Effect of In-Situ Laser Polishing on Microstructure, Surface Characteristics, and Phase Transformation of LPBF Martensitic Stainless Steel

Abstract Metal additive manufacturing recently has made advances in terms of mechanical properties and microstructure. Martensitic stainless steel (15-5PH) is well known for its corrosion resistance, high stiffness, and tensile strength. Due to the poor surface roughness of additively manufactured parts, further surface treatment techniques are essential. Using Laser Powder Bed Fusion (LPBF) enables in-situ laser polishing that can be applied after the part is fabricated. This technique results in better surface roughness, an improvement in mechanical properties, and fine microstructure over the final layer. In this study, the influence of laser polishing on surface roughness, hardness, and phase transformation are characterized using microscopy, surface roughness test, Vickers hardness test, and X-ray diffraction (XRD) methods, respectively. The LPBF process is monitored using a thermal camera to understand the effect of thermal history on the surface quality and phase transformation after applying single and double passes of the laser polishing. The results indicate that high energy density results in rougher surfaces, a higher amount of retained austenite phase, and lower material hardness. Performing energy input with 2.27 J/mm2 under one laser pass has shown better values in terms of surface hardness and martensitic phases for martensitic stainless steel.