FIELD

The present invention generally relates to bond coatings for use with environmental barrier coatings on ceramic components, along with methods of their formation and use.

BACKGROUND

Higher operating temperatures for gas turbine engines are continuously being sought in order to improve their efficiency. However, as operating temperatures increase, the high temperature durability of the components of the engine must correspondingly increase. Significant advances in high temperature capabilities have been achieved through the formulation of iron, nickel, and cobalt-based superalloys. Still, with many hot gas path components constructed from super alloys, thermal barrier coatings (TBCs) can be utilized to insulate the components and can sustain an appreciable temperature difference between the load-bearing alloys and the coating surface, thus limiting the thermal exposure of the structural component.

While superalloys have found wide use for components used throughout gas turbine engines, and especially in the higher temperature sections, alternative lighter-weight substrate materials have been proposed, such as ceramic matrix composite (CMC) materials. CMC and monolithic ceramic components can be coated with environmental barrier coatings (EBCs) to protect them from the harsh environment of high temperature engine sections. EBCs can provide a dense, hermetic seal against the corrosive gases in the hot combustion environment.

Silicon carbide and silicon nitride ceramics undergo oxidation in dry, high temperature environments. This oxidation produces a passive, silicon oxide scale on the surface of the material. In moist, high temperature environments containing water vapor, such as a turbine engine, both oxidation and recession occurs due to the formation of a passive silicon oxide scale and subsequent conversion of the silicon oxide to gaseous silicon hydroxide. To prevent recession in moist, high temperature environments, environmental barrier coatings (EBC's) are deposited onto silicon carbide and silicon nitride materials.

Currently, EBC materials are made out of rare earth silicate compounds. These materials seal out water vapor, preventing it from reaching the silicon oxide scale on the silicon carbide or silicon nitride surface, thereby preventing recession. Such materials cannot prevent oxygen penetration, however, which results in oxidation of the underlying substrate. Oxidation of the substrate yields a passive silicon oxide scale, along with the release of carbonaceous or nitrous oxide gas. The carbonaceous (i.e., CO, CO2) or nitrous (i.e., NO, NO2, etc.) oxide gases cannot escape out through the dense EBC and thus, blisters form. The use of a silicon bond coating has been the solution to this blistering problem to date. The silicon bond coating provides a layer that oxidizes (forming a passive silicon oxide layer beneath the EBC) without liberating a gaseous by-product.

However, the presence of a silicon bond coating limits the upper temperature of operation for the EBC because the melting point of silicon metal is relatively low. In use, the silicon bond coating melts at coating temperatures of about 1414° C., which is the melting point of silicon metal. Above these melting temperatures, the silicon bond coating may delaminate from the underlying substrate, effectively removing the bond coat and the EBC thereon. As such, it is desirable to improve the properties of a silicon bond coating in the EBC to achieve a higher operational temperature limit for the EBC.

BRIEF DESCRIPTION

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

A coated component is generally provided, along with method of forming the same. In one embodiment, the coated component includes a substrate having a surface, a silicon-based bond coating on the surface of the substrate, and an EBC on the silicon-based bond coating. The silicon-based bond coating includes a silicon-phase contained within a refractory phase. The silicon-phase, when melted, is contained within the refractory phase and between the surface of the substrate and an inner surface of the environmental barrier coating. Such a coated component may be, in particular embodiments, a turbine component.

Methods are generally provided for forming a coated component. In one embodiment, the method includes forming a silicon-based bond coating on a surface of a substrate and forming an environmental barrier coating on the silicon-based bond coating such that the silicon-phase. The silicon-based bond coating comprises a silicon-phase contained within a refractory phase and, when melted, is contained within refractory phase between the surface of the substrate and an inner surface of the environmental barrier coating.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

