Effects of Laser Polishing on Surface Characteristics and Wettability of Directed Energy-Deposited 316L Stainless Steel

Directed energy deposition (DED) is one of the most used additive manufacturing processes for the fabrication of 3D-metal components. However, surface quality is not always within the limits required for most applications. Post-processing operations can overcome such a limitation. Laser polishing (LP) can be performed with the use of a same energy source and same gripping position, thus improving both surface roughness and functional characteristics (e.g., wettability). However, the literature lacks studies on the process parameters and their influence on roughness and wettability characteristics. This article investigates the influence of LP on surface roughness and wettability of AISI 316L SS produced by DED and proposes equations that predict surface roughness and remelted layer thickness (RLT) as a function of laser power (P). The surfaces were characterized by metallographic analysis, microhardness, surface roughness parameters (S_a, S_z, S_ku, and S_sk), and contact angle. The results showed a reduction of up to 86% in S_a, and the S_z/S_a ratio as a P-function was correlated to a surface improvement. S_ku and S_sk help to better characterize the surface, thus affecting its wettability. The RLT displayed a linear and P-dependent behavior. No alteration in the microstructure/microhardness was observed after the LP.