Patent Application
20180015536
The invention relates to methods for forming cooling passages in superalloy substrates of combustion turbine components, such as engine blades, vanes, or transitions. More particularly, the invention relates to formation of partially completed cooling passages in such superalloy components during investment casting, by use of ceramic shell inserts, with projecting ceramic posts, then completing the passages in the castings.
Known turbine engines, including gas/combustion turbine engines and steam turbine engines, incorporate shaft-mounted turbine blades circumferentially circumscribed by a turbine casing or housing. The remainder of this description focuses on applications within combustion or gas turbine technical application and environment, though exemplary embodiments described herein are applicable to steam turbine engines. In a gas/combustion turbine engine, hot combustion gasses flow in a combustion path that initiates within a combustor and are directed through a generally tubular transition into a turbine section. A forward or Row 1 vane directs the combustion gasses past successive alternating rows of turbine blades and vanes. Hot combustion gas striking the turbine blades cause blade rotation, thereby converting thermal energy within the hot gasses to mechanical work, which is available for powering rotating machinery, such as an electrical generator.
Engine internal components within the hot combustion gas path are exposed to combustion temperatures approximately well over 1000 degrees Celsius (1832 degrees Fahrenheit). The engine internal components within the combustion path, such as for example combustion section transitions, vanes and blades are often constructed of high temperature resistant superalloys. Blades, vanes, and transitions often include cooling passages terminating in cooling holes on component outer surface, for passage of coolant fluid into the combustion path.
Turbine engine internal components often incorporate a thermal barrier coat or coating (“TBC”) of metal-ceramic material that is applied directly to the external surface of the component substrate surface or over an intermediate metallic bond coat (“BC”) that was previously applied to the substrate surface. The TBC provides a thermal insulating layer over the component substrate, which reduces the substrate temperature. Combination of TBC application along with cooling passages in the component further lowers the substrate temperature.
Fabrication of cooling passages in, and application of TBC layers to superalloy components, creates conflicting manufacturing constraints. Traditionally, cooling passages are formed by removing superalloy material from the intended passage path within the component, with exemplary removal tools including mechanical cutting/drilling bits, or various ablation devices, such as high-pressure water jet, percussion laser pulsation, and electric discharge machining (“EDM”). Cut cooling passage path, profile and size are limited by the physical capabilities of the cutting instrument. For example, drilled passages are linear and have cross sectional symmetry to match the drill bit. Ablated passages are limited by the size of the ablation instrument and ability to maneuver the instrument along a cutting path.
Investment cast turbine engine components are fabricated by creating a hardened wax pattern, in a wax injection mold, which replicates the profile of the finished superalloy component. The wax pattern is enveloped in ceramic slurry, which is subsequently hardened by firing, into a ceramic shell casing. When wax is removed from the ceramic shell casing, the internal cavity is filled with molten superalloy material. Typically, more particularly, wax patterns for investment cast, superalloy components for combustion turbine engines, are injected into hard tool wax molds, and removed from the tools with precise and smooth surfaces. The wax patterns are then dipped in various ceramic slurry mixtures and processed to form the ceramic outer shell, which is subsequently sintered to form a vestibule in which molten metal is poured. Upon cooling and solidification, the outer ceramic shell is removed by mechanical and/or chemical methods and the metal part is then prepared for further processing. Further processing of the metal part includes ceramic core removal, finish machining, drilling of cooling holes, and application of a thermal barrier coating (“TBC”). Current state of the art processes often require the investment cast surface be lightly grit blasted to prepare the surface for bond coat application. At this point a bond coat, typically a metallic Cramoium, Aluminum, Yitria (“MCrAlY”) coating is applied to the substrate via a spray deposition technique, such as High Velocity Oxy Fuel (“HVOF”) or Low Pressure Plasma Spray (“LPPS”). After this a ceramic thermal barrier such as YSZ (Yttria Stabilized Zirconia) is applied to the surface of the MCrAlY via atmospheric or air plasma spray (“APS”) to complete the coating system. In some cases, a two layer ceramic coating is applied via APS for low thermal conductivity.
The investment casting wax pattern does not have sufficient, reliable, structural integrity to form cooling passages directly therein. When cooling passages are formed in the mold that forms the wax pattern, there is more than insignificant chance that the cooling passage profile in the wax pattern will deform, or that the wax pattern passage will not fill completely with ceramic slurry; in either case the resultant passage in the metal casting does not confirm to design specification.
