Temperature-dependent tensile properties of ultrafine-grained C-doped CoCrFeMnNi high-entropy alloy

Metallic materials can be strengthened by various kinds of plastic deformation strategies. However, the deformed materials suffer poor ductility and thermal stability due to the high-density defects. In this work, we prepared fully recrystallized ultrafine-grained (UFG) 1%C-CoCrFeMnNi high-entropy alloy (C-HEA) through cold rolling and annealing process. Quasi-static tensile tests were performed at temperatures between 77 and 823 K. Deformation microstructures of the samples after tensile tests were characterized, and deformation mechanisms were discussed. There is a transition of deformation mechanisms from twinning and dislocation slip to dislocation slip and grain boundary sliding with temperature increasing. The UFG C-HEA exhibits balanced strength and ductility from the cryogenic temperature to high temperatures, indicating highly adaptive microstructure and mechanical properties. The strength and uniform elongation of the UFG C-HEA decrease monotonously with temperature increasing, but the elongation to failure exhibits the lowest value at the medium temperature. The grain boundary sliding is supposed to assist the unconventionally high elongation at 823 K.