Thermomechanical fatigue behavior and life prediction of a cast nickel-based superalloy

The cyclic deformation and lifetime behavior of a cast nickel-based superalloy M963 was investigated under both thermomechanical fatigue (TMF) and isothermal fatigue (IF) conditions. Two types of TMF tests, i.e. in-phase (IP) and out-of-phase (OP), were performed in temperature range of 450–900 °C, and IF tests were conducted at a temperature of 900 °C. All tests were carried out under mechanical strain control at a given strain rate of 1.0 × 10−4 s−1. Results revealed that isothermal fatigue exhibited a longer lifetime than both types of TMF at corresponding mechanical strain amplitude in spite of its higher fraction of plastic strain amplitude. Different cracking behavior occurred in IP and OP TMF. In IP loading, cracks tended to initiate and propagate intergranularly or interdendritically, while totally transgranular cracking occurred in OP loading. Three life prediction models were selected and compared to evaluate the possibility of predicting TMF lifetime by using IF data.