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ÓASM International 1059-9495/$19.00

Electrodeposition and Characterization of Ni-Al2O3 Nanocomposite Coatings on Steel Khalida Akhtar, Zia Ullah Khan, Muhammad Gul, Naila Zubair, and Syed Sajjad Ali Shah (Submitted April 20, 2017; in revised form March 1, 2018) Monodispersed alumina particles were synthesized by the homogeneous precipitation under reflux boiling. The particles were employed as reinforcement additives in the electrodeposited Ni-Al2O3 composite coatings on steel. The deposited pure Ni and Ni-Al2O3 composite coatings were analyzed by SEM, XRD, and microhardness tester. The wear resistance and friction coefficient of the coated samples were determined by using a ball-on-disk tribometer. Furthermore, XRD analysis showed that coating temperature and the presence of particles in the deposited coatings had a noticeable effect on the preferred orientation of the crystalline faces of the nickel grains. Significant differences were noted in the texture coefficient of the pure Ni and Ni-Al2O3 composite coatings produced at different temperatures. These differences were attributed to the changes in the microstructure of the matrix caused by the embedded Al2O3 particles. Results revealed that wear resistance and the friction coefficient were turned out to be higher and smaller, respectively, for the composite coatings as compared to pure Ni coating at a given sliding distance. It was noted that the corrosion resistance of these specimens increased in the following order: bare substrate < pure Ni coating < Ni-Al2O3 nanocomposite coatings. Keywords

aluminum oxide, nanocomposite coating, preferred orientation, steel coating, texture coefficient

1. Introduction Metal oxide powders, comprised of particles of uniform morphology, have become of great interest in the field of material science due to their importance in the reproducibility of performance. Moreover, it has been observed by researchers that the properties of these powder materials strongly depend upon their particle size and shape (Ref 1). Among these oxides, aluminum oxide (Al2O3) is of vital importance due to its wide range of applications in various areas such as metallurgy, hydrogenation, automotive emission control, ceramic composite, catalysis, electronics, optoelectronics, refractories, and wear protection (Ref 2, 3). It has shown significant hardness and high resistance toward temperature, acids, and bases (Ref 4). The methods for synthesis of alumina can be classified as chemical and physical. These methods include precipitation, sol–gel, combustion process, microemulsion, hydrothermal, and vapor deposition. Conversely, physical methods included laser ablation, thermal decomposition in plasma, and the flame spray method (Ref 5-9). In each of these methods, various parameters such as temperature, aging time, pH, concentration of the reactants, and materials have a crucial role in obtaining particles of the desired size and shape (Ref 10). In the methods as mentioned above, the homogeneous precipitation process is a fast and simple chemical route and is mo