Segregation enabled outstanding combination of mechanical and corrosion properties in a FeCrNi medium entropy alloy manufactured by selective laser melting

Selective laser melting (SLM) has the advantage in preparing supersaturated solid solutions due to its unique thermal field and high solidification rate. In this study, a face-centered cubic single-phase FeCrNi medium entropy alloy (MEA) with an ultrahigh Cr content (~35 at.%) was additively manufactured by SLM. The as-built MEA shows a hierarchical microstructure of coarse columnar grains and submicron dislocation cell structures, where the cell boundaries are probed segregated with Cr and C and decorated with nano carbides. The appearance of these dislocation barriers results in an excellent combination of strength (σ_0.2=745 MPa, σ_UTS=1007 MPa) and ductility (ε_f=31%). The current MEA also shows a superb corrosion resistance with a corrosion current density of 0.06 μA cm⁻² in 3.5 wt.% NaCl solution, which is far lower than that of 316 L. The high content of solutioned Cr in the MEA ensures sufficient Cr supply to form an integrated Cr₂O₃ passive film, and the large number of cell boundaries acting as the diffusion channels lead to the fast formation of a stable passive film over the alloy surface.