Sliding wear of titanium nitride thin films deposited on Ti–6Al–4V alloy by PVD and plasma nitriding processes

Considerable progress has been made in improving the tribological properties of titanium alloys by application of surface engineering technologies such as physical vapour deposition (PVD) and plasma nitriding. PVD coatings produce very hard, low friction surfaces, but may be susceptible to coating fracture and delamination under high normal load sliding wear conditions. Plasma nitriding produces a nitrogen-strengthened diffusion layer beneath the coating, which should have beneficial effects on the coating's ability to support high normal load sliding wear. There do not appear to be any published works which clearly demonstrate and quantify this effect for TiAlV alloy under controlled experimental conditions. The current work investigates the comparative sliding wear behaviour of TiN and TiN/Ti2N thin films deposited by PVD and plasma nitriding processes, respectively, and seeks to quantify the relative improvements to sliding wear behaviour afforded by the two surface treatments. The results confirm the theory, showing that the increased hardness/strength of the substrate in the plasma nitrided material is responsible for a significant improvement in sliding wear behaviour under all normal loads considered.