Glassy solidification criterion of Zr₅₀Cu₄₀Al ₁₀ alloy

We examined the solidification morphology and structure of arc-melted Zr₅₀Cu₄₀Al₁₀ glass-forming alloys in order to determine the impurity influences using two grades of Zr metals: "sponge Zr" purified somewhat but not highly by the Kroll method, and highly purified "crystal Zr". When crystal Zr is used, arc-melted Zr ₅₀Cu₄₀Al₁₀ alloy exhibits superior glass-forming ability in forming glassy phase, even in a 40-g master alloy. When sponge Zr is used, on the other hand, we can see distinct a chain reaction of exothermic heat due to crystallization after vitrification during solidification. We conclude that the origin of the crystallization in arc-melted Zr₅₀Cu₄₀Al₁₀ alloy with sponge Zr is probably chlorine as an impurity in sponge Zr metals. Furthermore, vitrification in front of the solidification interface of arc-melted Zr₅₀Cu ₄₀Al₁₀ alloy with crystal Zr can occur when the crystalline growth phase is an Al-supersaturated B2 (B19′)-type ZrCu phase.