Strengthening mechanism of Ni–Cu nanotwins with void under different tensile directions based on Molecular Dynamics simulation

Abstract

Defects such as voids and inclusions are inevitably inserted in the process of improving the mechanical properties by adjusting the microstructure, which results in alteration of deformation mechanism and ductile failure of the material. Although this is a macroscopic phenomenon, it is related to the mechanism at the atomic scale. In this paper, the uniaxial tension processes of Ni–Cu nanotwins containing a void are simulated using the molecular dynamics method, and the effects of the loading direction of perpendicular and parallel to the twin boundary (TB) on the mechanical properties are investigated, and the emphasis is on the hardening behavior after yielding. The results show that the yielding of the material is attributed to the emission of dislocation shear loops on the void surface. The elastic modulus and yield strength are greater under the loading direction of perpendicular to TB. The peak stress is equal to the yield stress under perpendicular loading, while the peak stress is greater than the yield stress under parallel loading. In addition, the hardening behavior is found after yielding under two tensile directions, but the hardening mechanisms are different. For perpendicular loading, the hardening behavior is controlled by the TB and the Lomer-Cottrel lock. While for parallel loading, the hardening behavior is controlled by the stacking faults that distributes uniformly and symmetrically along the TB. The general conclusions obtained may provide new insights into the microscopic properties and deformation mechanisms of nanotwins in depth.