Effects of hot-forging and subsequent annealing on microstructure and mechanical behaviors of Fe35Ni35Cr20Mn10 high-entropy alloy

Abstract Effects of hot-forging and subsequent annealing on the microstructure and mechanical behaviors of Fe35Ni35Cr20Mn10 high-entropy alloy (HEA) were investigated by the microstructure observation and mechanical property test. The hot-forging results in a significant rise in the strength of the prepared HEA but a great reduction in the fracture elongation too. The dominant fine sub-grain structure and much higher density of dislocations formed during forging are responsible for it. The annealing treatment after forging and increasing the annealing temperature make the strength decreased but the elongation improved. With the increase of the annealing temperature, the combined effects of the reduced dislocation density, the coarsened recrystallized grains and the decreased number of annealing twins make the yield strength decreased but the elongation improved significantly. Different microstructure features in the prepared HEAs before the tensile test results in various softening mechanisms and diverse mechanical behaviors during the tensile deformation. In as-annealed HEA at 1000 °C, the relatively low dislocation density and the coarse recrystallization grains become the main features of microstructure. Besides the formation of dislocation cells, another softening mechanism, the formation of a large number of fine deforming twins during the tensile deformation, is found to stand up to further strain hardening in this HEA, and thus its strain hardening exponent is high to 0.48.