Dwell fatigue crack growth at elevated temperatures in an advanced nickel disc superalloy

This thesis studies dwell fatigue crack growth in an advanced nickel disc alloy RR1000 at elevated temperature. RR1000 with different grain sizes and γ’ precipitate distributions are tested at both 650 and 700°C to investigate the effect of microstructure and testing temperature on dwell fatigue crack growth. Dwell fatigue tests with different dwell times at the peak load are conducted to study the effect of dwell time on crack growth rate and crack propagation mechanism. A transition from cycle-dependent transgranular fatigue crack growth to time-dependent oxide induced intergranular crack growth is found when the dwell time exceeds a critical value. Linear elastic stress intensity factor (K) threshold values for intergranular crack growth under sustained load are also measured to evaluate conditions when intergranular crack growth occurs progressively during the dwell period. Impacts of prior dwell fatigue loading on subsequent fatigue crack growth are also studied