Chemical and electrochemical surface modification and fatigue response of PBF-LB/M 316L stainless steel

Abstract Laser beam-powder bed fusion/metal (PBF-LB/M) offers significant advantages for manufacturing 316L stainless steel components. However, inherent surface roughness can limit their application in sectors requiring high-quality surfaces. This study investigates the influence of two electrochemical post-processing techniques, Hirtisation and DLyte, on surface topography and fatigue behavior of PBF-LB fabricated 316L stainless steel. Vertically built cylindrical fatigue specimens were subjected to both the treatments. Following surface treatment, surface roughness, residual stress, microstructure, and high-cycle fatigue properties were studied. Hirtisation significantly reduced the average surface roughness (S a ) around 70%, with a further improvement to around 80% after DLyte treatment. The mean roughness depth and deepest valley depth also decreased after post-processing. Notably, uniaxial fatigue testing revealed a 20% increase in fatigue life for specimens subjected to Hirtisation while around 40% for a combination treatment, Hirtisation + DLyte compared to the as-built condition. However, these specimens exhibited higher surface tensile residual stress levels. This suggests a trade-off between the benefits of a smoother surface (reduced fatigue crack initiation sites) and the detrimental effects of higher residual stress (promoting crack propagation). Despite the improvement in surface quality, the treated specimens exhibited higher surface residual stress, which may counteract some fatigue benefits.