Preparation Of High Temperature Lubricating Coating Phosphate And Study Of Performance

Nowadays, scientists all over the world have been paying more attention to phosphate binder, as it has some advantages such as higher temperature adhesive strength and less environmental pollution and lower curing temperature. Phosphate binder with excellent performance of heat resistance was prepared by adding curing agents to phosphoryl binder. Then, solid lubricants (MoS₂ and graphite) were added to the system , the synergy effects of these two lubricants were studied, and the optimal formulation was researched. At last, the coatings, with fine properties of high temperature resistance and lubrication and wear resistance, were successfully prepared. The microstructure and friction properties of the coatings were investigated.The main contents of this paper were as follows:1. By using Al(OH)₃ and H₃PO₄ as raw materials, the best synthetic conditions of phosphate binder were researched and the influence of P/Al molar ratio and reaction temperature on the formation of Al(H₂PO₄)₃ was dicussed. The crystal structure of phosphate binder and thermal properties of coatings were analyzed by XRD and TG-DSC. The changes in peak position of major functional groups of phosphate binder obtained at different temperatures, such as P-O and P=O and P-OH, were construed by IR. The results showed that under the conditions of P/Al molar ratio 3:1.4 and reaction temperature 120～200℃, the phosphate binder had best bond property.2. The curing properties of phosphate binder was dicussed by using MgO, ZnO and CuO as curing agents. The effects of curing process and thermal stability of the binder and curing agents on the mechanical properties and crystal structure of the binder were discussed in details by DSC, TGA, XRD and universal material tensile machine. The experimental results indicated: the addition of 5% MgO could make that phosphate binder was cured at 167℃and the shear strength of the binder was up to 1.2MPa at 500℃; the addition of 5% ZnO could make that phosphate binder was cured at 222℃and the shear strength of the bunder was up to 3.1MPa at 500℃; the addition of 5% CuO could make that phosphate binder was cured at 237℃and the shear strength of the binder was up to 1.6MPa at 500℃.3. By using phosphate as the base material, adding aluminum powder and MoS₂ and graphite, the coatings with high temperature resistance and lubrication were obtained. The study manifested that the aluminum powder could be propitious to the evaporation of the adsorptive water on the surface of the binder and the dehydration of crystal water of phosphate molecule, which improved the temperature tolerance and cohesive affinity of the coatings. When adding MoS₂ and graphite respectively, the microhardness and wear time of the coatings presented the trend of first increase then decrease with the increase of the content of lubricants, while friction coefficient reversed to the above. When the mass fraction of lubricants were 20% and 30%, respectively, the property of wear resistance of the coatings was best. The main wear mechanism of the coatings is adhesive wear and fatigue abrasion. The addition of lubricants could reduce the adhesive wear. By orthogonal experiments, there was synergetic effect between MoS₂ and graphite, which were added to the system at the same time and improved the properties of the coatings. Under the conditions that the mass fraction of MoS₂,graphite,aluminium powder and ZnO were 15%,5%,10% and 5% respectively, the obtained coatings had optimum tribological properties that were superior to those of coatings obtained by using lubricants alone.