Method for providing cooling channel systems for high-temperature components coated with coatings

Abstract

A method for providing a fluid cooling system in a high-temperature component comprising the following steps: a) providing a high-temperature component (100) having an outer surface (104); b) creating a plurality of adjacent separate microchannels (110) as open grooves extending into and along at least a portion of the outer surface (104) of the high-temperature component (100), wherein the microchannels (110) are created in the outer surface (104) by means of a technique selected from the group consisting of laser machining, abrasive liquid jet cutting, electrical discharge machining (EDM), milling electrical discharge machining, electron beam drilling, and CNC machining; c) creating one or more coolant passage holes (112) extending from at least one of the microchannels (110) to an interior region (114) of the high-temperature component (100); d) filling the microchannels (110) and the one or more coolant passage holes (112) with a filler material (120); e) applying a first layer of a metallic build-up coating (130, 152) over the outer surface (104); f) creating at least one slot (132) or a set of relatively small passive cooling holes (132) through the first layer of the metallic buildup coating (130, 152), the slot or passive cooling holes (132) extending into at least a portion of one of the filled microchannels (110) formed substantially beneath the slot or passive cooling holes (132); g) removing the filling material (120); and h) applying at least a second coating layer (140, 158, 160) over the first layer.

Description

BACKGROUND OF THE INVENTIONGenerally, the invention relates to methods for providing cooling channel systems for high temperature components covered by protective coatings and cooled by various airflow systems. In some specific applications, the high temperature components are part of a gas turbine engine.Turbine systems are widely used in fields such as power generation. A conventional gas turbine system used for power generation includes a compressor, a combustor, and a turbine. Typically, such a gas turbine system produces high temperature streams of gas through a flow path defined by the components of the turbine. Higher temperature flows are generally desirable because they can result in improved performance, efficiency, and energy output of the gas turbine system. The high temperature flows are typically associated with or indicate combustion types and flow conditions associated with proper functioning of the gas turbine system. (Generally, combustion gases may exceed about 1600-1700° C., which is higher than the melting points of the engine components), for example, during gas turbine operation.As expected, such high temperatures can cause too much heating of the components in the flow path. Such heating, in turn, may cause one or more of these components to be damaged or to move outside of the "specification", resulting in a shortened operating life. Thus, due to the desirability of these high temperature flow conditions in a correctly operating system, the components exposed to high temperature flows must be cooled to enable operation of the gas turbine system with flows at elevated temperatures.A number of strategies may be employed for cooling components exposed to high temperature flows. These components are typically known as "hot gas path components.". However, many of the cooling strategies employed result in comparatively low heat transfer rates and non-uniform component temperature profiles, which may be insufficient to achieve desired cooling. Some of the cooling strategies may also reduce overall efficiency of the turbine because they redirect too much cooling air from the compressor of the engine.For additional protection from the high temperature gas flow, the exposed outer walls of the hot gas path components may be covered with a thermal barrier coating (TBC) system that provides thermal insulation. TBC systems typically include at least one ceramic coating and an underlying metallic bonding layer. The advantages of thermal barrier coating systems are generally known.In most of these exemplary gas turbine engine components, thin metal walls of high strength superalloy metals are typically used for improved durability while minimizing their cooling requirements. Various cooling circuits and features are tailored for these individual components in their respective environments in the engine. For example, a series of internal cooling passages or serpentines may be formed in a hot gas path component. A cooling fluid may be supplied to the serpentines from a plenum and the cooling fluid may flow through these passages to cool the substrate and the coatings of the hot gas path component. However, this cooling strategy results in relatively low heat transfer rates and non-uniform component temperature profiles.Microchannel cooling has the potential to significantly reduce cooling requirements by placing the cooling devices as close to the heated zone as possible. In this way, the temperature difference between the "hot side" and the "cold side" of the main load bearing substrate material of a component can be significantly reduced for a given heat transfer rate. The formation and use of micro-cooling channels is described in pending U.S. application S.N. 12 / 953,177 (Ronald Bunker et al.) filed November 23, 2010, and assigned to the assignee of the present application. Additional details regarding these channels are discussed below. Substantially, the channels are created in an outer surface of the hot gas path component and are configured to allow passage of a cooling fluid, such as compressed air, originating from the turbine compressor. The flow of the cooling fluid can thereby cool adjacent or directly adjacent regions of the components by convective cooling. For example, this type of cooling system may remove