Abstract:
A gas turbine blade having a surface may have a bond layer applied to a first section of the surface, wherein the bond layer is not applied to a second section of the surface. One or more protective layers may be applied such that the protective layers cover and overlap the bond layer making direct contact with an area of the surface immediately outside the first section of the surface and forming a mechanical constraint geometry about the edge of the bond layer.

Description:
STATEMENT OF FEDERALLY SPONSORED RESEARCH 
       [0001]    This invention was made with Government support under contract number DE-FC26-05NT42643 awarded by the Department Of Energy. The Government has certain rights in this invention. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to gas turbine blades and in particular to creep resistant coatings for gas turbine blades. 
       BACKGROUND 
       [0003]    Gas turbines, which may also be referred to as combustion turbines, are internal combustion engines that accelerate gases, forcing the gases into a combustion chamber where heat is added to increase the volume of the gases. The expanded gases are then directed towards a turbine to extract the energy generated by the expanded gases. Gas turbines have many practical applications, including use as jet engines and in industrial power generation systems. 
         [0004]    The acceleration and directing of gases within a gas turbine are often accomplished using rotating blades. Extraction of energy is typically accomplished by forcing expanded gases from the combustion chamber towards turbine blades that are spun by the force of the expanded gases exiting the gas turbine through the turbine blades. Due to the high temperatures of the exiting gases, turbine blades must be constructed to endure extreme operating conditions. In many systems, complex turbine blade cooling systems are employed. While turbine blades are commonly constructed from metals, more advanced materials are now being used for such blades, such as ceramics and ceramic matrix composites. When using such advanced materials, coatings may be applied to provide added protection to the blades and increased heat resistance. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    A gas turbine blade is disclosed that may include a surface and a first bond layer applied to a first section of the surface and not applied to a second section of the surface. One or more protective layers may be applied such that the protective layers cover and overlap the first bond layer making direct contact with an area of the surface immediately outside the first section of the surface and forming a mechanical constraint geometry about the edge of the first bond layer. 
         [0006]    A method is disclosed for applying a first bond layer to a first section of a surface of a gas turbine blade, leaving a second section of the surface exposed. One or more protective layers may be applied such that the protective layers cover and overlap the first bond layer making direct contact with an area of the surface immediately outside the first section of the surface and forming a mechanical constraint geometry about an edge of the first bond layer. 
         [0007]    The foregoing summary, as well as the following detailed description, is better understood when read in conjunction with the drawings. For the purpose of illustrating the claimed subject matter, there is shown in the drawings examples that illustrate various embodiments; however, the invention is not limited to the specific systems and methods disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features, aspects, and advantages of the present subject matter will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein: 
           [0009]      FIG. 1  is a non-limiting example of coatings applied to a blade surface. 
           [0010]      FIG. 2  is another non-limiting example of coatings applied to a blade surface and the creeping that may result. 
           [0011]      FIG. 3  is a non-limiting example of coatings applied to a blade surface such that a slanted edge is formed. 
           [0012]      FIG. 4  is another non-limiting example of coatings applied to a blade surface such that a slanted edge is formed, showing a viscous fluid layer that may form under certain conditions. 
           [0013]      FIG. 5  is a non-limiting example of coatings applied to a blade surface such that a straight edge is formed. 
           [0014]      FIG. 6  is another non-limiting example of coatings applied to a blade surface such that a straight edge is formed, showing a viscous fluid layer that may form under certain conditions. 
           [0015]      FIG. 7  is a non-limiting example of coatings applied to a blade surface such that a stepped edge is formed. 
           [0016]      FIG. 8  is another non-limiting example of coatings applied to a blade surface such that a stepped edge is formed, showing a viscous fluid layer that may form under certain conditions. 
           [0017]      FIG. 9  is a non-limiting example of a blade surface with no coatings applied. 
           [0018]      FIG. 10  is a non-limiting example of a blade surface with a bond layer applied. 
           [0019]      FIG. 11  is a non-limiting example of a blade surface with a bond layer applied and environmental barrier coating (EBC) layers applied. 
           [0020]      FIG. 12  is a non-limiting example of a blade surface with two bond layers applied and EBC layers applied. 
           [0021]      FIG. 13  is a non-limiting example of a blade surface with two bond layers applied and two EBC layers applied. 
