Patent Publication Number: US-2023151483-A1

Title: Coating system having synthetic oxide layers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 16/026,176, filed Jul. 3, 2018, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Exemplary embodiments of the present disclosure pertain to the art of oxide coatings and thermal barrier coatings. 
     The high temperature exposure of nickel-based superalloys in turbine engines continues to increase. It is important that the superalloy substrates be protected by thermal barrier coatings which enable their use in high temperature environments. Thermal barrier coatings provide a means to shelter the structural element, i.e. the turbine blade or vane, from the highest temperatures in the engine. However, oxidation of the metal surface of the substrate takes place as the thermal barrier coating is oxygen transparent. Metallic bond coats are added to the metallic surface of the substrate to form a reaction product of thermally grown oxide (TGO), typically alumina, between the bond coat and the thermal barrier coating topcoat. 
     BRIEF DESCRIPTION 
     Disclosed is a coating system for a turbine engine component. The coating system includes a substrate, an optional bond coat, a synthetic oxide layer and a top coat. The synthetic oxide layer is formed by atomic layer deposition and includes two or more oxides. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the bond coat is disposed between the substrate and the synthetic oxide layer. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the substrate includes a nickel based superalloy, an alloy of Al, Co, Fe, Mg, Ti, Zr, W, Mo or combinations thereof, or a Si-based material. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the synthetic oxide layer includes a primary oxide and a dopant. The primary oxide may include an oxide of Al, Cr, Si, Ti, Zr, Hf, Mg, Y, Ta, Nb, La, Yb, or combinations thereof. The dopant may include an oxide or cation of La, Ce, Gd, Dy, Yb, Lu, Ca, Ba, Sr, or combinations thereof. The synthetic oxide layer may include a reaction product of the primary oxide and the dopant. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the synthetic oxide layer includes a gradient of the at least two oxides. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the synthetic oxide layer includes sublayers of differing oxide composition. Each sublayer may have a thickness of 0.5 Angstroms to 10 micrometers. The sublayers may be arranged in a pattern. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the synthetic oxide layer includes non-crystalline portions, crystalline portions, nanostructured portions, turbostratic portions, semi-crystalline portions or combinations of these. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the synthetic oxide layer may have a thickness of 100 nanometers to 10 micrometers. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the synthetic oxide layer includes an oxide which is the reaction product of the two oxides. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the top coat includes a thermal barrier coating, an environmental barrier coating, abradable coating, erosion resistant coating, or a coating that provides a combination of such functions. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the synthetic oxide layer further includes a nitride. 
     Also disclosed is a method of forming the coating system. The method includes applying a mixture using atomic layer deposition to a substrate or a bond coat disposed on a substrate to form a synthetic oxide layer, wherein the mixture includes two oxides or an oxide and a dopant and the synthetic oxide layer includes two oxides. 
     Also disclosed is a method of forming the coating system. The method includes applying a mixture using atomic layer deposition to a substrate or a bond coat disposed on the substrate, wherein at least a portion of the mixture reacts to form a mixed oxide and forms a synthetic oxide layer comprising at least two oxides. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the mixture includes two oxides. 
     In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the mixture includes an oxide and a dopant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. 
       The FIGURE shows a representative coating system. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the FIGURE. 
     Turbine engine components, such as turbine blades, vanes, and combustor components, are subjected to high temperatures. Thermal barrier coatings have been developed to allow use of the turbine engine components in such environments. When using a thermal barrier coating, it is important that the thermal barrier coating be well adhered to the substrate. 
     As mentioned above, thermally grown oxide layers (TGO) form at the interface of the bond coat and the thermal barrier coating (TBC) topcoat. The thermally grown oxide layer impacts the life of the thermal barrier coating and therefore the underlying substrate due to one of more of a number of factors. These include failure at the TGO/metal interface due to thermal cycling, TGO growth with time, bond coat rumpling due to localized stress, and tramp element (i.e. sulfur) segregation to the substrate/TGO interface causing spallation of the TGO and TBC. Replacement of the TGO with a synthetic oxide layer comprising two oxides can address some or all of these issues. 
