Variation of the wettability of DLC-coatings by network modification using silicon and oxygen

Research in recent years has shown that it is possible to combine the well-known properties of diamond-like-carbon coatings (DLC) with a less noticed property, the surface energy. It is known that doping the DLC-matrix with fluorine causes a decrease of the surface energy to 20 mN/m. Fluorine-containing DLC-coatings with such low surface energies exhibit a similar behaviour like PTFE. The chemical instability of DLC-coatings with a high fluorine content as well as the environmental discussions about fluorine-containing hydrocarbons have shown the necessity for a new approach to these kind of thin films. This paper presents the variation of the wettability of DLC by modifying it with silicon and the influence of oxygen in silicon-modified DLC. From tribological research it is known that by doping with silicon a decrease of friction can be achieved. A coating system which is chemically stable up to temperatures of 270 degrees C and which has PTFE-like properties can also be deposited by doping the DLC-matrix with silicon. The properties of silicon-containing DLC-coatings are high hardness and wear resistance combined with a PTFE-like wettability. The silicon-containing DLC-coatings are 20-times less wear resistant than DLC-coatings, but are 10-times more wear resistant compared with uncoated 100Cr6-steel. The surface energy stretches from 32 to 22 mN/m. (C) 1998 Elsevier Science S.A.