In some investment casting, component manufacturing processes, refractory metal core (“RMC”) inserts that conform to the desired profiles and paths of cooling passages are placed in the molds prior to component metal casting. The RMC inserts have to be aligned precisely within the molds, and are removed after casting by chemical dissolution processes, adding to manufacturing complexity and expense. TBC layer application adds additional sequencing challenges to the manufacturing process.
If cooling passages are formed in the blade, vane, transition, or other superalloy component prior to application of the TBC layer, the passages will become obstructed by the TBC material as the latter is applied to the component surface. Obstruction can be mitigated by temporarily masking the cooling passages on the component surface prior to the TBC application, which adds additional, costly, steps to the manufacturing processes. In the alternative, excess TBC material obstructions within cooling passages can be removed subsequently by the aforementioned cutting processes. Post TBC-application cooling passage obstruction removal increases risk of TBC layer damage and/or delamination along the margins of cooling passages on the component surface. In some manufacturing processes, cooling passages are formed after application of a TBC layer to the component substrate. In one known post TBC-coating cooling passage formation process, a pulsed laser ablates TBC material from the component at the intended cooling passage entry point, and then ablates the superalloy material to form the passage.
As previously noted, there is risk of damage to the previously applied TBC layer, or delamination of the layer from the component substrate, as cooling passages are subsequently created within the component. Due to differences in thermal expansion, fracture toughness and elastic modulus, among other things, between typical metal-ceramic TBC materials and typical superalloy materials used to manufacture the aforementioned exemplary turbine components, there is potential risk of thermally- and/or mechanically-induced stress cracking of the TBC layer as well as TBC/turbine component adhesion loss at the interface of the dissimilar materials as the TBC layer and superalloy material are removed during cooling passage formation or cooling passage cleaning to remove TBC obstructions. The cracks and/or adhesion loss/delamination negatively affect the TBC layer's structural integrity and potentially lead to its spallation (i.e., separation of the TBC insulative material from the turbine component).
In this invention a ceramic insert, which incorporates an engineered surface with one or more projecting posts, conforming to respective partially completed cooling passage(s), is incorporated into the casting mold. In some embodiments, the ceramic insert is a partially sintered, ceramic material (similar to typical core material used in investment casting processes) that is positioned onto and/or embedded within the wax pattern. Alternately, the ceramic shell insert is placed into the wax injection tool and embedded within the wax pattern when it is injected.
Exemplary embodiments of the methods described herein form cooling passages in combustion turbine engine components, such as blades, vanes, or transitions, during investment casting, through use of ceramic shell inserts within the casting mold. Ceramic posts formed in the ceramic shell insert have profiles conforming to profiles of partially completed cooling passages. The shell insert surface, including its posts, is embedded in a hardened wax pattern, whose profile conforms to the component profile. The wax pattern and its embedded shell insert are enveloped in ceramic slurry that is hardened to form an outer ceramic shell. After removal of the hardened wax, the cavity within the outer ceramic shell is filled with melted superalloy material, and thereafter hardened to form a superalloy component casting. The ceramic outer shell, shell insert and any cores are removed from the casting, which now has cast-in-place, partial cooling passages formed therein. The cooling passages are completed by removing remaining superalloy material in the cooling passage path.
Passage path profile is selectively varied easily by varying profile of the ceramic insert posts, which are affixed to the ceramic insert, and which do not need additional alignment effort within the casting molds, compared to standard, known RMC inserts. The partially completed cooling path passages are easily cleared of any subsequently applied TBC layer obstructions, prior to completion of the passages. The cooling passage is completed by removing the rest of the superalloy material from the casting to match a corresponding, completed cooling passage profile in the corresponding component.
