Prediction of texture evolution and crack growth rate of nickel based superalloys in thermo-mechanical fatigue by ultrasonic technique

In this research, texture evolution and crack growth rates were investigated by ultrasonic technique in Hastelloy X during thermo mechanical fatigue (TMF) and also in Inconel 718 during isothermal fatigue. For this purpose, TMF tests were performed at various modes, i.e. constant temperature, in-phase (IP) and out of phase (OP) in addition to application of linear elastic fracture mechanics (LEFM) and elastic-plastic fracture mechanics (EPFM). The existing ultrasonic model for predicting the texture evolution was modified and a model on the base of the relationships between ultrasonic wave velocity, elastic constants and texture parameters was developed. For predicting the TMF crack growth rate, an integrated ultrasonic model was proposed on the base of dislocation density and cyclic J-integral for ultrasonic wave velocity. The validation tests for texture evolution and TMF crack growth rates show a good correlation between experimental results and those predicted by ultrasonic method. For predicting the initiation and growth of unstable cracks up to failure of the specimen during TMF, a new parameter in the form of critical ultrasonic wave velocity has also been introduced in this research.