Predominant factor related to stress intensity factor range on creep-fatigue crack growth of nickel-superalloy FGH97

The scanning electron microscopy was adopted to identify the fracture features of specimen in FGH97, which had been tested under the conditions of stress-ratio of 0.05, 750℃ and various dwell times. It was found that, for dwell time of 90s, the fatigue striation feature gradually disappeared with the increment of the stress intensity factor range values, and the turning point of neglecting fatigue loads located at the medium stress intensity factor range evel. But the corresponding stress intensity factor range values located at the lower levels for 450s and 1500s dwell time. Based on the trinomial model including fatigue item, creep item and creep-fatigue interaction item, the time-dependent and cycle-dependent components were employed to describe the test data of creep-fatigue crack growth in FGH97. The proportions of contribution to crack growth rate (CGR) of the two components are significantly influenced by stress intensity factor range values at different dwell times. The model for describing the time-dependent crack growth rate is proposed according to the analysis results. Furthermore, the stress intensity factor range values, which could affect the predominant factor of time-dependent component or time-dependent and cycle-dependent component on CGR, are obtained at various dwell times.