新型铌基高温合金热处理组织性能研究

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Nb-base Superalloys

研究了热处理对一种HRS定向凝固技术制备Nb/Nb5Si3原位复合材料组织和性能的影响。采用扫描电子显微镜(SEM)、X射线衍射(XRD)和电子探针(EPMA)等分析手段对热处理过程中组织演变进行了分析:铸态合金主要由Nbss、γ-(Nb,Ti)_5Si_3、β-(Nb,Ti)_5Si_3以及初生碳化物组成;热处理后,铸态组织中部分β-(Nb,Ti)_5Si_3向α-(Nb,Ti)_5Si_3转变以及二次碳化物析出,同时硅化物相逐渐溶解或破碎成小块并发生球化;1150℃时效可促进(Nb,Ti)_5Si_3向(Ti,Nb)5Si3转变。热处理后,合金压缩以及室温拉伸强度提高,而1000℃拉伸强度变化不明显;温度对断裂方式有明显影响,低温下为脆性解理断裂,高温下为韧性断裂。

The effect of heat treatment on the microstructure and mechanical properties of Nbss/Nb5Si3 in situ composites prepared by conventional high-rate-solidification Bridgeman process（HRS） was investigated. The microstructure evolution of samples during heat treatment process were analyzed by SEM, XRD and EPMA. Results show that the as-cast alloy consists of Nbss, γ-（Nb, Ti）5Si3, β-（Nb, Ti）5Si3 and primary carbide phase; after heat treatment, the β-（Nb,Ti）5Si3 phase is transformed to α-（Nb,Ti）5Si3 phase and the secondary carbide is precipitated. Meanwhile, the silicide phase gradually dissolves or breaks into small pieces, with the morphology changing from the needle into granules. The transformation（Nb,Ti）5Si3 →（Ti,Nb）5Si3 occurs when aging at 1150 ℃. The compressive strength and room temperature tensile strength of heat-treatment specimens are improved, while the tensile strength of as-cast and heat-treated samples at 1000 ℃ is at the same level. The temperature has a great influence on the fracture mode, which is cleavage fracture at low temperature and ductile fracture at high temperature.