Creep-fatigue damage evolution in a nickel-based superalloy: An experiment-inspired modeling approach for life prediction

Abstract

Creep-fatigue experiments were conducted on IN740H, a γʹ-lean Ni-based superalloy, at 750 °C with a strain ratio of −1, a strain amplitude of either 0.3 or 0.5 %, and a dwell period at the maximum strain of 0, 120 and 600s. Results indicate that the number of cycles to failure decreased with the dwell period, although overall rupture time increased. Grain boundary fracture was more prevalent at higher strain amplitudes, whereas intragranular micro-void-dominant fracture, along with some grain boundary cavitation, occurred at lower strain amplitudes, and the cavity size increased with the dwell period. Additionally, Schmidt factor-based micro-texture analysis showed that grains with lower Schmidt factors deflected cracks toward grain boundaries while cracks propagated through high Schmidt factor grains. Furthermore, twinning and weakening of subgrain definition were observed with an increase in the strain amplitude. Finally, a strain energy density-based model that accounted for primary creep parameters was developed to predict creep-fatigue lifetime. The developed model is in good agreement with experimental results, with predicted life within a factor of 2 of the experimental observations. The developed micro-mechanics-based understanding of creep-fatigue damage paves a path for a better design of high-temperature components of Ni-based superalloys, such as those to be used in advanced ultra-supercritical powerplants, aero-engines, etc.