Abstract:
A method of making a multilayer environmental barrier coating for a ceramic matrix composite is provided, comprising the steps of: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite and depositing a columnar top coat over the oxide-based bond coat.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/178,437, filed Feb. 12, 2014, which claims priority to U.S. Provisional Patent Application Ser. No. 61/777,054, filed on Mar. 12, 2013. The contents of U.S. patent application Ser. No. 14/178,437 and U.S. Provisional Patent Application Ser. No. 61/777,054 are hereby expressly incorporated by reference in their entirety. 
     
    
     SUMMARY 
       [0002]    This present disclosure relates to methods of fabricating multilayer environmental barrier coatings for substrates such as ceramic matrix composites, and in particular, to methods of fabrication that include the combination of plasma spraying and either electron beam physical vapor deposition or directed vapor deposition. 
         [0003]    An illustrative embodiment of the present disclosure includes a method of making a multilayer environmental barrier coating for a ceramic matrix composite, comprising the steps of: plasma spray coating an oxide-based bond coat over top of the ceramic matrix composite; selecting a method of applying a columnar top coat over the oxide-based bond coat, wherein the method of applying the columnar top coat is selected from the group consisting of electron beam physical vapor deposition and directed vapor deposition; and depositing a columnar top coat over the oxide-based bond coat according to the selected method of applying the columnar top coat. 
         [0004]    In the above and other embodiments, the method of making the multilayer, environmental barrier coating may further include: selecting the method of applying the columnar top coat, being decided by evaluating the benefits and detriments of either the electron beam physical vapor deposition and the directed vapor deposition methods and how those benefits and detriments affect the columnar top coat when sprayed on the oxide-based bond coat; the oxide-based bond coat is selected from the group consisting of mullite, mullite +Si, HfSiO 4 +SiO 2 +Si, HfSiO 4 +SiO 2 +Al 2 O 3 +Si, RE 2 Si 2 O 7 +Al 2 O 3 +Si, RE 2 Si 2 O 7 +Al 2 O 3 +SiO 2 +Si, HfSiO 4 +Al 2 O 3 +Si, HfSiO 4 +Si, and SiO 2 +Al 2 O 3 +Si, (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), the columnar top coat is selected from the group consisting of RE 2 Si 2 O 7  and RE 2 SiO 5  (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), RE 2 O 3 -stabilized ZrO 2  (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium), and RE 2 O 3 -stabilized HfO 2  (wherein RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium); the oxide-based bond coat being the mullite +Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, with the balance being mullite; the oxide-based bond coat being the HfSiO 4 +SiO 2 +Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO 2  is present in an amount between about 10 wt % and about 30 wt %, and the balance being HfSiO 4 ; the oxide-based bond coat being the HfSiO 4 +SiO 2 +Al 2 O 3 +Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO 2  is present in an amount between about 10 wt % and about 30 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being HfSiO 4 ; the oxide-based bond coat being the RE 2 Si 2 O 7 +Al 2 O 3 +Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being RE 2 Si 2 O 7 ; the oxide-based bond coat being the RE 2 Si 2 O 7 +Al 2 O 3 +SiO2+Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO 2  is present in an amount between about 10 wt % and about 30 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being RE 2 Si 2 O 7 ; the oxide-based bond coat being the SiO2+Al 2 O 3 +Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance being SiO 2 ; the oxide-based bond coat being HfSiO 4 +Al 2 O 3 +Si; wherein the Si is present in an amount between about 10 wt % and about 40 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is HfSiO 4;  and the oxide-based bond coat being HfSiO 4 +Si, wherein the Si is present in an amount between about 10 wt % and about 40 wt %, and the balance being HfSiO 4 . 
         [0005]    Additional features and advantages of these methods will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrated embodiment exemplifying the best mode of carrying out these methods as presently perceived. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0006]    The present disclosure will be described hereafter with reference to the attached drawing which is given as a non-limiting example only, in which: 
           [0007]      FIG. 1  is a cross-sectional diagram of a ceramic matrix composite material with an oxide-based bond coat deposited thereon and a columnar top coat deposited on the oxide-based bond coat. 
       
