High Efficiency Surface Finishing of Direct Energy Deposition Manufactured 17-4PH Stainless Steel: Roughness Reduction and Corrosion Protection

Abstract

Additive manufacturing (AM) of metallic parts has gained significant attention in the materials manufacturing industry. Despite the advantages of complex shape, flexibility, rapid prototyping, and ease of processing, AM parts have associated disadvantages of surface roughness and esthetics that limit wider industrial applications. Specifically, the problem of roughness is more severe in complex intricate geometries that involve high internal surface area. The present study aims to decrease the roughness with minimal material loss of in-house fabricated direct energy deposition specimens using the electropolishing technique. The control over polishing time, in minimizing surface roughness and its associated material loss is demonstrated. Furthermore, surface passivation of electropolished surfaces is determined with potentiodynamic polarization, Mott–Schottky, and electrochemical impedance spectroscopy. Electropolishing performed at 60 °C for 40 min, show a maximum mass loss of 6%. The methodology reported in this study, optimized to reduce the surface roughness (Ra) by 48% with an associated improvement in corrosion resistance by 99%. The results indicate a significant positive shift in corrosion mitigation, with current density of 7.722 μA cm−2 and 0.024 μA cm−2 for as-fabricated and polished surface, respectively. Furthermore, the passive film formed on the 40 min polished surface, demonstrates 2-orders of magnitude reduced carrier density demonstrating improved passivation to Cl− penetration.