Effects of deformation direction and temperature on mechanical properties of nanopolycrystal Ni–Co alloy with gradient twin structure

Abstract

Molecular dynamics was used to study the uniaxial tensile process of Ni–Co alloy with gradient nanotwin structure, and the microstructure and deformation mechanism of mechanical properties of gradient nanotwin Ni–Co alloy were studied from the micro perspectives of dislocation, twin layer and grain boundary movement. The results show that when the twin structure Ni–Co alloy is uniaxial stretched along the gradient direction and perpendicular to the gradient direction, the twin layer has different strengthening effects on the structure and strengthening mechanism, the stretching in different directions has greater influence on the dislocation movement and stacking fault nucleation of the nanogradient twin structure. The yield strength of Ni–Co alloy is 11.3 Gpa and 5.5 Gpa, respectively, after stretching along gradient and vertical gradient directions, Young’s modulus reaches 221.16 Gpa and 127.90 Gpa. It is found that the gradient twin structure stretched along gradient direction has greater strength and the twin layer breaks into fragments and distributes in the system during the process of strain increase. At different temperatures, it was found that the strength and plasticity of the material decreased sharply with the increase of temperature, the dislocation density in the system also decreased with the increase of temperature, resulting in poor performance of the material.