Microstructural evolution and mechanical properties of Al_xCoCrFeNi high-entropy alloys under uniaxial tension: A molecular dynamics simulations study

In this work, the microstructure evolution, deformation mechanism and the mechanical properties of the Al_xCoCrFeNi high-entropy alloy (HEAs) under uniaxial tension have been explored using molecular dynamics simulations. The influencing factors including Al concentration, temperature and strain rate have been considered. Results show that the phase transforms from the original single face-centered cubic (FCC) structure into body-centered cubic (BCC), hexagonal close-packed (HCP) and amorphous structure and the atoms with BCC, HCP and amorphous structure increase whereas the atoms with FCC structure decreases with the increase of strain, especially after the yield strain. The increase of both Al concentration and temperature has a negative impact in the tensile properties of Al_xCoCrFeNi HEAs including the Young’ modulus, yield stress and yield strain. The dislocation densities decrease whereas the shear strain becomes larger and distributed uniformly with the increase of the temperature. The high Al concentration can inhibit the reduction of Young's modulus and yield stress with increasing the temperature. In contrast, the increase of strain rate leads to an appreciable hike in the yield stress and yield strain of HEAs but exhibits negligible influence on the Young's modulus. The high Al concentration can amplify the effect of increasing strain rate on the Young's modulus and yield stress. The dislocation density does not monotonically change with increasing the strain rate within the considered strain rate range of 10⁸-2 × 10¹⁰/s, nonetheless in most cases the dislocation density decreases with increasing strain rate and also temperature.