           [0022]      FIG. 14  is a non-limiting example of a blade surface with two bond layers applied, two EBC layers applied, and a top layer applied. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    In an embodiment, an environmental barrier coating (EBC) may be applied to gas turbine blade constructed from a ceramic matrix composite (CMC). An EBC may help protect the blade from the effects of environmental objects such as hot gas, water vapor and oxygen that may come in contact with the blade while a gas turbine is in operation. An EBC may be silicon-based, and it may be applied as several layers of various materials. In the embodiments of the present disclosure, the materials in each layer may be any material, and such materials may be applied using any means or methods, including Atmospheric Plasma Spray (APS), Chemical Vapor Deposition (CVD), Plasma enhanced CVD (PECVD), dip coating, reactive ion implantation, and electro-phoretic deposition (EPD). 
         [0024]      FIG. 1  illustrates an example coating that may be applied to a CMC blade. Blade  110  may be coated with bond layer  120  that may serve as a bond coat and assist in bonding EBC layers to blade  110 . In an embodiment, bond layer  120  may be a silicon bond coat. EBC layer  140  may be applied on bond layer  120 . Additional EBC layers  150 ,  160 , and  170  may further be applied over EBC layer  140 . Any number of EBC layers may be applied to blade  110  and any other blade or surface disclosed herein, using any means and methods, and any material may be used for any blade, bond layer, and EBC layer disclosed herein, including bond layer  120 , EBC layers  140 ,  150 ,  160 , and  170  and for blade  110 . All such embodiments are contemplated as within the scope of the present disclosure. 
         [0025]    In the gas turbine environment in which blade  110  may be configured, hot gasses may cause bond layer  120  to oxidize and melt due to the elevated temperatures caused by such gases. Upon melting and oxidation, bond layer  120  may form viscous fluid layer  130 , which in one embodiment may be composed of thermally grown oxide (TGO). As shown in  FIG. 2 , viscous fluid layer  130  may move under the shear stress caused by the centrifugal load applied to blade  110  and the mismatch of co-efficient thermal expansion (CTE) with the outer EBC layers, such as layers  140 ,  150 ,  160 , and  170 . Such movement may be referred to as “creep”. The creep of EBC layers  140 ,  150 ,  160 , and  170  may limit the usable lifespan of blade  110 , especially when cracking of any of layers  140 ,  150 ,  160 , and  170  occurs. 
         [0026]    To prevent or mitigate creep, in an embodiment the EBC layers may be applied such that a mechanical barrier is introduced that constrains the movement of a bond coat, such as bond layer  120 , even when such a layer may form a viscous fluid layer (e.g., of TGO) upon melting and/or oxidation. 
         [0027]      FIG. 3  illustrates one embodiment of a layer structure that may mechanically constrain a bond coat and/or a viscous fluid layer formed at least partially thereby. In  FIG. 3 , the EBC layers  340 ,  350 , and  360  and bond layer  320  are applied to create slanted edge sections  380  (only one of two slanted edge sections is circled in  FIG. 3 ) that may mechanically constrain the bond coat and/or any viscous fluid layer. As can be seen in  FIG. 3 , blade  310  is coated with bond layer  320  such that bond layer  320  does not completely cover the surface of blade  310 . Rather, bond layer  320  covers portions of blade  310  while other portions are left uncovered by bond layer  320 . Bond layer  320  may be applied so that the edges of bond layer  320  form a slanted edge as seen in  FIG. 3  in slanted edge sections  380 . 
         [0028]    EBC layer  340  may be applied over bond layer  320  and directly onto blade  310  beyond the edge of bond layer  320 , forming a slanted edge over the slanted edge formed by bond layer  320 , as seen in  FIG. 3  in slanted edge sections  380 . EBC layer  350  may be applied over EBC layer  340  and directly onto blade  310  beyond the edge of EBC layer  340 , forming a slanted edge over the slanted edge formed by EBC layer  340 , as seen in  FIG. 3  in slanted edge sections  380 . EBC layer  360  may be applied over EBC layer  350  in a similar fashion, and any additional EBC layers may be applied in a similar fashion. Final EBC layer  370  may be applied over all other layers without making any direct contact with blade  310  as shown in  FIG. 3 . 
