Effect of Al Addition on the Microstructural Evolution of Equiatomic CoCrFeMnNi Alloy

The present investigation reports the effect of Aluminium-addition on the microstructural evolution in the equiatomic CoCrFeMnNi high entropy alloy. Aluminium was added to the alloy in varying quantity using the vacuum arc melting technique, and phase formation have been probed using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results indicate that the FCC phase in the alloy remains unaltered up to Al of 5 at.%. The higher amount of Al addition leads to the precipitation of B2 Al(Ni, Cr) in the FCC matrix. For Al  7%, typical phase separated microstructure consisting of FCC, and B2 phases have been observed. The microstructural changes lead to hardness variation from 1.3 to 2.2 GPa, mainly due to precipitation and solute solution hardening of FCC phase. For FCC phase, Al atoms being smaller in size can cause and lead to lattice distortion and improve yield strength. The results have been explained by detailed thermodynamical analysis using HEA3 database.