| With the excellent properties of wear-friction properties, corrosion resistance and oxidation resistance, Cu-Sn alloy has been widely used in sliding bearing. But under the conditions of oil-poor or non-lubricated,the property of wear resistance and antifriction is unable to satisfy the requirements. As an excellent surface treatment technology,nano-composite electrodeposition technique can achieve a variety of functional nano-composites. At the same time, the pulse current was applied to the nano-composite electrodeposition process, it can reduce the concentration polarization around the cathode surface, and promote the codeposition of nano-particles with metal ions. Currently, most studies mainly concentrate on the unified nano-composite coatings preparation.This research combines the synergy of pulsed electrodeposition technology and multivariate nano-composite technology to prepare composite coatings. PTFE with excellent lubricating property was selected as self-lubricating phase. Based on the nano-reinforcement theory, traditional grains were replaced by TiO2 Sol to strengthen the electrodeposition coating. In the paper, four kinds of different coatings were respectively prepared, including Cu-Sn, Cu-Sn-PTFE, Cu-Sn-TiO2 and Cu-Sn-PTFE-TiO2.Firstly,the codeposition mechanisms of pyrophosphate-stannate Cn-Sn alloy and nanoparticles dispersion method were studied. TiO2 Sol was prepared by sol-gel method.PTFE powder and TiO2 Sol were dispersed by surfactant TX-10 and mechanical force, and the dispersity was tested.Secondly, the influence on deposition rate, surface topography, composition, hardness and corrosion resistance of Cu-Sn-PTFE-TiO2 composite coating was observed when current density, duty cycle, frequency, addition of PTFE particles and TiO2 Sol was changed. Test results show that Cu-Sn-PTFE-TiO2 composite coating has fine grain and leveled surface. The main component of the coatings is copper-tin alloy, and the proportion of F element is between 1 ?3%,and Ti element proportion is between 0.1 ?1%. Under the optimum process conditions,Cu-Sn-PTFE-TiO2 composite coating shows excellent wear-friction properties and corrosion resistance. The proper technical parameters are respectively as follows,hardness value 465.1 HV, corrosion potential 0.256 V, the corrosion current 1.443A·cm-2, and the average friction coefficient 0.1.Then the differences in surface appearance, hardness, corrosion resistance and tribological properties of Cu-Sn, Cu-Sn-PTFE, Cu-Sn-TiO2 and Cu-Sn-PTFE-TiO2 were analyzed, and their mechanisms were discussed. The results show that the addition of nano-PTFE particles improves the corrosion resistance and self-lubricating property of the coating, but the hardness value is decreased, only 375.2 HV. Relative to Cu-Sn-PTFE composite coatings, the hardness and wear-resisting performance of Cu-Sn-TiO2 is obviously improved through the fine-grain strengthening and dispersion strengthening effect of nano-TiO2 particles, but the friction coefficient is increased. The observation on corrosion morphology and polishing scratch shows that each coating mainly appeared pitting corrosion in the corrosion process, and that the different levels of adhesive wear and abrasive wear happened in the friction process.In conclusion, adding PTFE particles and TiO2 particles to Cu-Sn alloy simultaneously,the hardness of the composite was enhanced due to the synergy effect. At the same time, the tribological properties, corrosion resistance and comprehensive performance were greatly improved. |
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