Effect of alumina nanoparticles as nanocomposites on morphology and corrosion resistance of electroless Ni-P coatings

Electroless Ni-P-Al2O3 nanocomposite coating was obtained by adding alumina nanoparticles to the nickel electroless plating bath. Particles of similar to 74 nm in size were selected in order to study the influence of the particle incorporation to the coating properties. The composite coatings were heat treated at 200, 400 and 600 degrees C for 1 h (60 min) and structural changes were evaluated by X-ray diffraction (XRD) analysis. Surface morphology of composite deposits has been investigated by scanning electron microscopy (SEM). Electrochemical impedance spectroscopy and potentiodynamic polarisation method have been used to evaluate the coating performance before and after heat treatment. The Ni-P electroless coating contains 9.18 wt-%P while the alumina composite coating contains 8.30 wt-%P. The composite coatings, which contains alumina nanoparticles, exhibit better properties of hardness and corrosion resistance.