ABSTRACT
Composite electrodeposition technology is one of the methods used to fabricate metal matrix composite coating materials. The basic process is conducted in the composite electrodepositing solution in which a large amount of insoluble micropowders
are suspended by stirring the solution and the micropowders are embedded into the coating during the direct current (DC) and pulse current (PC) electrodeposition process of metal matrix. The excellent performance of electrodeposited composite coatings, especially in mechanical and chemical processes [1, 2], account for the widespread use of the process. It is well known that nickel electro composite coatings can be easily obtained from a nickel bath and number of studies on electro composites by using a nickel bath have been reported from a technological point of view [3-12]. Pulse electrodeposition has proven to be one of the most effective methods in fabrication of metal coatings. As compared with traditional DC electrodeposition, pulse electrodeposition offers more process controllable parameters, which can be adjusted independently and can withstand much higher instantaneous current densities. Therefore, metal coatings fabricated by pulse electrodeposition possess more unique compositions and microstructures when compared to DC electrodeposition. Electrodeposition of composite coatings, based on hard particles dispersed in a metallic matrix, is gaining importance for potential engineering applications [13]. The second phase can be hard oxide (Al2O3, TiO2, SiO2), carbides particles (SiC, WC), diamond, solid lubricate (PTFE, graphite, MoS2), and even liquid containing microcapsules [14]. A well known application of codeposition to improve the corrosion resistance of coatings is the production of microporous chromium layers by codepositon of nonconducting particles on the underlying Ni layer [15]. Corrosion of Ni occurs over an increased surface resulting in a smaller depth of attack. In an oxygenenriched atmosphere, Ni-Al2O3 composite coatings possess better oxidation resistance than unreinforced nickel [16]. Improvement in the wear resistance has also been reported for electrodeposited Ni-SiC composites [17]. With these considerations, many investigators have successfully codeposited hard particles (like Al2O3, TiO2, SiC, WC, Cr3C2, TiC, diamond, etc.) in a range of metal matrices such as Ni, Cr, Co, Re, and so on [18]. Tungsten carbide (WC) or WC-Co is a technologically important material and has been widely used as cutting tools, rock drills, punches, and wear resistant coating materials [19]. For example, WC-Co coatings have been extensively used in industry to prevent wear, erosion, and corrosion of many metallic components. Although extremely important, engineering WC thin films on various important materials remains an open area in nanotechnology.
