Judgment criterion of the dominant factor of creep-fatigue crack growth in a nickel-based superalloy at elevated temperature

Creep-fatigue crack growth (CFCG) tests on FGH97 at a temperature range from 650 °C to 750 °C with 90-s dwell time and at 750 °C with dwell time range 0-1500 s were performed. Based on the trinomial model including fatigue item, creep item, and creep-fatigue interaction item, the contributions of these three items to CFCG behavior at different stress intensity factor range (ΔK) under different loading conditions, including different temperatures for a given dwell time and various dwell time for a given temperature, were discussed. The time-dependent component (creep item + creep-fatigue item) and cycle-dependent component (fatigue item) were used to describe the test data and reveal the influence of ΔK levels on crack growth mechanism. The method to determine the dominant factor of CFCG behavior was discussed, and the judgment criterion of the dominant factor related to the ΔK level was built. The microscopic morphology of fracture surfaces under different loading conditions was observed by scanning electron microscope to confirm the results.