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

In present work, the ternary Ni-Ti-CeO 2 composite coatings were electrodeposited on Al matrix composite (CNT/7075) in traditional Watts' solution containing various concentrations of CeO 2 nanoparticles and constant concentration of Ti microparticles . The effects of CeO 2 nanoparticles on microstructure and corrosion resistance of the obtained composite coatings were comprehensively investigated. The incorporation of moderate CeO 2 nanoparticles (less than 10   g   L −   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-CeO 2 composite coatings in 3.5   wt% 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 CeO 2 nanoparticles facilitated the formation of a compact passive film on the surface of the composite coatings during corrosion and promoted the formation of TiO 2 on the surface of Ti microparticles. The formation of TiO 2 not only protected the Ti metal particles but also helped to improve the corrosion resistance of the composite coatings, because the TiO 2 coated Ti microparticles decreased the attack probability of nickel deposits by corrosive medium. Typically, the Ni-Ti-CeO 2 composite coating electrodeposited in Watts' solution containing 10   g   L −   1 CeO 2 nanoparticles possessed the best corrosion resistance and excessive CeO 2 nanoparticles deteriorated the corrosion resistance.