalline materials is heavily influenced by a hierarchy of microstructures, as for example precipitate structure, dislocation arrangement, grain boundaries, or crystallite orientation distribution. To arrive at computationally efficient material models various coarse-graining steps are necessary to incorporate the small-scale behaviour in effective continuum descriptions. Simulation can replace expensive and time-consuming experiments in the design of components as well as of the tools for their production. However, accurate material models of polycrystal mechanics, which take the microstructure evolution into account, are indispensable for the achievement of such potential cost-savings and reduction in development times. The symposium shall provide an up-to-date overview on the multi-scale modelling and simulation of polycrystal plasticity of metals. Special attention shall be given to industrially relevant multi-phase materials and materials showing mechanical twinning and phase transformations as for instance complex-phase steels, TRIP/TWIP steels, and Magnesium. In this spirit, we are looking forward to experimental, theoretical and computational contributions on all involved length scales. Topics include but are not restricted - fundamental mechanisms of crystal plasticity - TWIP/TRIP effect - behavior of grain ensembles - coarse-graining in polycrystal deformation - materials processing … The event will take place on July 14th and 15th, 2014 in the Max-Planck-Institut für Eisenforschung at Max-Planck-Straße 1, 40237 Düsseldorf, Germany. If you would like to attend this event, then please register online before April 30st 2014. We emphasize that registration is mandatory and that there are limited places only. A participation fee of 100 Euros applies. [more]

Dear Colleagues, we are happy to invite you to the workshop focused on "Bridging Scales in Tribology and Wear", which is scheduled at the Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf on the 25th of June 2014. 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. The current program, confirmed external speakers and further details are available at http://wear.mpie.de. With kind regards, Steffen Brinckmann and Markus Valtiner [more]

The Max-Planck-Institut für Eisenforschung in Düsseldorf is organizing a workshop on hydrogen embrittlement in January, 23rd 2014 and we would like to invite you and your research colleagues to participate in this event. The workshop is part of a series of topical one-day meetings at our institute. The intention is to bring together leading experts from academia and industry in a workshop format to enable in-depth discussions of fundamental and applied research regarding both current and preliminary research in this area. A broad variety of topics concerning hydrogen embrittlement in steels will be presented; covering topics from fracture criterion to new techniques for hydrogen detection. The program also includes a lab session where new approaches used in material characterization and modeling will be demonstrated. We also invite all interested participants to contribute with poster presentations on H-embrittlement related discussions during coffee and lunch breaks. Note that there are no restrictions on the poster lay-outs. The participation is for free. [more]