Fatigue Life Improvement in Laser Powder Bed Fusion of Stainless Steel via Electropolishing

Abstract

Additive manufacturing of metallic components with industrial-grade materials has shown great progress, but still face several challenges. In the present study the use of electropolishing to improve the surface finish of parts generated via laser powder bed fusion in stainless steel 316L is explored. A thorough assessment of the impact of the before-mentioned post-processing techniques on the fatigue life of the components was performed. Fatigue testing was conducted via rotating cantilever bar with solid samples and samples with lattice structures with strut sizes in 250 and 500 m. The stress amplitude for fatigue testing is set at 70% of the ultimate tensile strength of the samples. Considering 5 replications of each testing condition, the electropolishing surface treatment improves the average fatigue life from 20.5 cycles to 24.6 cycles when comparing with as build samples. The machining of the same kind of additively manufactured parts was used as a reference, achieving 29.6 cycles of average fatigue life. The samples with lattice geometries show an improvement in surface finish but did not achieve a significant improvement in fatigue life due to excessive loss of mass in the extremely small struts with 250 and 500 microns. The study reported here shows that electropolishing is a viable alternative for fatigue life improvement compared to other more expensive and/or complex post-processing approaches.