Improvement of the erosion-corrosion resistance of magnesium by electroless Ni-P/Ni(OH)2-ceramic nanoparticle composite coatings

In this study, Ni-P/Ni(OH)(2)-ceramic nanoparticle composite coatings were directly deposited onto commercially pure magnesium in order to improve its resistance to erosion-corrosion damage. The effect of three incorporated ceramic nanoparticles (TiO2, SiC and diamond) on the erosion-corrosion resistance of the composite coatings was also investigated. The composite coatings were obtained by an electroless process and were characterized using scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The erosion-corrosion behavior of fabricated composite coatings was elucidated using in situ techniques of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). It was found that the simultaneous formation of Ni-P and beta-Ni(OH)(2) phases in the coating and the improvement in the micro hardness of the coating were due to the incorporation of nanoparticles. According to the polarization curves and EIS spectra, the beta-Ni(OH)(2) compound behaves like a pre-passive film which is responsible for substantial improvement in the anticorrosion properties of the coating. Better erosion-corrosion resistance was obtained for the composite coatings than the neat Ni-P coating. This was a consequence of the beta-Ni(OH)(2) co-deposition. The formation of the beta-Ni(OH)(2) compound in the coating does not depend on the nature and concentration of the nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.