The Effect of Cathodic Cage Plasma TiN Deposition on Surface Properties of Conventional Plasma Nitrided AISI-M2 Steel

In this study, a combination of conventional plasma nitriding and cathodic cage plasma deposition (CCPD) at different temperatures (400 and 450^◦ C) is implemented to enhance the surface properties of AISI-M2 steel. This combination effectively improves the surface hardness and the formation of a favorable hardness gradient toward the core, which would benefit the load-bearing capacity of substrate. The duplex-treated samples exhibit iron nitrides (Fe₄ N, Fe₂₋₃ N) and titanium nitride (TiN) phases. The thickness of the hard-TiN layer is 1.35 and 2.37 µm, whereas the combined thickness of the hard film and diffusion layer is 87 and 124 µm, for treatment at 400 and 450^◦ C, respectively. The wear rate and friction coefficient are dramatically reduced by duplex treatment. The oxidative wear mechanism and adhesive wear mechanism are dominant for duplex-treated samples. This study suggests that the cathodic cage plasma deposition technique can attain a combination of hard film and diffusion layer. The plasma nitriding before CCPD is beneficial for attaining an adequate nitrogen diffusion layer thickness. The drawbacks of conventional TiN film deposition, such as “egg-shell” problems, can be removed.