Effect of C addition on microstructure and mechanical properties of as-cast HEAs (Fe50Mn30Co10Cr10)100-xCx

The microstructure and mechanical properties of the as-cast (Fe50Mn30Co10Cr10)100-xCx (x = 0, 0.5, 1, 2, 4, 6 at.%) alloys have been investigated. The results show that at x = 0, the alloy consists of FCC and HCP phases. At x＜4, C is completely dissolved into the as-cast (Fe50Mn30Co10Cr10)100-xCx alloys. The HCP volume fraction decreases and the FCC volume fraction increases with the C content increasing. During tensile process, there is a change from transformation-induced plasticity to twinning-induced plasticity with the increase of C content, resulting in the remarkable improvement of the plasticity. At x = 2, the plastic strain is almost three times larger than that of the Fe50Mn30Co10Cr10 alloy. At x > 4, however, the nano-carbides present and their volume fraction increases with the increase of C content. The carbides and FCC matrix have the eutectic lamellar morphology and coherent relationship. The solid solution strengthening and formation of carbides decrease the plasticity and increase the yield strength.