Surface characteristics enhancement and morphology evolution of selective-laser-melting (SLM) fabricated stainless steel 316L by laser polishing

Abstract

Additive manufacturing (AM) metal parts often have internal defects and rough surfaces. Particularly for materials with corrosion resistance requirements, such as stainless steel 316L, the AM parts require post-treatment processes. Laser polishing is an efficient and environmentally friendly polishing technique to enhance their serviceability. Nevertheless, investigations into the evolution of surface morphology, defect formation, and surface characteristics of laser-polished AM parts are still lacking nowadays. To investigate the evolution of surface morphology and defect formation, orthogonal experiments on the laser polishing process were conducted on SS316L fabricated by selective laser melting (SLM). The influences of laser power, scanning rate, and spacing distance on surface roughness and integrity were investigated. The surface roughness Sa was reduced from 7.02 µm to 0.28 µm. The conditions for the development of porosity defects on the polished surface were analyzed. Multi-physics models were established to simulate the molten metal flow and surface morphology evolution, as well as defect formation in the cooling stage. The convergence and overflow of sub-surface defects were likely to form pores with excessive laser power. To compare the surface characteristics with the common polishing method, the potentiodynamic polarization curve, energy dispersive X-ray spectroscopy, and X-ray diffraction analysis were conducted. The corrosion resistance and surface microstructure after laser polishing and abrasive blasting were compared. The effectiveness of the optimized laser polishing process was verified, which is essential for broadening the application of AM parts.