Elevated temperature oxidation protection coatings for titanium alloys and methods of preparing the same
AssigneeHoneywell International Inc.
InventorsDerek Raybould, Paul Chipko, William E. Fischer
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Abstract
Oxidation protection of a titanium-based alloy is provided with improved fatigue properties by a titanium aluminide coating of between 2 to 12 microns by diffusing the Al into the Ti at a temperature below the melting point of the Al. The coating is gas deposited and protects the titanium-based alloys from oxidation at high temperature utilization.
Claims22
A method of coating a surface of a titanium based substrate to provide oxidation protection and improved fatigue properties at elevated temperatures, comprising:
- applying an aluminum conversion layer to the surface to form a coated substrate, wherein the aluminum conversion layer is applied at a temperature below the melting point of aluminum so that aluminum does not appreciably react with titanium, and wherein the aluminum conversion layer is applied to a thickness of from about 2 to 12 microns;
- and
- heat treating the coated substrate in a two-step process so that:
- i) a first portion of the aluminum conversion layer oxidizes to form an alumina layer;
- and
- ii) a second portion of the aluminum conversion layer interacts with the titanium within the titanium based substrate to form titanium aluminide below the alumina layer.
A method of applying a coating to a brazed substrate comprising:
- applying an aluminum conversion layer on a braze of the substrate by gaseous deposition, the layer being deposited at a temperature below the melting point of aluminum so that aluminum does not appreciably react with titanium;
- and
- heat treating the aluminum conversion layer so that the aluminum diffuses into the braze to form a solid solution within the braze, and the aluminum further oxidizes to form an alumina surface layer on the braze.
A method for forming an oxidation protective coating on a titanium-based substrate, comprising:
- a) depositing an aluminum conversion layer on a surface of the titanium-based substrate, wherein the aluminum conversion layer comprises aluminum;
- b) oxidizing a first portion of the aluminum to form an outer alumina layer;
- and
- c) reacting a second portion of the aluminum with titanium of the titanium-based substrate to form a layer of titanium aluminide beneath the alumina layer, wherein step b) is performed at a first temperature, and step c) is performed at a second temperature, and wherein the second temperature is higher than the first temperature.
A method for forming an oxidation protective coating on a surface of a titanium-based substrate, comprising:
- a) depositing an aluminum conversion layer on the surface of the titanium-based substrate;
- b) oxidizing a first portion of the aluminum conversion layer to form an outer alumina layer;
- and
- c) diffusing a second portion of the aluminum conversion layer into the titanium-based substrate, wherein a titanium aluminide layer is formed beneath the alumina layer, wherein step b) is performed at a first temperature, step c) is performed at a second temperature, and wherein the second temperature is substantially higher than the first temperature.
A method for forming an oxidation protective coating on a surface of a titanium-based substrate, comprising:
- a) depositing an aluminum conversion layer on the surface of the titanium-based substrate, wherein the aluminum conversion layer is deposited at a temperature of less than about 550° C.;
- b) heat treating the aluminum conversion layer at a controlled rate, wherein the rate is from about 25 to 100° C. per hour when the temperature during this step is above 500° C., to form a coated substrate comprising an outer alumina layer and a titanium aluminide layer, wherein the titanium aluminide layer is formed between the titanium-based substrate and the alumina layer;
- and
- c) cooling the coated substrate at a controlled rate, wherein the rate is from about 15 to 60° C. per hour, whereby cracking of the titanium aluminide layer is prevented.
Dependencies are inferred from the claim text.