Relating metallic glass mechanical properties to liquid structure

Molecular dynamics simulations indicate that the mechanical properties of a model metallic glass depend critically on the degree of supercooling attained in the liquid prior to vitrification. A well-characterized binary glass-forming system roughly analogous to ZrTi was quenched instantaneously from a series of liquid temperatures. These temperatures ranged from approximately twice that of the onset of supercooled liquid behaviour down to just above the mode-coupling temperature (TMCT). The low-temperature mechanical properties of these glass samples is studied in simple shear at constant strain rate while the density of the system is held constant. All the glasses exhibit an initial linear response at small strain and approached a steady-state flow regime at large strain. However, glasses obtained by quenching from supercooled liquids just above TMCT, which we will refer to as TMCT glasses, exhibit higher shear strength and modulus than glasses obtained by quenching from higher temperature liquids. The TMCT glasses also exhibit pronounced shear softening. The change in pressure during shear is markedly different in these glasses, and indicates that the TMCT glasses retain aspects of the quenched-in structure out to as much as 25% strain. The changes in pressure also indicate significant structural changes occur even during nearly linear stress–strain response.