Tribological properties of nanocrystalline diamond films

In this paper, we present the friction and wear properties of nanocrystalline diamond (NCD) films grown in Ar-fullerene (C-60) and Ar-CH4 microwave plasmas. Specifically, we will address the fundamental tribological issues posed by these films during sliding against Si3N4 counterfaces in ambient air and inert gases. Grain sizes of the films grown by the new method are very small (10-30 nm) and are much smoother (20-40 nm, root mean square) than those of films grown by the conventional H-2-CH4 microwave-assisted chemical vapor deposition process. Transmission electron microscopy (TEM) revealed that the grain boundaries of these films are very sharp and free of nondiamond phases. The microcrystalline diamond films grown by most conventional methods consist of large grains and a rough surface finish, which can cause severe abrasion during sliding against other materials. The friction coefficients of films grown by the new method (i.e. in Ar-C-60 and Ar-CH4 plasmas) are comparable with those of natural diamond, and wear damage on counterface materials is minimal. Fundamental tribological studies indicate that these films may undergo phase transformation during long-duration, high-speed and/or high-load sliding tests and that the transformation products trapped at the sliding interfaces call intermittently dominate friction and wear performance. Using results from a combination of TEM, electron diffraction, Raman spectroscopy, and electron energy loss spectroscopy, we describe the structural chemistry of the debris particles trapped at the sliding interfaces and elucidate their possible effects on friction and wear of NCD films in dry N-2. Finally, we suggest a few potential applications in which NCD films can improve performance and service lives. (C) 1999 Published by Elsevier Science S.A. All rights reserved.