Molecular dynamics simulation of diffusion in supercooled Cu–Zr alloys

Abstract

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_64.5Zr_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 ∼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.

Keywords:

• diffusion
• liquid alloys
• diffraction
• molecular dynamic simulations

Acknowledgements

We would like to thank Bob Hyers and Stacy Canepari of the University of Massachusetts, Amherst and Jan Rogers of NASA Marshall Space Flight Center, Huntsville, Alabama for their contributions to collecting the liquid density and scattering data. Work at the Ames Laboratory was supported by the Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-07CH11358. The high-energy X-ray work at the MUCAT sector of the Advanced Photon Source was supported by the US Department of Energy, Office of Science, Basic Energy Sciences under Contract No. DE-AC02-06CH11357.