Coating and coating method for gas turbine engine component

Abstract

The present invention provides a protective coating for a gas turbine blade or other component wherein the duplex coating includes an aluminum-bearing coating, such as a diffusion aluminide, formed on a first, relatively higher temperature region of the blade / component and a later-applied chromium-bearing diffusion coating formed on an adjacent relatively lower temperature region of the blade / component subject to hot corrosion in service. The chromium-bearing coating is applied after the aluminum-bearing coating by masking that coating and depositing a metallic chromium coating on the adjacent region followed by diffusing the chromium into the blade / component alloy to form a chromium-enriched diffusion coating thereon.

Description

RELATED APPLICATION[0001]This application claims benefit and priority of U.S. provisional application Ser. No. 61 / 633,935 filed Feb. 21, 2012, the entire disclosure of which is incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates to a protective coating for a gas turbine blade or other component wherein the coating includes an aluminum-bearing coating applied at a relatively high temperature region of the component and a chromium-bearing coating applied at another relatively lower temperature region of the component depending on coating functionality needed.BACKGROUND OF THE INVENTION[0003]Current gas turbine designs are requiring that a variety of coatings be applied to different areas of the turbine part for different functional reasons. Examples of coating functionality include wear, oxidation, thermal barrier, and hot corrosion. Turbine designers choose an appropriate coating for a particular functionality in the gas turbine environment.[000...

AI Technical Summary

Benefits of technology

[0006]The present invention provides in an embodiment a method of forming a protective coating on a gas turbine component wherein the duplex coating includes an aluminum-bearing coating applied at one region of the gas turbine component where relatively higher temperatures are encountered in service and a chromium-bearing coating applied at another region of the turbine blade or other component where relatively lower temperatures and hot corrosion are encountered in service, thereby providing coating functionality for the different temperatures and oxidation / corrosion environments to be encountered by the gas turbine component.

[0008]In the event the substrate is a gas turbine component, the method is practiced by first applying a mask on a root region of the component, then applying an aluminum-bearing coating, such as a diffusion aluminide coating, on an airfoil region, de-masking the root portion, and then masking the already-coated airfoil region. Then, the method involves depositing a metallic coating comprising chromium on at least a portion of a relatively lower temperature root region that will be subject to hot corrosion, de-masking the airfoil region followed by diffusing the chromium into the alloy at the coated portion of the root region to form a chromium-enriched diffused surface coating on the portion of the root region. The aluminum-bearing coating optionally can be applied to cover the airfoil region and also an intermediate platform region and root shank region. An attachment portion, such as a fir tree portion, of the root region may be left uncoated to enhance fatigue life of the root region where it is connected to a turbine disk.

Problems solved by technology

Since pack and vapor phase chromizing require high temperature application above 1900 F and are difficult to apply to localized part areas of interest, these processes must be applied early in the part routing to the entire the part.

Masking has not been effective in these processes as a means for controlling the localized deposition of the chromium on certain areas of interest and, as a result, has not been applied in these high temperature processes.

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