Phase separation and morphology formation of Co-Cu-Si ternary alloy

The rapid solidification of Co₄₅Cu₄₅Si₁₀ and Co₂₅Cu₂₅Si₅₀ ternary alloys under free fall is achieved. The experimental undercooling of Co₄₅Cu₄₅Si₁₀ and Co₂₅Cu₂₅Si₅₀ alloys is up to 357 K(0.22T_L) and 320 K(0.20T_L), respectively. The liquidus temperature of Co₄₅Cu₄₅Si₁₀ and Co₂₅Cu₂₅Si₅₀ alloys is determined as 1600 K and 1592 K, and the solidus temperature of Co₄₅Cu₄₅Si₁₀ and Co₂₅Cu₂₅Si₅₀ alloys is determined as 1358 K and 1105 K, respectively. The critical undercooling of liquid phase separation of Co₄₅Cu₄₅Si₁₀ ternary alloy is only 8 K. The L+α-Co→ε-Co peritectic transformation takes place during metal droplets whose diameters are larger than 100 μm, and solidified microstructure is composed of (Cu), ε-Co and α-Co phases. If the diameter of alloy droplet is smaller than 100 μm, the solidified microstructure is mainly composed of (Cu) and ε-Co phases. The critical separation undercooling does not exist in Co₂₅Cu₂₅Si₅₀ ternary alloy melt, and no phase separation microstructure is found in this alloy. The rapid solidification microstructure of Co₂₅Cu₂₅Si₅₀ alloy is composed of CoSi, CoSi₂ and Cu₃Si three intermetallic compounds. Though nucleation rate of Cu₃Si phase is maximal, it never acts as the leading phase. When ΔT>127 K, the primary phase is dendritic of CoSi₂ phase. Once ΔT>127 K, the primary phase changes to the dendritic of CoSi phase.