(1. 桂林电子科技大学 材料科学与工程学院，桂林 541004；
2. 哈尔滨工业大学 材料科学与工程学院，哈尔滨 150001；
3. 三峡大学 机械与动力学院，宜昌 443002)
摘 要: 基于CALPHAD方法和Thermo-Calc软件构建了Nb-Ti-Co三元合金富Nb角相图，而后结合微观偏析统一模型研究58种合金的凝固路径，探讨固相反扩散系数和冷却速率对凝固路径的影响规律，并利用Bridgman定向凝固实验对其验证，最后通过SEM和XRD观察上述合金的微观结构，并与数值模拟计算结果进行比较，建立了Nb-Ti-Co相图中的渗氢成分区域。结果表明：1) Nb-Ti-Co三元合金相图富Nb角存在两个三元四相平衡反应，分别为L+α-Nb→TiCo+Co6Nb7 (1225.35 ℃)和L+TiCo→α-Nb+Ti2Co (1099.06 ℃)；2) Nb相区中至少存在四种不同的凝固路径，分别为(L+α-Nb)、(L+α-Nb)→(L+α-Nb+Co6Nb7)→(L+α-Nb+Co6Nb7+TiCo)、(L+α-Nb)→ (L+α-Nb+TiCo)和(L+α-Nb)→(L+α-Nb+TiCo)→(L+α-Nb+TiCo+Ti2Co)；3) 冷却速率(Rf)对渗氢区域内合金凝固路径影响较小，相反，固相反扩散系数(Ф)对其凝固路径影响较大；4) 渗氢区域内合金显微组织中初生α-Nb相体积分数随着Nb含量和Ti/Co比率的增加而增加，相反，两相共晶体积分数随之而降低。
关键字: Nb-Ti-Co合金；CALPHAD；凝固路径；渗氢区域
（1. School of Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, China;
2. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;
3. College of Mechanical and Power Engineering, Three Gorges University, Yichang 443002, China）
Abstract:In the present work, Nb-Ti-Co phase diagram in the Nb-rich region was constructed by using CALPHAD method and Thermo-calc software, and then the solidification paths of 58 kinds of alloys were studied by using the uniform microsegregation model. The influences of solid back diffusion coefficient and solidification rate on their solidification path were discussed. The microstructure of these alloys was observed by SEM and XRD, which was compared with the numerical simulation results. Finally, the hydrogen permeable component region in the Nb-Ti-Co phase diagram was established. The results show that: (1) Two equilibrium reactions, i.e. L+α-Nb→TiCo+Co6Nb7 and L+TiCo→ α-Nb+Ti2Co, exist in the Nb-Ti-Co phase diagram. (2) There are at least four different solidification paths in the Nb-rich region, as follows, (L+α-Nb), (L+α-Nb)→(L+α-Nb+Co6Nb7)→(L+α-Nb+Co6Nb7+TiCo), (L+α-Nb)→(L+α-Nb+TiCo) and (L+α-Nb)→(L+α-Nb+TiCo)→(L+α-Nb+TiCo+Ti2Co), respectively. The cooling rates have no obvious effect on the solidification path whereas the solid back diffusion coefficient has a great effect on it. The volume fraction of primary phase increases with the increase of Nb content and Ti/Co ratio, whereas the volume fraction of eutectic phase decreases.
Key words: Nb-Ti-Co alloy; CALPHAD; solidification path; hydrogen permeable component region
