Microstructure of Co-Ni-Al₂O₃ composite coatings by electroforming

The metal matrix composite coatings of Co-Ni-Al₂O₃ were studied by electrolytic codeposition of Co-Ni alloys and Al₂O₃ on a Cu substrate from a sulfamate electrolyte containing Al₂O₃ particles. It was illustrated from the examined results of SEM, AFM and XRD that surface morphology and microstructure of Co-Ni-Al₂O₃ coatings appear to be mainly influenced by the variation of Co content. The high Co content coatings with hcp lattice structure have a more uniform and fine structure than low Co content coatings with fcc lattice structure. The codeposition of Al₂O₃ particles in Co-Ni alloys can not change the phase structure of solid solution, only affects the growth and the orientation of crystal planes and mostly increase the d value of lattice.