Process for producing elevated temperature corrosion resistant metal articles

Claim 2

In a process for providing a coating on a metallic substrate, the coating renderng the substrate resistent to corrosion at elevated temperatures, said process comprising the steps of providing a ductile metallic overlay on the substrate surface, said overlay being of a composition normally resistant to corrosion at elevated temperatures, and applying an outer layer on said overlay, said outer layer being formed of a material more resistant to corrosion at elevated temperatures, the outer layer comprising an encapsulating means thereby preventing penetration of gas, the improvement comprising the steps of thereafter subjecting said coated substrate to a hot isostatic pressing operation by locating the coated substrate in a pressure-tight chamber, and subjecting the coated substrate to a temperature and pressure applied through a gaseous atmosphere sufficient to eliminate porosity, said temperature and pressure application also causing diffusion of substrate ingredients from one direction into the overlay and diffusion of outer layer ingredients from the other direction into the overlay thereby modifying the composition of the coating composed of said overlay and said outer layer.

Claim 3

A process in accordance with claim 1 wherein said outer layer comprises an aluminide coating.

Claim 4

A process in accordance with claim 1 wherein said overlay comprises an alloy having as a base constituent at least one of the elements selected from the group consisting of iron, cobalt and nickel. .[.4. A process in accordance with claim 3 wherein said overlay is applied to said article surface by one of the methods selected from the group consisting of plasma spraying, pressure bonding, electron beam or vapor deposition, sputtering, ion plating and slurry sintering..]. .[.5. A process in accordance with claim 3 wherein said aluminide coating is applied by one of the methods selected from the group consisting of pack cementation, dipping, spraying,

Claim 5

metallizing, and electrophoresis..]. 6. An article produced in accordance

Claim 6

metallizing, and electrophoresis..]. 6. An article produced in accordance

Claim 7

with the process of claim 1. 7. A process in accordance with claim 1 wherein the base metal of the substrate alloy is selected from the group consisting of Ni, Co and Fe. .[.8. A process in accordance with claim 3 wherein said overlay is applied to said article surface by one of the methods selected from the group consisting of plasma spraying and slurry sintering..]. .Iadd. 9. A process in accordance with claim 2 wherein said aluminide coating is applied by pack cementation, dipping, spraying, metallizing, or electrophoresis. .Iaddend. .Iadd. 10. A process in accordance with claim 3 wherein said overlay is applied to said article surface by plasma spraying, pressure bonding, electron beam or vapor deposition, sputtering, ion plating or slurry sintering. .Iaddend..Iadd. 11. A process in accordance with claim 3 wherein said overlay is applied to said article surface by plasma spraying or slurry sintering. .Iaddend. .Iadd. 12. A method for coating a superalloy substrate with an oxidation-corrosion protective MCrAlY type coating where M is selected from the group consisting of nickel, cobalt and iron, comprising the steps of: (a) plasma spraying the MCrAlY coating onto the superalloy substrate, the coating being characterized as having pores, voids and similar defects, some of which extend to the free surface of the coating, said defects reducing the protectiveness of the coating: (b) sealing the free surface of the MCrAlY coating by providing a metallic envelope thereover, said envelope spanning and sealing the defects which extend to the free surface of the coating (c) hot isostatically pressing the coated substrate at a sufficient pressure and temperature and for a sufficient time to close the defects internal of the MCrAlY coating and those intersecting said free surface and to diffuse at least a portion of the metallic envelope into the MCrAlY coating, closure of said defects and diffusion of said metal envelope into the coating significantly enhancing the oxidation-corrosion protective properties of the coating. .Iaddend..Iadd. 13. The method of claim 12 wherein the metallic coating is aluminum. .Iaddend..Iadd. 14. The method of claim 12 wherein the metallic envelope is provided by electroplating the free surface to deposit a metallic coating thereon. .Iaddend.