Environmental and Thermal Effects on the Tribological Performance of DLC Coatings

Diamond-like carbon (DLC) coatings have low friction and high wear resistance compared to bulk materials and to other wear-resistant coated surfaces. The surrounding environment, gas atmosphere, humidity and temperature, affect the friction and wear performance of DLC films dramatically. In dry and inert atmospheres, the highly hydrogenated DLC films typically exhibit low friction performance, but the hydrogen-free DLC films have high friction accompanied with increased wear. In humid environment, the friction coefficient of both types of DLC films is similar varying in the range 0.05–0.2 and the best wear resistance can be achieved with hydrogen-free ta-C films. At elevated temperatures, the advantageous tribological properties of hydrogenated DLC films may be disturbed due to effusion of hydrogen and graphitization of the film structure in rather low temperatures. The hydrogen-free ta-C films on the other hand can survive in higher temperatures, even though the friction coefficient reaches higher values.