Carbide and nitrocarbide layers produced by glow-discharge treatment on titanium

The glow-discharge nitriding treatment is able to produce hard ceramic compounds on the surface of titanium alloy components, improving their poor tribological properties. The aim of the present research was to evaluate the influence of adding methane to the nitriding treatment atmosphere on the surface characteristics of titanium. Treatments were performed on ASTM grade 2 titanium at 1073 and 1173 K using different nitrogen - methane gas mixtures. Depending on the used gas mixture, the surface layers of the treated samples consist of nitrides, carbonitrides or carbides, which markedly increase the surface hardness up to ~ 2260 HK0.05. The surface layers of the treated samples show a friction coefficient, evaluated in dry sliding conditions, which is about three times lower than the one of the untreated samples. The critical surface tension of wettability for the different treatment types was also evaluated.