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

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.