| We add PTFE(polytetrafluoroethylene) particles to the Ni coating to prepare Ni-PTFE composite coating. Ni-PTFE composite coating can improve the tribology capability of pure Ni plating. In previous studies, the preparations of Ni-PTFE composite coating usually adopt composite co-deposition or chemical composite plating technology. The particle content prepared by composite co-deposition is low, so it is difficult to fully develop self-lubricating of the particles. The composite coating prepared by chemical composite plating technology needs high solution temperature. It is prone to break down and it is unstable. Furthermore, the composite has stress crack problems.In order to improve the PTFE particles in the composite coating and the property of it, this paper adopts electrophoretic deposition and electro-deposition for the preparation of the Ni-PTFE composite coating. The process contains two steps. First, deposit a layer of PTFE on the substrate surface. Then, embed substrate metal Ni into the pore of the PTFE layer by electro-deposition. The main results and conclusions of this paper are as follows:(1) First, Research on the existing theory of electrophoretic deposition. On the basis of it, try on the PTFE particles(5 microns) of electrophoretic deposition. The technology improved can prepare compact and uniform layer. At the same time, discuss influences of the electrophoretic deposition parameters: electrophoretic voltage, electrophoretic time, concentration of PTFE, concentration of Mg Cl2·6H2O. The research found electrophoresis time, electrophoresis voltage, concentration of PTFE are directly proportional to the deposition quantity, but the electrophoretic time can reduce the electrophoretic deposition efficiency and affect the stability of the electrophoretic liquid. Concentration of Mg Cl2·6H2O has important influences on electrophoretic sediment distribution density.(2) Research on the preparation technology by orthogonal experimental design. Analyze and summarize the rule of influence. The research found current density has the greatest effect on the deposition rate and it also has important effect on the thickness of the coating and deposition efficiency. Electrophoretic time has the greatest influence on surface roughness, micro-hardness and PTFE content of the composite coating. The increases of PTFE concentration can advance the PTFE content in composite coating, but PTFE reunion phenomenon is more serious than before. PTFE composite volume is the most important factors influencing the composite coating on micro-hardness and PTFE dispersion also has certain impact on it.(3) Research on the PTFE content in composite coating and its influences on the tribological properties. The research found that the two-step method can remarkably advance the PTFE content in composite coating. This technology can prepare the content of PTFE up to 63.4 vol.%. Due to the increase of the PTFE particles in composite coating, it can fully perform its self-lubricating and greatly improve its tribological properties. When PTFE volume fraction in composite coating is 44%, it has the best anti-friction effect and the friction coefficient is 0.067. When PTFE volume fraction in composite coating is 63.4%, the wear resistance of PTFE composite coating is best.(4) Explore the preparation technology of Ni-PTFE-Al2O3 composite coating. Research found that electrophoretic co-deposition can prepare relatively homogeneous electrophoresis sediments compared with continuous electrophoretic deposition. At the same time, compare wear resistance of Ni-PTFE, Ni-Al2O3, Ni-PTFE-Al2O3. Research found Ni-Al2O3 composite coating has the best wear resistance. The wear resistance of Ni-PTFE-Al2O3 has close relationships on PTFE and Al2O3 content.When the Al2O3 content is low, its wear resistance is poorer than Ni-PTFE. When the Al2O3 content is high, its wear resistance is better than Ni-PTFE composite coating. |
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