Diamond-like carbon-based functionally gradient coatings for space tribology

Abstract

Abstract Solid lubricant coatings for vacuum and space mechanisms are widely used when conventional liquid lubrication is prohibited, either when the operating conditions become too severe (extreme temperatures, ultrahigh vacuum) or when a clean environment is required. While the well-known MoS2 lamellar solid lubricant is the most extensively used material today, diamond-like carbon (DLC) coatings are studied as potential candidates for a wear resistant material with low friction in vacuum conditions. Diamond-like carbon-based functionally gradient Ti/a-CH(Ti) films have been deposited by the hybrid technique of magnetron sputtering and d.c. plasma-enhanced chemical vapor deposition, in various conditions. Analytical characterization coupled with tribological tests in ultrahigh vacuum and ambient humid air have been performed to identify relationships between the deposition conditions, the composition and the properties (stress, friction) of the films. Depending on the properties of the DLC which are in turn dependent on the deposition procedure, the investigated films present a wide range of tribological behavior, including friction coefficients in UHV below 0.02. Typical DLC structures and compositions allowing the achievement of extremely low friction in vacuum and good behavior under air are identified and discussed.