Protection of thermal barrier coating by impermeable barrier coating

Abstract

According to an embodiment of the invention, disclosed is a composite comprising a porous thermal barrier coating on a metallic part and an impermeable barrier coating adjacent to the outer surface of the thermal barrier coating. The impermeable barrier coating is dense and non-porous and comprises a rare earth silicate, the impermeable barrier coating thereby preventing infiltration of the contaminant composition into the thermal barrier coating.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] The subject application shares certain attributes with U.S. Ser. No., entitled, Protection of Thermal Barrier Coating By A Sacrificial Coating, which is filed concurrently herewith. The contents of this application are hereby incorporated by reference.GOVERNMENT RIGHTS [0002] The invention was made in part under contract number N00019-96-C-1076 awarded by the Government (Navy). Accordingly, the Government has certain rights in this invention.FIELD OF THE INVENTION [0003] The invention generally relates to a method for protecting thermal barrier coatings deposited on gas turbine and other heat engine parts from the deleterious effects of environmental contaminants. More particularly, the invention relates to a method of using an impermeable coating, where the impermeable coating reduces infiltration of liquid contaminant compositions into the thermal barrier coating, as well as articles coated with the impermeable coating. BACKGROUND OF T...

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Benefits of technology

[0013] In accordance with embodiments of the invention, we have advantageously determined that the use of rare earth silicates will advantageously prevent CMAS from coming in contact with the thermal barrier coating. The CMAS will not infiltrate and build up stress in or chemically react with the thermal barrier coating and the thermal barrier coating will advantageously remain intact.

[0014] Accordingly, in one embodiment of the invention, a composite is disclosed. The composite comprises a porous thermal barrier coating on a metallic part and an impermeable barrier coating adjacent to the outer surface of the thermal barrier coating. The impermeable barrier coating is dense and non-porous and comprises a rare earth silicate. The impermeable barrier coating advantageously prevents infiltration of the contaminant composition into or reaction with the thermal barrier coating.

[0015] In accordance with another embodiment of the invention, a composite is disclosed. The composite comprises a thermal barrier coating on a gas turbine engine metallic part, which has a contaminant composition present that adheres on an outer surface of the thermal barrier coated part. The thermal barrier coating comprises a ceramic material admixed or graded with a rare earth silicate, to prevent infiltration of the contaminant composition into the thermal barrier coating.

Problems solved by technology

However, as operating temperatures increase, the high temperature durability of the components within the engine must correspondingly increase.

When exposed to the demanding conditions of gas turbine engine operation, particularly in the turbine section, the base alloy alone may be susceptible to damage, such as oxidation and corrosion attack, and may not retain adequate mechanical properties.

Under service conditions, thermal barrier coated engine parts can also be susceptible to various modes of damage, including erosion, oxidation, and attack from environmental contaminants.

At temperatures of engine operation, adherence of these environmental contaminants on the hot thermal barrier coated surface can cause damage to the thermal barrier coating.

Molten contaminant compositions can dissolve the thermal barrier coating or can infiltrate its pores and openings, initiating and propagating cracks causing delamination and loss of thermal barrier coating material.

Damage to thermal barrier coatings occurs when the molten CMAS infiltrates the thermal barrier coating.

The stress build up in the thermal barrier coating may cause cracking and / or spallation of the coating material and loss of the thermal protection that it provides to the underlying part.

Alternately or in addition, the CMAS can react chemically with the TBC to accelerate thermal sintering or dissolve stabilizing components such as Y2O3 resulting in damage to the TBC coating.

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