Effects of Twin Boundary on Tensile Properties and Deformation Mechanism of Ni–Co Alloy Nanopillars

Abstract

The influence mechanism of twin boundary in Ni–Co alloys is responsible for their deformation and technological applications. Herein, the uniaxial tensile loading of the Ni–Co single crystal nanopillars with twin boundaries is carried out by simulation. When the number of twin boundaries exceeds two layers, the effect of twinning boundary on dislocation is obvious, and the migration and reaction of twin boundaries lead to an increase in the number of dislocations accommodated inside, which is conducive to increasing the strength of the nanopillars. At low temperature, the dislocations are easy to penetrate and expand the twin grain boundary, while at high temperature, due to the aggravation of thermal motion, the resulting dislocations decrease. Meantime, the reaction between dislocations and twin boundaries leads to the disappearance of some original twin grain boundaries. As the strain rate increases, the main deformation mode of the nanopillar changes from the reaction of dislocation and twin boundary to twin boundaries migration. When the volume ratio of grain boundary void is less than 2.3%, the plastic deformation fluctuation is relatively stable. Nevertheless, when the volume ratio is greater than or equal to 2.3%, the fluctuation of the plastic deformation stage decreases rapidly.