Multiscale structures of Zr-based binary metallic glasses and the correlation with glass forming ability

Thermal behaviors and structures of three Zr-based binary glass formers, Zr₅₀Cu₅₀, Zr₆₄Cu₃₆ and Zr₆₄Ni₃₆, were investigated and compared using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), high energy X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). The high energy XRD results show that the bulk glass former Zr₅₀Cu₅₀ has a denser atomic packing efficiency and reduced medium-range order than those of marginal glass formers Zr₆₄Cu₃₆ and Zr₆₄Ni₃₆. Based on TEM observations for the samples after heat treatment at 10 K above their crystallization onset temperatures, the number density of crystals for Zr₅₀Cu₅₀ was estimated to be 10²³–10²⁴ m⁻³, which was four-orders higher than that in Zr₆₄Cu₃₆ and Zr₆₄Ni₃₆ metallic glasses. SAXS results indicate that Zr₅₀Cu₅₀ has higher degree of nanoscale inhomogeneities than those in Zr₆₄Cu₃₆ and Zr₆₄Ni₃₆ at as-cast state. The observed multiscale structures are discussed in terms of the phase stability and glass-forming ability of Zr-based binary glass formers.