Tribological Properties of Plasma-Based Low-Energy Nitrogen Ion Implanted 17-4PH Martensitic Stainless Steel

This study investigates the tribological properties of 17-4PH martensitic stainless steel modified by plasma-based low-energy nitrogen ion implantation to enhance its surface hardness and wear resistance. The steel was nitrided at temperatures of 350 °C, 450 °C, and 550 °C for 4 h, and the resultant layers were characterized with respect to microstructure, hardness, and composition. Tribological tests were performed using a ball-on-disk tribometer under dry sliding conditions against an Si₃N₄ ceramic ball, with normal loads of 2-8 N and sliding speeds of 0.15-0.60 m/s. The results demonstrate that the nitrided layer thickness increased from 11 μm to 27 μm and the surface nitrogen concentration rose from 29.7 at.% to 33.1 at.% with increasing temperature, accompanied by an increase in nanocrystallite size from 2 nm to 15 nm and enhanced hardness from 13.51 GPa to 15.66 GPa. All nitrided layers exhibited significantly improved wear resistance relative to the unmodified steel. The layer nitrided at 450 °C demonstrated optimal performance due to a refined nanostructure and minor CrN that enhance plastic deformation resistance and facilitate oxide film formation. While, the 350 °C treated layer exhibits diminished thickness and reduced hardness, and the 550 °C treatment induces excessive CrN precipitation and micro-cracking, consequently compromising both toughness and wear resistance.