在定向凝固钴基高温合金中采用V型缺口分别垂直和平行于凝固方向的板状热疲劳试样, 并在缺口位置预制再结晶组织, 研究了在最高温度为1000 ℃, 最低温度为室温的冷热循环下, 缺口取向和再结晶对定向凝固钴基高温合金热疲劳性能的影响. 结果表明, 缺口取向垂直于凝固方向时, 基体在应力作用下循环氧化开裂; 缺口平行于凝固方向时, 热疲劳性能下降, 裂纹沿枝晶间扩展. 再结晶降低定向凝固钴基高温合金的热疲劳性能, 再结晶晶界氧化开裂, 晶界析出的M₂₃C₆型碳化物氧化脱落后形成的孔洞加速了裂纹扩展; 连接枝晶间碳化物的再结晶晶界成为缺口平行于凝固方向时热疲劳裂纹的优先扩展通道.

The directionally solidificated (DS) Co-based superalloys are widely used in aircraft turbine vanes due to the good stress-rupture parameters and excellent hot corrosion resistance. The cyclic change of temperatures and complex stress state thermal fatigue (TF) cracks happen frequently in vanes during service. However, most of the work are conducted in Ni-based superalloys and there is rare report concerning the TF behavior of DS Co-based superalloys. Furthermore, due to the residual strain accumulated during processing, shot peening, grinding and recrystallization (RX) frequently occur when the DS components are exposed to high temperatures. It is believed that RX may change the microstructure, especially adding more grain boundaries to DS alloys, and result in the reduction of the mechanical properties of DS superalloys. Therefore, in this work, V-notch plate specimens with notch direction perpendicular and parallel to the DS orientation are machined from the DS plate. Local RX grains are prepared (local indented and then heat treated) in the notch areas of some samples. TF test is conducted between 1000 ℃ to room temperature. The effect of DS orientation and RX on TF properties of a DS Co-based superalloy is investigated. The results indicate that the cracks propagate along the interdendritic regions in the samples with notches parallel to the DS direction, which exhibites lower TF properties than samples with notches vertical to the DS direction. TF cracks initiate and propagate along RX boundaries in samples containing RX grains. Precipitation of M₂₃C₆ carbides is found along the RX boundaries during TF tests. Due to the oxidation at the tip of crack, M₂₃C₆ desquamates and leads to the formation of micro voids, which accelerates the crack propagation and decreases TF properties of tested alloy. In samples with notches parallel to the DS direction, cracks preferentially propagate along the RX grain boundaries.