Enhancing surface quality, mechanical properties, and biocompatibility of laser powder-bed fusion-fabricated SS316L part through laser polishing

Abstract

Laser powder bed fusion (LPBF) is a well-known process for fabricating metallic bio-implants. However, the printed implants exhibit higher surface roughness along the build direction due to powder adhesion, lack of fusion of powder particles, and staircase effect caused by layer-on-layer deposition. This study investigated the influence of laser polishing (LP) on surface characteristics, mechanical properties, and biocompatibility of LPBF-fabricated SS316L parts. LP significantly reduced surface roughness (84 %) compared to the as-built state. The pyrometer captures the temperature in the rapid heating, melting, and solidification stages during laser polishing. The rate of heating and cooling is about 10⁷ºC/s in both cases, which resulted in a columnar and lathe-type microstructure with a micro-hardness of 270 HV. Wear resistance after LP is enhanced due to surface hardening, but its effectiveness might be limited to its remelted layer thickness. XRD analysis confirmed no alteration in material phases (Fe₁Ni₁ and γ-Fe). The cytotoxicity analysis of the powdered and as-built samples showed less cell viability and proliferation. Laser-polished surfaces fostered the highest cell viability, highlighting their superior biocompatibility. Overall, this study suggests laser polishing as a promising approach to improve surface quality, mechanical properties, and biocompatibility of LPBF-made SS316L parts, particularly for biomedical applications.