A STUDY OF THE CORROSION-RESISTANCE OF BRUSH-PLATED NI-FE-W-P FILMS

Electrochemical metallization by means of brush plating has been developed for coating of Ni-Fe-W-P compound films. The hardness of this compound film is about 800-910 HV, which is similar to that of plated chromium film. The corrosion resistance of this compound film in various corrosive environments was studied. Results showed that the corrosion resistance of this compound film was 1.7 times and 1.4 times that of plated chromium film in the corrosive environments of NaCl (ISO3768) and H2SO4 respectively. This indicates that Ni-Fe-W-P brush plating is one of the alternatives to substitute chromium plating. X-ray diffraction, transmission electron microscopy and scanning tunneling microscopy were applied to study the microstructure and the fine surface morphology of this compound him. It was found that the film is composed of an Ni-base amorphous and dispersive precipitated intermetallic compound of Ni3Fe. The surface characteristics of this compound film, analyzed by X-ray photoelectron spectroscopy and Auger electron spectroscopy, revealed that a preferential diffusion of W to the surface would be induced in the corrosive environments. The excellent corrosion resistance of brush-plated Ni-Fe-W-P film attributed to its microstructure and surface characteristics will be discussed.