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DEPOSITION OF REFRACTORY COATINGS WITH THE USE OF PLASMA
FOREIGN TECHNOLOGY DIV WRIGHT-PATTERSONAFB OH
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The effects of metal surface preparation and of plasma deposition conditions on the properties of deposited refractory coatings were examined. The coating of low and medium carbon steel with aluminum oxide 30-70 micron or aluminum oxide containing oxygen-resistant enamel or base enamel was carried out using a plasma apparatus and argon, nitrogen, helium, or their mixtures as plasma-forming gases. Optimum distance between plasma generator and surface of the material to be coated was 150-200 mm. Comparison of different gas mixtures showed the mixture of nitrogen plus 10 percent helium most effective. The metal surfaces were prepared by various methods--sandblasting with subsequent sodium nitrite passivation, sulfuric acid etching at 70C with washing and neutralizing, chemical nickel or cobalt plating, or conventional coating with base enamel. Plasma deposition of the aluminum oxide onto the nickel - or cobalt-plated metal resulted in poor adherence to the metal. Deposition onto the enamel-primed material gave coatings with good impact resistance that withstood thermal cycling better than did coatings deposited directly on the metal.
APPROVED FOR PUBLIC RELEASE