| Synthetic diamond is widely used in industry, with high hardness, high thermal conductivity, low coefficient of friction, and many other excellent properties. There are some questions in the use of diamond tools. However, the poor infiltration between diamond and matrix caused by high interface energy makes the diamond tools with a short service life. In addition, the thermal stability of synthetic diamond is not high, so it is easily suffered oxidized weightlessness or graphitization under the condition of high temperature. At present, the main solution is to make metallization on synthetic diamond surface with electroless plating. Meanwhile, it improves the oxidation resistance thermal stability, abrasion resistance and other characteristics of diamond. With the rapid progress of science and technology, the traditional binary metallic coating such as Ni-P and Ni-B coating cannot satisfy the needs of industrial development.In this paper, on the basis of Ni-P coating which is deposited by electroless plating, the process is carried on by optimization and improvement, during which sodium molybdate is added into the reaction system, so molybdenum(Mo) of high strength, high hardness at high temperature, low expansion coefficient, good corrosion resistance properties becomes one of components and form a Ni-Mo-P alloy coating, owing the characteristics of high hardness, less porosity, high corrosion resistance and so on.At first the synthetic diamond was pretreated, this process includes degreasing, roughening, sensitization, activation, dispergation, and the bath was prepared by choosing main salt and additives. Coating with Ni-Mo-P of synthetic diamond was obtained by electroless plating. Coating with metallic luster is dense and uniform. The whole powder is coated. Secondly, The best way to coating was obtained through orthogonal experiment, integrating with deposition rate and the effect of plating. It is composed of 0.8g/L sodium molybdate, 25g/L nickel sulfate, 29g/L sodium hypophosphte, 0.1g/L sodium dodecyl sulfate, 1.5g/L sodium fluoride, pH 4.5, temperature 86℃. The test methods of SEM and EDS were used to analyze the surface topography, plating effect and the composition of plating coating. The result of particle size of the coated synthetic diamond powder conducted by laser particle analyzer showed that the particle sizes distribute narrowly and the powder shows good performance. Finally, the sintering experiment was conducted and the result reflected that surface plating coating can improve the heat resistance of synthetic diamond.The theoretical research, process optimization and testing analysis shows that the theory and technology of Ni-Mo-P alloy plating is feasible, which enjoys good coating performance, reduces the application cost, and improves the service life of the synthetic diamond. The achievements of the principle and the process on Ni-Mo-P alloy plating enrich the development of new diversified alloy coating and provide theoretical basis and technical support for industrial application of Ni-Mo-P alloy plating which is on the surface of synthetic diamond. |
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