Patent Publication Number: US-2013251941-A1

Title: Thermal barrier coated article and a method of manufacturing a thermal barrier coated article

Description:
The present invention relates to a thermal barrier coated article and to a method of manufacturing a thermal barrier coated article and in particular relates to a thermal barrier coated combustor tile, a thermal barrier coated turbine blade or a thermal barrier coated turbine vane. 
     Combustor tiles are provided with thermal barrier coatings to enable the combustor tiles to operate at higher temperatures. Combustor tiles are provided with effusion apertures to provide a film of coolant on the surface of the combustor tiles to also enable the combustor tiles to operate at higher temperatures. 
     Effusion apertures are conventionally produced in combustor tiles by laser machining, electro-discharge machining or electro-chemical machining. 
     Combustor tiles provided with thermal barrier coatings and effusion apertures suffer from problems. 
     If the thermal barrier coating is deposited on the combustor tile before the effusion aperture are produced in the combustor tile then the high energy associated with the laser machining, drilling, of the effusion apertures can result in the delamination of the thermal barrier coating from the combustor tile. If the laser machining, drilling, is performed at a much lower energy to avoid delamination of the thermal barrier coating then this is not suitable for mass production because of the increased time and cost of producing the effusion apertures. 
     If the thermal barrier coating is deposited on the combustor tile before the effusion aperture are produced in the combustor tile then it is not possible to electro-discharge machine, or electro-chemically machine, effusion apertures through a ceramic thermal barrier coating of a thermal barrier coating because the ceramic thermal barrier coating is not electrically conductive. 
     If the effusion apertures are produced in the combustor tile before the thermal barrier coating is deposited on the combustor tile then the deposition of the thermal barrier coating can result in partial or full blockage of the effusion apertures. A blockage in an effusion aperture is not acceptable because it reduces the flow of coolant and results in local overheating of the combustor tile. 
     It is known from U.S. Pat. No. 4,743,462, U.S. Pat. No. 6,335,078, EP1245691A2, US20040048003A1 and DE102006029071A1 to provide masks within the effusion apertures to prevent blockage of the effusion apertures during deposition of the thermal barrier coating. The masks are subsequently removed. However, this increases the manufacturing time and cost of producing the effusion apertures due to the extra processes. 
     It is known from U.S. Pat. No. 6,004,620 and US20110076405A1 to remove blockages from the effusion apertures after the thermal barrier coating has been deposited. However, this increases the manufacturing time and cost of producing the effusion apertures due to the extra processes. 
     Accordingly the present invention seeks to provide a novel coated thermal barrier article which reduces, preferably overcomes, the above mentioned problems. 
     Accordingly the present invention provides a thermal barrier coated article, the article having a first surface and a second surface, the article having at least one projection extending from the first surface in a direction away from the first surface and away from the second surface, the projection having a first end adjacent the first surface and a second end remote from the first surface, the second end of the at least one projection having a surface, the article having at least one passage extending from the second surface of the article through the article and through the at least one projection to the surface at the second end of the at least one projection, the at least one passage being an effusion cooling aperture and the article having a thermal barrier coating on the first surface around the at least one projection. 
     The article may have a plurality of projections extending from the first surface in a direction away from the first surface and away from the second surface, each projection having a first end adjacent the first surface and a second end remote from the first surface, the second end of each projection having a surface, the article having a plurality of passages extending from the second surface of the article, each passage extending from the second surface of the article through the article and through a respective one of the projections to the surface at the second end of the respective projection and the article having a thermal barrier coating on the first surface around each of the projections. 
     The second end of the at least one projection may be arranged at a first distance from the first surface of the article and the thermal barrier coating has a first thickness. 
     The first distance may be equal to or greater than the first thickness. 
     The thermal barrier coating may comprise a metallic bond coating on the first surface of the article and a ceramic thermal barrier coating on the metallic bond coating. 
     The metallic bond coating may comprise a MCrAlY coating or an aluminide coating, where M is one or more of Ni, Co and Fe. 
     The ceramic thermal barrier coating may comprise stabilised zirconia. 
     The ceramic thermal barrier coating may comprise yttria stabilised zirconia. 
     The article may be a combustor tile, a turbine blade or a turbine vane. 
