Plasma nitriding of additively manufactured 316L austenitic stainless steel produced by laser power bed fusion and metal binder jetting

Abstract

Among the additive manufacturing methods, laser powder bed fusion (L-PBF) and metal binder jetting (MBJ) are well established technologies for producing complex-shaped 316L components. Plasma nitriding provides an effective approach to enhance their surface properties, thereby broadening their application potential. Since L-PBF and MBJ generate distinct microstructures, it is essential to evaluate their influence on the resulting mechanical and tribological performance. Therefore, L-PBF- and MBJ-316L are plasma nitrided at temperatures of TPN1 = 380 °C and TPN2 = 430 °C for 10 h and compared with conventionally wrought 316L. The thickness of the S phase is independent of the initial microstructure, exhibiting values of δPN1 ≈ 3 μm at TPN1 and δPN2 ≈ 12 μm at TPN2. Nanoindentation reveals a significant increase in near-surface hardness to 1230–1400 HVIT at TPN1 and 1420–1520 HVIT at TPN2, associated with austenite lattice expansion caused by interstitial dissolution of nitrogen. In contrast, Vickers microhardness is additionally influenced by the core microstructure, with plasma nitrided MBJ-316L showing lower values than L-PBF-316L. The enhanced surface hardness significantly improves the resistance against abrasive wear of all 316L variants. Overall, the plasma nitriding processes developed for conventionally manufactured 316L steels can be successfully applied to additively manufactured 316L.