Tribological Properties of Graphite Like and Diamond Like Carbon Coatings

Two carbon based coatings with exceptional tribological properties have been developed. One is a Graphite like Carbon known as Graphit-iC (trademark), the other is a hydrogenated Diamond like Carbon known as Dymon-iC (trademark). There are some important differences between the two coatings. The Graphit-iC has excellent properties under water with wear rates better than 10-19m3/Nm but it has poor properties in vacuum. This is consistent with its graphite like properties. Dymon-iC has poor properties under water and early tests indicate that the properties in vacuum are good but more tests are needed. Both coatings have excellent tribological properties with oil under boundary lubrication conditions. In long term testing comparing Graphit-iC and Dymon-iC with a hard CrN coating no wear could be detected for any of the coatings but the bearing steel counterface had significant wear against the CrN coating with little wear against the carbon coatings. The mechanism of low friction for the Graphit-iC. has been studied in some detail and the results will be presented and discussed. The differences between the coatings lead to different types of application and some of these are presented.