TRIBOLOGY OF CARBON COATINGS - DLC, DIAMOND AND BEYOND

There is considerable interest in carbon films at present because they can exhibit high hardness, low friction, chemical inertness and transparency. Amorphous carbon films, containing both sp(2) and sp(3) bonding and generally some hydrogen, sometimes called ''diamond-like'' carbon (DLC), have considerably poorer properties than diamond, but the low cost, low deposition temperature and ability to deposit on large structures make DLC a competitive coating material. However, the superior tribological properties of polycrystalline diamond coatings can provide greater benefits in applications where high deposition temperatures are not a problem. Recent theoretical predictions have indicated that carbon nitride coatings may offer superior properties to diamond but to date it has proved difficult to make the material and films with approximately the correct composition are mostly amorphous and have properties very similar to DLC. In this paper are reviewed the tribological properties of DLC, diamond and more novel carbonaceous coatings. The tribological performance of the coatings will be discussed in light of their adhesion, residual stress and hardness. The mechanisms of friction and wear of the coatings will also be introduced and the implications for the development of improved carbonaceous coatings will be highlighted.