How can H content influence the tribological behaviour of W-containing DLC coatings

http://www.sciencedirect.com/science/article/B6W6W-4VCH71Y-1/2/9b50f04850d12009018cd55f8983a39

Tribological behaviour of W-alloyed carbon-based coatings in dry and lubricated sliding contact

Carbon-based coatings with different W contents were deposited by direct current magnetron sputtering in reactive and non-reactive atmospheres. All deposited coatings have compact morphologies with amorphous (tungsten-free) or nanocrystalline structures (tungsten-doped). The latter one was indicated by very broad peaks in X-ray Diffraction spectra in the position of tungsten carbide suggesting W-carbide nanoparticles embedded in an amorphous carbon matrix. The hardness increased from 10 to 15 GPa with increasing W content. The coatings were tribological tested at dry and lubricated conditions with increasing temperature in a coating/steel configuration. In dry sliding, the friction coefficient increases with the increase of the temperature reaching values higher than 1.0. The friction is significantly lower in lubricated contact using three different oils: poly-alpha-olefin, paraffin and olive oil. The olive oil shows promising lubricating properties at the temperature lower than 70°C; however, at higher temperature, the coatings were quickly worn through