Progress has been achieved in continuing research directed toward increasing the wear resistance and enhancing the self- lubrication properties of chemical-vapor-deposited (CVD) diamond films. Such films are potentially useful as friction- and wear-reducing coats on sliding mechanical components (e.g., seals, gears, and journal bearings). A major issue that has been addressed in this research is the variation of the friction and wear properties of CVD diamond with environment: In air, CVD diamond exhibits a low coefficient of friction and high resistance to wear; in vacuum, it exhibits a high coefficient of friction and low resistance to wear. In three experimental studies, it was found that friction and wear of CVD diamond films in both vacuum and air can be reduced by use of suitable surface treatments.

Wear Rates and Coefficients of Friction of as-deposited and modified CVD diamond films were measured in ultrahigh vacuum. The results plotted here indicate that suitably modified CVD diamond films could be useful as wear-resistant, self-lubricating surface layers on sliding mechanical components.
In the first study, a fine-grained CVD diamond film in the as-deposited condition was tested in comparison with two similar CVD diamond films that were coated with thin (< 1 μm thick) films of amorphous, non-diamond carbon [more specifically, hydrogenated carbon, also known as diamondlike carbon (DLC)]. The DLC coating layers were deposited by direct impacts of ion beams at kinetic energies of 1.5 keV and 0.7 keV, respectively. In tribological tests (diamond-tipped pins sliding on disks coated with the various CVD diamond films) at room temperature in ultrahigh vacuum, the DLC films were found to reduce the coefficient of friction and the wear rate significantly (see figure).

The second study was similar to the first study. Fine-grained CVD diamond films were modified by implantation of, variously, carbon ions at a kinetic energy of 60 keV or nitrogen ions at a kinetic energy of 35 keV. In both cases, the implantation resulted in the formation of amorphous, non-diamond carbon surface layers

The subject matter of the first and second studies overlaps with that of a prior study reported in “Ion-Beam-Deposited DLC Coatings on Fine-Grain CVD Diamond” (LEW-16564), NASA Tech Briefs, Vol. 22, No. 7 (July 1998), page 62. The third study addressed the issue of a friction- and wear-resistant couple of materials; that is, a pair of materials that exhibit low friction and low wear when slid against each other. This study included ultrahigh-vacuum tests in which CVD-diamond-tipped pins were slid against a disk coated with cubic boron nitride films. The wear rate of the boron nitride films was found to be acceptably low (of the order of 10–6 mm3/N⋅m), the wear rate of the diamond films was found to be much lower, and the coefficient of friction was found to be very low (of the order of 0.02).

This work was done by Kazuhisa Miyoshi of Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center,
Commercial Technology Office,
Attn: Steve Fedor,
Mail Stop 4–8,
21000 Brookpark Road,
Cleveland, Ohio 44135.

Refer to LEW-17150.

NASA Tech Briefs Magazine

This article first appeared in the August, 2002 issue of NASA Tech Briefs Magazine.

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