组织特征对粉末高温合金FGH96疲劳裂纹扩展速率的影响

Effects of Microstructure Characteristics on Fatigue Crack Growth Rate of Powder Metallurgy Superalloy FGH96

通过对不同热处理后获得3种典型显微组织的粉末高温合金FGH96合金试样在650℃进行保载90 s和5 s并恒载荷循环应力作用下的疲劳试验,研究组织特征对疲劳裂纹扩展速率的影响规律,确定不同载荷条件下孕育期、萌生期、扩展期及瞬断期所占的比率。结果表明,γ'相特征显著影响疲劳裂纹扩展速率;疲劳行为对保载时间存在敏感性,随保载时间的延长,在疲劳-蠕变的交互作用下会明显加快合金疲劳裂纹扩展;在整个疲劳破坏过程中,萌生比率均高于扩展比率,说明该合金抗裂纹萌生的能力要高于抗裂纹扩展的能力;此外,该合金疲劳裂纹扩展四个阶段在整个断裂周次所占的比率分配上,孕育期比率一般较小,萌生期和扩展期比率较大,瞬断期的比率很小,表明该合金裂纹扩展一旦失稳将高速扩展并迅速断裂。

Fatigue crack growth rate is investigated at 650 ℃ and constant stress for holding times for 90 s and 5 s in powder metallurgy（P/M） superalloy FGH96 with three microstrucmre characteristics. Microstructure effects on fatigue crack growth rate of P/M superalloy FGH96 are obtained and the fatigue ratios of different stages, such as Incubation, Initiation, Extension and Interruptions periods, also are determined. The results indicate that crack growth rate is affected significantly by i＇ characteristics. Fatigue behavior is found to be sensitive to holding time, and fatigue crack growth rate is evidently accelerated by the interaction of fatigue and creep behaviors with the increase of holding time. Initiation period of a crack is observed to be longer than crack propagation, indicating that the alloy has a better capability of crack propagation resistance than crack initiation resistance. Besides, the comparison of the ratios of four periods, including incubation, initiation, propagation and interruption, on the whole fatigue process shows that incubation and interruption periods are shorter but initiation and propagation periods are relatively longer. In other words, crack propagation is mainly responsible for the rapid failure of the alloy.