Effect of annealing on microstructure and mechanical properties of an ultrafine-structured Al-containing FeCoCrNiMn high-entropy alloy produced by severe cold rolling

Abstract

Severe cold rolling (SCR) and annealing were applied to a face-centered cubic (FCC) Al0.3FeCoCrNiMn high entropy alloy. The crystal structure, microstructure, and mechanical properties of this SCRed Al-containing HEA were studied systematically. The coarse-grained alloy is substantially refined after SCR resulting in great improvement of the hardness and strength. With Al addition into the FeCoCrNiMn alloy, the thermal stability of this alloy is declined, and the precipitation of σ and B2 phases in the FCC matrix is greatly promoted. The microstructure evolution of the SCRed alloy during annealing can be divided into three stages: the combined precipitation of σ and B2 phases blow 1000 °C; the dissolution of σ phases and only B2 phase precipitates at 1000 °C; recovering to a single FCC phase at 1100 °C. The SCRed alloys annealed at 500–700 °C show a high strength but with a low ductility due to formation of a large number of σ and B2 phases. With increasing annealing temperature, the strength is gradually reduced that is attributed to grain growth of the matrix and dissolution of precipitates. In addition, these precipitates effectively suppress the grain growth of the matrix during annealing. A fully recrystallized and ultrafine-grained alloy with multiphase structure is obtained as the SCRed alloy annealing at 800 °C, which shows the YS, UTS and the elongation to failure of this alloy are 970 MPa, 1080 MPa and 8%, respectively. The high strength of this alloy is attributed to the grain refinement strengthening and precipitation strengthening.