Employing sequential experiments to gain insights on the interaction between creep and fatigue damage in Ni-base superalloys

The interaction between creep and fatigue damage in Ni-base superalloy CMSX-8 was explored using a sequential workflow that decouples creep and fatigue steps to quantify how accumulated creep damage interacts with subsequent isothermal low-cycle fatigue (LCF) and vice versa. Two workflows were considered: creep followed by LCF and LCF followed by creep. For the first workflow, the subsequent LCF was evaluated at temperatures of 20 degrees C, 750 degrees C, and 1100 degrees C. It was found that the extent of deleterious interaction of prior creep on LCF depended on increasing subsequent fatigue test temperature. For the LCF followed by creep, fatigue tests were first conducted at 20 degrees C and 1100 degrees C to 60% of life, and then creep was conducted at 800 degrees C, where primary creep is promoted, or 900 degrees C, where primary creep is absent. LCF damage accumulated at 1100 degrees C accelerated creep and decreased ductility, while fatigue damage at room temperature had minimal effect on the creep behavior.