Thermo-mechanical fatigue failure of a single crystal Ni-based superalloy

Behavior of thermo-mechanical fatigue (TMF) of a single crystal Ni-based superalloy, CMSX-4, was studied, compared with that of isothermal low cycle fatigue (LCF). Strain-controlled TMF and LCF tests of CMSX-4 were carried out under various test conditions, where the experimental variables were strain rates, strain ratio, temperature range, and strain/temperature phase angle. It was shown experimentally that the TMF and LCF failures took places, associated with some noteworthy characteristics which were rarely seen in the traditional polycrystalline heat-resistant alloys. They could not be explained reasonably, based on the historical approaches. A new micromechanics model was proposed to predict the TMF and LCF lives, applying the Eshelby’s theory. The model enabled us to successfully estimate the characteristics in the TMF and LCF failures.