Cu+Si3N4 and Ni+Si3N4 composite coatings deposited by brush plating
Jarosław Grześ Politechnika Warszawska, Instytut Technologii Materiałowych, ul. Narbutta 85, 02-524 Warszawa
Annals 3 No. 6, 2003 pages 64-68
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abstract This paper presents the results of the investigation of composite surface layers deposited by the brush plating method. The single and multiplayer metal-ceramic coatings (Cu+Si3N4, Ni+Si3N4) have been produced in frame of the research. The Copper Alkaline #1 and Nickel Extreme High Speed solution have been utilized during coating process. Different operating voltages and several fractions of Si3N4 powder inside the solution have been tested. The average size of Si3N4 grains was 0.5 μm. The brush plating parameters are shown in Table 3. Copper and nickel coatings have been also deposited for the comparison purposes, using the operating parameters presented in Table 2. The surface of the substrate has been cleaned (electrocleaning), activated and covered with a special Ni sublayer both for metal and metal-ceramic coatings. The parameters of surface preparation are summarized in Table 1. The investigation work covered microscopic analysis of coating surfaces and cross-sections, microhardness measurements, X-ray analysis of crystallites size and linear distribution of elements. The coatings deposited by the brush plating method using electrolytes with Si3N4 powder addition have shown the possibility of producing composite metal-ceramic coatings both from the standard and „high speed” type electrolytes. The effect of Si3N4 powder in the electrolyte on the character of coating surface is shown in Figures 1 and 2. These coatings shown higher microhardness comparing to Ni and Cu coatings deposited with the same operating voltage. By the proper selection of the operating voltage of each layer the FGM structure have been obtained in the coatings (Figs. 3, 4). A special agent lowering the surface tension added into the electrolyte resulted in the formation of increased Si3N4 concentration in some areas in the coatings (Fig. 5). No microcracks have been observed in Ni+Si3N4 coatings that are usually reported in nickel coatings. The size of crystallites in these coatings ranged from 12,9 to 13,2 nm which was lower comparing to these found in Cu+Si3N4 coatings. Key words: brush plating, coatings, composites, property gradient