         [0029]    The slanted edges created by EBC layers  340 ,  350 , and  360  and the direct contact of these layers with blade  310  provide a mechanical constraint geometry that may effectively encapsulate bond layer  320  and thereby prevent and/or mitigate creep when a viscous fluid layer forms at bond layer  320 .  FIG. 4  illustrates the embodiment of  FIG. 3  where viscous fluid layer  330  has formed between bond coat  320  and EBC layer  340  in response to oxidation and/or melting at bond layer  320 . EBC layers  340 ,  350 , and  360 , being directly bonded to blade  310 , prevent and/or mitigate any movement or creep of EBC layer  340  and the EBC layers above EBC layer  340 . Since there is no bond coat at the contact area of EBC layers  340 ,  350 , and  360  and blade  310 , there may be no opportunity for a viscous fluid layer to develop at that area. Thus, EBC layers  340 ,  350 , and  360  remain affixed to blade  310  at the point of contact with blade  310 , thereby restraining any movement of the EBC layers due to viscous fluid layer  330 . 
         [0030]      FIG. 5  illustrates another embodiment of a layer structure that may mechanically constrain a bond coat and/or a viscous fluid layer formed at least partially thereby. In  FIG. 5 , bond layer  720  is applied to create a slanted edge at bond layer  520  and EBC layers  540 ,  550 , and  560  are applied to create a straight edge as seen in straight edge sections  580  (only one of two straight edge sections is circled in  FIG. 5 ) that may mechanically constrain the bond coat and/or any viscous fluid layer. As can be seen in  FIG. 5 , blade  510  is coated with bond layer  520  such that bond layer  520  does not completely cover the surface of blade  310 . Rather, bond layer  520  covers portions of blade  510  while other portions are left uncovered by bond layer  520 . Bond layer  520  may be applied so that the edges of bond layer  320  form a slanted edge as seen in  FIG. 5  in straight edge sections  580 . 
         [0031]    EBC layer  540  may be applied over bond layer  520  and directly onto blade  510  beyond the edge of bond layer  520  such that a vertically (in the perspective of  FIG. 5 ) straight edge is formed over the slanted edge formed by bond layer  520 , as seen in  FIG. 5  in straight edge sections  580 . EBC layer  550  may be applied over EBC layer  540  and directly onto blade  510  beyond the edge of EBC layer  540 , forming another straight edge over the straight edge formed by EBC layer  540 , as seen in  FIG. 5  in straight edge sections  580 . EBC layer  560  may be applied over EBC layer  550  in a similar fashion, and any additional EBC layers may be applied in a similar fashion. Final EBC layer  570  may be applied over all other layers without making any direct contact with blade  510  as shown in  FIG. 5 . 
         [0032]    The straight edges created by EBC layers  540 ,  550 , and  560  and the direct contact of these layers with blade  510  provide a mechanical constraint geometry that may effectively encapsulate bond layer  520  and thereby prevent and/or mitigate creep when a viscous fluid layer forms at bond layer  520 .  FIG. 6  illustrates the embodiment of  FIG. 5  where viscous fluid layer  530  has formed between bond coat  520  and EBC layer  540  in response to oxidation and/or melting at bond layer  520 . EBC layers  540 ,  550 , and  560 , being directly bonded to blade  510 , prevent and/or mitigate any movement or creep of EBC layer  540  and the EBC layers above EBC layer  540 . Since there is no bond coat at the contact area of EBC layers  540 ,  550 , and  560  and blade  510 , there may be no opportunity for a viscous fluid layer to develop at that area. Thus, EBC layers  540 ,  550 , and  560  remain affixed to blade  510  at the point of contact with blade  510 , thereby restraining any movement of the EBC layers due to viscous fluid layer  530 . 
         [0033]      FIG. 7  illustrates yet another embodiment of a layer structure that may mechanically constrain a bond coat and/or a viscous fluid layer formed at least partially thereby. In  FIG. 7 , bond layer  720  is applied to create a slanted edge at bond layer  720  and EBC layers  740 ,  750 , and  760  are applied to create a stepped edge as seen in stepped edge sections  780  (only one of two stepped edge sections is circled in  FIG. 7 ) that may mechanically constrain the bond coat and/or any viscous fluid layer. As can be seen in  FIG. 7 , blade  710  is coated with bond layer  720  such that bond layer  720  does not completely cover the surface of blade  710 . Rather, bond layer  720  covers portions of blade  710  while other portions are left uncovered by bond layer  720 . Bond layer  720  may be applied so that the edges of bond layer  720  form a slanted edge as seen in  FIG. 7  in stepped edge sections  780 . 
