| The nickel tungsten alloy coating has advantages of high hardness, good wear resistance, good heat resistance, good corrosion resistance, as well as has good protective and decorative functions. But traditional electroplating nickel tungsten alloy technology has many deficiencies, such as rough metal plating surface, heterogeneous material distribution and some clear pitting shown on the surface, which severely limits the application and development of nickel tungsten alloy. In order to improve the performance and appearance quality of coating, the influence of experimental process conditions, heat treatment process and additives on the properties of coating were studied and the results were shown as follows:the effects of current density, temperature, [W]/[W]+[Ni], pH, time on Ni-W alloy coating deposition rate and hardness was studied by univariate analysis, The process parameters of electrodeposited Ni-W alloy were optimized by five factors and four levels orthogonal test. Orthogonal test were measured through the magnetic thickness gauge, poor quality, Vickers hardness tester, file test, stick filter paper method, gold equal to the experimental method of Ni-W alloy thickness, deposition rate, micro hardness, bonding strength, porosity, and surface morphology respectively. And the data of orthogonal test was analyzed by range analysis method, and the influence of the factors on the performance of the coating was obtained, and the optimum technological parameters of each performance were also obtained. Comprehensive optimum parameters of the performance were analyzed, giving optimal performance of the coating when the current density was 15A/dm2, pH of 8, [W]/ [W]+[Ni] of 0.7, a temperature of 75? and the time of 50min.Space Ni-W alloy was electroplated by using the optimal parameters,The various properties of the coating were shuwn as follows:space the deposition rate was 4.581 g/(h dm2),space thickness was 59.60?m,space hardness was 647.50Hv, bonding strength was one level,space porosity was 0.78/cm2,The content of W in the coating reached 49.36% by the analysis of EDS.The coating structure was mico-crystal by the analysis of XRD.the effect of heat treatment on Ni-W alloy hardness, corrosion resistance nature, grain size, surface morphology was studied through Vickers hardness tester, electrochemical experiments, XRD, microscope and other experimental methods. Through the heat preservation treatment of Ni-W alloy coating at 200??700? for 1 h, the micro hardness of the coating was found to increase at the beginning and then decrease, and the corrosion rate firstly increased and then decreased. Ni-W alloys exhibited the maximum hardness of 1196Hv under the conditions of heat preservation treatment at 500? for 1 h, and the lowest corrosion rate was 0.12375mm/y. By maintaining constant temperature of 500?, the influence of holding time on the performance of the coating was studied.The results showed that the coating hardness and corrosion resistance were reduced with increasing holding time. It can be concluded that the optimum heat treatment process of the coating was 500? with the thermal insulation for 1 h.Based on the optimal formula obtained in the orthogonal experiment, the effect of three additives on the deposition rate, thickness, hardness, coating W content, corrosion resistance, and surface morpHology was studieded by adding 1,4-butynediol, rare earth additives, and lauryl sodi?m sulfate to the plating solution. It was found that the micro hardness of the coatings slightly decreased, but the corrosion resistance and appearance of the coatings were significantly improved with the addition of three kinds of additives. |
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