Strain rate effect on cyclic deformation behaviour of advanced ultra-supercritical boiler grade wrought Ni-based superalloy IN740H at 760 °C

In order to understand the simultaneous operation of fatigue and creep mechanisms, strain rate (ε̇) effect on low cycle fatigue (LCF) behaviour of recently developed power plant grade wrought Ni-based superalloy IN740H was studied. Fatigue experiments were conducted in air, at 760 °C at ε̇ values 10−2, 10−3 and 10−4 s−1. The fatigue life significantly decreased at lower ε̇ values. Bilinear Coffin-Manson slopes were obtained for all ε̇ values. Through microstructural studies, it was ascertained that decrease in fatigue life at lower ε̇ value can be attributed to ingress of oxygen by grain boundary diffusion and intergranular crack initiation and growth.