Morphology Replication Effects in Hybrid-treated MIM 17-4PH Stainless Steel and Their Influence on Friction and Wear Behavior

Abstract

This study investigated the morphology replication and resulting structural and tribological effects of different surface treatment methods on metal injection-molded (MIM) 17-4PH martensitic precipitation-hardenable stainless steel. Three conditions were evaluated: untreated, TiAlN + TiCN PVD-coated, and hybrid-treated samples combining low-temperature plasma nitriding (LTPN) with PVD coating. The specimens were characterized for surface roughness and morphology, phase composition, hardness, adhesion, friction behavior, and wear resistance. The results showed that LTPN significantly modified the substrate surface through crack formation, grain boundary shear offsets, and grain surface uplifts, with the latter two morphological features being subsequently replicated by the deposited coating, leading to increased roughness parameters (R_pk, R_vk, and R_k). The nitrided layer improved coating support and increased the hardness of the PVD-coated system. In addition, the altered surface morphology was associated with changes in the coating's preferred crystalline orientation, including the appearance of the (220) and strengthening of the (222) TiAlN/TiCN reflections. Tribological testing demonstrated that the hybrid-treated samples exhibited improved tribological performance, including lower steady-state friction and enhanced wear resistance, attributed to the combined effects of the modified surface morphology and enhanced load-bearing capacity of the nitrided substrate. The findings highlight the role of substrate grain morphology in governing LTPN-induced surface modifications and their subsequent replication by the PVD coating, suggesting that further optimization of MIM processing parameters could enable control of the surface morphology and, consequently, the tribological properties of hybrid surface-treated MIM components.