Mechanical and tribological properties of duplex treated TiN, nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings deposited on 410 low alloy stainless steel

The use of hard and superhard nanocomposite (nc) coatings with tailored functional properties is limited when applied to low alloy steel substrates due to their low load carrying capacity. Specifically in this work, in order to enhance the performance of martensitic SS410 substrates, we applied a duplex process which consisted of surface nitriding by radio-frequency plasma followed by the deposition of single layer (TiN, nc-TiN/a-SiNx or nc-TiCN/a-SiCN) or multilayer (TiN/nc-TiN/a-SiNx, TiN/nc-TiCN/a-SiCN) coating systems prepared by plasma enhanced chemical vapor deposition (PECVD). We show that plasma nitriding gives rise to a diffusion layer at the surface due to diffusion of nitrogen and formation of the α-Fe and ε-Fe2N phases, respectively, leading to a surface hardness, H, of 11.7 GPa, compared to H = 5 GPa for the untreated steel. Among the TiN, nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings, the latter one possesses the highest H value of 42 GPa and the highest H3/Er2 ratio of 0.83 GPa. Particularly, the TiN/nc-TiCN/a-SiCN multilayer coating system exhibits superior tribological properties compared to single layer TiN and multilayer TiN/nc-TiN/a-SiNx coatings: this includes excellent adhesion, low friction (Cf = 0.17) and low wear rate (K = 1.6 × 10− 7 mm3/N m). The latter one represents an improvement by a factor of 600 compared to the bare SS410 substrate. The significance of the relationship between the H/E and H3/Er2 ratios and the tribological performance of the nano-composite coatings is discussed.