Molecular dynamics simulation of diffusion in supercooled Cu-Zr alloys

Molecular dynamics (MD) simulations of diffusion in Cu-Zr alloys in their liquid and supercooled liquid states were performed using a recently developed Finnis-Sinclair many-body interatomic potential. To help assess how well the interatomic potential describes the energetics of the Cu-Zr system, the liquid structure determined by MD simulations was compared with wide-angle X-ray scattering measurements of the liquid structure for a Cu(64.5)Zr(35.5) alloy. Diffusion was examined as a function of composition, pressure and temperature. The simulations reveal that the diffusion exhibits strong compositional dependence, with both species exhibiting minimum diffusivities at similar to 70% Cu. Moreover, the MD simulations show that the activation volumes for Zr and Cu atoms exhibit a maximum near 70% Cu. Evidence is obtained that the glass transition temperature also changes strongly with composition, thereby contributing to the diffusion behaviour. The relationship between this minimum in diffusion and the apparent best glass-forming composition in the Cu-Zr system is discussed.