Influence of interstitial carbon content on the microstructure, mechanical and electrochemical corrosion properties of CoFeNiMn multi-principal component alloys

In this study, the effects of carbon content on the microstructural evolution as well as compression and electrochemical corrosion properties of CoFeNiMn multi-principal component alloys (MPCAs) were investigated. A series of (Co25Fe25Ni25Mn25)100−xCx (x = 4, 5, 6, 7, 8) alloys were prepared by vacuum arc melting. Increasing carbon content, the structure transits from a single face-centered-cubic (FCC) phase into a mixed structure containing FCC phase and M23C6 carbides. The yield strength and hardness of the (Co25Fe25Ni25Mn25)100−xCx alloys were enhanced by increasing carbon content, which in turn decreases the ductility. The alloys containing eutectic carbides had a good combination of high yield strength (880 MPa), high fracture strength (2773 MPa), and large fracture strain (47%). Electrochemical measurements indicated that carbon content evidently affects the corrosion resistance of (Co25Fe25Ni25Mn25)100−xCx alloys in 3.5 wt% NaCl solution. Their corrosion resistance initially increases and then decreases with increasing carbon content. The increase in M23C6 carbides can accelerate pitting corrosion and degenerate their corrosion resistance. These findings not only provide comprehensive understanding of the carbon-alloyed behavior in FCC-type MPCAs but also show their potential engineering application as high-performance structural materials.