         [0034]    EBC layer  740  may be applied over bond layer  720  and directly onto blade  710  beyond the edge of bond layer  720  such that a single step stepped edge is formed over the slanted edge formed by bond layer  720 , as seen in  FIG. 7  in stepped edge sections  780 . EBC layer  750  may be applied over EBC layer  740  and directly onto blade  710  beyond the edge of EBC layer  740 , forming another stepped edge having two steps over the stepped edge formed by EBC layer  740 , as seen in  FIG. 7  in stepped edge sections  780 . EBC layer  760  may be applied over EBC layer  750  in a similar fashion creating an additional step at that layer, and any additional EBC layers may be applied in a similar fashion. Final EBC layer  770  may be applied over all other layers without making any direct contact with blade  710  as shown in  FIG. 7 . 
         [0035]    The stepped edges created by EBC layers  740 ,  750 , and  760  and the direct contact of these layers with blade  710  provide a mechanical constraint geometry that may effectively encapsulate bond layer  720  and thereby prevent and/or mitigate creep when a viscous fluid layer forms at bond layer  720 .  FIG. 8  illustrates the embodiment of  FIG. 7  where viscous fluid layer  730  has formed between bond coat  720  and EBC layer  740  in response to oxidation and/or melting at bond layer  720 . EBC layers  740 ,  750 , and  760 , being directly bonded to blade  710 , prevent and/or mitigate any movement or creep of EBC layer  740  and the EBC layers above EBC layer  740 . Since there is no bond coat at the contact area of EBC layers  740 ,  750 , and  760  and blade  710 , there may be no opportunity for a viscous fluid layer to develop at that area. Thus, EBC layers  740 ,  750 , and  760  remain affixed to blade  710  at the point of contact with blade  710 , thereby restraining any movement of the EBC layers due to viscous fluid layer  730 . 
         [0036]      FIGS. 9-14  illustrate an embodiment of applying the various layers described herein to a blade that, in an embodiment, may be constructed of a ceramic matrix composite. The layers and coatings described in regard to  FIGS. 9-14  may be applied using any means and methods, including Atmospheric Plasma Spray (APS), Chemical Vapor Deposition (CVD), Plasma enhanced CVD (PECVD), dip coating, and electro-phoretic deposition (EPD). The geometric shape of the various layers (e.g., slanted, straight, stepped) may be formed during the application process or after application using any means or methods to remove applied material to form the geometric shape, including any deposition methods, any masking method, using infra-red, laser incisions, chemical reactions, ion milling, reactive ion etching (RIE), sputtering, mechanical etching, chemical etching, and any combination of these means and methods. 
         [0037]    In  FIG. 9 , blade  910  is shown prior to the application of any of the layers. Note that blade  910  may be constructed entirely, or at least in part, of materials that are commonly used for gas turbine blades. Blade  910  may not be specially prepared in any way. For example, the surface of blade  910  need not be treated, machined, or otherwise physically altered in any way in many embodiments of the present disclosure. 
         [0038]    As shown in  FIG. 10 , the surface of blade  910  may coated with bond layer  920  in certain sections, leaving other sections, such as section  915 , with no bond layer applied. As seen in  FIG. 11 , other layers may be applied, such as EBC layers  930 , over bond layer  920 , such that the particular geometry desired is formed. For example, EBC layers  930  may be applied such that a slanted, straight, or stepped edge is formed in the area where EBC layers  930  encapsulate bond layer  920  and come into direct contact with the surface of blade  910 . Upon application of EBC layers  930 , sections of the surface of blade  910  may remain exposed, such as section  916 . 
         [0039]    As shown in  FIG. 12 , second bond layer  940  may be applied to exposed sections on the surface of blade  910 , such as section  916 . All remaining exposed surface sections of blade  910  may be covered by second bond layer  940 , and some sections that were previously covered by EBC layers  930  may also be covered by second bond layer  940 . As seen in  FIG. 13 , second EBC layers  950  may be applied to the sections of blade  910  that have not yet had EBC layers applied. Finally, as seen in  FIG. 14 , top layer  960 , that may include any type of coating, may applied over all surfaces of blade  910 . 
         [0040]    By using the embodiment contemplated herein, the geometry and microstructure of EBC layers may be modified to improve creep resistance using the same coating materials currently in use today. Thus the lifespan of blades used in gas turbines may be extended with little additional cost. 
         [0041]    This written description uses examples to disclose the subject matter contained herein, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of this disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.