SUPERHARD, FUNCTIONALLY GRADIENT, NANOLAYERED AND NANOCOMPOSITE DIAMOND-LIKE CARBON COATINGS FOR WEAR PROTECTION

Recent progress in the development of advanced carbon-based tribologic al coatings is reviewed. Pulsed laser deposition (PLD) was used to pro duce superhard (60-70 GPa) self-lubricating diamond-like carbon (DLC) with low friction and low wear rate. Attention was given to the improv ement of coating toughness. A hybrid of magnetron sputtering and PLD w as used to deposit coatings with architectures designed to withstand 1 -10 GPa contact stress. This included: (1) composite coatings combinin g hydrogen-free and hydrogenated DLC; (2) functionally gradient metal- ceramic-DLC and nanolayered coatings with crystalline metal and carbid e interlayers (about 10 nm thick) between DLC layers (about 60 nm thic k); and (3) nanocrystalline-amorphous composite coatings with 10-50 nm diameter carbide particles encapsulated in a DLC matrix. The research led to the fabrication of thin (2-3 mu m) DLC-based coatings for stee l substrates, which could maintain friction coefficients of about 0.1 for several million cycles of unlubricated sliding at contact pressure s above 1 GPa. Their scratch resistance exeeded that of conventional c eramic (TiN, TiC) coatings. (C) 1998 Elsevier Science S.A.