heat from the component or transfer heat from one or more of the protective layers disposed on the component to the cooling medium.Although the use of microchannels can provide the aforementioned attributes, some disadvantages remain in this type of cooling system scheme - particularly in the case of gas turbine components. For example, in some cases, the deposition of protective layers over the channels typically requires the use of a sacrificial material to fill the channels and the underlying vias prior to the deposition process. The required removal of the sacrificial material (e.g., by leaching after the coatings are applied may be a slow process). There are only a limited number of outlets for the sacrificial material, such as the lower access points for the outlet holes, and these outlets are relatively small.Further, in this type of cooling system, the TBC system is particularly important for protecting the substrate from adverse environmental and thermal effects. (The TBC also provides an aerodynamically smooth surface for the coolant flow.). However, loss of parts of the TBC system, due to damage or general coating failure, leaves the underlying microchannel open on its outer surface and thereby exposed directly to the hot gas temperatures. This, in turn, can result in severe damage to the component.In view of these considerations, new methods and structures for improving cooling capabilities in gas turbines and other high temperature components would be justified in the art. The innovations should improve the performance of the cooling system and the use of microchannels and cooling apertures without significantly reducing turbine efficiency. Further, there is considerable interest in improving manufacturing processes used in forming the cooling system and protective coating systems. Further, cooling system structures that provide additional coolant flow in the event of a partial TBC failure become of considerable value. The film cooling structures should also not compromise the strength and integrity of the turbine part.DE 197 37 845 A1 discloses a method for providing a fluid cooling system in a high temperature component comprising: casting a high temperature component while simultaneously forming a plurality of pin shaped protrusions on an outer surface of the high temperature component defining a single continuous cavity around the plurality of pin shaped protrusions; forming coolant vias at a plurality of locations from the continuous cavity to an interior of the component; filling the continuous cavity with a filler material; applying a layer of a metallic pattern coating over the outer surface of the high temperature component; inserting a plurality of film cooling holes therethrough into the layer of the metallic pattern coating; and removing the filler material from the continuous cavity, for example, by leaching.EP 1 375 825 B1 discloses applying an additional bonding layer and a thermal barrier coating on the outer surface of a high temperature component to seal film cooling holes formed through the wall of the high temperature component to achieve passivation of the cooling holes, to reduce the amount of cooling air required and to improve cooling efficiency.Brief Description of the InventionThe invention is directed to a method of providing a fluid cooling system in a high temperature component. The method comprises the steps of: a) providing a high temperature component having an outer surface; b) creating a plurality of adjacent separate microchannels as open grooves extending into and along at least a portion of the outer surface of the high temperature component, the microchannels being created in the outer surface using a technique selected from the group consisting of laser machining, abrasive fluid jet cutting, electrical discharge machining (EDM), milling electrical discharge machining, electron beam drilling, and CNC machining; c) creating one or more coolant through holes extending from at least one of the microchannels to an interior of the high temperature component; d) filling the microchannels and the one or more coolant through holes with a filler material; e) applying a first layer of a metallic build-up coating over the outer surface; f) creating at least one slot or set of relatively small passive cooling holes through the first layer of the metallic build-up coating, the slot or passive cooling holes extending into at least a portion of one of the filled microchannels formed substantially below the slot or passive cooling holes; g) removing the fill material; and h) applying at least one second coating layer over the first layer.Brief Description of the DrawingsFIG. 1 is a schematic illustration of a gas turbine system. FIG. 2 is a schematic cross-section of an exemplary airfoil configuration with a coating system applied over an outer surface of the airfoil. FIG. 3 is a cross-sectional view of a high temperature substrate in which microchannels and passive cooling holes are formed. Fig. 4 is a cross-sectional view of the substrate of Fig. 3 in which microchannels have been formed. Fig. 5 is a cross-sectional view of the substrate of Fig. 4 in which through holes have been formed through the substrate. FIG. 6 is a cross-sectional view of the substrate of FIG. 5 in which a filler material has been deposited. Fig. 7 is a cross-sectional view of the substrate of Fig. 6 in which a first coating layer has been deposited. Fig. 8 is a cross-sectional view of the substrate of Fig. 7 in which passive cooling holes have been formed. Fig. 9 is a cross-sectional view of the substrate of Fig. 8 in which the filler material has been removed. Fig. 10 is a perspective view of the substrate of Fig. 9. FIG. 11 is a perspective view of a substrate similar to FIG. 9 according to an alternative embodiment. Fig. 12 is a cross-sectional view of the substrate of Fig. 9 in which a second layer of make-up coating material has been applied over