Preparation And Properties Of Ni-Al₂O₃-MoS₂ Composite Coatings By Electrophoretic-pulse Electrodeposition

Composite coating, with excellent physical and chemical properties, is widely researched and applied. At present, composite coating is prepared by adding particles into the plating solution, which can achieve metal and particles codeposition on the matrix. However, the particle concentration of composite coating by this technology is generally low. The performance of composite coating is restricted by the particle concentration. Electrophoretic-pulse electrodeposition composite technology combines electrophoretic deposition and pulse electrodeposition,and can significantly improve the particle concentration of the composite coating. The excellent physical and chemical properties of the particle is sufficient developed, which improve the wear-resisting, anti-corrosion and high temperature resistance of composite coating.Electrophoretic electrodeposition technology was introduced in this paper and used to prepare the N i base composite coating with high particle concentration.The influence of particle concentration on the mechanical properties and morphology of composite coating was studied.Scanning electron microscope（SEM）, X-ray diffraction（XRD） and micro-hardness tester were used to study the organizational structure and microscopic morphology of the coatings. Anti- wear performance of composite coatings was evaluated using an abrasion HT-1000 tester. The corrosion resistant properties of composite coating were tested by the electrochemical workstation. The main research concentrations and results are as follows:（1） The influences of electrophoretic deposition parameters on the electrophoresis film were studied. The dispersion medium, dispersant, Mg²⁺concentration on the effect of Al₂O₃ particles to form a stable suspension of electrophoretic liquid were analyzed; The influences of sedimentary voltage, Al₂O₃ particles concentration, deposition time and temperature on electrophoretic sediments were discussed. The electrophoretic deposition process was optimized. Using an ethanol bath containing 0.5 g/L MgCl₂·6H₂O and a suspension of 10g/L of Al₂O₃ particles. Triethanolamine as dispersant was used. Electrophoretic deposition was performed under electric field strength of 90 V for 200 s at 25℃.（2） The microscopic morphology and mechanical properties of composite coating by electrophoresis-pulse electrodeposition and pulse electrodeposition was studied. The results showed that the volume concentration of Al₂O₃ particles in composite coating prepared by electrophoretic electrodeposition was 58.85%, and Al₂O₃ particles evenly distributed without reunion. Compared to pulse electrodeposition, the N i-Al₂O₃ composite coating prepared by electrophoretic-pulse electrodeposition has the higher micro- hardness, better wear resistance and corrosion resistance.（3） The influence of MoS₂ concentration in the electrophoretic liquid on microscopic morphology, micro-hardness and friction and wear performance of N i-Al₂O₃-MoS₂ composite coating were analyzed. The results showed that with the increase of MoS₂ concentration in electrophoresis liquid, the micro- hardness of composite coating was decreased, and the friction coefficient and wear loss of composite coating were decreased then increased. During the wear process, MoS₂ particles could form a layer of lubrication film between the friction pair, which can make composite coating has anti- friction property. When the concentration of MoS₂ particles in electrophoretic liquid was 1.0g/L, the friction coefficient and wear loss of composite coating were minimal and MoS₂ particles exhibited the excellent lubrication performance.