Interfacial strength and deformation mechanism of Ni/Co multilayers under uniaxial tension using molecular dynamics simulation

Abstract

This report investigates the deformation behaviors and mechanical properties of Ni/Co multilayers under tensile tests by using molecular dynamics (MD) simulations. The effects of orientations, layer thicknesses, temperature, and strain rates, on the tensile strength, phase transformation, dislocation density, stress-strain relationships, and Young's modulus of the Ni/Co multilayers are examined. The results show that reducing layer thickness leads to an increase in dislocation density. The dislocation density of the vertical sample is higher than the horizontal sample. The FCC structure of the Ni layers is strongly transformed to HCP, BCC, and amorphous structures during uniaxial tension. On the contrary, only a minor percentage of the HCP structure of Co layers is changed to FCC or amorphous structure. For both the horizontal layers and vertical layers specimens, stacking faults appear from the interface and then expand towards the Ni layers. Notably, the yield strength of the horizontal sample is higher than the vertical one. When increasing the strain rate from 108 to 1010 s−1, the yield stress of the vertical varies slightly from 9.1 GPa to 10.6 GPa. While in the horizontal direction, the yield strength oscillates around 9.1–12.6 GPa. Increasing the strain rate results in a growth in the yield strength. Moreover, increasing the temperature leads to the reduction of Young's modulus and tensile strength.