    
    
       [0008]    The exemplification set out herein illustrates embodiments of the methods and such exemplification is not to be construed as limiting the scope of the methods in any manner. 
       DETAILED DESCRIPTION 
       [0009]    This present disclosure is directed to methods of fabricating multilayer environmental barrier coatings (EBCs) to suit the characteristics of certain materials such as Silicon-containing ceramics including ceramic matrix composites (CMCs). Plasma spraying, electron beam physical vapor deposition (EB-PVD), or directed vapor deposition (DVD) are three methods of coating CMCs. 
         [0010]    Each deposition method has its own benefits and detriments. One embodiment may use plasma spraying and electron beam physical vapor deposition. Another embodiment may use plasma spraying and directed vapor deposition. By combining layers using these different methods, the benefits of each create distinctive properties to the coatings. For example, an EBC may be formed by combining a plasma sprayed layer which provides the capability to fabricate complex chemistry coatings, with a layer formed by either DVD or EB-PVD which provides the capability to fabricate highly strain-tolerant columnar microstructures and smooth surface finishes. The results are high performance EBCs with a multiple oxide-based bond coat having &gt;2700F temperature capability and a top coat having -3000F temperature capability. The following table identifies the benefits and detriments of the various coating processes. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Process 
                 Benefits 
                 Detriments 
               
               
                   
               
             
             
               
                 Plasma 
                 Amenability to complex 
                 Inability to coat non- 
               
               
                 Spraying 
                 coating chemistries 
                 line-of-sight areas 
               
               
                   
                 Relatively low 
                 Rough coating surface 
               
               
                   
                 manufacturing cost 
                 finish 
               
               
                   
                   
                 Low deposition 
               
               
                   
                   
                 efficiency 
               
               
                   
                   
                 Low erosion resistance 
               
               
                 EB-PVD 
                 Smooth coating surface 
                 Inability to coat non- 
               
               
                 (Conventional) 
                 finish 
                 line-of-sight areas 
               
               
                   
                 Ability to create highly 
                 Difficulty in fabricating 
               
               
                   
                 strain-tolerant 
                 complex coating 
               
               
                   
                 columnar microstructures 
                 chemistries 
               
               
                   
                 High erosion resistance 
                 Low deposition 
               
               
                   
                   
                 efficiency 
               
               
                   
                   
                 High manufacturing 
               
               
                   
                   
                 cost 
               
               
                 DVD 
                 Smooth coating surface 
                 Difficulty in fabricating 
               
               
                 (Enhanced 
                 finish 
                 complex coating 
               
               
                 EB-PVD) 
                 Ability to create highly 
                 chemistries 
               
               
                   
                 strain-tolerant 
                 High manufacturing 
               
               
                   
                 columnar microstructures 
                 cost, but likely 
               
               
                   
                 Ability to coat non-line- 
                 lower than conventional 
               
               
                   
                 of-sight areas 
                 EB-PVD 
               
               
                   
                 High deposition 
               
               
                   
                 efficiency 
               
               
                   
                 High erosion resistance 
               
               
                   
               
             
          
         
       
     
