Enhanced performance of Pennzane greases for space applications by both additive formulations and smooth hard coatings

摘要

Tribological requirements of the moving mechanical assemblies (MMAs) of spacecraft are usually satisfied by a variety of lubricants and materials. When the lubricant elastohydrodynamic film is broken, metal-to-metal contact occurs in the MMAs. This may lead to lubricant overheating, and breakdown, and then to increased wear and failure. Wear related failure can also occur due to evaporation and/or creep of the lubricant over the lifetime of space assembly. As requirements for spacecraft performance and lifetime increase, improved lubrication systems for MMAs are needed. A considerable amount of progress has been made in developing improved lubricants with advanced additives; however their performance has not been evaluated and ranked. In the present work, four-ball and reciprocating tribometer tests were conducted to evaluate and rank the performance of various Pennzane based greases. Employing the reciprocating tribometer technique, Pennzane based greases were also evaluated with hard coatings such as titanium nitride (TiN) and titanium carbonitride (TiCN) in a metal-on-coating configuration. Viability of a filtered cathodic arc technique for obtaining very smooth, hard coatings is demonstrated. The importance of coating deposition temperature for certain bearing steel materials is also discussed. It is demonstrated that wear is substantially reduced with an optimized Pennzane grease formulation on a smooth, hard TiCN surface coating.