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Physics of Surfaces

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Department of Materials Science

  • 2017/12/12

    Mixing instabilities during shearing of metals

    a) A schematic drawing showing the high-pressure torsion (HPT) | b) A parallelepiped-shaped volume section

    Nature article 1611 (2017): Mohsen Pouryazdan, employee of the Joint Research Laboratory Nanomaterials

    Mohsen Pouryazdan1, Boris J.P. Kaus2, Alexander Rack3, Alexey Ershov4,5 & Horst Hahn1,6

    DOI: 10.1038/s41467-017-01879-5

    Severe plastic deformation of solids is relevant to many materials processing techniques as well as tribological events such as wear. It results in microstructural refinement, redistribution of phases, and ultimately even mixing. However, mostly due to inability to experimentally capture the dynamics of deformation, the underlying physical mechanisms remain elusive. Here, we introduce a strategy that reveals details of morphological evolution upon shearing up to ultrahigh strains. Our experiments on metallic multilayers find that mechanically stronger layers either fold in a quasi-regular manner and subsequently evolve into periodic vortices, or delaminate into finer layers before mixing takes place. Numerical simulations performed by treating the phases as nonlinear viscous fluids reproduce the experimental findings and reveal the origin for emergence of a wealth of morphologies in deforming solids. They show that the same instability that causes kilometer-thick rock layers to fold on geological timescales is acting here at micrometer level.

  • 2017/10/20

    #1 cited paper published in the past 10 years in the Materials Science, Ceramics category

    Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics

    by Paolo Colombo, Gabriela Mera, Ralf Riedel, Gian Domenico Sorarù:

    Abstract

    Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. (…)

    Journal of the American Ceramic Society

  • 2017/10/11

    Metalle an der Grenze der Verformbarkeit

    Simulationsmodell eines verformten Tantalkristalls. Ausgehend von den einzelnen Atomen (gelb) hat ein Algorithmus die Form der Versetzungsdefekte (grüne Linien) und der Zwillingsgrenzen (graue Flächen) rekonstruiert. Bild: Alexander Stukowski

    Darmstädter Forscher entwickelt hochpräzise Computermodelle

    Forscher der Technischen Universität Darmstadt und des Lawrence Livermore National Laboratory in Kalifornien können erstmals mit neu entwickelten, präzisen Computermodellen den Verformungsprozess metallischer Werkstoffe bis auf einzelne Atome genau vorhersagen. Ihre Arbeit ist jetzt in „Nature“ erschienen.