Preparation And Tribological Properties Of Inorganic Phosphate Composite Coatings

Lubrication protective coating is a coating to reduce friction and wear between two contact surfaces.The harshest environment for spacecraft materials is atomic oxygen radiation when the spacecraft is run in low-Earth orbit,so the solid lubricating coating applied to the surface of spacecraft materials need to have a good characteristic of anti-atomic oxygen erosion.Phosphate bonded solid lubrication coating have great application potential due to its excellent properties such as good bondability,oxidation resistance,high temperature resistance,simple preparation process and low price.Phosphate resin has good space environment adaptability,but its rigidity as an inorganic material is relatively large,which results in poor toughness and easy wear when used as a base resin for lubricant coating.In order to further improve its friction properties,this paper uses chromium phosphate aluminum?ACP?as a binder and which was modified by Teflon?PTFE?emulsion to obtain modified resin,and on this basis,molybdenum disulfide?MoS₂?as a solid lubricant was added to the modified resin,the phosphate composite coating was prepared.The tribology properties of modified resins and composite coating were investigated systematically and the mechanism of the effects of atomic oxygen irradiation on their structure and tribology properties were cleared preliminarily.The main research conclusions are drawn as follows:?1?ACP binders were prepared using phosphoric acid,chromium trioxide and aluminum hydroxide and which was modified by Teflon?PTFE?emulsion to obtain modified resin.The effect of modifier content on the tribology properties of modified resins were studied.The results showed the tribology performance of modified resins was improved and then worse with the increases of the content of PTFE.The tribological performance of the modified resin is the best when the quality ratio of ACP and PTFE is 1:0.35,the PTFE in the modified resin has a plastic deformation under the influence of the additional load and friction which improve the frictional performance of the resin.However,the resin cannot form a continuous plastic deformation in the friction process when the PTFE content is too low;when the PTFE content is too high,the adhesive content in the modified resin is relatively reduced which caused the wear resistance of the coating becomes worse.?2?This paper carried out atomic oxygen irradiation test on modified resin.The effect of atomic oxygen irradiation on the tribology properties of modified resins were studied.The results showed Atomic oxygen irradiation did not have a significant effect on the coefficient of friction of modified resins,but the quality loss and wear rate of the coating increased with the increase of the duration of irradiation,and when the irradiation time increased to 40h,the quality loss and wear rate of the modified resin did not obvious change.?3?The phosphate composite coating was prepared by adding the molybdenum disulfide solid lubricant to the modified resin,and the effects of molybdenum disulfide content on the mechanical and tribological properties of the composite coating were investigated.The results show that the mechanical and tribological properties of the composite coating are the best when the mass ratio of the modified resin and molybdenum disulfide is 1:0.3.The friction coefficient of the coating under atmospheric environment is 0.065,and the wear mechanism is abrasive wear.It is that the synergy between PTFE and MoS₂ makes the coating has a better tribological properties under atmospheric environments.The friction coefficient of the coating under vacuum is 0.02 and the main wear mechanism is fatigue wear.The reason why the coating has better tribological properties under vacuum is that molybdenum disulfide is enriched on the surface of the wear scar which forms a continuous lubricating film and improves the tribological properties of the coating.?4?Atomic oxygen irradiation test was carried out on the phosphate composite coating with the optimal disulfide content,and the erosion mechanism and the effect of friction properties of atomic oxygen irradiation on the coating were analyzed.The results show that the coefficient of friction and wear of the composite coating in the atmospheric environment after 10h of atomic oxygen irradiation has increased,and the change of the friction coefficient of the composite coating in the vacuum environment is not obvious,the wear rate is increased.The PTFE of the coating surface is completely eroded by the atomic oxygen after 20h of atomic oxygen irradiation.The content of MoS₂ is basically unchanged,the PTFE inside the coating is protected by ACP binder,the quality of the coating is no longer reduced,the quality of the composite coating and the tribology performance is no longer reduced.