Molecular dynamics simulation of nanocrack closure mechanism and interface behaviors of polycrystalline austenitic steel

Void-type defects in heavy forgings deteriorate their mechanical properties and service life. In this work, the evolutions of a pre-crack closure and the healing and mechanical properties of FeCrNi polycrystalline samples are assessed under different loading conditions using molecular dynamics simulation. The stress–strain curves show that the sample with interface exhibits higher Young’s modulus and yield strength than those with cracks, despite the loading conditions. These results imply that samples under compression loading have a higher ability to resist plasticity, while the shear stress facilitates plastic flow. Crack closure and healing occur under compression stress by dislocation-dominant plastic deformation, while the crack length shrinks and the crack tips expand along grain boundaries (GBs) and the interface because of its higher stress under shear loading. Dislocation activities, including dislocation emission, slip, and interactions with cracks, grain boundaries, and dislocations, contribute to the plasticity of the specimen under compressive loading. In addition to dislocation activities, grain boundary slip, grain rotation, and twinning are potential plastic-deformation mechanisms under shear loading.