the first layer. FIG. 13 is a cross-sectional view of a portion of another high temperature component.DETAILED DESCRIPTION OF THE INVENTIONEach embodiment presented below enables explanation of certain aspects of the invention and should not be viewed as limiting the scope of the invention. Furthermore, an approximating language, as used throughout the specification and claims herein, may be used to modify any quantitative representation that may vary as permitted without resulting in a change in the basic function to which it relates. Accordingly, a value modified by a term or terms such as "about" is not limited to the specified precise value. In some cases, the approximating language may correspond to the accuracy of an instrument for measuring the value.In the following description and claims, the singular forms "a," "an," and "the" are intended to include multiple referents unless the context clearly dictates otherwise. As used herein, the terms "may" and "may be" indicate a possibility of occurrence in a set of possibilities; ownership of a specified property, characteristic, or function, and / or qualify another verb by expressing one or more of an skill, fitness, or possibility associated with the qualified verb. Accordingly, the use of "may" and "may be" indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capability, function, or use, while simultaneously considering that in some circumstances the modified term is not appropriate, capable, or suitable.FIG. 1 is a schematic illustration of a gas turbine system 10 in simplified form. The system may include one or more compressors 12, burners 14, turbines 16, and fuel nozzles 20. The compressor 12 and the turbine 16 may be connected by one or more shafts 18.The gas turbine system 10 may include a number of hot gas path components 100. A hot gas path component is any component of the system 10 that is at least partially exposed to a high temperature gas flow through the system 10. For example, blade assemblies (also known as rotor blades or rotor blade assemblies), nozzle assemblies (also known as vanes or vane assemblies), shroud assemblies, transition pieces, support rings, and compressor output components are all hot gas path components.FIG. 2 is a top view cross-section of an exemplary airfoil component 50 shown in simplified form (e.g., coolant feed holes are not shown). The airfoil 50 includes a substrate 52 having an outer surface 54 and an inner surface 56. the inner surface defines at least one hollow interior 58. As discussed further below, the outer surface 54 includes one or more microchannels 59 extending into the surface region. As will also be detailed in the description below, a coating system 60 is disposed on the outer surface.Referring to FIG. 3, a component or part 100 (e.g., a portion of the airfoil shown in FIG. 2 ) may be manufactured by any conventional means, such as casting. The component includes a substrate 102 in which one surface 104 is the exterior or outward facing surface of the component and the opposing surface 106 is an internal or inward facing surface. The part is typically cast prior to the formation of microchannels described below.Component 100 may be made from various alloys used in high temperature components. Many are described in U.S. Patent 5,626,462, the entire contents of which are incorporated herein by reference. Depending on the desired application for the component, it may be made of Ni-based, Co-based or Fe-based superalloys. The component may also be made of an intermetallic NiAl alloy, since these alloys are known to have a combination of superior properties including high temperature strength and high temperature creep resistance. (These properties are advantageous for use in turbine applications used for aircraft and land-based power generation).Referring to FIG. 4, microchannels 110 (also sometimes referred to herein as "microcooled channels", or simply "channels") are created in the outer surface 104 of the part 100 according to these embodiments. As used in this specification, the term "microchannel" is essentially (although not always) meant as a reference to a channel or passage that is at least an order of magnitude smaller, e.g., in the width direction, than other passages or channels formed in or adjacent to a gas turbine or other high temperature component. As described further below, a microchannel may have an average width of about 1 mm, while other types of passages associated with the component may have an average width of greater than about 10 mm. Further, most microchannels are disposed on or in a surface of a part, while many of the types of larger channels are not formed on a surface, but instead are enclosed within the casting envelope of the part or are incorporated within the boundaries of the casting.In accordance with most embodiments, the channels 110 illustrated in FIG. 4 are configured to allow a cooling fluid to flow therethrough. The flow of cooling fluid may thereby cool adjacent or immediately adjacent portions of component 100 by convection cooling, as further described below. As also mentioned below, the microchannels may extend transversely across a considerable length or span of the component, e.g., substantially along the course of the hot gas path, in a selected region of the component, although in some cases they may also extend only across a portion of the span.The channels 110 may be formed or machined under the control of a programmed or otherwise automated process (such as a robotic process) to achieve the desired size, placement, and / or configuration of channels in the exterior surface 104. The channels 110 are created in the outer surface 104 using laser machining, abrasive liquid jet (e.g., micro water abrasive jet (AμWJ)), electrical discharge machining (EDM), milling electrical discharge machining (milling EDM), electron beam drilling, or CNC machining capable of creating channels of appropriate sizes