     The aforementioned turbine engine components typically have a substrate  12 . The substrate may be formed from a superalloy such as a nickel-based superalloy, alloys of Al, Co, Fe, Mg, Ti, Zr, W, Mo, or Si-based materials, including SiC ceramics. An optional bond coat  16  may be deposited onto a surface of the substrate  12 . The optional bond coat  16  may be formed from a MCrAlY material where M is selected from the group of Ni and/or Co, a platinum-aluminide material, or any other suitable aluminide material. The bond coat may have a thickness of 50 to 500 microns. In the case of Si-based substrates, including SiC, the bond coat may additionally comprise a silicon-containing alloy or intermetallic component. 
     A synthetic oxide layer  20  is deposited on the substrate or on the optional bondcoat when present. The synthetic oxide layer  20  includes at least two oxides. The synthetic oxide layer  20  is formed using atomic layer deposition (ALD). ALD allows the deposition of low porosity, conformal and pin hole free materials having a thickness of 0.5 Angstroms up to the desired thickness. ALD is used to deposit a mixture of materials. The mixture includes at least two oxides or a combination of one or more oxides and one or more dopants. During deposition the oxides or oxide(s) and dopant(s) may react to form one or more mixed oxides. This may also occur during normal use of the coated article, for example, in a gas turbine engine. When it occurs during normal use of the coated article the oxides or oxide(s) and dopant(s) may react with components of the substrate, the optional bond coat or any coating applied to the synthetic oxide layer. 
     The synthetic oxide layer  20  may comprise sub-layers, may be doped or may comprise sub-layers at least some of which are doped. ALD provides an opportunity to dope a primary oxide with additional materials to further enhance thermal and environmental stability. As understood by one of skill in the art an excess of dopant can result in a secondary phase. Exemplary primary oxides include oxides of Al, Cr, Si, Ti, Zr, Hf, Mg, Y, Ta, Nb, and combinations thereof. Exemplary dopants include oxides and cations of both rare earth and alkaline earth metals such as La, Ce, Gd, Dy, Yb, Lu, Ca, Ba, Sr, and combinations thereof. Additionally, the primary oxide may be doped with another oxide that may also be a primary oxide— for example, Al 2 O 3  may be doped with Y 2 O 3 . 
     The synthetic oxide layer  20  may optionally include a nitride. Exemplary nitrides include nitrides of Al, Cr, Si, Ti, Zr, Hf Ta and B. 
     The synthetic oxide layer may have a concentration gradient. For example, the concentration of the dopant may be higher in the portion of the synthetic oxide layer closer to the bond coat or metallic substrate. 
     In some embodiments, the synthetic oxide layer includes sublayers of differing oxide compositions. These sublayers and their pattern(s) can be designed to tailor the properties of the synthetic oxide layer as a whole to provide one or more desired properties. For example, the sublayers can be designed to more effectively transition between materials having different coefficients of thermal expansion, enhance radiative heat transfer, and/or reduce thermal conductivity or oxygen diffusion. 
     The individual thickness of each sublayer may vary. For example, the individual thickness of each sublayer may range from 0.5 Angstroms to 10 micrometers. The sublayers may be arranged in any pattern or may be arranged without a pattern. The pattern may be a symmetric, periodic, or non-periodic pattern. 
     Furthermore, ALD allows the structure of the synthetic oxide layer to be tailored. For example, the synthetic oxide layer may comprise non-crystalline or amorphous portions, crystalline portions, nanostructured portions, turbostratic portions, semi-crystalline portions or combinations of these. 
     The synthetic oxide layer  20  may have an overall thickness of 100 nm to 10 micrometers. The synthetic oxide layer  20  provides the foundation for the component&#39;s oxide protection as well as the foundation for the thermal barrier coating topcoat. It is the presence of this oxide layer  20  which improves the adherence of the thermal barrier coating  14  to the substrate  12 . 
     After the synthetic oxide layer  20  has been deposited, a top coat, such as a thermal barrier coating  14  is typically deposited thereon. The thermal barrier coating  14  may comprise any suitable thermal barrier coating known in the art. Exemplary thermal barrier coatings include zirconia— most typically yttria stabilized zirconia (but also dysprosia, calcia or magnesia stabilized), gadolinium zirconate, hafnium oxide, gadolinium hafnate, aluminum oxide, mullite, and rare earth silicates and disilicates. It is further contemplated that the top coat may be an environmental barrier coating, abradable coating, or erosion resistant coating or a coating that provides a combination of such functions. 
     The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.