Effects of temperature and microstructure on low cycle fatigue behaviour of a PM Ni-based superalloy: EBSD assessment and crystal plasticity simulation

The macro and mesoscale deformation and damage of the PM nickel-based superalloy FGH4098 under low cycle fatigue loading at elevated temperatures were investigated using both SEM/EBSD characterization and crystal plasticity finite element (CPFE) simulations. The results indicate that higher temperature leads to more severe macroscale damage i.e. larger areas of hysteresis loops and shorter fatigue life with transgranular failure mode at both 650℃ and 750℃. The misorientation parameters derived from EBSD characterization show similar deformation at both temperatures, but more intense localized deformation in the crack initiation region at 750℃. Based on the accumulated shear-strain energy dissipation density and Fatemi-Socie fatigue indicator parameter, the distribution and evolution of fatigue damage are shown to be strongly affected by local stress-strain state and temperatures, and more severe and homogeneous damage is found at 750℃. The CPFE simulation results also show higher damage propensity, as indicated by the fatigue indicator parameters used here, in the vicinity of annealing twin boundaries with high difference in elastic modulus.