     The present invention also seeks to provide a novel method of manufacturing a coated thermal barrier article which reduces, preferably overcomes, the above mentioned problems. 
     The present invention also provides a method of manufacturing a thermal barrier coated article comprising the steps of:
         a) forming an article having a first surface and a second surface, the article having at least one projection extending from the first surface in a direction away from the first surface and away from the second surface, the at least one projection having a first end adjacent the first surface and a second end remote from the first surface, the second end of the at least one projection having a surface,   b) depositing a thermal barrier coating on the first surface of the article around the at least one projection and on the surface at the second end of the at least one projection,   c) removing the thermal barrier coating from the second end of the at least one projection, and   d) forming at least one passage through the at least one projection extending from the second surface of the article through the article and through the at least one projection to the surface at the second end of the at least one projection, the at least one passage being an effusion cooling aperture.       

     Step a) may comprise forming an article having a plurality of projections extending from the first surface in a direction away from the first surface and away from the second surface, each projection having a first end adjacent the first surface and a second end remote from the first surface, the second end of each projection having a surface, step b) may comprise depositing the thermal barrier coating on the first surface of the article around each of the projections and on the surface at the second end of each of the projections, step c) may comprise removing the thermal barrier coating from the second end of each of the projections and step d) may comprise forming a passage through each projection extending from the second surface of the article through the article and through the respective projection to the surface at the second end of the respective projection. 
     The second end of the at least one projection may be arranged at a first distance from the first surface of the article and the thermal barrier coating has a first thickness. 
     The first distance may be equal to or greater than the first thickness. 
     Step b) may comprise depositing a metallic bond coating on the first surface of the article and depositing a ceramic thermal barrier coating on the metallic bond coating. 
     The metallic bond coating may comprise a MCrAlY coating or an aluminide coating, where M is one or more of Ni, Co and Fe. 
     The ceramic thermal barrier coating may comprise stabilised zirconia. 
     The ceramic thermal barrier coating may comprise yttria stabilised zirconia. 
     The article may be a combustor tile, a turbine blade or a turbine vane. 
     Step a) may comprise forming the article and the at least one projection by casting. 
     Step a) may comprise forming the article and the at least one projection by direct laser deposition. 
     Step c) may comprise machining, e.g. linishing. 
     Step d) may comprise electro-discharge machining. 
     Step b) may comprises depositing the metallic bond coating by plasma spraying, thermal spraying or HVOF. 
     Step b) may comprise depositing the ceramic thermal barrier coating by plasma spraying, thermal spraying or HVOF. 
     Step d) may comprise removing at least a portion of the projection such that the first distance is less than the first thickness. 
    
    
     
       The present invention will be more fully described with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view through a turbofan gas turbine engine having a combustion chamber according to the present invention. 
         FIG. 2  is an enlarged cross-sectional view through the combustion chamber shown in  FIG. 1 . 
         FIG. 3  is a perspective view of a tile used in the combustion chamber shown in  FIG. 2 . 
         FIG. 4  is an enlarged cross-sectional view through a portion of the tile shown in  FIG. 3  as initially manufactured. 
         FIG. 5  is an enlarged cross-sectional view through the portion of the tile shown in  FIG. 3  after deposition of a thermal barrier coating. 
         FIG. 6  is an enlarged cross-sectional view through the portion of the tile shown in  FIG. 3  after removal of the thermal barrier coating. 
         FIG. 7  is an enlarged cross-sectional view through the portion of the tile shown in  FIG. 3  after forming a passage through the tile. 
         FIG. 8  is a perspective view of a further tile used in the combustion chamber shown in  FIG. 2 . 
         FIG. 9  is a perspective view of a turbine aerofoil used in the turbine shown in  FIG. 1 . 
