Evaluation of tribological response of molybdenum disulphide-based coatings to varying environments

Molybdenum disulphide-based coatings are the standard solid lubricant coatings for mechanisms intended to operate in low earth orbit. These coatings are known to provide low friction in a high-vacuum environment. In my study, a variety of hard metallic and solid lubricant coatings were tested in a self-mated configuration at temperatures ranging from -80°C to 180°C to evaluate the friction response to varying temperature. The tests were performed using a pin-on-disk tribometer inside an environment chamber at fixed normal load and sliding velocity. Systems where the contact was dominated by plastic deformation and wear debris generation showed no evidence of thermal sensitivity and had friction coefficients ranging from 0.2 to 0.9. However systems where motion was accommodated by interfacial sliding experienced as high as an order of magnitude increase in friction coefficient (0.02 to 0.2) as the temperature of the system was decreased from 180°C to -80°C.; The low friction coefficients of many solid lubricant coatings have been attributed to interfacial sliding in the material. In these experiments, the goal was to prove the systems were interfacially sliding by analyzing the evolution of surface topography. The results indicated that for the MoS 2-based coatings it took an average of 30 cycles to remove a single atomic layer of MoS2 (6 angstroms). This showed that interfacial sliding was occurring in a majority of the contact.; The end goal of the study was to comment on the application specific performance of the coatings in a bushing-shaft configuration. In this system, the friction coefficient showed athermal behavior caused by severe wear in the contact area. Ultimately designers of space mechanisms will have to determine the severity of the tribological contact in order to estimate the fluctuations in friction coefficient that may be experienced by varying temperature.