Mechanism of Ag and Al on improving the glass forming ability of CuZr-based alloys

By a mean field theoretical computation, the equilibrium distributions of additional Ag and Al in the crystalline phase of CuZr-based alloys were determined to occupy the two sublattices of the B2 structure randomly. With the molecular dynamics technique, the effects of Ag and Al on the enthalpy difference (ΔH) between the supercooled melt and the crystalline phase were evaluated. The improved glass forming ability of Cu45Zr45Al10 and Cu45Zr45Ag10 can be attributed to their remarkably smaller ΔH than that of CuZr. The calculated diffusion coefficients are more sensitive to the atomic weight of the component atoms than to their interaction strength. As the component atom with the largest mass, the additional Ag increases the viscosity of the supercooled melt significantly and the experimentally stronger glass formation ability of Cu45Zr45Ag10 than Cu45Zr45Al10 can be well understood.