Nickel-chromium corrosion coating and process for producing it
AssigneePraxair S.T. Technology, Inc.
InventorsAdil A. Ashary, Robert C. Tucker, Jr.
Life of this patent
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Abstract
An impervious corrosion resistance nickel-chromium coating on a metallic substrate, such as an iron-containing alloy substrate that protects the substrate from a corrosive media and the process for producing the coating on the substrate.
Claims19
A process for protecting a metallic alloy from corrosion by applying an impervious coating to such alloy consisting essentially of the steps:
- (a) preparing a metallic alloy substrate,
- (b) preparing a powder comprising between 21 to 23 weight percent chromium;
- between 8 to 10 weight percent molybdenum;
- between about 2.5 to 3.5 weight percent iron;
- between about 3 to 4 weight percent niobium and remainder substantially nickel;
- (c) thermal spraying the powder composition of step (b) at a selected gas temperature and gas pressure onto the metallic alloy substrate to produce a coating in excess of 0.0035 inch thick and having the characteristics such that when subjected to the ASTM G-61 corrosion test, a current density of less than 50 microamperes per square centimeter results when a potential of 400 millivolts is applied;
- and
- (d) depositing a coating on top of the coating of step (c), said coating selected from the group consisting of chromium oxide, aluminum chromium oxide, titanium oxide, mixed oxides of aluminum chromium and titanium, tungsten carbide cerments, tungsten carbide-cobalt cermets, tungsten carbide-nickel cermets, tungsten carbide-chromium-cobalt cermets, tungsten carbide-chromium-nickel cermets, chromium carbide-nickel-chromium cermets, chromium-carbide-IN-625 cermets, and tungsten-titanium carbide-nickel cermets.
A coated iron-containing alloy substrate wherein the coated layer is a barrier coating consisting essentially of a composition of between 21 to 23 weight percent chromium;
- between about 8 to 10 weight percent molybdenum;
- between about 2.5 to 3.5 weight percent iron;
- between about 3 to 4 weight percent niobium and remainder substantially nickel;
- and said coating being impervious such that when subjected to the ASTM G-61 corrosion test, a current density of less than 50 microamperes per square centimeter results when a potential of 400 millivolts is applied and having a top coat over the barrier coating which is selected from the group consisting of chromium oxide, aluminum oxide, titanium oxide, mixed oxides of aluminum chromium and titanium, tungsten carbide cermets, tungsten carbide-cobalt cermets, tungsten carbide-nickel cermets, tungsten carbide-chromium-cobalt cermets, tungsten carbide-chromium-nickel cermets, chromium carbide-nickel-chromium cermets, chromium-carbide- IN-625 cermets, and tungsten-titanium carbide-nickel cermets.
A coated metallic alloy substrate consisting essentially of an impervious barrier coated layer of a composition of 21 to 23 weight percent chromium;
- between about 8 to 10 weight percent molybdenum;
- between about 2.5 to 3.5 weight percent iron;
- between about 3 to 4 weight percent niobium, and the remainder substantially nickel and having a top coated layer of a wear resistant coating.
Dependencies are inferred from the claim text.