Devitrification behavior and crystal-glassy mixed-phase structures observed in partially crystallized Cu-based glassy alloys

We studied Cu-Zr-based alloys having exceptionally high glass-forming ability (GFA), and investigated the influence of Ag and A1 on the GFA and crystallization behavior. Most of the bulk glassy alloys studied do not contain any crystals in the as-solidified state. The crystallization kinetics of Cu ₅₅Zr₄₅, Cu₅₀Zr₅₀, Cu _55-xZr₄₅Ag_x (x = 0, 10, 20), Cu ₄₅Zr₄₅Al₅Ag₅, Cu₅₅Zr ₃₀Ti₁₀Ag₅, Cu₅₅Hf ₂₅Ti₁₀Ag₅, Cu₄₄Ag ₁₅Zr₃₆Ti₅ and Cu₄₅Zr ₄₅Al₅Ag₅ glassy alloys was analyzed. Cu ₃₅Zr₄₅Ag₂₀ alloy exhibits possible phase separation upon heating within the supercooled liquid region prior to crystallization. The depletion of Ag in the residual glassy phase results in the higher thermal stability of Cu₃₅Zr₄₅Ag₁₀ versus Cu₃₅Zr₄₅Ag₂₀, Cu₅₀Zr ₅₀ undergoes primary crystallization, forming a metastable monoclinic CuZr phase, while Cu₅₅Zr₅, Cu₄₅Zr ₄₅Ag₁₀, Cu₃₅Zr₄₅Ag₂₀ and Cu₁₅Zr₅Al₅Ag₅ undergo eutectic crystallization, forming mostly stable phases. Cu₅₀Zr₅₀, Cu₅₅Zr₃₀Ti₁₀Ag₅ and Cu ₅₅Hf₂₅Ti₁₅Ag₅ undergo nanocrystallization. Although some differences in the crystallization behavior between Cu_55-xZr₄₅Ag_x (x = 0, 10, 20) and Cu₁₅Zr₁₅Al₅Ag₅ were found, this may not be the only reason A1 and Ag additions improve the GFA of the Cu-Zr alloy. The difficulty in nucleating the tP4 AgZr^ss phase may be responsible for the high glass-forming ability of the Cu₃₆Zr₄₈Al ₈Ag₈ and Gu₄₄Ag₁₅Zr ₃₆Ti₅ alloys.