Molecular dynamics study of fatigue mechanical properties and microstructural evolution of Ni-based single crystal superalloys under cyclic loading

The fatigue performance and deformation mechanism of Ni-based single crystal superalloys under cyclic tension-compression loading are studied by molecular dynamics simulations. The effects of temperature and strain rate on the cyclic deformation of superalloys are discussed. The results show that there are three different cyclic deformation mechanisms at different temperature ranges. In the low temperature range, dislocations and stacking faults shearing gamma' phase is the main deformation mechanism. In the high temperature range, Orowan bypassing and climbing mechanism dominates the deformation. While in the medium temperature range, the deformation mechanism gradually transforms from the dislocation and stacking faults shearing the gamma' phase to the Orowan bypassing and climbing. The simulation results also reveal that the superalloys exhibit a cyclic saturation stage after the initial cyclic hardening. The cyclic saturation stage is a dynamic equilibrium of dislocation proliferation and annihilation, indicating that the superalloys have excellent fatigue mechanical properties. Moreover, the dislocation density and the proportion of stacking faults increase with increasing strain rate, resulting in faster cyclic stability and higher stress amplitude for the superalloys. These results provide important information for understanding the fatigue mechanisms of superalloys from an atomistic perspective.