Electroless nickel plating of electropolished and chempolished Additively Manufactured (AM) steel components in various surface orientations

Electroless coating brings the advantage of providing films on the complex geometry of additively manufactured components. However, there is a knowledge gap about the impact of AM part surface and postprocessing parameters on the quality of electroless coating. This study explores the application of three solution-based surface finishing techniques on the microstructure and surface hardness of additively manufactured stainless steel components coated with electroless nickel films. Given that AM techniques for metal parts often yield surfaces with inherently rough textures and differences in properties along the different planes, we investigated their relationship with nickel coating. To mitigate the impact of surface irregularities on electroless nickel coating quality, this research evaluated the effectiveness of chemical polishing (CP) and Electropolishing (EP) as post-processing treatments for AM stainless steel. Characterization of the treated samples was conducted using the analytical Digital Microscope, Scanning Electron Microscope (SEM), and scratch tester. Additionally, the study incorporated an instant segmentation machine learning algorithm to overcome image analysis challenges. The findings indicate that EP and CP significantly improve surface smoothness, decreasing the arithmetical mean height (Ra) by as much as 4 µm and 10 µm, respectively. Furthermore, the nickel-coated AM samples demonstrated an enhancement in scratch resistance, exhibiting up to a two-fold increase in surface hardness compared to their as-built counterparts. Taguchi design of the experiment was applied to investigate the effect of process parameters. This study provides insights for developing improved surface quality and acquiring new properties via the coating process to make AM parts suitable for challenging environments and novel applications.