Effect of Temperature on Deformation and Fracture Behaviour of Nanostructured Polycrystalline Ni Under Tensile Hydrostatic Stress by Molecular Dynamics Simulation.

Abstract

Real materials have structural defects that are normally brought in during the processes of manufacturing and storage and often have a structure with abundant grains, as well as being subjected to multi-directional force conditions. The study of temperature's effect on plastic deformation mechanisms in polycrystalline materials bathed by a multi-axial force is still very rare and not clear. Therefore, we conducted very large-scale molecular dynamics simulations to study the deformation and fracture behaviour of nanostructured polycrystalline Ni under a pre-existing external tensile hydrostatic stress with various temperatures. By characterizing the deformation and fracture mechanisms at an atomic scale, our results elucidate the effect of temperature on brittle versus ductile fracture behaviour by analysing the local stresses for void nucleation and crack propagation and the associated interplays of grain boundary, dislocation/twin and void/crack activities. The lower temperature results in a more brittle fracture manner. This is because the decreasing temperatures contribute to more sources of local stress concentrators for void/crack nucleation and propagation, and suppress the plastic deformation achieved by the activities of grain boundary, twin and dislocation. Our findings shed a light on a fundamental understanding of polycrystalline Ni metals subjected to complex working environments.