报告摘要

  Internal interfaces, such as grain-or phase boundaries have a strong impact on almost all properties of any material. Despite their importance, the understanding of the atomic structure, structure-property relations or structural transformations of these defects still leaves open questions and even open conceptual issues, particularly when more general internal interfaces are addressed. Naturally, materials with high specific internal interface areas, i.e. nanocrystalline or ultrafine grained materials are more strongly affected by the presence of internal interfaces. Particularly the development of high-strength metals has driven the endeavor of pushing the limit of grain size reduction according to the Hall-Petch law. However, a continued grain refinement is technologically particularly challenging, and incorporates issues concerning microstructural stability. However, utilizing structural transformations at / of grain boundaries as well as more complex interactions of dislocations at / with grain boundaries can provide additional options and new pathways for optimizing the mechanical properties and / or the stability of ultrafine grained-or nanocrystalline materials. The interplay of several of these influencing factors can yield complex situations concerning the temperature-dependence of properties such as e.g. grain boundary self-diffusivity and provide a rich field yet to be explored. Correlative measurements of the atomistic structure and the kinetic properties of the grain boundaries via TEM-based analyses and tracer diffusion measurements provide unique insights into the interplay of GB structure and kinetics with respect to GB-related segregation, precipitation and phase transformations. This is true irrespective of the grain size or chemical complexity. Thus, selected examples include grain sizes that span the range from bi-crystals to nanocrystalline materials and cover also the range from pure metals to high-entropy alloys.
 

  报告人简介

  Gerhard Wilde‌现任德国明斯特大学材料物理研究所所长。研究领域包括纳米结构、纳米晶材料、固体材料的组织演变、缺陷和扩散等‌，于1997年获得德国柏林技术大学的博士学位。2010年获得洪堡终身科学家成就奖,2019年获得‌阿里·雷扎·亚瓦里杰出高级科学家奖。