Analysis of microwear experiments on thin DLC coatings: friction, wear and plastic deformation

Linear oscillating microwear experiments have been performed on thin diamond-like carbon (DLC) coatings on glass, using a Hysitron Triboscope with a conical diamond tip of 0.6 μm tip radius and loads in the range of some milliNewtons. The friction coefficient μ has been determined as a function of load L and the number of wear cycles. The results can be understood in terms of a combination of Hertzian elastic contact and an additional ploughing term:μ=c1L−1/3+c2Lm where m changes strongly during the first wear cycles. The residual wear depth of the wear trace has been compared to the residual indentation depth on the same material using the same tip. The comparison shows that in some cases the apparent wear volume is not due to a real material loss, but mainly to plastic deformation or densification of the material, while in other cases plastic deformation and material loss both contribute to the observed wear volume.