Title: The effects of cooling rate on reversibility and elasticity in model glasses

Author (Talk): Meng Fan, Yale University

Abstract:

Bulk metallic glasses (BMGs) possess promising mechanical properties, such as superior strength and hardness and a high elastic strain limit. However, we do not currently have a sufficient theoretical understanding of BMGs to predict, design, and optimize their mechanical behavior. For example, we do not fully understand how BMGs respond to applied stress. In addition, there is no theoretical framework for connecting atomic-scale rearrangements and irreversibility to macro-scale elasticity. We employ molecular dynamics simulations to cool binary Lennard-Jones liquids to zero temperature over a wide range of cooling rates $R_c$. We then apply quasistatic pure shear at constant pressure to the glasses and identify neighbor-switching atomic rearrangement events. We exert backward shear after each rearrangement to zero strain and quantify the state-irreversibility $D_0$ and path-irreversibility $I$. We show that glasses lose their reversibility significantly within their "elastic region". Irreversibility $D_0$ and $I$ turn out to increase with $R_c$, accompanying the increase of rearrangement frequency and mean size. We then build up a dynamic potential energy landscape in the strain direction and link its geometry with irreversibility and ductility of metallic glasses as a function of $R_c$.