Tribological Properties of TiN Hard Film Lubricated With Different Liquid Lubricants

Liquid lubricants can improve the tribological properties of hard films. The tribological performance of titanium nitride (TiN) hard film against bearing steel and silicon nitride respectively was evaluated using a ball-on-disk tribo-tester under lubrication of several kinds of lubricating oils. The morphologies and element contents of wear tracks were characterized by scanning electron microscopy and energy dispersive spectrometer. The results show that the lubricating oils reduced the friction coefficient, and enhanced the test duration markedly. And lubricating oils with longer alkyl carbon chains exhibited better lubricating properties than that with shorter chains. Moreover, the materials of upper balls had distinct influence on the lubricating performance. Better lubricating property was obtained using a silicon nitride ball in comparison with a bearing steel ball. The analysis results show that wear tracks were smoother under lubrication of lubricating oils with long carbon chains than silicone oil with short alkyl carbon chain. However, the latter silicone oil contains element chlorine, which was one of the key ingredients of extreme pressure additives. Wear and friction coefficient of TiN hard film lubricated with short alkyl carbon chain silicone oil were higher than that lubricated by the rest lubricating oils. The boundary lubricating film, which was formed by tribochemical reaction between element chlorine and elements of the substrate was not compact and continuous, was poor in wear resistance.