Effects of carbon addition on microstructure and mechanical properties of Fe50Mn30Co10Cr10 high-entropy alloy prepared by powder metallurgy

Abstract

To improve the mechanical properties of Fe50Mn30Co10Cr10 high entropy alloy (HEA), a series of carbon-containing HEAs based on Fe50Mn30Co10Cr10 were successfully prepared by powder metallurgy. The effects of carbon content on microstructural evolution and mechanical properties of the as-sintered HEAs were investigated. The improved FCC phase stability and the decreased Σ3 twin grain boundary proportion as the increase of carbon content are mainly due to the increased stacking fault energy. As the carbon content increases, the phase structure of the as-sintered HEAs changes from FCC + HCP phases to FCC phase and then to FCC + M23C6 phases, and the deformation-induced martensitic transformation from FCC to HCP weaken gradually. The solid solubility of carbon in the as-sintered Fe50Mn30Co10Cr10 HEAs is below 2 at.%. A large number of carbides can be observed in the microstructure of the alloys at higher carbon content. The yield strength of the alloys increases approximately linearly with carbon content, while the uniform elongation first increases and then decreases. The (Fe50Mn30Co10Cr10)98C2 HEAs with nano-carbides and ultrafine manganese oxide exhibited a yield strength of 362 MPa, an ultimate tensile strength of 792 MPa, and uniform elongation of 36.7%, showing simultaneous improvement in strength and ductility compared with the carbon-free alloy. This is due to the joint contribution of multiple strengthening mechanisms in the carbon-containing HEA. Interstitial solid solution strengthening and grain boundary strengthening act as the dominant strengthening mechanism. Alloying with carbon element is a feasible method to enhance the mechanical properties of HEAs prepared by powder metallurgy.