and tolerances.The channels are formed in a wide variety of shapes and sizes. The aforementioned copending application S.N. 12 / 953,177 (Bunker et al.), incorporated herein by reference, describes many possible features for various types of microchannels. Other features, such as "recessed" shaped channels, are described in S. N. 12 / 943,624 (Bunker et al., filed November 10, 2010), which is also incorporated herein by reference. (In this disclosure, the open portion of the channel is sometimes referred to as a "groove"). Illustration may be provided with reference to FIG. 6 of S. N. 12 / 943,624 and with reference to FIG. 7 of the present disclosure discussed below. In this alternative, the base 111 of the microchannel could be substantially larger than the top region 113 of the microchannel, e.g. at least 2 times wider. This type of geometry may sometimes be helpful during deposition of the overlying metallic coating.In some embodiments, the channels 110 may have depths ranging from about 0.2 mm to about 2 mm, or from about 0.5 mm to about 1 mm. Further, in certain embodiments, the channels 110 may have widths in a range from about 0.2 mm to about 2 mm, or from about 0.5 mm to about 1 mm. Further, the widths and / or depths may be substantially constant for a channel 110, or may vary (e.g., increase, decrease, taper, etc.) over the path of the channel 110.Further referring to FIG. 4, the channels 110 may have cross-sections of any suitable geometric shape, such as square, rectangular, oval, or triangular, or any other geometric shape that allows a cooling medium to flow through the channel 110. It should be understood that different channels 110 may have cross-sections with a particular geometric shape, while other channels 110 may have cross-sections with a different geometric shape. Additionally, in certain embodiments, the surface (i.e., the sidewalls and / or the bottom) of a channel 110 may have a substantially smooth surface, although in other embodiments, all or portions of the channel surface may have protrusions, recesses, a surface texture, or other features such that the surface of the channel is not smooth. For example, surface features that may be present on the surface of the channel may include, but are not limited to, lamellar protrusions, cylindrically shaped protrusions, swirl elements, or any other combination, as well as any other suitable geometric shape. It should be appreciated that the dimensions of all surface features that are present may be selected to optimize the cooling provided by the corresponding channel 110.The channels 110 may be substantially straight channels, or may be substantially curved or serpentine channels. For example, all or a portion of the channels 110 may be provided as complex curves, or as a three-dimensional configuration with respect to the outer surface 104 of the substrate 100. Indeed, the configuration of the channels 110 may be specific to the component being manufactured such that certain portions of the component may have a higher density of cooling channels 110 than others. That is, the configuration of the channels can be specially adapted in use, taking into account the expected heat profile of the component, as is also described in application S. N. 12 / 953,177 (Bunker et al.).Referring to FIG. 5, one or more through holes 112 may be pierced or drilled to connect some or all of the channels 110 to an interior region 114 of the component, such as a spar interior. The through holes are sometimes referred to herein as "coolant supply holes" or "coolant through holes", describing their typical function. As shown, the holes 112 may extend substantially through the substrate 102 and may fluidly connect the channels 110 to the interior 114, as well as fluidly connect some or all of the channels 110 to each other via the interior 114. For example, each channel 110 may be fluidly connected to at least one of the holes 112. The size of the through holes may vary somewhat, but usually have an average diameter of about 0.25 mm to about 0.76 mm (10 mils to 30 mils). Further, although the holes are depicted as being perpendicular within the substrate 102 with respect to surfaces 104 and 106, the angle of the hole may vary substantially, depending in part on the desired cooling configurations. Many techniques can be used to create the vias, such as the methods referred to for microchannels.Once the manufacture of the part 100 is complete and the channels 110 are covered with a build-up coating layer and / or other layer as discussed below, the through holes 112 may allow a cooling medium provided via the interior 114 to flow to the channels 110. For example, once a build-up coating layer is present over the respective channels 110, at least one cooling circuit may be defined in or on the surface of the part 100 by a respective fluidic connection of the interior space 114 to one or more channels 110 via respective through holes 112. As described below with reference to FIG. 13, the cooling circuit may also include an exhaust hole constituting a part of the exhaust area for the microchannels. These exit holes are sometimes referred to as "film holes" that penetrate all coatings to reach an exterior region 115 of component 100.With further reference to FIG. 5, the cooling medium may flow through a cooling circuit defined by these features depending on the total pressure difference from the inlet to the outlet of the cooling circuit. This pressure differential may cause a portion of the cooling medium enclosed in the cooling circuit to flow into and through the through holes 112 and from the holes 112 into and through the channels 110 to one or more exit holes, thereby completing the cooling circuit from the interior of the portion to the exterior.Referring to FIG. 6, and in accordance with this embodiment, microchannels 110 and through holes 112 are then filled with one or more solid fill materials 120. These