Silicon addition as a way to control properties of tribofilms and friction of DLC coatings

Abstract

DLC-Si coatings obtained by cathodic arc evaporation on the (CrAlSi)N sublayer were investigated. The effect of Si addition to DLC on the ID/IG ratio, surface morphology, elastic modulus of surface layers, distribution of elastic modulus and microhardness (over the surface and depth of the coating), specific surface energy, coefficient of friction, wear, and thickness of nanoscale layers formed during friction was studied. The nanoscale thickness of the secondary structures has been evaluated by atomic force microscopy for the first time. It has been established that secondary structures are assembled into nanosized layers and chains, which is explained by sp2 bonds between nanosized clusters. The most hardened layer after friction is formed on the DLC + 0.8 % Si coating. The maps of the elasticity modulus and microhardness distributions are presented. The significant contact pressure is the driving force causing the transformation of the DLC phases during friction. According to the results of microtribotests in wear tracks after macrotests, the average values of the coefficient of friction from microtests correlate with the thickness of the secondary structures on the silicon content of the coatings and with the specific volumetric wear of the coating (for the DLC + 5 % Si coating have the highest values).