CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 39 (2013) 7759–7766 Deposition and characterization of nanocrystalline and amorphous Ni–W coatings with embedded alumina nanoparticles Saeed Yari, Changiz Dehghanian n School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran Received 14 December 2012; received in revised form 2 March 2013; accepted 2 March 2013 Available online 27 March 2013 Abstract Nanocrystalline and amorphous Ni–W coatings containing Al 2 O 3 nanoparticles were electrodeposited from three different ammoniacal citrate baths by direct current (DC) method. The effects of nanoparticles on compositional, structural and morphological features of Ni–W coatings were investigated. The effects of bath chemical composition and current density on codeposition behavior of nanoparticles were also studied. Guglielmi model for particle deposition was applied to identify the kinetics of particle deposition. The presence of nanoparticles may affect on coating grain size, tungsten content and the rate of metal deposition. In addition, nanoparticles can result in more compact coatings with fewer defects. The extent of these effects depends on bath chemical composition and may be influenced by the synergistic effect of Ni on deposition of W. It was also found that the kinetics of particle deposition and the effect of current density on codeposition behavior of nanoparticles are highly dependent on bath chemical composition. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Nanocomposite; Electrodeposition; Guglielmi model; Ni–W coating 1. Introduction Ni–W alloy coating has potential corrosion, wear and high temperature resistant properties. Therefore, in recent years, it has been proposed for a variety of applications such as environmen- tally safe substitute for hard chromium coating or a high temperature coating for bearings, plungers and dies [1–7]. This alloy coating is obtained from citrate baths with or without ammonium ions that contain tungstate and nickel ions. Deposition of this coating occurs through a series of compli- cated reactions that according to Brenner [8] has been called “induced codeposition”. This is due to the fact that tungsten cannot be electrodeposited alone and, in fact, iron group metals such as Ni, Fe and Co can induce the deposition of W and the result will be an alloy. Several mechanisms have been suggested to explain this process. Younes et al. [1,2] proposed that the mixed metal complex of [(Ni)(HWO 4 )(Cit)] 2− can form in the bath from which the solid solution of tungsten in nickel can be formed, and deposition of nickel can also proceed from its complexes with ammonium or citrate. Podlaha and Landolt [9,10] have studied the induced codepo- sition of Ni–Mo alloy, which is claimed to have a similar behavior as Ni–W alloy [8]. They believe that the precursor for the deposition of the Ni–Mo alloy is an adsorbed intermediate of the form [NiCit(MoO 2 )] – ads which can be reduced to allow Mo deposition and the reduction of Ni ions follows an independent path. Many other mechanisms have been also suggested that are available in the literature [10,11]. The common facts in all the proposed mechanisms is the synergis- tic effect of iron-group metals on deposition of W and Mo and that an increase in ammonium and nickel ion concentrations and a decrease in tungstate or molybdate and citrate ion concentrations will boost the rate of alloy deposition. It is well known that incorporation of micro- or nano-sized carbides and oxides into coatings can enhance their hardness, corrosion, and wear properties [12–20]. This method has been also expanded into Ni–W electrodeposits and in recent years several works have been reported on Ni–W composite coatings with embedded nano- or micro-sized particles. Yao et al. [21] deposited SiC nanoparticles into the Ni–W matrix and an improvement in microhardness, corrosion and wear behavior www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.03.033 n Corresponding author. Tel./fax: +98 21 82084103. E-mail address: cdehghan@ut.ac.ir (C. Dehghanian).