materials, which can be chemically removed during a step discussed below, are often referred to as "sacrificial materials.". Its primary object is to prevent the penetration of a coating material into the microchannels and through holes during subsequent coating steps.A variety of different sacrificial or fill materials may be used. They are usually ceramic materials (e.g. ceramic core materials) or metallic materials (e.g. metal alloys or metal inks). However, in some cases (depending on the temperatures used for subsequent coating depositions), UV curable resins (e.g., polymeric materials) or graphite may be used as sacrificial material. The material should be one with a consistency that allows insertion into the depth of the through holes.Suitable metallic materials that may be used to produce the solid metal fill material may include, but are not limited to, copper, aluminum, molybdenum, tungsten, nickel, monel, and nichrome. In some specific embodiments, the fill material 120 is a solid wire fill material made of an elemental or alloy metal material. For example, the filler material may be a deformable material, such as an annealed metal wire, which, when mechanically pressed into the channel 110, is deformed to conform to the shape of the channel 110. The above-mentioned pending application S.N. 12 / 953,177 describes this technique. (It will be appreciated that the term "wire" as used herein refers to a solid continuous piece of material that conforms to the cross-sectional shape of the respective channels 110 or can be mechanically deformed to conform.).With continued reference to FIG. 6, in some embodiments, the metal or metal alloy material may be provided as a powder that is pressed into the channel 110 and conforms to the channel to substantially fill the channels 110 and the through hole 112. Any portion of the solid metal fill material that protrudes from the channel 110 (i.e., overfill) may be polished or worked prior to the application of coatings as discussed below. The outer surface 104 of the substrate 102 may then be cleaned and prepared for coating. Exemplary treatment techniques include machining, sandblasting, washing, polishing, or various combinations thereof.A metallic build-up coating 130 is then applied over the substrate surface as shown in Figure 7. A number of metallic coatings may be employed if they can be deposited to form a substantially nonporous structure. (The metallic coatings also adhere strongly to the substrate as compared with a ceramic coating.). Non-limiting examples of such metallic coatings include metal aluminides such as nickel aluminide (NiAl) or platinum aluminide (PtAl). Further examples include compositions having the formula MCrAl (X) wherein "M" is an element selected from the group consisting of Fe, Co, and Ni, and combinations thereof, and "X" is yttrium, tantalum, silicon, hafnium, titanium, zirconium, boron, carbon, or a combination thereof. Other suitable metallic coatings (including other types of "MCrAl(X)" compositions) are also described in the referenced application S.N. 12 / 953,177, U.S. Patent 6,511,762 (Lee et al.), which is incorporated herein by reference, and in the aforementioned U.S. Patent 5,626,462. Further, in some cases, the build-up coating 130 may be constructed from a superalloy (Ni-, Co-, or Fe-based) material, such as a material similar or identical to that forming the substrate 102.The first build-up coating 130 may be applied using a variety of techniques. Non-limiting examples include physical vapor deposition (PVD) processes such as electron beam (EB), ion plasma deposition, or sputtering). Thermal spraying processes may also be used, such as air plasma spraying (APS), low pressure plasma spraying (LPPS), high speed oxygen / fuel spraying (HVOF), or high speed air / fuel spraying (HVAF). The choice of a particular technique will depend on various factors, such as the specific type of coating applied, the desired thickness, the size of the channel, the size and number of parts to be coated, and the type of sacrificial material used. In some cases, ion plasma deposition is particularly suitable. One such system is referred to as cathodic arc ion plasma deposition. It is described in U.S. Patent Application Publication No. 2008 / 0138529, Weaver et al., issued June 12, 2008, which is incorporated herein by reference.The thickness of the metallic build-up coating depends on various factors. These include: the specific type of coating, the type of coatings applied thereover, and the design stress / stress characteristics of the coating at its interface with the substrate. Typically, the coating is at least about 0.13 mm (5 mils) thick. In most embodiments, the thickness is in the range of about 0.1 mm to about 1 mm.A set of relatively small passive cooling holes is then formed through the metallic build-up coating along the course of one or more of the microchannels. As shown in FIG. 8, the passive holes 132 extend through the metallic coating 130 and into the sacrificial material 120 filling the microchannels 110. The passive cooling holes may be formed by a variety of techniques, most of which have been described above with reference to the through holes 112. Examples of these techniques include EDM, lasers and abrasive water jet systems.Passive holes 132 are typically (but not always) equidistantly spaced in a uniform pattern. Although the passive holes are shown as being perpendicular with respect to the surface 104, they may be formed or "angled" at various angles from the perpendicular orientation. Further, the passive holes need not be aligned with the center of the microchannel (e.g., in the width direction in the figure) and may (even individually) be off-center on the bottom of the channel.As mentioned above, the passive cooling holes 132 are relatively small compared to the size of the cooling passage holes 112 as shown in FIG. 9. Typically, the passive cooling holes have an