Influence of normal load on the coefficient of friction of WC/C coating using experimental and numerical analyses

Full text: The performance of mechanical components can be increased by PVD coatings, for example by means of a reduction in the coefficient of friction in given applications. However, during the deposition process, imperfections such as macroparticles can occur and they can affect the tribological performance of the system. In this work, the influence of macroparticles on the tribological and fracture behavior of a commercial WC/C multilayer coating was evaluated using lubricated reciprocating ball-on-disc tests and dry scratch tests. The tribological pair was AISI H13 disc and AISI 52100 ball coated with WC/C. Specimens were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM). In addition, numerical simulations of the scratch tests were conducted to complement the experimental tests. The mechanical properties of the coating and of the macroparticles were evaluated by combining experimental (Bruker TI950 triboindenter) and numerical analyses (Abaqus ®). Results indicated two distinct mechanisms for macroparticles mechanical failure: detachment and fragmentation. Those failure modes were correlated with the applied normal load and the presence of WC_1-x crystalline phase detected by XRD and XPS analyses. The macroscale reciprocating tests showed that the increase of the normal load promoted a reduction in the friction coefficient. (author)