High temperature gaseous oxidation for passivation of austenitic alloys
AssigneeBabcock & Wilcox Canada Ltd.
InventorsPeter J. King, David M. Doyle
Life of this patent
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Abstract
A method for forming a chromium-rich layer on the surface of a nickel alloy workpiece containing chromium includes heating the workpiece to a stable temperature of about 1100° C., and then exposing the workpiece to a gaseous mixture containing water vapor and one or more non-oxidizing gases for a short period of time. The process conditions are compatible with high temperature annealing and can be performed simultaneously with, or in conjunction with, high temperature annealing.
Claims20
A method of forming a chromium-rich layer on a surface of a nickel-based alloy workpiece containing chromium, comprising:
- a. heating the workpiece to a temperature sufficient to oxidize the chromium;
- b. exposing at least one portion of the surface of the workpiece to a gaseous mixture of water vapor and at least one non-oxidizing gas to oxidize the chromium contained within the workpiece to form a chromium-rich layer on the at least one portion of the surface of the workpiece.
A method of forming a chromium-rich layer on a surface of a nickel-based alloy workpiece containing chromium, comprising:
- a. heating the workpiece to a temperature of about 1100° C.;
- b. exposing at least one portion of the surface of the workpiece to a flowing gaseous mixture of hydrogen and water vapor having a water content in the range of about 0.5% to 10%;
- c. maintaining the workpiece at a temperature of about 1100° C. for at least about 3 to 5 minutes to oxidize the chromium contained within the workpiece to form a chromium-rich layer including chromium oxide on the at least one portion of the surface.
A method of forming a chromium-rich layer on a surface of a nickel-based alloy workpiece containing chromium, comprising:
- a. heating the workpiece to a temperature of about 1100° C.;
- b. exposing at least one portion of a surface of the workpiece to a flowing gaseous mixture of hydrogen and water vapor having a water content in the range of about 0.5% to 10%;
- c. maintaining the workpiece at a temperature of about 1100° C. for at least about 3 to 5 minutes to oxidize the chromium contained within the workpiece to form a chromium-rich layer consisting essentially of chromium oxide on the at least one portion of the surface.
A method of forming a chromium-rich layer on a surface of a nickel-based alloy workpiece containing chromium, comprising:
- a. heating the workpiece to a temperature sufficient to ozidize chromium;
- b. exposing at least one portion of a surface of the workpiece to a flowing gaseous mixture of water vapor and at least one non-oxidizing gas wherein the gaseous mixture has a water content in the range of about 0.08% to 40%;
- c. preferentially oxidizing the chromium contained within the workpiece to form a chromium-rich layer on the at least one portion of the surface of the workpiece.
Dependencies are inferred from the claim text.