     
    
    
     A turbofan gas turbine engine  10 , as shown in  FIG. 1 , comprises in flow series an inlet  12 , a fan section  14 , a compressor section  16 , a combustion section  18 , a turbine section  20  and an exhaust  22 . The fan section  14  comprises a fan  24 . The compressor section  16  comprises in flow series an intermediate pressure compressor  26  and a high pressure compressor  28 . The turbine section  20  comprises in flow series a high pressure turbine  30 , an intermediate pressure turbine  32  and a low pressure turbine  34 , The fan  24  is driven by the low pressure turbine  34  via a shaft  40 . The intermediate pressure compressor  26  is driven by the intermediate pressure turbine  32  via a shaft  38  and the high pressure compressor  28  is driven by the high pressure turbine  30  via a shaft  36 . The turbofan gas turbine engine  10  operates quite conventionally and its operation will not be discussed further. The turbofan gas turbine engine  10  has a rotational axis X. 
     The combustion section  18  comprises an annular combustion chamber  42 , which is shown more clearly in  FIG. 2 . The annular combustion chamber  42  has a radially inner annular wall  44 , a radially outer annular wall  46  and an upstream end wall  48  connecting the upstream ends of the radially inner annular wall  44  and the radially outer annular wall  46 . The annular combustion chamber  42  is surrounded by a casing  50 . The upstream end wall  48  has a plurality of circumferentially spaced fuel injector apertures  52  and each fuel injector aperture  52  has a respective one of a plurality of fuel injectors  54 . The radially inner annular wall  44  is a double skin annular wall and the radially outer annular wall  46  is a double skin annular wall. The radially inner annular wall  44  comprises a radially inner wall  56  and a radially outer wall  58  and the radially outer annular wall  46  comprises a radially inner wall  60  and a radially outer wall  62 . 
     The radially outer wall  58  of the radially inner annular wall  44  comprises a plurality of tiles  58 A and  58 B and the radially inner wall  60  of the radially outer annular wall  46  comprises a plurality of tiles  60 A and  60 B. The radially inner wall  56  has a plurality of apertures  55  to supply coolant, e.g. air, into the chamber, or chambers,  57  radially between the radially inner wall  56  and the tiles  58 A and  58 B of the radially outer wall  58  of the radially inner annular wall  44  and to provide impingement cooling of the surfaces  68  of the tiles  58 A and  58 B remote from the combustion chamber  42 . The tiles  58 A and  58 B have effusion apertures  59  to supply the coolant, e.g. air, from the chamber, or chambers,  57  onto the surfaces  66  of the tiles  58 A and  58 B adjacent to the combustion chamber  42  to provide film cooling of those surfaces. The effusion apertures  59  extend through each tile  58 A and  58 B from the second surface  68  to the first surface  66  of the respective tile  58 A and  58 B. Similarly the radially outer wall  62  has a plurality of apertures  61  to supply coolant, e.g. air, into the chamber, or chambers,  63  radially between the radially outer wall  62  and the tiles  60 A and  60 B of the radially inner wall  60  of the radially outer annular wall  46  and to provide impingement cooling of the surfaces  68  of the tile  60 A and  60 B remote from the combustion chamber  42 . The tiles  60 A and  60 B have effusion apertures  65  to supply the coolant, e.g. air, from the chamber, or chambers,  63  onto the surfaces  66  of the tiles  60 A and  60 B adjacent to the combustion chamber  42  to provide film cooling of those surfaces. The effusion apertures  65  extend through each tile  60 A and  60 B from the second surface  68  to the first surface  66  of the respective tile  60 A and  608 , 
     One of the tiles  58 A,  58 B is shown more clearly in  FIG. 3  and one of the tiles  60 A,  60 B is shown more clearly in  FIG. 8 . The tiles  58 A,  58 B,  60 A,  60 B are shown in the as manufactured condition, e.g. after casting or after forming by direct laser deposition. Each tile has a first surface  66  and a second surface  68 . Each tile has a plurality of studs  64  secured to and extending away from the second surface  68 . The studs  64  are used to fasten the tiles  58 A and  58 B to the radially inner wall  56  of the radially inner annular wall  44  and the studs  64  are used to fasten the tiles  60 A and  60 B to the radially outer wall  62  of the radially outer annular wall  46 . It is to be noted that each tile has at least one projection  70 , and preferably has a plurality of projections  70 , secured to and extending from the first surface  66  in a direction away from the first surface  66  and away from the second surface  68 . Each projection  70  has a first end  72  adjacent the first surface  66  and a second end  74  remote from the first surface  66 . Each projection  70  is provided at a position on the respective tile where an effusion aperture, or passage, for coolant is required. The tiles  58 A,  58 B,  60 A,  60 B are manufactured from a suitable metal or metal alloy for example an iron superalloy, a cobalt superalloy or preferably a nickel superalloy. 
