Electroless nickel-phosphorus composite coatings are formed by addition of the material to be codeposited in powder form and by maintaining it in suspension during the deposition process so that it is incorporated into the deposit. Materials so codeposited are either hard substances such as silicon carbide and aluminum oxide, or they are dry lubricants such as graphite, polytetrafluoroethylene (PTFE) or molybdenum disulfide. Molybdenum disulfide affects tribological behavior by reduction of friction7 and has advanced rapidly in importance in the past two decades from its initial success as a vacuum lubricant to its present general utilization in a broad range of applications. As with graphite, molybdenum distide has a layer-lattice structure. Strong bonding exists within each sulfur/molybdenum/ sulfur layer, whereas weak sulfur-sulfur bonds allow easy sliding between layers. Solid lubricants. The use of ultrasonics does not offer an advantage for acid hypophosphite baths. The ultrasonic agitation produces a more porous deposit, and also bath stability decreases, so that spontaneous decomposition occurs at times. These findings, together with the relatively
large capital costs of ultrasonic equipment, have restricted the use of this technique.
In plating processes very high energy agitation has been found to discourage the formation of metal whiskers and to increase deposit hardness by promoting dislocations.” The present work investigates the effects of different types and rates of agitation on hardness, chemical composition, and morphology of the deposits, and the rate of deposition of the composite coating. The agitation of an electroless nickel bath containing molybdenum disulfide particles with air purging is better than other techniques used in this study. Among the agitation techniques studied, air agitation permits greater uniformity and thickness and less agglomeration than the bath using magnetic stirring. The topography of the surface depends on the agitation type and rate: when using air agitation, lower flow rates produced a more uniform surface and higher flow rates produced nonuniform surfaces, whereas when using magnetic stirring, higher rates produced more uniform surfaces, and lower flow rates, nonuniform surfaces.
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