On the low cycle fatigue behaviors of Ni-based superalloy at room temperature: Deformation and fracture mechanisms

Understanding the deformation behavior of Ni-based superalloy IN718 across various temperature ranges is crucial due to its working temperature variability, despite its primary application in high temperatures. This study investigates the deformation and fracture mechanisms of IN718 alloy under room temperature (RT) low cycle fatigue (LCF) conditions. The findings shed light on the transition from single-slip to multi-slip dislocation configurations during cyclic deformation, which is accompanied by the formation of micro-twins that contribute to plastic deformation accommodation. Precipitate shearing mechanisms dominate the cyclic hardening in the early deformation stages, while the stabilization stage is characterized by the emergence of dislocation wall/cell-like structures resulting from the synergistic interactions between precipitation, element segregation, and dislocations. Cracks initiate near grain boundaries as the softening stage approaches and the dominant fracture mode is referred by grain boundary energy as substantiated by a detailed analysis of grain size and misorientation. Moreover, the growth of transgranular cracks is significantly influenced by grain orientation and local plastic deformation. This study advances the understanding of the deformation and fracture mechanisms exhibited by Ni-based alloys under RT LCF conditions and helps to further fracture observations and simulations.