SUPERLOW FRICTION CARBON FILMS FROM HYDROGEN RICH HYDROCARBON PLASMAS*

Ali Erdemir

Energy Technology Division

Argonne National Laboratory

Argonne, IL 60439

USA

ABSTRACT

Carbon-based coatings combine many attractive properties that make them good candidates for a wide range of critical engineering applications. Systematic studies in our laboratory on carbon films over the last decade have resulted in the development of a new class of amorphous diamondlike carbon (DLC) films providing friction and wear coefficients of 0.001 and 10^‑11 mm³/N.m, respectively (when tested in dry nitrogen or inert-gas environments). These films were synthesized in a plasma-enhanced chemical vapor deposition system that uses high proportions of gaseous hydrogen in addition to hydrocarbon source gases, such as methane and acetylene. Comprehensive tribological studies of the films revealed the existence of a close correlation between the chemistry of the hydrocarbon source gases and the friction and wear coefficients of the DLC films. Those films grown in source gases with higher hydrogen-to-carbon ratios had much lower friction and wear coefficients than did films derived from source gases with lower hydrogen-to-carbon ratios. Fundamental and surface analytical studies have led us to conclude that the presence of protonic, atomic, and molecular hydrogen either within the films or near the sliding surfaces plays a critical role in the friction and wear properties of these films. Based on the findings of experimental and surface analytical studies, a mechanistic model is proposed to explain the superlow friction and wear properties of the films

*Work supported by the U.S. Department of Energy, Office of Science, under Contract W-31-109-Eng-38.