Diamond-Like Coatings for Friction Units of Space Applications

When developing materials for moving joints and friction units operating in outer space, the wear resistance of friction pairs with friction coefficients from 0.05 to 0.1 is of particular importance. The values of the friction coefficients determine the heating of the interfaces and the power of the drives. Wear resistance regulates the service life of friction units. The choice of diamond-like coatings as one of the elements of the friction pair determines the high wear resistance of the interface when working with solid lubricant coatings due to their high chemical inertness and the absence of substance transfer from the solid lubricating coating to the diamond-like coating. This paper presents the results of testing diamond-like coatings during friction on EONIT-3 solid lubricant coating and tests in air and vacuum up to 10^–6 mm Hg according to the shaft-bushing scheme in the temperature range from –50 to +50°C. A diamond-like single-crystalline coating 20 μm thick was applied to a shaft made of ShKh-15 hardened steel; EONIT-3 coating with a thickness of 15 μm is applied to a steel bushing. Tests were carried out under a normal load of 100 N; shaft rotation speed—200 rpm; sliding speed—0.12 m/s; and test duration—1 h. The friction coefficients and wear of the solid lubricant coating were measured. No wear of the diamond-like coatings was detected. The wear of the solid lubricant coating ranged from 1.065 × 10^–8 mm³/m to 3.195 × 10^–8 mm³/m at temperatures from –50 to +50°C in air and in vacuum of 10^–6 mm Hg.