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

摘要

In order to understand the simultaneous operation of fatigue and creep mechanisms, strain rate (ε) 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 ℃ at ε values 10~(-2), 10~(-3) and 10~(-4) s~(-1). The fatigue life significantly decreased at lower ε values. Bilinear Coffin-Manson slopes were obtained for all ε values. Through microstructural studies, it was ascertained that decrease in fatigue life at lower ε value can be attributed to ingress of oxygen by grain boundary diffusion and in-tergranular crack initiation and growth.