DEVELOPMENT, TESTING AND CHARACTERIZATION OF MOS2 THIN-FILM BEARINGS

The vacuum friction performance and temperature insensitivity of MoS2 makes it the lubricant of choice for many spacecraft mechanism applications. However, most of these applications historically utilized bonded MoS2 lubricants where control of thickness and film quality were not optimum. This paper reviews the development and problems encountered in applying recently developed sputtered MoS, films to precision spacecraft gimbal bearings which require low torque signatures and long life. Monolithic metal cosputtered and metal interlayered films were evaluated. The vacuum life of MoS, film lubricated bearings under gimbaling improved substantially with self-lubricating polytetrafluoroethylene composite retainers. Some bearings exceeded 45 x 10(6) cycles. Multilayer MoS, films on even long-lived bearings were found to have fractured early in bearing life from the combined effects of poor film toughness and substrate surface roughness. Debris from these films produced irregular torque signatures. Increasing the metal interlayer thickness in multilayer films provided greater him ductility and Fracture toughness. Bearing torque levels were also reduced. Application of a more fracture-resistant multilayer film to large spacecraft-quality bearings did not completely eliminate the film fracture mode. The scale-up of the sputter deposition system for larger bearings produced some questionable effects on film quality. Large thin-section bearings appeared more torque sensitive to wear debris than the smaller screening-test bearings.