Effect of Si content and annealing temperatures on microstructure, tensile properties of FeCoCrNiMn high entropy alloys

Abstract

In the present study, FeCoCrNiMnSix (x = 0, 0.1, and 0.2, molar ratio) high-entropy alloys (HEAs) were prepared via arc melting, and subsequently deformed via cold rolling and annealing (CRA). The effects of Si content and annealing temperature on the microstructural evolution and tensile properties of the alloys were systematically investigated. The results indicate that a single-phase FCC structure of coarse-grained FeCoCrNiMnSix HEAs was obtained after homogenized annealing (HOA), and the distribution of each element was uniform. When the molar ratio of Si was increased from 0 to 0.2, the strength of the HOA HEAs increased by nearly 50%, and the elongation did not decrease, largely due to solid solution strengthening and the reduction in stacking fault energy. Conversely, as Si content increased, the recrystallization ratio decreased during annealing. A heterogeneous grain structure composed of recrystallized and residual deformation regions (high density of dislocations and deformation twinning) was obtained by changing the CRA temperature and Si content. A heterogeneous grain structure of CRA HEAs with an annealing temperature of 700 ℃ and Si content of 0.2 exhibits approximately fourfold higher yield strength (733 MPa) compared to that of HOA FeCoCrNiMn HEAs (185.27 MPa). The structure’s tensile strength and ductility were measured at 959 MPa and 29.5%, respectively. The high strength was mainly attributed to the combined effect of multiple strengthening mechanisms. Heterogeneous deformation-induced strain hardening and twinning-induced plasticity provide good ductility.