Abstract:
A hot gas path component ( 100 ) including: a metallic substrate ( 102 ) disposed beneath an outer surface ( 112 ) of the component ( 100 ) that is exposed to a hot gas present during operation of an internal combustion engine; a thermal barrier coating (TBC) ( 110 ) disposed on the metallic substrate ( 102 ) and defining a first portion ( 118 ) of the component outer surface ( 112 ); and a powder metallurgy structure ( 104 ) bonded to the metallic substrate ( 102 ) and in contact with the TBC ( 110 ).

Description:
FIELD OF THE INVENTION 
     The disclosure is related to powder metallurgy structures used in internal combustion engine components exposed to a hot working fluid. More particularly, the disclosure is related to components with powder metallurgy structures bonded to a metallic substrate and in contact with a thermal barrier coating. 
     BACKGROUND OF THE INVENTION 
     Gas turbine engines and other combustion engines operate using working fluid that generates tremendous forces at increasingly higher temperatures. As a result, different coatings have been employed to protect the metallic substrate from the high temperatures of the working fluid. However, these coatings are susceptible to ablation resulting from the operating forces and conditions resulting from high temperatures. In addition to protective coatings, various cooling fluid schemes have been utilized to cool the component, including those which cool the component from within, and those which form a protective film between the component and the working fluid. 
     However, even with existing coatings and cooling schemes, such extreme operating temperatures decrease the service life of the components. Furthermore, although it is possible and desirable to generate higher temperature working fluids, components utilizing existing materials and cooling schemes are unable to withstand such higher temperature working fluids and the components thereby limit the maximum operating temperature of the working fluid. As a result, improvements in materials and innovative cooling schemes may better protect hot gas path components from the extreme heat of the working fluid, which may in turn prolong component life, and even make possible the use higher temperature hot gasses. Consequently, there remains room in the art for improved protection schemes for hot gas path components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a schematic cross section of a hot gas path component showing powder metallurgy structures. 
         FIG. 2  is a schematic cross section showing a powder metallurgy structure filling in an excavation in a hot gas path component. 
         FIG. 3  is a schematic cross section of  FIG. 2  wherein the powder metallurgy structure also provides increased surface area for TBC adherence. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present inventors have devised an innovative way to use a powder metallurgy structure to help protect hot gas path components from high temperature working fluids. The versatility of the powder metallurgy structure enables improvements in both thermal barrier coating (TBC) (e.g. ceramic insulating material) layer protection schemes and cooling fluid protection schemes. In particular, with regard to TBC protection, the powder metallurgy structure provides opportunities to improve TBC adherence to the substrate. With regard to cooling fluid protection, the powder metallurgy structures improved distribution and control of cooling fluid within the component near the surface and fluid delivered to form a protective film between the component and the working fluid. These improvements can be employed individually or together in a single component. 
     As used herein, a substrate refers to a fully densified substrate, and a powder metallurgy structure refers to a green body of powder metal and a binder material that has been sintered into a powder metal structure. The powder metal may be nickel superalloy powder and may be the same chemical composition as the metallic substrate or may be of a different chemical composition. Control of the chemical composition of the powder metal and of the sintering process enables one to tailor properties of the resulting powder metal structure. Such properties include, but are not limited to, thermal properties and interconnected porosity. Control of thermal properties allows tailoring of the powder metal structure so that it may conduct or insulate as desired during operation of the internal combustion engine. When porous, the powder metal structure can be used to conduct fluid, in particular cooling fluid, therethrough. Control of the degree of interconnected porosity allows for control of the flow rate of the fluid flowing therethrough. 
     During manufacture of an internal combustion engine hot gas path component, a fully densified substrate (referred to hereafter as a metallic substrate), may be in its final form, and powder metallurgy structures may be positioned on the metallic substrate and heated, thereby simultaneously sintering the green body and adhering the green body to the metallic substrate as a powder metallurgy structure. The metallic substrate and the powder metallurgy structure together form a substrate. The metallic substrate may be plated prior to placing the powder metallurgy structure thereon, in order to aid bonding of the powder metallurgy structure to the metallic substrate. A TBC may then be applied to the metallic substrate and powder metallurgy structure (i.e. the substrate) to produce a component in final form. 
     The powder metallurgy structure chemical composition may be controlled such that the powder metallurgy structure may have an ability to withstand operating conditions on par with the metallic substrate, beyond that of the metallic substrate, or even less than that of the metallic substrate, depending on that for which the powder metallurgy structure is to be used. 
     In one embodiment, the powder metallurgy structure may be used to improve adherence of TBCs. TBCs are effective to provide thermal protection when properly anchored. However, if not sufficiently anchored, forces from the working fluid may be sufficient to damage the TBC, which may then flake and separate from the surface to which it is adhered. Loss of TBC or reduction of TBC layer thickness may in turn expose the protected material to more heat, and thereby reduce its service life. A powder metallurgy structure may be added to the surface of the metallic substrate and be shaped in such a manner that it provides more surface area for the TBC to adhere to than the powder metallurgy structure takes from the metallic substrate. As a result, there is a net increase in surface area to which the TBC may adhere, thereby increasing the strength of the TBC and reducing the changes that TBC will be lost during operation. 
     In another embodiment, the powder metallurgy structure may disposed on the surface of the metallic substrate and surrounded by TBC, but exposed to the working fluid, thereby defining part of the hot gas path surface of the component. The powder metallurgy structure may be in fluid communication with cooling fluid delivered by a compressor that is also part of the internal combustion engine. The fluid may pass through the powder metallurgy structure which, by virtue of its interconnected porosity, controls the rate of flow of the fluid. The fluid may subsequently form a protective film between the component and the working fluid. 