average diameter in the range of about 0.13 mm (5 mils) to about 0.51 mm (20 mils), and in some cases from about 0.13 mm to about 0.38 mm (5 mils to 15 mils).After the passive cooling holes 132 are formed, the sacrificial / fill material is removed from the microchannels 110 and from the through holes 112. A number of conventional techniques may be used to remove the sacrificial material. Non-limiting examples include leaching, dissolving, melting, oxidizing, etching, and combinations thereof. The choice of the particular technique will depend on various factors, such as the particular composition of the sacrificial material, the internal shape of the coolant passages, and the composition of the substrate and the coating. Often, the removal of the filler material is carried out by immersing the component in a suitable treatment bath. As described below, the presence of the passive cooling holes (see, for example, FIG. 9 ) may advantageously accelerate removal of the filler material.FIG. 10 is a perspective view of the general structure of FIG. 9 illustrating a substrate 102, an outer surface 104, microchannels 110, and an ordered array of through holes (e.g., coolant feed holes) 112. Passive cooling holes 132 are also shown extending through the metallic layer 130 into different portions of microchannels 110. As mentioned above, the passive holes 132 need not be arranged in an ordered array and need not be arranged along a uniform axis along the course of any microchannel 110.Figure 11 is a perspective view of an alternative embodiment in which at least one row of passive cooling holes in Figure 10 is replaced with a slot 133. (All other elements in the figure may be considered to be the same as those for Fig. 10). Although only one slot (and with any width) is shown here, in some embodiments, one slot is present instead of each row of passive cooling holes. It may be desirable to form these slits in some cases instead of the holes in order to more evenly distribute the compressive stress that may result from the layers deposited over the slit. The layers may be formed by many of the techniques described above, e.g., abrasive liquid jet, EDM, and the like. Further, instead of just one slot along a particular dimension on the surface, a series of discrete smaller slots may be used.The size of the slots is somewhat variable, although in many cases the width of the slot (i.e. the direction horizontal to that of the slot span) is approximately equal to the diameter of the passive holes used in the other embodiment. Further, the slits may be thought of as having an average width smaller than about 50% of the average diameter of the coolant supply holes (not shown in this figure). Further, the slots need not be positioned directly above a central longitudinal axis of the microchannels, but may be off-center. The slots may also include inclined side walls. Most of these variations are determined by the particular cooling configuration desired for the component.With further reference to the formation of the passive cooling holes last described with reference to FIG. 8, a second metallic make-up coating layer 140 is then applied over the first coating 130 in this embodiment as shown in FIG. 12. The second coating layer 140 covers and makes the upper outlet 142 of each of the passive cooling holes 132 "passive" as described below. As in the case of the first coating, the second coating for this embodiment is also substantially nonporous and may be formed from any of the metallic materials described above, such as superalloys, metal aluminides, MCrAl(X) materials, and the like. As a non-limiting example, the second coating could be formed of an MCrAl(X) material if the first coating is formed of a superalloy material. The coating may also be applied by any of the techniques described above.The thickness of the second metallic make-up coating depends on various factors, such as some of those listed above for the first layer. The second layer should be sufficiently thick to "bridge" the passive cooling holes 132 and adequately support a subsequently deposited ceramic material. Typically, the second coating is at least about 0.1 mm thick. In most cases, the thickness is in the range of about 0.1 mm to about 0.5 mm. (In some embodiments, at least one metallic coating may be applied more (e.g., a third layer).In some embodiments, a component as described herein may be adequately protected with two or more metallic coatings covering selected exterior surfaces. However, in many embodiments, the high temperature component may also include at least one overlying ceramic coating as mentioned above. In these cases, the underlying metallic coating often functions in part as an adhesion layer, as also already mentioned above.Thus, in many embodiments, at least one ceramic coating is deposited over the second metal build-up layer (or over the top surface of the upper metal layer if more than two layers are disposed on the substrate). As mentioned above, the ceramic coating is typically in the form of a thermal barrier coating (TBC), and may include a variety of ceramic oxides such as zirconia (ZrO 2), yttria (Y 2 O 3), magnesia (MgO), and combinations thereof. In a preferred embodiment, the TBC comprises yttria stabilized zirconia (YSZ). Such a composition creates a strong bond with the underlying metallic layer and provides a relatively high degree of thermal protection for the substrate. (United States Patent 6,511,762 provides a description of some aspects of TBC coating systems.).The TBC may be deposited using a number of techniques. The choice of a particular technique will depend on various factors such as the coating composition, its desired density, the composition of the underlying metallic layer(s), the area to which the coating is applied, and the shape of the component. Non-limiting examples of suitable coating techniques include PVD and plasma spraying techniques. In some cases, it