Tailored laser power in selective laser melting for enhanced high-temperature oxidation resistance of CoCrNi medium-entropy alloys

Abstract

Developing medium-entropy alloys (MEAs) with consistent and predictable microstructures and compositions is crucial for their application in specific high-temperature and corrosive environments. In this work, a series of CoCrNi MEAs is prepared by adjusting the laser power (175–250 W) of selective laser melting (SLM). All SLM-fabricated samples exhibit greater oxidation resistance than that of the rolled alloy, attributed to their higher grain boundary densities. The oxide scales formed on SLM-fabricated samples comprise a continuous Cr₂O₃ layer, whereas those on the rolled sample feature an inner Cr₂O₃ layer with an outer (Co, Ni)Cr₂O₄ spinel structure. Among the samples, sample III, produced at a laser power of 225 W, exhibits an increased proportion of high-angle grain boundary (HAGB), which can facilitate Cr outward diffusion, and a reduced proportion of low-angle grain boundary (LAGB) and <100> preferred orientation, which can hinder oxygen inward diffusion. These unique characteristics of sample III facilitate the formation of a protective oxide films, thereby reducing mass gain and resulting in enhanced high-temperature corrosion resistance.