Exemplary embodiments of the invention feature a method for forming a cooling passage in an investment cast, superalloy component for a combustion turbine engine, by providing a wax injection mold defining a mold cavity, whose mold cavity surface conforms to a corresponding surface profile of a component for a combustion turbine engine. A ceramic shell insert is provided, having an insert surface profile and at least one ceramic post projecting from the inner surface, which in combination conform to a corresponding surface profile of a partially completed cooling passage in the engine component. The ceramic shell insert is inserted into the wax injection mold. The shell insert surface and each ceramic post forms part of the mold cavity surface, with each post projecting into the mold cavity. The mold cavity is filled with wax, enveloping each post therein. The wax is hardened, creating a wax pattern that embeds the ceramic shell and each post therein. The wax injection mold is removed. The hardened wax pattern, along with the insert surface and each ceramic post conforms to the component surface profile. The hardened wax pattern and embedded shell insert are enveloped in ceramic slurry. The ceramic slurry is fired, thereby hardening the slurry into an outer ceramic shell, which is joined to the ceramic shell insert, and eliminating the wax. The joined outer ceramic shell and ceramic shell insert define a shell internal cavity, which conforms to the engine component profile, including each partially completed cooling passage. The shell internal cavity is filled with molten superalloy material. The superalloy material is cooled, to form a component casting therein. The casting includes each partially completed cooling passage. The outer ceramic shell and ceramic insert, including each ceramic post, are removed from the casting, exposing each partially completed cooling passage. At least one cooling passage is completed by removing hardened, cast superalloy material from the casting to match a corresponding, completed cooling passage profile in the corresponding component.
Other exemplary embodiments of the invention feature a method for forming a cooling passage in an investment cast, superalloy blade or vane component for a combustion turbine engine. The component has a component wall delimited by a wall outer surface, and a wall inner surface that defines a component cavity therein, with the cooling passage extending through the component wall between its respective outer and inner surfaces. A wax injection mold is provided, defining a mold cavity, whose mold cavity surface conforms to a corresponding profile of an outer surface of a hollow blade or vane component for a combustion turbine engine. A ceramic shell insert is provided, having an insert surface profile and at least one ceramic post projecting from the insert surface, which in combination conform to a corresponding surface profile of a partially completed cooling passage in the engine component wall. A ceramic core is provided, whose core outer surface conforms to a corresponding profile of a wall inner surface of the same component. The ceramic core is inserted into the mold cavity, and the ceramic shell insert is inserted into the mold, with the shell insert surface in opposed, spaced relationship with the ceramic core outer surface, forming a cavity void there between, which corresponds to a corresponding profile of the component wall respective outer and inner surfaces. The mold cavity void is filled with wax, enveloping each ceramic post therein. The wax is hardened, forming a wax pattern that embeds the ceramic core, and ceramic shell insert, including each ceramic post therein. The wax injection mold is removed, with the hardened wax pattern, along with the ceramic insert surface and each ceramic post conforming to the component wall respective outer and inner surfaces profiles. The hardened wax pattern and embedded shell insert are enveloped in ceramic slurry, which is fired, thereby hardening the slurry into an outer ceramic shell, which is joined to the ceramic shell insert and the ceramic core. The wax is eliminated, with the joined outer ceramic shell and ceramic insert defining a shell internal cavity, which conforms to the engine component wall outer surface profile, including each partially completed cooling passage. Similarly, the ceramic core outer surface conforms to the engine component wall inner surface profile, and the ceramic shell cavity void conforms to the engine component wall. The ceramic shell internal cavity void is filled with molten superalloy material, which is then cooled to form a component casting therein. The casting includes each partially completed cooling passage in the component outer wall surface. The ceramic core, ceramic outer shell, and ceramic insert, including each ceramic post, are removed from the casting, exposing each partially completed cooling passage in the outer surface of the component wall. At least one cooling passage is completed through the component wall, by removing hardened, cast superalloy material that blocks remaining path of the cooling passage.
The respective features of the exemplary embodiments of the invention that are described herein may be applied jointly or severally in any combination or sub-combination.
The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale.
Exemplary method embodiments of the invention form partially completed cooling passages directly in turbine engine components during investment casting of the superalloy material. The partial cooling passages are formed by use of ceramic shell inserts, having projecting posts, and optionally additional engineered surface features. The ceramic posts have sufficient strength to maintain structural integrity and alignment as they are being embedded in wax during the wax pattern formation of the manufacturing process. After the wax hardens, the composite hardened wax pattern and embedded ceramic shell, along with any other casting mold segments, such as central cores, are in turn enveloped in ceramic slurry. The slurry is fired, hardening it into an outer ceramic shell. Any wax that was not previously eliminated during the outer ceramic shell firing is removed, leaving a mold cavity, for receipt of molten superalloy material. The ceramic posts of the ceramic shell insert project into the mold cavity. Molten superalloy material poured into the mold cavity hardens around the ceramic posts. After the casting cools and hardens, the ceramic mold material, including the outer shell, shell insert and the projecting ceramic posts are removed; leaving partially formed or completed cooling passages in the component substrate.
