TG700A镍基合金在持久过程中的晶界析出相转变及断裂行为

Change of Grain Boundary Precipitates and Fracture Behavior of TG700A Nickel-based Alloy during Stress Rupture Process

在770℃、不同应力(160,200,260MPa)下对TG700A镍基合金进行持久试验,研究了该合金的显微组织及持久断裂行为。结果表明:试验合金的原始显微组织为等轴奥氏体,晶粒内部析出有均匀分布的细小球状γ′相,晶界处存在颗粒状的富铬M_(23)C_6碳化物;持久断裂后组织中未发现新析出相,晶界附近出现严重粗化的γ′相,晶界上存在γ′相贫化区;试验合金的持久断裂模式以沿晶断裂为主,晶界处的局部塑性变形导致了局部应力集中,促进了蠕变空洞或裂纹的形成,裂纹沿γ相和γ′相界面或γ′相贫化区扩展。

The stress rupture tests at 770℃ under different stresses(160,200,260 MPa)were conducted on TG700A nickel-based alloy.The microstructure and stress rupture behavior of the alloy were studied.The results show that the original microstructure of the tested alloy was composed of equiaxed austenite;fine spherical γ′ phase precipitated in the grains uniformly,and granular Cr-rich M23C6 carbides existed at the grain boundaries.After stress rupture,no new precipitates were found in the microstrucutre,and coarsened γ′ phase near grain boundaries and γ′ phase depletion zone at grain boundaries appeared.The stress rupture mode of the tested alloy was mainly intergranular fracture.The localized plastic deformation at grain boundaries led to localized stress concentration,promoting the formation of creep voids or cracks.The crack propagated along the interface between γ and γ′ phases or the γ′ phase depletion zone.