High packing density of Zr- and Pd-based bulk amorphous alloys

Abstract

With the aim of evaluating a packing density of the new bulk amorphous alloys, the densities of bulk Zr60Al10Cu30, Zr55Al10Cu30Ni5 and Pd40Cu30Ni10P20 alloys were measured in cast amorphous and annealing-induced crystallized states. The densities of the as-cast amorphous and crystallized phases were measured to be respectively 6.72 and 6.74 Mg/m3 for the Zr-Al-Cu alloy, 6.82 and 6.85 Mg/m3 for the Zr-Al-Cu-Ni alloy, 9.27 and 9.31 Mg/m3 for the Pd-Cu-Ni-P alloy. The annealing leading to the fully relaxed amorphous state induced slight increases of density to 6.83 Mg/m3 for the latter Zr-based alloy and to 9.28 Mg/m3 for the Pd-based alloy. The increase in density due to crystallization is evaluated to be in the range of 0.30 to 0.54% which is much smaller than that (2 to 3%) for the previously reported amorphous alloys. This result indicates that the new bulk amorphous alloys have more packed atomic configurations than ordinary amorphous alloys which require high cooling rates above 104 K/s for glass formation. It is therefore thought that the higher packing density achieves the high glass-forming ability through the decrease of atomic diffusivity and the increase of viscosity. The present information obtained from the density data is consistent with the previously proposed concept for the achievement of high glass-forming ability for multicomponent amorphous alloys.