Nickel and nickel-phosphorous matrix composite electrocoatings Nicolas SPYRELLIS, Evangelia A. PAVLATOU, Styliani SPANOU, Alexandros ZOIKIS-KARATHANASIS General Chemistry Laboratory, School of Chemical Engineering, National Technical University of Athens, 9 Heroon Polytechniou Str, Zografos Campus, Athens 15780, Greece Received 18 June 2008; accepted 10 March 2009 Abstract: Nickel and nickel-phosphorous matrix composite coatings reinforced by TiO 2 , SiC and WC particles were produced under direct and pulse current conditions from an additive-free Watts’ type bath. The influence of the variable electrolysis parameters (type of current, frequency of current pulses and current density) and the reinforcing particles properties (type, size and concentration in the bath) on the surface morphology and the structure of the deposits was examined. It is demonstrated that the embedding of ceramic particles modifies in various ways the nickel electrocrystallisation process. On the other hand, Ni-P amorphous matrix is not affected by the occlusion of the particles. Overall, the imposition of pulse current conditions leads to composite coatings with increased embedded percentage and more homogenous distribution of particles in the matrix than coatings produced under direct current regime. Key words: nickel electrodeposition; pulse plating; composite coatings; nickel-phosphorus alloy; structure 1 Introduction Electrodeposited composite coatings consist of a metal or alloy matrix containing hard particles like Al 2 O 3 , TiO 2 , SiC, WC or SiO 2 as second phases. For several decades considerable research work has been focused on the impact of the electrodeposition parameters, such as the electrolysis conditions (composition and agitation of the electrolytic bath, the presence of additives, temperature, pH), the current conditions (values of current density and mode of current) and the reinforcement properties (type, size, shape, concentration, conductivity, surface charge) on the structure, morphology and properties of the composite coatings[1]. The major challenges for the codeposition of ceramic particles seem to be the occlusion of a sufficient number of non-agglomerated particles combined with a good dispersion of the particles in the metal matrix. In general, it has been observed that the amount of embedded ceramic particles increases with increasing concentration of suspended particles in the electrolyte[2]. Additionally, the reduction of particle size increases the agglomeration tendency of the particles, due to their enhanced surface energy, while decreases their codeposition content in the metal matrices and the mean grain size of the matrix crystallites[3]. Moreover, recent research has pointed out that the physico-chemical properties of the ceramic particles are crucial to the understanding of the codeposition mechanism of each type of particles[4]. A significant number of reports have shown that the microstructure and properties of pure Ni deposits may be effectively altered under the application of specific pulse current conditions. Pulse electrodeposition (PC) has been found to be an effective means of perturbing the adsorption-desorption phenomena occurring at the electrode/electrolyte interface and hence the electrocrystallization process[5−6]. Regarding Ni-P composite coatings, most of research concerns mainly electroless plating to obtain deposits with enhanced properties[7]. In the present work, the effects of electrolysis parameters on the structure and the morphology of Ni and Ni-P matrix composite coatings reinforced by TiO 2 , SiC and WC particles were examined. 2 Experimental Metal and alloy composite coatings were produced Corresponding author: Evangelia A. PAVLATOU; Tel: +30210-7723110; E-mail: pavlatou@chemeng.ntua.gr DOI: 10.1016/S1003-6326(08)60353-2