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 0.06μA 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.

Formation process and mechanical properties in selective laser melted multi-principal-element alloys

Additive manufacturing is believed to open up a new era in precise microfabrication,and the dynamic microstructure evolution during the process as well as the experiment-simulation correlated study is conducted on a prototype multi-principal-element alloys FeCrNi fabricated using selective laser melting(SLM).Experimental results reveal that columnar crystals grow across the cladding layers and the dense cellular structures develop in the filled crystal.At the micron scale,all constituent elements are evenly distributed,while at the near-atomic scale,Cr element is obviously segregated.Simulation results at the atomic scale illustrate that i)the solid-liquid interface during the grain growth changes from horizontal to arc due to the radial temperature gradient;ii)the precipitates,microscale voids,and stacking faults also form dynamically as a result of the thermal gradient,leading to the residual stress in the SLMed structure.In addition,we established a microstructure-based physical model based on atomic simulation,which indicates that strong interface strengthening exists in the tensile deformation.The present work provides an atomic-scale understanding of the microstructural evolution in the SLM process through the combination of experiment and simulation.