FORMATION AND GROWTH OF VOIDS IN NI-BASED SUPERALLOYS: A PHASE FIELD CRYSTAL STUDY

The presence of micro-voids breaks material continuity, which can cause stress concentration and become the initiation sites of cracks under loading. In Ni-based single crystal superalloys, it is hard to avoid micro-voids due to their compositions and casting processes, which seriously affect the service performance of superalloys. The formation and growth of voids in Ni-based single crystal superalloys under periodic strain rate cyclic loading and constant strain rate tensile loading are simulated using the phase field crystal method in this study. The simulation results indicate that the growth of voids is closely related to the accumulated strain and cyclic strain rate loading has little effect on void growth due to its slow or even non-cumulative strain. However, the rapid accumulation of strain under tensile strain rate loading results in a rapid growth of voids. This is because tensile strain rate loading easily induces the emission of dislocations from voids, which absorb vacancies and form voids. Moreover, under strain rate disturbance, the local vacancy concentration will reach saturation earlier, leading to the nucleation and formation of new voids. The growth mechanism of voids depends on the magnitude of the strain rate. When the applied strain rate is low, the void growth is mainly controlled by diffusion, while when the strain rate is high, the strain rate loading dominates the rapid growth of voids in the short term, and later the voids become vacancy sources, releasing vacancies and promoting vacancy rebalancing through diffusion. These findings can provide references for the composition design and void suppression of Ni-based superalloys.