Corrosion Resistance Enhancement of Selective Laser Melted Cost-Effective Interstitial Medium-Entropy Alloy via Deep Cryogenic Treatment

An economically interstitial FeMnCrNiCu medium-entropy alloy (MEA), which exhibits preferable corrosion resistance in 3.5 wt% NaCl solution, is fabricated by selective laser melting (SLM). Compared with annealing, which is one of the posttreatments for additive manufacturing, deep cryogenic treatment (DCT) also contributes significantly to the alloy properties and is expected to improve corrosion resistance. Herein, the corrosion behavior of SLM-MEA after DCT in 3.5 wt% NaCl solution is investigated. DCT improves corrosion resistance by promoting the uniform distribution of precipitates in SLM-MEA and changing the cation ratio in the passive film. After DCT, the corrosion current density of the SLM-MEA in original and annealed state decreases by 27.07% and 62.69%, respectively. The annealed SLM-MEA exhibits the worst corrosion resistance as a result of the precipitation of continuous Cr-rich M23C6 carbides at grain boundaries. The face-centered cubic structure of MEA does not change after annealing or DCT. Significantly, the number, size, and distribution of the precipitates are greatly affected. DCT after annealing promotes the uniform diffuse distribution of M23C6 carbides and nanoscale Cu-rich particles while increasing the Cr+Ni/Fe+Mn ratio in the passive film, resulting in a significant improvement in corrosion resistance.