Wear and corrosion characteristics of alumina dispersed Ni–P nanocomposite coating developed by electroless technique

Advances in materials performance require the development of nanocomposite coatings. The paper aims to study the comparative wear and corrosion performance of Ni–P and Ni–P–Al2O3 nanocomposite coatings developed by electroless technique. The effect of heat treatment (400 °C, 1 h) on the coating performance is also studied. The second-phase Al2O3 nanoparticles of average size 15 nm were synthesized by chemical precipitation route. The synthesized Al2O3 nanoparticles (4 g/l) were added into the alkaline Ni–P bath to develop Ni–P–Al2O3 nanocomposite coatings on the mild steel substrate. The coating thickness was found to be about 20 µm. The phases and morphology of Al2O3 nanoparticles and coatings were examined by XRD and FESEM, respectively. Chemical composition of the coating was analysed by EDX. Wear and friction behaviour of the coatings were measured at different loads (1, 1.5 and 2 N) and velocities (0.1, 0.2 m/s) using ball-on-disc method. Tafel polarisation test was employed to evaluate corrosion behaviour of the coatings in acidic (pH 4.5) and alkaline (pH 8) environments. Ni–P–Al2O3 nanocomposite coatings showed higher hardness and wear and corrosion resistance compared with plane Ni–P coatings. An improvement in corrosion resistance was observed by Ni–P and Ni–P–Al2O3 coatings in both acidic and alkaline environments. Heat treatment significantly improves hardness and wear and corrosion resistance of the coatings.