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.