| Brush plating is a kind of specific method and new development of electroplating technique. It requires some simple operating equipment and high current density, offers portability, suitability, high speed and quality deposites and coatings. Therefore, the kind of technique has been widespreadly applicated in Surface Engineering. Composite coatings is a new study orientation in the filed of composite materials, is also a study hotspot in Surface Engineering technique. Therefore, the application of composite coatings obtained by brush plating technique will be used widely.In the paper, Ni-P alloy brush plating coatings were firstly obtained. The electrolyte composition and operating process parameters were analyzed and decided. Some main influence factors on P content and quality of Ni-P coatings were discussed. Based on these, SiC / Ni-P composite brush plating coatings were co-deposited by adding some SiC particle and surfactants into the Ni-P electrobath and rightly adjusting operating process parameters. The SiC particle size and its content and distribution state were some important factors for the quality of SiC / Ni-P composite coatings. The microstructure and surface morphology of SiC / Ni-P coatings were observed with metalloscope and SEM, its element composition and structure were investigated by EDS and XRD. These test results showed that SiC / Ni-P composite coatings with 17.8vol% and uniformity of SiC particle and amorphous structure of Ni-P alloy matrix could be prepared by appropriately modulating the solution composition and operating process parameters. Compared with the Ni-P coatings, the surface of SiC / Ni-P composite coatings was much leveler, much smoother and more homogeneous. The quantity and length of microscopic crack were evidently less than those of Ni-P alloy coatings. These results showed that SiC particle could make crystalline be refiner and reduce significantly the internal stress of SiC / Ni-P composite brush plating coatings. The 30 period neutral salt spray corrosion test results showed that the corrosion resistance of SiC / Ni-P composite coatings was superior to that of Ni-P and Ni brushplating coatings. There were several reasons as following for this. First, the trend ofmicroscopic crack was reduced when SiC particle was added into the Ni-P coatings, so the compactness of SiC / Ni-P composite brush plating coatings was improved; Second, during the corrosion course the microscopic crack area as corrosion anodic was reduced, correspondly the cathode/anodic area ratio would be augmented, thus the whole corrosion course was controlled by anodic process. The anodic polarization which was caused from large ratio of cathode/anodic area reduced markedly the corrosion velocity. Finally, Some corrosion products which formed and collected in the microscopic crack zone blocked the corrosion routeways by which corrosion medium could enter into the interior of SiC / Ni-P composite coatings. All factors above mentioned improved the corrosion resistance of SiC / Ni-P composite brush plating coatings.When SiC / Ni-P and Ni-P brush plating coatings were oxidized from 400℃ to 800℃ for 2h, the experiment results showed that the oxidation resistance of composite coatings was superior to that of Ni-P coatings. When the two kinds of coatings were oxidized at 800℃ for 100h, the experiment results showed that their oxidation kinetics curves followed closely a parabolic oxidation law, indicating that the oxidation reaction was controlled by diffusion. During the same oxidation time as far as the weight change of oxidation product concerned, the results showed the SiC / Ni-P composite brush plating coatings had better oxidation resistance than Ni-P alloy coatings. The oxidation product might be fixed and adhesived by the SiC particle during the oxidation process. Therefore the oxidation product did not easily fall off and the oxidation resistance of SiC / Ni-P coatings were improved. In addition, the quantity of microscopic crack and other flaw on the surface of SiC / Ni-P c...
|
PDF Full Text Request