The issue, composition dependence of glass-forming ability (GFA) in metallic glasses (MG), has been investigated by systematic experimental measurements coupled with theoretical calculations in Cu-Zr and Ni-Nb alloy systems. It is found that the atomic-level packing efficiency strongly relates to their GFA. The best GFA is located at the largest difference in the packing efficiency of the solute-centered clusters between the glassy and crystal alloys in both MG systems. This work provides an understanding of GFA from atomic level and will shed light on the development of new MGs with larger critical sizes.

Change in local atomic environment during crystallization of Zr-based glassy alloys was studied by extended x-ray absorption fine structure (EXAFS) spectroscopy. The formation of icosahedral quasicrystalline phase followed by crystallization of tetragonal ${\mathrm{CuZr}}_2$ has been observed in the ${\mathrm{Zr}}_{70}{\mathrm{Cu}}_{29}{\mathrm{Pd}}_1$ glassy alloy during annealing up to 850 K. On the other hand, the binary ${\mathrm{Zr}}_{70}{\mathrm{Cu}}_{30}$ alloy shows a single glassy to crystalline ${\mathrm{CuZr}}_2$ phase transformation. The local atomic environment of as-quenched ${\mathrm{Zr}}_{70}{\mathrm{Cu}}_{30}$ alloy is matched to an icosahedral local atomic configuration, which is similar to that of the as-quenched ${\mathrm{Zr}}_{70}{\mathrm{Cu}}_{29}{\mathrm{Pd}}_1$ alloy and the alloy annealed at 593 K containing icosahedral phase. Considering that the supercooled liquid region appears prior to crystallization in the ${\mathrm{Zr}}_{70}{\mathrm{Cu}}_{30}$ glassy alloy, the observed results support the theory claiming a strong correlation between the existence of local icosahedral short-range order and stability of the supercooled liquid state.