Very high cycle fatigue, Dislocation movement, Ni-based superalloy, Interior crack initiation, Life prediction modeling, Mining engineering. Metallurgy, TN1-997

Microstructures of polycrystalline materials under elevated temperature plays a crucial role in determining the fatigue performance of mechanical structures. In this study, tension-tension fatigue tests at 25 °C, 750 °C and 1000 °C were performed respectively to investigate the effect of microstructure on high-cycle/very-high-cycle fatigue behavior of a Ni-based superalloy. The results showed that fatigue life peaked at 750 °C due to dislocation entanglement and pinning effect. Microcracks were preferentially nucleated at high-angle grain boundary in coarse-grained regions, assisted by defects and slip in adjacent grains. Microstructural interaction was found temperature dependent: (i) γ′ phase sheared with stacking fault and antiphase boundary at 25 °C, (ii) γ/γ′ interface sliding controlled by Orowan looping at 750 °C, and (iii) γ matrix channel failure was induced by plastic instability through dislocation climbing at 1000 °C. Finally, an energy-based model for predicting crack initiation life was established by considering the critical resolved shear stress of the γ′ phase with favorable accuracy.