主讲人：张会军 (Huijun Zhang)
题 目：Identifying the boundary of non-equilibrium states: Compression-induced polycrystal-glass transition in binary crystals
A polycrystal will transform into a glass when its grain size is sufficiently reduced. However, it is not clear how the polycrystal-glass boundary can be identified, whether the boundary is a sharp point or a crossover regime, and what features exist at this boundary. These questions have rarely been explored. Here we compress binary single crystals composed of hard and soft disks into polycrystals and further into glasses by simulation. Through this approach, we can continuously increase the fraction of mismatched particles and produce tiny grains not accessible before. Such full spectrum of grain size enables us to study the polycrystal-glass transition. We observe rich structural, mechanical, dynamical, and thermodynamic features at the sharp polycrystal-glass boundary. These features could serve as criteria for the polycrystal-glass transition. Our analyses reveal the Hall-Petch and inverse Hall-Petch behaviors in two-dimensional polycrystals and identify three glass regimes. Our approach can guide the fabrication and stabilization of ultrafine-grained polycrystals. The observations cast light on the crossover regime of polycrystals and glasses.
Huijun Zhang is a postdoctoral research fellow at Department of Physics in The Hong Kong University of Science and Technology. He graduated in Materials Science from USTB and then moved to Condense Matter Physics for his PhD. He started his research on the search for technologies to produce glass/amorphous states using computer simulations at HKUST since 2015. He is interested in glass transition, both in searches for new physics and in function design. In addition, he has contributed to identification of non-equilibrium states.