On the development and the oxidation of novel Ni-Cr and Ni-Al nanocoatings by composite electrodeposition

Novel Ni-based nanostructured coatings against high temperature oxidation were fabricated by composite eleoctrodeposition. The electrodeposited nanocoatings (ENCs) were prepared, separately from a nickel sulphate electrolyte bath with addition of Cr nanoparticles in an average size of 39 nm, or with Al nanoparticles in an average size of 75 nm. The Cr or Al nanoparticles were dispersed among the nanocrystalline Ni grains of ENCs. The ENC Ni-10.9Cr at 900degreesC and the ENC Ni-28.0Al at 1050degreesC exhibited a superior oxidation resistance as a result of the formation of continuous chromia or alumiuna scale, respectively. It is proposed that the dispersion of the Cr or Al nanoparticles among the nanocrystalline Ni grains greatly increased the surface density of the nucleation sites for Cr2O3 or Al2O3; simultaneously, the nanostructured coatings favored rapid healing of the narrowed Cr2O3 or Al2O3 nuclei during a very short transient period, which consequently led to the suppression of NiO growth.