Optimisation of microstructure and corrosion resistance of Ni-Ti composite coatings by the addition of CeO2 nanoparticles

Abstract

In present work, the ternary Ni-Ti-CeO2 composite coatings were electrodeposited on Al matrix composite (CNT/7075) in traditional Watts' solution containing various concentrations of CeO2 nanoparticles and constant concentration of Ti microparticles. The effects of CeO2 nanoparticles on microstructure and corrosion resistance of the obtained composite coatings were comprehensively investigated. The incorporation of moderate CeO2 nanoparticles (less than 10gL−1 in Watts' solution) gave rise to grain refinement, random-orientation growth of nickel deposit and smooth surface of the composite coating. Corrosion tests of the Ni-Ti-CeO2 composite coatings in 3.5wt% sodium chloride (NaCl) at 25°C illustrated the optimised microstructure favoured the enhancement of corrosion resistance. Further analyses of the corrosion behavior demonstrated that the embedded CeO2 nanoparticles facilitated the formation of a compact passive film on the surface of the composite coatings during corrosion and promoted the formation of TiO2 on the surface of Ti microparticles. The formation of TiO2 not only protected the Ti metal particles but also helped to improve the corrosion resistance of the composite coatings, because the TiO2 coated Ti microparticles decreased the attack probability of nickel deposits by corrosive medium. Typically, the Ni-Ti-CeO2 composite coating electrodeposited in Watts' solution containing 10gL−1 CeO2 nanoparticles possessed the best corrosion resistance and excessive CeO2 nanoparticles deteriorated the corrosion resistance.