Improved wear resistance of AISI-1045 steel by hybrid treatment of plasma nitriding and post-oxidation

In this work, high-temperature plasma nitriding is used to improve the surface hardness and wear resistance of AISI-1045 steel. Subsequently, plasma nitrided samples are post-oxidized for 30 and 60 min to investigate its resultant effect. The treated samples are analyzed by X-ray diffraction, Raman spectroscopy, microhardness tester, scanning electron microscopy, elemental dispersive spectroscopy, and ball-on-disc wear tester. The nitrided sample contains a white layer Fe4N,Fe2−3N, and its post-oxidation form hematite Fe2O3 and magnetite Fe3O4phases. A significant improvement in hardness (~1050 HV) is attained for nitrided samples, while post-oxidation causes a small decrease in hardness. The thickness of the nitrided layer is 8.2 µm, and it is further increased to 9.3 and 13.2 µm by post-oxidation due to further diffusion of nitrogen. The thickness of the oxide layer is 1.5 µm and 2 µm. The presence of a white layer causes abrasive wear of sample, whereas sample with post-oxidation shows outstanding wear resistance with adhesive wear mechanism. The friction coefficient of the nitrided sample is further reduced by plasma post-oxidation. This work suggests that detrimental effects of the white layer due to the removal of hard abrasive particles can be avoided by plasma post-oxidation.