A novel high entropy alloy with outstanding strength by low temperature annealing after severe cold rolling

The as-cast (Fe50Mn30Co10Cr10)97C2Mo1 HEA (high entropy alloy) was cold rolled to 90 % (CR90 %), followed by annealing at different temperatures (400 °C, 500 °C, 600 °C). Their microstructure and mechanical properties have been systematically investigated. The results show that this HEA has a single FCC structure, and that annealing at 500 °C and 600 °C leads to the formation of Cr-rich σ phase. The CR90 % HEA exhibits the tensile strength of 1926 MPa and 4 % elongation. However, annealing at 400 °C and 500 °C makes the tensile strength improve to ∼2078 MPa and ∼2060 MPa, respectively, while their plasticity does not change significantly. Annealing at 600 °C results in a significant reduction in the strength (∼1650 MPa) while a slight increase in plasticity. The element segregation and the formation of nano-sized (Fe, Mn)-rich precipitates are contributed to the significant increase in tensile strength of the HEA annealed at 400 °C. Nevertheless, annealing at 600 °C leads to a decrease in the density of defects (e.g. dislocations) caused by cold rolling and the increase in the grain size, which finally resulting in a reduction in strength.