       FIGS. 4 to 7  show steps in the manufacture of a thermal barrier coated tile  58 A. In particular  FIG. 4  shows a portion of the tile  58 A shown in  FIG. 3  in the as manufactured condition after the first step of casting the tile or forming the tile by direct laser deposition. The tile  58 A as mentioned previously is formed such that it has at least one projection  70  extending from the first surface  66  of the tile  58 A. The tile  58 A and the at least one projection  70  are formed integrally by casting or alternatively the tile  58 A and the at least one projection  70  are formed integrally by direct laser deposition. The second end  74  of each projection  70  has a surface  75  which is arranged substantially parallel to the first surface  66  of the tile  58 A and in this example each projection  70  has an angled side surface  73 . It is preferred that each projection  70  is produced in the tile by producing a recess at the corresponding position in the corresponding surface of the casting mould so that all the projections  70  are produced in the tile by the casting process. 
       FIG. 5  shows the portion of the tile  58 A after a thermal barrier coating  76  has been deposited onto the first surface  66  of the tile  58 A. The thermal barrier coating  76  is deposited onto the first surface  66  of the tile  58 A by depositing a metallic bond coating  78  on the first surface  66  of the tile  58 A and then by depositing a ceramic thermal barrier coating  80  on the metallic bond coating  78 . it is to be noted that the thermal barrier coating  76  is deposited onto the first surface  66  of the tile  58 A around each of the projections  70  and on the surface  75  at the second end  74  of each projection  70  and also on the angled side surface  73 . The metallic bond coating  78  may comprise a MCrAlY coating or an aluminide coating, where M is one or more of Ni, Co and Fe. The aluminide coating may be a platinum-group metal aluminide, where the platinum-group metal is platinum, palladium, rhodium, iridium or osmium, a silicon aluminide coating, a chromium aluminide, or a combination of one two or more of these. The MCrAlY coating may be deposited by plasma spraying, thermal spraying or HVOF. The plasma spraying may be vacuum plasma spraying or air plasma spraying. The aluminide coating may be deposited by aluminising, by depositing a platinum-group metal and diffusion heat treating and then aluminising, by silicon aluminising, chrome aluminising etc. The ceramic thermal barrier coating  80  may comprise stabilised zirconia, for example the ceramic thermal barrier coating  80  may comprise yttria stabilised zirconia. However, other suitable ceramics may be used. The ceramic thermal barrier coating may be deposited by plasma spraying, thermal spraying or HVOF. The plasma spraying may be vacuum plasma spraying or air plasma spraying. 
       FIG. 6  shows the portion of the tile  58 A after the thermal barrier coating  76  has been removed from the surface  75  at the second end  74  of each projection  70 . The thermal barrier coating  76  may be removed from the surface  75  at the second end  74  of each projection  70  by machining, e.g. by linishing or automated linishing or other suitable machining process. It is not necessary to remove the thermal barrier coating  76  from the angled side surfaces  73  of the projections  70 . 
       FIG. 7  shows the portion of the tile  58 A after effusion apertures, or passages,  82  have been formed through the tile  58 A. Each effusion aperture, or passage,  82  extends from the second surface  68  of the tile  58 A through the tile  58 A and through the respective projection  70  to the surface  75  at the second end  74  of the respective projection  70 . The tile  58 A has a thermal barrier coating  76  on the first surface  66  around each of the projections  70 . The effusion apertures, or passages,  82  are formed by machining from the surface  75  at the second end  74  of each projection  70  firstly through the respective projection  70  and then the main body of the tile  58 A to the second surface  68  of the tile  58 A. Preferably each effusion aperture, or passage,  82  is formed by electro-discharge machining, but other suitable methods may be used. 
     The surface  75  at the second end  74  of each projection  70  may be arranged at a first distance from the first surface  66  of the tile  58 A and the thermal barrier coating  76  has a first thickness. The first distance may be equal to or greater than the first thickness. The second end  74  of each projection  70  is cooled by the coolant, air flowing through the respective effusion aperture  82  and this prevents burning or loss of metal from the second ends  74  of the projections  70 . 
