Metal and metal-ceramic composite coatings produced by the brush plating method
Jarosław Grześ Politechnika Warszawska, Instytut Technologii Materiałowych, ul. Narbutta 85, 02-542 Warszawa
Annals 2 No. 5, 2002 pages 359-363
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abstract The aim of the paper is focused on brush plating possibilities of producing metal and metal-ceramic composites. The short characteristic of brush plating method is presented in first part of the paper. Schematic of brush plating is shown in Figure 1. The brush plating technique belongs to the bath plating methods of surface coatings, but has several advantageous which the most important are shorter deposition time (10÷20), lower processing costs (materials and energy), easier operation of the deposition equipment, mobility, no limit for workpiece dimensions, possibility to deposit metal and non-metal substrates. This method can be applied for the repair and regeneration of machine parts and surface modification and for the build-up the dimension and the geometric form of the overproof machine parts. The main parameters of this process are operating voltage and relative moving speed of the tampon. The number of available solutions reaches almost 250, which allows producing single and multilayer coatings with, desired properties. The basic properties of selected brush plating solutions are presented in Table 1. The maximum thickness of the layers obtained during plating is one of the most important problem in brush plating. Table 2 shows the barrier of maximum thickness for the most common nickel and copper solutions. The plating solutions presented in Table 1 can be used for producing metal composite coatings, including gradient properties. Figure 2 shows the idea of nano-multilayer Ni-Cu system. These kinds of coatings can be deposit from several different solutions. Another solution is to apply single solution to produce alloy coatings. Ni-W-Co coatings deposited from single nickel-tungsten-cobalt alloy solution like nano-multilayer system is shown in Figure 3. One of the possible applications of brush plating method is to deposit intermediate layers in joining. The idea of complex coatings used as intermediate layer in metal joints is shown in Figure 4 (copper-nickel joint). The real structure of such layer is presented in Figure 5. The brush plating method can also be used to coat surfaces with metal deposits and dispersed metals or ceramic phases i.e. SiC (Fig. 6). Figure 7 shows Cu-Si3N4 multilayer coating with microhardness and chemical composition gradient, deposited from the Copper Alkaline #1 solution. Visible Cu-Si3N4 layers are separated by the thin Ni layers. Different operating voltages were used for coating all layers. The composite coatings obtained from solution containing metal or ceramic nanocrystalline additive can be characterized by a new material properties. The results obtained from the experiment allow us to draw several conclusions with respect to the composite coatings obtained from the solutions containing ceramic powder: in order to lower the tampon degradation the tampon press onto the substrate shall not be too high; if the solution is fed through the tampon then the powder grain size shall not be too large, so as to keep the uniform flow rate of the solution; the operating voltage shall be kept within the factory suggested range; the solutions with ceramic or metal powder additions shall be prepared just before the brush plating begins.