Effects of different surface modifications on the fatigue life of selective laser melted 15–5 PH stainless steel

Abstract

Effects of machining, electro-polishing and laser surface re-melting (LRM) on the fatigue life of Selective Laser Melted (SLM) 15–5 precipitation hardening (PH) stainless steel are reported. Electro-polished surface showed ~97.4% reduction of surface roughness (Ra) and hence improved the fatigue life drastically (~100%) as compared to as-built specimens. Synergic effect of both compressive residual stress and reduction in surface roughness caused drastic improvement (~138%) in fatigue life of machined SLM specimens when compared to its as-built counterpart. Laser Surface Re-melting is found to be an effective technique to reduce the surface roughness (~91.2%) as well as sub-surface defects of geometrically complex as-built SLM specimen and thus improved its fatigue life by ~119%. Fractography analysis showed surface roughness, sub-surface defects and micro notches as the primary crack initiating factors for SLM specimens. High surface roughness in as-built part causes multiple crack initiation sites for specimens failed under both low and high stress amplitude. However, for machined, electro-polished and LRM SLM specimens distinct and multiple crack initiation sites could be observed when specimen failed under high cycle and low cycle regime respectively. However, for all the cases, fatigue life is found to be less compared to its wrought counterpart. Present study could be used as a guideline to select proper surface modification methods for SLM 15–5 PH stainless steel for a desired fatigue life.