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

Abstract

• A face-centered cubic single-phase FeCrNi medium entropy alloy with a high Cr (~35 at.%) content was successfully manufactured by selective laser melting (SLM). • This as-SLMed MEA presents a hierarchical microstructure of coarse columnar grains and submicron cell structures. Cr, and also interstitial C , are found segregated to the cell boundaries. • The as-SLMed FeCrNi MEA shows a good combination of strength (σ0.2 = 745 MPa, σUTS=1007 MPa) and ductility (εf=31%), as well as a superb corrosion resistance ( i corr =0.06 μA/cm 2 ). 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 Cr 2 O 3 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.