Structural mechanisms of enhanced mechanical property in ZrCu metallic glass at low temperatures

The application of traditional crystalline materials as structural materials cannot meet critical design challenges due to low-temperature brittleness. To address this issue, this study investigates the deformation behavior of Zr2Cu metallic glass (MG) model at ambient and low temperature states by molecular dynamics (MD) simulations to unravel the governing mechanisms associated with mechanical performance. Structurally representative amorphous models of the MG were developed and their evolutions under tensile loadings at ambient (300 K) and low temperatures (250 K, 200 K, 150 K, 100 K, 50 K) were captured. Notably, significant variations in maximum stress and corresponding strains characterized the stress-strain behavior as elastic-plastic properties increased with decreasing temperatures. Stress activations of the atomic mass were rapidly incipient at the ambient condition, but largely constrained at low temperatures by which the density variations of activated zones and the emerging strain of first shear transformation zones (STZ's) established a negative correlation with temperature as inferred by the wider strain range of deformation. Disparities in strain thresholds accounted for the higher free volume content at the ambient state, but as temperatures declined, fine structural differences stimulated the formation of densely-packed structures in the amorphous model at low temperatures by the spontaneous annihilation of excessive free volumes. Consequently, the higher growth rates of the average atomic potential energy and the retarded emergence of high-potential-energy atomic mass suggest that at low temperatures, there is a higher resistance to shear band nucleation and higher barrier for atomic migration. As a result, the generation of free volumes, formation of STZs and shear bands were retarded, leading to the enhanced ductility. Thus, at low temperatures, unique tuning mechanisms of structural performance were evolved in the amorphous model that suitably enhanced the constitutive properties of Zr2Cu MG.