The behavior of metal-containing, diamond-like-carbon (Me-DLC) coatings in rolling contact is significantly different from their behavior in pure sliding. The former contact type often leads to a coating failure mechanism of brittle fracture in an adhesive and/or cohesive manner, and the latter contact type often leads to an increase in the actual area of contact with sliding distance through shear deformation of the coatings. Moreover, the degradation behavior of Me-DLC coatings depends strongly on both composition and processing. Applications that include both rolling and sliding contact, such as power-transmission gears, exhibit behavior that is intermediate between the two extremes, often acting more similarly to behavior in pure sliding than in pure rolling.

The authors have conducted a systematic study to determine the behavior of two types of metal-containing DLC coatings, those containing W and Cr, through experiments that impose pure sliding and both rolling and sliding. Using post-test characterization techniques that include focused-ion-beam (FIB) SEM and atomic force microscopy (AFM), interesting contrasting behavior of the coatings in sliding contact has been observed. Measurements to determine coating residual stress and interfacial fracture energy have enabled the development of a model that describes the observed behavior. In addition, using a first-principles approach, the authors are developing a model to express coating lifetime that includes contributions from chemical interactions, phase transitions, and fracture. The results of this systematic study will be presented and compared to results reported in the literature.