题目: Heterogeneities and deformability in bulk metallic glasses

　　报告人：Dr. Simon Pauly ^1,2

　　　　¹ Institute for Complex Materials, IFW Dresden, Germany
　　　　² Technische Universität Dresden, Germany

　　时间：Feb. 20^th,2017 (Mon). 10:00-11:30 AM

　　地点：李薰楼356室， Room 356, Lee Hsun Building

　　Abstract:

　　Monolithic bulk metallic glasses suffer from shear softening and generally fail in a macroscopically brittle manner during uniaxial loading. Only when heterogeneities are introduced can the shear band generation and propagation be impeded and the overall plasticity be increased. However, it is very difficult to deliberately create such structural heterogeneities and, in doing so, to control their size and distribution. This is a vital aspect for optimizing their mechanical properties and for understanding the role of heterogeneities on the deformation mechanisms.

　　Here, we present results on glass-forming alloys, which can polymorphically precipitate shape-memory crystals. Two typical alloy systems are introduced and the effect of alloy composition on the phase formation and microstructure are discussed. Moreover, the deformation mechanisms are elaborated. Unfortunately, it is very difficult to precisely adjust and tailor their microstructure in terms of crystal sizes, numbers and distribution. This becomes feasible when bulk metallic glasses are flash-annealed, i.e. rapidly heated and subsequently quenched to freeze in the microstructure. Depending on the heating rate and the annealing temperature, the glasses can either be relaxed, rejuvenated or partially crystallized. At the later stages of flash-annealing uniformly dispersed fine crystals precipitate in the glass. The analysis of the number of crystals suggest the occurrence of heating rate-dependent transient nucleation. During crystallization a thermal front traverses the sample and its characteristics are evaluated and compared with levitation experiments. The microstructure as well as the mechanical properties reveal a clear dependence on the thermal history.

　　Brief Biography:

　　Dr. Simon Pauly did his PhD studies at Technischen Universität Darmstadt (TU Darmstadt) and Leibniz-Institut für Festkörper- und Werstoffforschung (IFW) under guidance of Prof. Dr. –Ing. Jürgen Eckert, and received his Dr.-Ing from Technische Universität Dresden (TU Dresden) in June, 2010. Later, he worked as a postdoctor at IFW Dresden. From Nov., 2012 to Aug., 2013, he was a Marie-Curie-Fellow in the group of Prof. A. Lindsay Greer at the University of Cambridge. Now he is the head of research group “Bulk metallic glasses and composites” at IFW Dresden, and lecturer at TU Dresden.