Electrodeposited Co – Ni – Al O composite coatings 2 3

Composite coatings of Co–Ni–Al O were studied by electrolytic codeposition of Co–Ni alloys and Al O from a sulfamate 2 3 2 3 electrolyte containing Al O particles. The influence of plating parameters on the content of the co-deposited Al O particles in 2 3 2 3 Co–Ni alloys was investigated. The maximum value of co-deposited Al O can be achieved at a particle content of 80 g l in y1 2 3 bath, a current density of 3 A dm , a pH of 4.5, and a stirring rate of 100 rpm. In the process of codeposition, cathodic y2 polarization increases with the increase of Al O concentration in bath and cobalt ions in electrolyte caused the reduction of 2 3 polarization while nickel ions do not change the polarization behavior. Surface morphology and microstructure of Co–Ni–Al O 2 3 coatings were determined by means of scanning electron microscopy, atomic force microscopy and X-ray diffraction. It was found that the phase structure of solid solution cannot be varied by codeposition of Al O particles in Co–Ni alloys, and it only 2 3 influences the growth and orientation of crystal planes. It was shown that the presence of Al O particles in deposit greatly 2 3 improves the hardness and the wear resistance of composite coatings. However, the codeposition of Al O increases the tensile 2 3 internal stress of Co–Ni–Al O deposit. The coefficient of thermal expansion and the thermal conductivity of Co–Ni–Al O 2 3 2 3 composite coatings are varied with the increase of Co contents and the temperature. 2003 Elsevier Science B.V. All rights reserved.