Effect of substrate roughness on the contact damage of DLC coatings

The effect of substrate roughness on the contact damage of diamond-like carbon (DLC) coatings has been investigated. The coatings were deposited on steel substrates of varying roughness by plasma-enhanced chemical vapour deposition (PEVCD) and subjected to nanoindentation. At high loads, pop-ins in the load-displacement curves were observed, associated with the formation of ring cracks initiated in the coating surface. The subsurface deformation and fracture of the coatings were inspected using focused ion beam (FIB) microscopy. It was found that the mean roughness of the coating have been increased relative to their substrates, except for the very rough substrate, in which the coating roughness was relatively decreased. The rougher substrates were found to lead to an increase in the load required to induce pop-ins in the nanoindentation load-displacement curves.