Study Of MoS₂-Ti Composite Coatings Deposited By Unbalanced Magnetron Sputtering

Though magnetron sputtering MoS₂ films have already been used in aerospace precision moving mechanical parts as one of the main surface lubricating modification methods, there are still some deficiencies existed in current deposition technology. For example , film has poor humidity-resistant ability; in vacuum the wear resistant life of the film is not long enough; and for mechanical parts with complicated configurations the film can't been deposited uniformly throughout the surface; additionally the current method has trouble on mass production. At present, spacecraft development on function expansion, life lengthening and manufacture periods shortening appeals to improve MoS₂ deposition technology to content their urgent engineering application needs. In this paper, we use unbalanced magnetron sputtering deposition system to obtain uniform MoS₂ film and by doping Ti in MoS₂ film to improve the film's properties. The study is emphasized on the effects and mechanisms of the deposition parameters on the structure and properties of the film. Ultimately we got optimized technology parameters for producing high quality film which can meet the need of aerospace engineering application.The main results and innovations of this study are :1. For the first time, the systematic and detailed relationships and alteration mechanisms between structure, properties of MoS₂ film and deposition parameters such as target sputtering power, unbalanced magnetron coil current, substrate bias, gas flow during deposition, substrate table rotation, deposition temperature and time are acquired, and the optimized deposition parameters are procured.2. For the first time, we find that in ambient and in vacuum environments, the Ti content allowed to be doped in MoS₂ film is different if the film's lubricating ability is maintained. In ambient environment, this value is between 17 wt.% and 20 wt.%; while in vacuum it is 12～15 wt.%. The result can be interpreted as in ambient environment , the oxidation of portions of MoS₂ to MoO₃ and Fe to Fe₂O₃ will promote the transfer of MoS₂ to opposite part and realize strong substrate-film-opposite part bonding.3. We find a simply method to predict film's wear resistant life in vacuum by measuring film's nano-indention and analyzing scratch testing pictures. If the film's nano- indention hardness is above 5 GPa or if there are jagged scores in the scratch testing picture, the film will has poor wear resistant life or even has no lubricating ability. It is proposed that since the size of the crystallite in the MoS₂ film is so small at higher ion flux bombardment, the intercrystallite or innercrystallite slips in MoS₂ film are prohibited.4. The effects of test conditions such as load, speed and substrate on film's tribological properties in vacuum are studied. We find that when test speed is changed between 250～1000 r/min, the film's wear resistant life keeps almost the same, then space moving mechanisms used such lubricating method can have effective accelerated life test method.5. For the first time we indicate that such film deposition technology can be used on aerospace precision ball bearings. The test data show that the change of bearing's friction torque in 30°C, 85% humidity environment which is beyond one year andthe bearing's running properties in 10^-3 Pa grade vacuum which is beyond 1.8×10⁸ round. These experimental data can provide strong support for the application of the technology in space.