A novel very-high-cycle-fatigue life prediction model with interior microstructure induced cracking behavior of Inconel-713C superalloy at 25 °C, 750 °C and 1000 °C

Asymmetric load tests with stress ratio of 0.1 at 25 °C, 750 °C and 1000 °C were performed to investigate the high-cycle and very-high-cycle fatigue properties of Inconel-713C Ni-based superalloy. Results show that the life at 750 °C is longer than that at 25 °C, but shortens as temperature keeps rising to 1000 °C. Relevant crack initiation and growth belong to the mixed Modes I & Ⅱ cracking along the maximum shear stress. Moreover, due to the effects of temperature and vacuum environment, threshold values for small and long cracks, and the transition crack size decreases as the temperature increases. Moreover, further analysis of dislocation structures such as tangled dislocations, dislocation loops and finer stacking faults shows that the deformation mechanism with faceting cracking at 750 °C should be the interaction of bypassing and shearing mechanisms, especially under stress concentration effect of crack. Based on these, a crystallographic version of fatigue index parameter model for crack nucleation life is proposed and the predicted results are within a factor of two with respect to experimental data. The present model can be applied to predict the fatigue life based on the microstructure attributes and load conditions at different temperatures, which can effectively improve operational safety and reliability of structural components in reality.