Metal treatment – Compositions – Heat treating
Patent
1975-09-19
1979-02-27
Kendall, Ralph S.
Metal treatment
Compositions
Heat treating
428653, 148 616, 427383D, 427192, 427405, C23F 710, C23C 902
Patent
active
041417607
ABSTRACT:
Aluminum diffusion can be effected from continuous coatings of leafing-type aluminum particles and such leafing coatings in very thin layers are more effective than coatings of non-leafing aluminum, with or without diffusion. Other protective metals in flake or leaf form can be substituted for or added to the leafing aluminum. Adhesion of the flakes to the substrate is greatly improved and can be effected at lower temperatures if the flakes are applied from a dispersion containing a volatilizable halogen-type carrier or an ammonium chromate. The leafing coatings can be sprayed on from aqueous dispersion containing wetting agents and if desired a polyethylenetrtrafluoroethylene and/or mixtures of phosphoric acid, chromic acid and magnesium, aluminum, calcium or zinc salts of these acids. A protective second coating of such mixtures can be applied as a cover layer over the layer containing the leafing aluminum, and this combination works best on a ferrous metal that has an aluminum diffusion coating, particularly a ferrous metal that contains less than 1% chromium and has such an aluminum diffusion coating. It also works very well on aluminum diffusion coatings from packs containing chromium, or chromium and silicon, in addition to the aluminum, and these alloys can be made by magnesothermic reduction of their mixed oxides or the like. The aluminum diffusion can also be made from a pack containing cobalt with or without a little chromium, and this forms a particularly desirable diffusion coating on nickel-base alloys. Aluminum diffusion coatings can be kept from undesired locations by covering those locations with an Ni.sub.3 Al-type masking layer containing thermoplastic resin over which is applied a powdered nickel masking layer containing thermoplastic resin. On firing this masking combination forms a strong shell that effectively masks without contaminating the surrounding coating pack.
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Alloy Surfaces Company, Inc.
Kendall Ralph S.
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