       FIG. 9  shows a turbine blade  90  which comprises a root portion  92 , a platform portion  94  and an aerofoil portion  96 . The aerofoil portion  96  is provided with a thermal barrier coating  98  on its outer surface and a plurality of effusion apertures, or passages,  100  extend through the aerofoil portion  96  of the turbine blade  90 . The effusion apertures  100  are provided in projections extending from the outer surface of the aerofoil portion  96  of the turbine blade  90  and the thermal barrier coating  98  surrounds all of the projections in a similar manner to that described for the tiles of the combustion chamber with respect to  FIGS. 2 to 8 . The turbine blade  90  is manufactured from a suitable metal or metal alloy for example an iron superalloy, a cobalt superalloy or preferably a nickel superalloy, e.g. CMSX4, CMSX10 and is produced by casting. The turbine blade, or turbine vane, may be produced by directional solidification to produce a directionally solidified component, or to produce a single crystal component, or alternatively may be an equiaxed component. 
     As shown in  FIGS. 4 to 7  the projections  70  are tapered at one side, they have an angled side surface  73 , to allow the effusion apertures  82  to be arranged at an angle between 90° and 0° to the first surface  66  of the tile  58 A. The projections  70  have a greater cross-sectional area at the first end  72  than the second end  74 . However, it may be possible for the projections  70  to be cylindrical in the case of effusion apertures  82  arranged at 90° to the first surface  66  of the tile  58 A. Other suitable shapes of projections  70  may be used, for example the projections  70  could be tapered on all sides, the angled side surface  73  extends all around the projection  70 , such that they have a greater cross-sectional area at the first end  72  than at the second end  74 , e.g. the projections  70  may be conical and decrease in diameter from the first end  72  to the second end  74 . 
     For example the effusion apertures have a diameter of at least 0.5 mm and up to 1 mm and the projections have a diameter of at least 1 mm and up to 2 mm. The thermal barrier coating may have a thickness of up to 1 mm, the ceramic thermal barrier coating may have a thickness of up to 0.5 mm and the metallic bond coating may have thickness of up to 0.5 mm and the projections have a height, a first distance from the surface of the article, of at least the thickness of the thermal barrier coating, e.g. up to 1 mm. 
     The present invention provides a thermal barrier coated article, the article having a first surface and a second surface, the article having at least one projection extending from the first surface in a direction away from the first surface and away from the second surface, the projection having a first end adjacent the first surface and a second end remote from the first surface, the article having at least one passage extending from the second surface of the article through the article and through the at least one projection to the second end of the at least one projection and the article having a thermal barrier coating on the first surface around the at least one projection. 
     In a preferred embodiment the present invention provides a thermal barrier coated article with a plurality of projections extending from the first surface in a direction away from the first surface and away from the second surface, each projection having a first end adjacent the first surface and a second end remote from the first surface, the article having a plurality of passages extending from the second surface of the article, each passage extending from the second surface of the article through the article and through a respective one of the projections to the second end of the respective projection and the article having a thermal barrier coating on the first surface around each of the projections. 
     The article may be a combustor tile, a turbine blade or a turbine vane for a gas turbine engine. 
     The advantage of the present invention is that it provides a positive feature, a projection, at each desired aperture position in the article which allows the thermal barrier coating to be removed from the projection thus revealing the metallic article at each desired aperture position. This allows the aperture to be formed through the projection and article by electro-discharge machining due to the formation of an electrically conducting path by the uncovering of the projection. The present invention provides an article with a robust thermal barrier coating with no delamination of the thermal barrier coating and un-blocked effusion apertures and the article can be produced in a production worthy cost effective method. 
     In a further method of the present invention if it is determined that there is a problem of burning of the second ends of the projections the dimensions, e.g. diameter, of the projections may be adjusted, made smaller, such that the electro-discharge machining process produces the effusion aperture and also machines away at least a portion of the projection, reduces the height of the projection, to obviate the problem of burning, e.g. the second end of the projection may be located at a first distance from the first surface which is less than the first thickness of the thermal barrier coating.