Tribological behavior of DLC coatings with functionally gradient interfaces

Initial evidence showed that soft substrate materials (such as Ti–6Al–4V alloy) might not be able to provide adequate support for hard DLC films, adversely affecting their tribological performance and durability. An innovative concept in the development of advanced tribological systems involves coatings with a functionally-graded interface (FGI). This concept was experimentally studied in the present work by developing a model system involving DLC coatings with FGI based on theoretical finite element analysis (FEA) predictions. It was found that the durability of the DLC film is affected by the presence of the FGI and the loading level. Under low loading, FGI has a small effect due to the limited yielding occurring in the substrate. Under high loading conditions, the presence of FGI produced significant improvements (∼80% increase in coating lifetime). In view of the FEA predictions, these effects can be attributed to reduction of the plastic zone size and prevention of yielding at the coating/substrate interface.