Age Hardening and Re-crystallization Softening of a CoCrFeMnNi High Entropy Alloy

Abstract

Age hardening and re-crystallization softening of a type of high entropy alloy, CoCrFeMnNi, was performed to investigate the relationship between microstructure and the property of mechanical hardness. Equiatomic CoCrFeMnNi was produced by casting followed by homogenizing, cold rolling and post heat treatments. TEM analysis revealed that the microstructure of the as-rolled alloy was composed of elongated grains with twin laths and a shear band with fine grains, which exhibited a hardness of 371 HV. Following a 500 degrees C heat treatment the microstructure was composed of nano-twins and nano-grains, which represented age hardening, with 454 HV hardness. The microstructure of 700 degrees C heat treated samples was composed of re-crystallized grains and annealing twins, which represented annealed softening, with 244 HV hardness. The 700 degrees C heat treatment also produced spherical particles of 0.1 mu m maximum grain size, identified as Cr23C6 type carbide.