A Sulfate Solution for Deposition of Ni-Cr-P Amorphous Alloys

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A stable Ni-Cr-P alloy plating solution was developed, based on the sulfate salts of the electroactive ingredients. This solution was successfully used at room temperature to produce bright, shiny and adherent deposits of Ni-Cr-P alloys. Electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to analyze the resulting deposits. The composition of the alloy was found to be controlled by current density, fluid dynamics and camphor presence. Unpublished data also indicate that it is controlled by the sodium hypophosphite concentration. The sodium hypophosphite acted as a reducing agent and the camphor served as an apparent selective membrane and a plating additive. Current efficiency was also found to be controlled by the same parameters. A potentiodynamic sweep method was used to test the corrosion resistance of the resulting deposits. The alloys produced in this solution displayed excellent corrosion resistance. The corrosion failure mode for these alloys was found to be cracking of the deposits followed by dissolution of the substrates from beneath. No dissolution of the deposits was apparent in the micrographs taken from the samples used in the corrosion tests. A small inclusion of indium in the alloy was attempted to modify the properties. It was found that the cracking was reduced but not eliminated by adding indium.

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