Friction properties of smooth nanocrystalline diamond coatings

Smooth nanocrystalline diamond coatings (NDC) have been deposited on spherical cemented carbide substrates. These coatings have been tested in dry and lubricated (water, oil) sliding against cemented carbide (CC), ball-bearing steel (BBS), stainless steel (SS), titanium (Ti) and aluminium (Al). In addition, the same types of coatings were subjected to tests against Ti and Al after polishing NDC. Comparative experiments were performed with self-mated BBS. Dry sliding conditions of as-deposited NDCs against CC, BBS, SS and lightly polished NDCs against Ti and Al gave a friction coefficient of 0.06-0.1. Lubricating the contact generally resulted in a small reduction in friction. The self-mated BBS showed a friction of 0.8, 0.4 and 0.14 when tested in dry-, water- and oil-lubricated conditions, respectively. A very low wear was detected for the NDC, and the counter surfaces displayed practically no wear at all. In dry sliding against SS, the wear resistance of the diamond was roughly 100 times higher than that of self-mated BBS tested with oil lubrication. All three test conditions of as-deposited NDCs against Ti and Al gave a high friction coefficient (0.3-0.6) and seizure except for oil-lubricated Al where the friction was 0.11. (C) 1998 Elsevier Science S.A. All rights reserved.