Superhard, functionally gradient, nanolayered and nanocomposite diamond-like carbon coatings for wear protection

Recent progress in the development of advanced carbon-based tribological coatings is reviewed. Pulsed laser deposition (PLD) was used to produce superhard (60-70 GPa) self-lubricating diamond-like carbon (DLC) with low friction and low wear rate. Attention was given to the improvement of coating toughness. A hybrid of magnetron sputtering and PLD was used to deposit coatings with architectures designed to withstand 1-10 GPa contact stress. This included: (1) composite coatings combining hydrogen-free and hydrogenated DLC; (2) functionally gradient metal-ceramic-DLC and nanolayered coatings with crystalline metal and carbide interlayers (about 10 nm thick) between DLC layers (about 60 nm thick); 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 steel substrates, which could maintain friction coefficients of about 0.1 for several million cycles of unlubricated sliding at contact pressures above 1 GPa. Their scratch resistance exeeded that of conventional ceramic (TiN, TiC) coatings. (C) 1998 Elsevier Science S.A.