Evaluation of Frictional Properties of Tungsten Disulfide Bonded Films at High Temperature in Vacuum Environments

Abstract

  Spacecraft which is used in harsh environments, may also encounter different problems on the ground. To prevent any problems, many of the sliding portions of a spacecraft are subjected to lubrication processing. WS₂ solid lubricant coatings were fabricated by the heat treatment of a mixture of WS₂ powder and an additive. To simulate deployment friction, experiments were conducted using a pin-on-disk of a tribometer at elevated temperatures in vacuum. The WS₂ coatings were analyzed by Scanning electron microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Imaging plate x-ray diffraction (IPXRD) after friction tests. It was found that WS₂ coatings showed a high performance with a friction coefficient of less than 0.1 at room temperature. This low friction coefficient was attributed to the reorientation of the (002) plane parallel to the disk surface. According to XRD analysis, the WS₂ (002) plane has not been appered in a virgin disk. At high temperature, WS₂ showed a low friction coefficient and it would had a sufficient lifetime up to 500℃. Although the initial friction coefficients were relatively high at elevated temperatures, friction coefficient at high temperature became the same as those at room temperatures. It can be rationalized that these WS₂ coatings showed a high friction coefficient because additional force is necessary to reorientation of the stable WS₂ aggregates.