         [0011]    The benefits of plasma spraying include amenability to complex coating chemistries and relatively low manufacturing cost, while its detriments include the inability to coat non-line-of-sight areas, rough coating surface finish, low deposition efficiency, and low erosion resistance. In contrast, the benefits of EB-PVD include smooth coating surface finish, ability to create highly strain-tolerant columnar microstructures and high erosion resistance. Its detriments include an inability to coat non-line-of-sight areas, difficulty in fabricating complex coating chemistries, low deposition efficiency and high manufacturing cost. The DVD (or enhanced EB-PVD) has non-line-of-sight coating capabilities and improved deposition efficiency as compared to conventional EB-PVD. 
         [0012]    Again, the fabrication method for each coating layer is selected by considering the benefits and detriments of each process in conjunction with the complexity of the chemistry and the function of each layer. EB-PVD or DVD may be used for the top coat of airfoils because of their smooth surface finish for aerodynamic performance and better erosion resistance as compared to plasma spraying. EB-PVD or DVD may also be used for layers with high coefficient of thermal expansion (CTE) mismatch with CMC. Layers having high CTE mismatch with CMC may cause high residual stresses and therefore experience short thermal cycling life. CTE mismatch stresses can be significantly mitigated by creating a highly strain tolerant columnar microstructure using the EB-PVD or DVD processes. Plasma spraying may be used for layers with a complex chemistry. Multiple phases react at high temperatures to form glass-containing reaction products that create strong chemical bonding for long steam cycling life. 
         [0013]    An illustrative embodiment provides a combination of a plasma-sprayed, complex oxide-based bond coat and either an EB-PVD or DVD-based rare earth silicate, stabilized zirconia or stabilized hafnia top coat. This combination provides the EBCs with a high temperature bond coat with a temperature capability exceeding the temperature capability of current Silicon (Si) bond coats (−2460F), along with a highly strain-tolerant and water-vapor-resistant, low thermal conductivity top coat. The high temperature bond coat enables the implementation of high temperature CMCs (2700F CMC) in gas turbines, while the highly strain-tolerant and water-vapor-resistant, low thermal conductivity top coat increases the EBC surface temperature capability to about −3000F. 
         [0014]    Examples of plasma sprayed layers include oxide-based high temperature bond coats with complex chemistry, such as mullite (3Al 2 O 3 -2SiO 2 ), mullite +Si, HfSiO 4 +SiO 2 +Si, HfSiO 4 +Al 2 O 3 +SiO 2 +Si, RE 2 Si 2 O 7 +Al 2 O 3 +Si, RE 2 Si 2 O 7 +Al 2 O 3 +SiO2+Si, HfSiO 4 +Al 2 O 3 +Si, HfSiO 4 +Si, and SiO 2 +Al 2 O 3 +Si, (where RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium). When the oxide-based bond coat is mullite +Si—the Si is present in an amount between about 10 wt % and about 40 wt % and the balance is mullite. When the oxide-based bond coat is HfSiO 4 +SiO 2 +Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO 2  is present in an amount between about 10 wt % and about 30 wt %, and the balance is HfSiO 4 . When the oxide-based bond coat is HfSiO 4 +SiO 2 +Al 2 O 3 +Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO 2  is present in an amount between about 10 wt % and about 30 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is HfSiO 4 . When the oxide-based bond coat is RE 2 Si 2 O 7 +Al 2 O 3 +Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is RE 2 Si 2 O 7 . When the oxide-based bond coat is RE 2 Si 2 O 7 +Al 2 O 3 +SiO 2 +Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the SiO 2  is present in an amount between about 10 wt % and about 30 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is RE 2 Si 2 O 7 . When the oxide-based bond coat is HfSiO 4 +Al 2 O 3 +Si;—the Si is present in an amount between about 10 wt % and about 40 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is HfSiO 4 . When the oxide-based bond coat being HfSiO 4 +Si—the Si is present in an amount between about 10 wt % and about 40 wt %, and the balance is HfSiO 4 . Lastly, when the oxide-based bond coat is SiO2+Al 2 O 3 +Si—the Si is present in an amount between about 10 wt % and about 40 wt %, the Al 2 O 3  is present in an amount between about 0.1 wt % and about 10 wt %, and the balance is SiO 2 . 
         [0015]    Examples of EB-PVD or DVD layers include EBC top coats of rare earth silicate (RE 2 Si 2 O 7  and RE 2 SiO 5 ), RE 2 O 3 -stabilized ZrO 2  and RE 2 O 3 -stabilized HfO 2  (where RE is selected from the group consisting of at least one of lutetium, ytterbium, thulium, erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, promethium, neodymium, praseodymium, cerium, lanthanum, yttrium, and scandium). Rare earth monosilicate (RE 2 SiO 5 ), RE 2 O 3 -stabilized ZrO 2  and RE 2 O 3 -stabilized HfO 2 , have CTEs substantially higher than CMC and therefore are desirable to be fabricated in low modulus, strain tolerant columnar microstructure to mitigate CTE mismatch stresses. 
         [0016]    The substrate may include any of the following: a Si-containing ceramic, such as silicon carbide (SiC), silicon nitride (Si 3 N 4 ), a CMC having a SiC or Si 3 N 4  matrix, silicon oxynitride, and silicon aluminum oxynitride; a Si-containing metal alloy, such as molybdenum-silicon alloys (e.g. MoSi 2 ) and niobium-silicon alloys (e.g. NbSi 2 ); and an oxide-oxide CMC. CMCs comprise a matrix reinforced with ceramic fibers, whiskers, platelets, and chopped or continuous fibers. 
         [0017]    A cross-sectional diagram of a ceramic matrix composite material with an oxide-based bond coat deposited thereon, and a columnar top coat deposited on the oxide-based bond coat is shown in  FIG. 1 . An illustrative example of an EBC that combines plasma sprayed, high temperature oxide-based bond coat  4  and either a DVD or EB-PVD processed, highly strain-tolerant columnar top coat  6 , on a CMC or other Si-containing ceramic  8 . The choice of whether columnar top coat  6  is formed from either DVD or EB-PVD is determined by the particular benefits one or the other imparts, as shown in the table above. 
         [0018]    Although the present disclosure has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present disclosure and various changes and modifications may be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as set forth in the following claims.