     In another embodiment, the powder metallurgy structure may be used to repair a hot gas path substrate that has sustained damage. Such damage may be a crack resulting from use in an internal combustion engine, or a production flaw. The damaged portion of the original substrate may be excavated so the entire damaged area is removed. The powder metallurgy structure may be shaped to fit into the excavation when sintered may return the repaired substrate to original dimensions, or may also provide additional surface area for a subsequently applied TBC to adhere. In an embodiment the repair may require multiple powder metallurgy structures and/or multiple sintering steps. 
     Turning to the drawings,  FIG. 1  shows a schematic cross section of a hot gas path component  100  (component). In this embodiment the component  100  comprises a metallic substrate  102 , powder metallurgy structures  104 ,  106 ,  108 , (“PM structures”) and a thermal barrier coating (TBC)  110 . Porous PM structures  104  comprise a degree of interconnected porosity effective to permit a fluid to flow therethrough. TBC adhering PM structures  106 ,  108  may or may not comprise a similar degree of interconnected porosity. TBC adhering PM assembled structures  106  comprise a plurality of PM structures (sub-structures) assembled and sintered together and to the metallic substrate  102 , while TBC adhering PM single structures  108  comprise a single PM structure sintered to the metallic substrate  102 . 
     In this embodiment the component  100  comprises a hot gas path surface  112  (path surface  112 ) that defines a hot gas path for a working fluid  114 . A thermal barrier coating (TBC)  110  is disposed on the metallic substrate  102  and surrounds the porous PM structures  104 . The path surface  112  comprises an exposed surface of the porous PM structure  116  (exposed surface  116 ) and an exposed surface of the TBC  118 . Disposed in the metallic substrate  102  are passageways  120  communicating a fluid  122 , such as a cooling fluid delivered by a compressor (not shown) to the exposed surface  116  of the powder metallurgy structure  104 . A passageway  120  and a respective powder metallurgy structure  104  form a cooling fluid path between the compressor and the exposed surface  116 , which is a portion of the hot gas path surface  112 . In operation, fluid  122  travels through a passageway  120  and into a porous PM structure  104 , cooling the metallic substrate  102  in the process. In particular, such a configuration provides cooling in a critical region of the component near the surface and the working fluid. Porous PM structure  104  may be configured to comprise a degree of interconnected porosity such that the porous PM structure  104  regulates the flow rate of the fluid  122 . Upon exiting the porous PM structure  104  through the exposed surface  116 , the fluid  122  flows along the path surface  112  to provide a protective film  124  between the working fluid  114  and the component  100 . This improved cooling may increase service life of the component, or even permit an increase in the temperature of the working fluid  114 . Furthermore, the porous PM structure  104  may better anchor the TBC  110  by increasing a surface to which the TBC  110  may adhere, and by providing mechanical interaction with the TBC  110 . 
     Porous PM structure  104  may comprise a concave surface  126  disposed over the passageway  122  if desired. Furthermore, the porous PM structure  104  may comprise a protruding undercut shape  128  effective to anchor the TBC  110  to the metallic substrate  102 . Metallic substrate  102  may comprise a recess  130  effective to position the porous PM structure  104  where desired, and also effective to increase an area of bonding  132  between the porous PM structure  104  and the metallic substrate  102 , thereby increasing a bonding force therebetween. Otherwise, an adhesive force of the bonding agent in the green body may be sufficient to adhere the green body to the metallic substrate  102  until sintered. 
     TBC adhering PM structures  106 ,  108  are bonded to the metallic substrate  102  and occupy a footprint  134  of a given surface area. However, the TBC adhering PM structures  106 ,  108  have an adhering surface  136  to which the TBC adheres, and the surface area of the adhering surface  136  is greater than the surface area of the footprint  134 . Consequently, the TBC adhering PM structures  106 ,  108  provide more surface to which the TBC may adhere, and this in turn increases the effectiveness of the TBC adherence. Improved adherence may better protect the component  100  from the high temperatures present in the working fluid  114 , thereby increasing service life of the component, or even permitting an increase in the temperature of the working fluid  114 . 
       FIG. 2  shows a repaired substrate  200  comprising an original substrate  202  where original substrate material has been removed to form an excavation  204 , and a PM repair structure  206 . In the context of a repair, the original substrate may have comprised only a metallic substrate or it may have comprised a metallic substrate and a powder metallurgy structure which together formed the original substrate. A repaired substrate  200  then comprises the original substrate less the excavated original substrate material and a powder metallurgy repair structure  206 . The original substrate incurred some sort of defect (not shown), such as a crack. The defect may have been in the metallic substrate portion or a powder metallurgy structure portion, or spanned both portions of the original substrate. The PM repair structure  206  may be formed through a replication process such that the PM repair structure  206  may be placed in the excavation  204  and sintered in place, and a subsequent powder metallurgy structure and subsequent sintering step may be employed. The repair may return the repaired substrate  200  to the same dimensions of the original substrate  202 . Alternatively, as shown in  FIG. 3 , the repaired substrate  300  may comprises a powder metallurgy repair structure  302  which comprises a projection  304  that extends beyond where original substrate stopped, thereby providing greater surface area than the original substrate. This may improve TBC adherence in the final component, and thus offer greater protection to the repaired substrate  300 . 
     It has been shown that the inventors have been able to use powder metallurgy structures to improve upon schemes used to protect a hot gas path component used in an internal combustion engine component. These powder metallurgy structures can be used to better anchor a TBC layer to a substrate, to improve cooling of a component internally and particularly near the surface of the component exposed to the hot working fluid, to protect the component from the working fluid by providing a film of cooling fluid between the component and the working fluid, or any combination of the above. Such improvements in component protection may extend the service life of the component and even permit higher working fluid temperatures. Consequently, the embodiments disclosed herein represent innovation in the art. 
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.