is desirable that the TBC have some degree of porosity. For example, a YSZ porous structure may be formed using PVD or plasma spraying techniques.The thickness of the TBC depends, in part, on the factors discussed above with respect to the metallic coatings. The thermal environment in which the component operates is a key factor, as is the end use of the part and the number of TBC layers deposited. Typically, but not always, TBCs used for stationary turbines have a total thickness in the range of from about 0.08 mm to about 1.14 mm (3 mils to 45 mils). Typically (but not always), for aeronautical applications (e.g., TBC's using jet engines), a total thickness is in the range of between about 0.03 mm to about 0.51 mm (1 mil to about 20 mils).In further embodiments, the TBC may be deposited directly over the first metallic build-up layer, i.e., over layer 130 in FIG. 9. For example, the TBC may sometimes provide sufficient coating strength for placement over only one metallic layer if the passive cooling holes are quite small in size, e.g., less than about 0.1 mm in diameter (4 mils). As in the other embodiments, multiple TBC layers may be deposited, such as is disclosed in the aforementioned U.S. Pat. No. 6,511,762 to Lee et al.Fig. 13 is a cross-sectional view of a portion of another high temperature component, e.g., a turbine airfoil, that may be made by the method of the present invention. In this figure, a microchannel 142 formed in the substrate 144 is illustrated. A coolant passage hole 146 is shown communicating with the channel 142 (i.e., with the opening in the channel bottom surface 148) and providing a conduit to an interior region 150 of the airfoil.A first build-up coating layer 152 formed from a metallic material is shown disposed over an outer surface 154 of the substrate 144. A series of passive cooling holes 156 are shown extending through build-up layer 152. In this embodiment, the build-up layer 152 is covered by a second metallic build-up layer 158. A ceramic-based thermal barrier coating 160 is disposed over the sheet 158. (The coatings 152, 158, and 160 may collectively be referred to as a "protective coating system" 162). (As noted above, in alternative embodiments, the layer 150 could be a ceramic TBC with or without a second TBC 160 in some cases.).The through hole 164 opens into an exit region or "trench" 166 defining an exit region for the microchannel 142. A number of trenches may be formed through the coating system 162 depending on the cooling flow pattern for the airfoil. The trenches may be formed by any of the techniques described above.In the context of a turbine airfoil serving as a high temperature component, the passive cooling holes described above represent at least some important attributes for cooling systems that rely on microchannels and thermal barrier coating systems. First, they provide additional outlets for the removal of filler materials (e.g., by the leaching technique mentioned above) after the initial coating is applied to the component. Second, they provide additional passages / paths for cooling air that travels to the exterior of the component in the event that the overlying protective coating fails, i.e., when a portion of the coating system 162 (FIG. 13 ) is damaged or separated from the substrate 144. In other words, cooling fluid flowing from a source in the interior region 150 of the component is directed into the through holes 146 on the bottom surface 147. A portion of the coolant may flow upward (as viewed in the orientation of FIG. 1 ) into the microchannel 142 and passive cooling holes 156. This airflow provides additional useful film cooling for portions of the airfoil lacking protection of the damaged or absent TBC. In this way, the small cooling holes are effectively converted from coating-sealed "passive holes" to bare "active holes".From the foregoing description, it should be appreciated that a high temperature component formed by the method of the present invention includes an outer metal wall having a plurality of microchannels therein, wherein a series of through holes (e.g., coolant feed holes) each extend from a bottom surface of one of the microchannels into an interior region of the component. The outer wall is covered by at least one metallic coating and in some cases by at least one overlying thermal barrier coating (TBC). One or more slits or a plurality of relatively small passive cooling holes extend through a first layer of the metallic coating into at least a portion of one or more of the microchannels. The slot or slots or passive cooling holes are closed at the top end (i.e. immediately outside the outer wall) by at least one second coating layer, e.g. at least one metallic layer or at least one TBC layer or some combination thereof.The present invention has been described in terms of specific embodiments. They are intended for illustration only and should not be considered in any way as limiting. Thus, it should be understood that modifications may be made thereto which are within the scope of the invention and appended claims. Further, all of the patents, patent applications, articles, and texts mentioned above are incorporated herein by reference.A method of providing a fluid cooling system in a high temperature component is described. At least one microchannel is formed in an outer surface of the component and one or more coolant vias are then formed extending from at least one of the microchannels to an interior region of the component. A layer of a metallic build-up coating is then applied over the outer surface. At least one slot or set of relatively small passive cooling holes are then created through the first layer of the metallic build-up coating that extend into at least a portion of the microchannels. A second coating layer is then applied over the first layer. A sacrificial material is deposited in the microchannels before the first coating layer is deposited.

