Plasma Immersion Ion Implantation of AISI 316L Stainless Steel Parts Manufactured by Laser Powder Bed Fusion

Austenitic stainless steel (SS) AISI 316L is highly compatible with laser powder bed fusion (LPBF), an advanced additive manufacturing (AM) technique for producing high-quality near-net-shape parts with complex geometries, especially for aerospace and medical applications. To further enhance its surface properties, temperature-controlled nitrogen plasma immersion ion implantation (TC-NPIII) was applied to LPBF-manufactured AISI 316L to obtain an expanded austenite ( γ N) layer, thereby enhancing surface performance and expanding the applicability of this material in demanding environments. The present work investigates the influence of TC-NPIII treatment temperature and duration on the microstructural evolution and mechanical performance of LPBF-manufactured AISI 316L. Samples were produced by LPBF in a laser-adapted powder bed system and subsequently treated by TC-NPIII, varying treatment duration for 1 and 3 h at controlled temperatures (450-520 °C). Microstructural analysis after treatment revealed a modified layer with a thickness that ranged from approximately 18.30 to 28.40 µm, superimposed on the characteristic LPBF microstructure. Grazing Incidence x-ray Diffraction (GI-XRD) analysis confirmed the formation of the desired γ N phase, while no diffraction peaks associated with chromium nitrides were detected within the investigated processing window. Cross-sectional nanoindentation measurements of the treated samples yielded hardness values of approximately 386-751 HV, representing a substantial increase compared with the untreated LPBF sample (238 HV). These results indicate that, among the treatment temperatures and durations investigated, 450 °C for 3 h represents the optimal processing condition, promoting γ N formation while preventing chromium nitride precipitation. The present work demonstrates that TC-NPIII can effectively produce expanded austenite and achieve significant surface hardening within treatment durations as short as 1-3 h. Moreover, these findings confirm the effectiveness of the TC-NPIII treatment in modifying the surface of LPBF-produced AISI 316L stainless steel, thereby enhancing its mechanical performance while preserving the characteristic hierarchical microstructure generated during LPBF.