In this study, we investigate the microstructure and the corrosion performance of an 18Ni 300 maraging steel after prepared by selective laser melting (SLM) technique and the effects of aging. The commercial 18Ni 300 maraging steel fabricated by rolling followed by aging acts as a comparison. The SLM specimens showed fine microstructures with homogeneous cellular and columnar dendrites, which resulted in relatively uniform corrosion, while the conventionally rolled specimens displayed a typical lath martensite microstructure. The aging treatment accelerated the corrosion rate possibly due to the galvanic corrosion between intermetallic precipitates Ni3(Ti, Mo) and martensite matrix, as well as the corrosion of Ni and Co which diffuses into the matrix. The formation of unmelted particles made of (Al, Ti)O during the SLM process is deleterious to the corrosion resistance as they lead to localized attack. The long-term immersion makes for the accumulation of thick and corrosion product layer, which prevents further dissolution of the metal substrate by preventing oxygen and ion species from contacting metals.

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