Abstract: 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 microstructure 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 γ 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.

Key words: Crack growth rate, Holding time, Microstructure characteristics, Powder metallurgy superalloy