Claims

A method of providing a fluid cooling system in a high temperature component, comprising the steps of: a) providing a high temperature component (100) having an outer surface (104); b) creating a plurality of adjacent separate microchannels (110) as open grooves extending into and along at least a portion of the outer surface (104) of the high temperature component (100), wherein the microchannels (110) are created in the outer surface (104) using a technique selected from the group consisting of laser machining, abrasive liquid jet cutting, electrical discharge machining (EDM), milling electrical discharge machining, electron beam drilling, and CNC machining; c) creating one or more coolant passage holes (112) extending from at least one of the microchannels (110) to an interior region (114) of the high temperature component (100); d) filling the microchannels (110) and the one or more coolant vias (112) with a filler material (120); e) applying a first layer of a metallic build-up coating (130, 152) over the outer surface (104); f) creating at least one slot (132) or a set of relatively small passive cooling holes (132) through the first layer of the metallic build-up coating (130, 152), wherein the slot or passive cooling holes (132) extend into at least a portion of one of the filled microchannels (110) formed substantially under the slot or under the passive cooling holes (132); g) removing the filler material (120); and h) applying at least one second coating layer (140, 158, 160) over the first layer.The method of claim 1, wherein each coolant passage hole (112) is created using a technique selected from the group consisting of electro-chemical dip (ECM) machining, laser machining, laser drilling, abrasive liquid jet cutting, electrical discharge machining (EDM), and electron beam drilling.The method of claim 1, wherein the filler material (120) is selected from the group consisting of ceramic materials, metals, metal alloys, metal inks, curable polymeric materials, graphite, and combinations thereof.The method of claim 1, wherein the coolant passage holes (112) have an average diameter of 0.25 mm to 0.76 mm (10 mils to 30 mils).The method of claim 1, wherein the average diameter of the passive cooling holes (132) is less than 50% of the average diameter of the coolant passage holes (112).The method of claim 1, wherein the passive cooling holes (132) have an average diameter of 0.13 mm to 0.51 mm (5 mils to 20 mils).The method of claim 1, wherein the slot has an average width less than 50% of the average diameter of the coolant passage holes (112).The method of claim 1, wherein the first layer of the metallic build-up coating (130, 152) is constructed from a superalloy material, a metal aluminide, or a material having the formula MCrAl(X), wherein M is iron, cobalt, nickel, or a combination thereof, and X is yttrium, tantalum, silicon, hafnium, titanium, zirconium, boron, carbon, or a combination thereof.The method of claim 1, wherein the total thickness of the first layer of the metallic build-up coating (130, 152) is in the range of 0.1 mm to 1.0 mm.The method of claim 1, wherein the second coating layer (140, 158, 160) is a metallic build-up coating comprising a superalloy material, a metal aluminide, or a material having the formula MCrAl(X), wherein M is iron, cobalt, nickel, or a combination thereof, and X is yttrium, tantalum, silicon, hafnium, titanium, zirconium, boron, carbon, or a combination thereof.The method of claim 1, wherein the second coating layer (140, 158, 160) comprises a ceramic material.The method of claim 11, wherein the ceramic material is selected from the group consisting of zirconia (ZrO 2), yttria (Y 2 O 3), magnesia (MgO), and combinations thereof.

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