Roles of growth mechanisms of Ni deposits on corrosion behaviors of NixAlyTi composite coatings

Abstract

Abstract To evaluate the influences of the conductive and nonconductive particles on the microstructures and properties of the Ni based composite coatings, various weight ratios of Al and Ti particles (Al/Ti ratios) were co-electrodeposited into Ni deposits to synthesize Ni xAl yTi composite coatings (x, y in weight percent). The microstructure and corrosion behaviors of the Ni xAl yTi coatings were investigated comprehensively. Results showed that an amorphous alumina layer was formed on the surface of the Al particle and led to the nonconductive behavior of the Al particle. The nonconductive Al particle and conductive Ti particle contributed to the different growth mechanisms of Ni deposits (surrounding growth mechanism and direct growth mechanism), consequently causing the decrease of crystallite size and [200] crystallographic orientation of the Ni deposits with decreasing Al/Ti ratio. In corrosion experiments, the XPS analysis showed that Al2O3, TiO2 and Ni(OH)2 together appeared in the coatings, causing a changing trend of decrease, increase and decrease of corrosion resistance of the Ni xAl yTi coatings with decreasing Al/Ti ratio. The best corrosion resistance of the coating was obtained at Al/Ti ratio of 1/2. The different growth mechanisms could account for the corrosion behavior evolutions of the Ni xAl yTi coatings with various Al/Ti ratios.