研究了3种铸造镍基高温合金在不同温度下的热疲劳行为, 利用OM和SEM对合金的组织和热疲劳裂纹形貌进行了观察. 结果表明: 3种合金的热疲劳裂纹均萌生于V型缺口尖端处, 应力诱导下氧化孔洞的产生、聚集和相互连通是裂纹萌生的主要方式, 晶界、碳化物及共晶促进了裂纹的萌生和扩展. IN738和DZ444合金的热疲劳裂纹分别沿晶界和枝晶间扩展, DZ445合金的裂纹扩展方式随着温度升高由沿枝晶间扩展转变为沿晶体学取向扩展. 高温氧化和热应力的交互作用是热疲劳的主要损伤机制, 各合金在较高温度 (950℃) 下发生的微观组织演化促进了热疲劳性能的降低.

Thermal fatigue (TF) behaviors of three Ni-based cast superalloys were investigated in the temperature ranges of 850, 900 and 950℃ to 20℃, respectively. OM and SEM were used to observe the microstructures and TF cracks of the tested specimens. The results demonstrated that the main style of crack initiation is the formation, gathering and interconnecting of oxidation cavities induced by thermal stress. Carbides, $\gamma$+$\gamma^{\prime}$ eutectics and grain boundaries can promote the initiation and propagation of TF cracks. The three alloys showed different mechanisms of TF crack propagation due to the distinct chemical compositions and microstructures. The TF cracks of equiaxial IN738 alloy propagate intergranularly, while those of the directional solidification (DS) DZ444 alloy propagate along interdendritical regions. The paths of TF crack propagation of DZ445 transfer from interdendrite to crystallographic orientation with increasing temperatures, i.e. (111)<110>, which is the easy slip system of face centered cubic alloy. The interaction of high-temperature oxidation and thermal stress is the main fractural mechanism in TF process. Some microstructural evolution at 950℃ accelerates the reduction of the TF property of three alloys.