Precipitation and Evolution Behavior of Peritectic Phase in Undercooled Co-20at%Ru Alloy

摘要:

通过深过冷凝固实验对Co-Ru包晶合金中不同相的析出及演化行为进行了研究。采用熔融玻璃净化与循环过热相结合的方法对该合金的深过冷实验获得了217 K (0.12 TL) 的最大过冷度。结合经典形核理论的计算结果，在全过冷度范围内ξ相始终作为先析相优先从熔体中析出。当过冷度（ΔT）小于临界过冷度 (ΔT* ≈ 180 K) 时，合金凝固组织表现为典型的包晶组织，此时包晶相的析出依赖于ξ相的形态改变；当ΔT>ΔT*时，虽然ξ相仍为先析相，但是包晶相α的析出不再依赖于ξ相，而是直接从过冷熔体中析出并与ξ相竞争长大。随着过冷度的增大，包晶相的相对含量先增加后减少最后再次增加

Abstract:

Undercooling solidification experiments were carried out to analyze the precipitation and evolution behavior of different phases of Co-Ru peritectic alloy. The maximum undercooling of this alloy up to 217 K (0.12TL) was obtained by applying glass fluxing combined with cyclic superheating method. According to the calculation results of the classical nucleation theory, the nucleation of stable phase (ξ) is favored in the whole temperature range. Results show that typical peritectic microstructures are observed if the initial undercooling (ΔT) was lower than critical value (ΔT* ≈ 180 K). In this condition, the precipitation of peritectic phase (α) depends on the different morphologies of ξ phase. When ΔT >ΔT*, α phase precipitates from the undercooled melt directly and grows competitively with ξ phase, although ξ phase is still the primary one in the undercooled melt. With increasing ΔT, the relative content of peritectic phase goes through a course of increasing, then decreasing and finally increasing again