In some embodiments, a TBC layer is applied over desired portions of the component substrate, including the partially completed cooling passages. Any TBC material obstructing the partial cooling passages is removed, allowing access to the terminus of the partial cooling passage. Thereafter the cooling passage path is completed by removing component superalloy material along the intended passage path.
Referring to
For convenience and brevity, further discussion of cooling passage formation and application of thermal barrier coat (“TBC”) layers on the combustion turbine engine components will focus on the turbine section 86 embodiments and applications, though similar constructions are applicable for the compressor 82 or combustion 84 sections, as well as for steam turbine engine components. In the engine's 80 turbine section 86, each turbine blade 92 has a concave profile high-pressure side 96 and a convex low-pressure side 98. Cooling passages 99 that are formed in the blade 92 facilitate passage of cooling fluid along the blade surface. The high velocity and pressure combustion gas, flowing in the combustion flow direction F imparts rotational motion on the blades 92, spinning the rotor 90. As is well known, some of the mechanical power imparted on the rotor shaft 90 is available for performing useful work. The combustion gasses are constrained radially distal the rotor 90 by turbine casing 100 and proximal the rotor 90 by air seals 102 comprising abradable surfaces.
Referring to the Row 1 section shown in
As previously noted, turbine component surfaces that are exposed to combustion gasses are often constructed with a TBC layer for insulation of their underlying substrates. Typical TBC coated surfaces include the turbine blades 92, the vanes 104 and 106, ring segments 110, abradable surfaces 120 and related carrier surfaces of turbine vanes, and combustion section transitions 85. The TBC layer for blade 92, vanes 104 and 106, ring segments 110, and transition 85 exposed surfaces are often applied by thermal sprayed or vapor deposition or solution/suspension plasma spray methods, with a total TBC layer thickness of 300-2000 microns (m).
Fabrication of Partially Completed Cooling Passages with Ceramic Shell Inserts in Investment Cast, Engine Components
Referring to
The cooling passage features are defined in the ceramic shell insert 130 by the projecting ceramic posts 134 that conform to the corresponding, partial cooling passage profiles. This casting method retains detail in the surface profile features, including the cooling passage profiles, which would otherwise be compromised in a wax pattern 150 due to fragility of the wax material composition. The ceramic shell insert 130 surface profile creation process for the superalloy component lends itself to modularity, where additional partially completed cooling passage forming ceramic posts 134, and engineered surface feature anchoring surfaces 140 are incorporated for exposed airfoil areas such as leading edges and trailing edges of turbine blades 92 or vanes 104, 106. In order to be compatible with ceramic outer casting shell 152 shrinkage, in some embodiments the ceramic shell inserts 130 are partially thermally processed prior to application to the wax injection tool 142. In the example of an engine vane 104, 106 or blade 92 of
The ceramic shell insert system 130 exemplary embodiments of
The main steps for investment casting of a combustion turbine component with partially completed cooling passages, in accordance with embodiments of the invention methods, are shown in
Referring to
The hardened wax pattern 150, which now captures the ceramic shell insert 130, the posts 134 and the ceramic inner core 144, is separated from the mold 142, leaving the composite pattern of
The composite ceramic vessel 152 hollow cavity 146 incorporates the surface features of the superalloy component, including the partial cooling passages/holes. In the embodiment of both of
In
The now ceramic-free metal casting 154 now has a partially completed cooling passage 156 of partial depth D compared to the total substrate thickness G. The partially completed cooling passage 156 includes an entrance 158 and a terminus or hole bottom 160, shown in
Referring to
As previously described, the ceramic shell insert 130 is manufactured with an array of ceramic posts that are profiled to mimic integrally cast, partial cooling passages, or holes. Typically, known, cut cooling holes, not formed by the methods of this invention, are 0.5-0.6 mm diameter, cylindrical in shape, and at 30-degree angle θ to the surface. As shown in
As previously noted, integrally cast, partial cooling passages, formed by the method embodiments of the present invention, allow cooling fluid flow, heat transfer, and TBC delamination inhibiting design options that cannot be easily replicated by known post-casting cooling passage formation processes, with easier manufacture than passages formed by known refractory metal core (“RMC”) insert processes. Cooling passage/hole configurations are not limited to simple cylindrical holes, as shown in
Additional embodiments for forming posts in ceramic inserts are shown in
As previously noted, cooling passages formed in superalloy engine components before application of thermal barrier coating (“TBC”) layers are masked to inhibit obstruction by the later applied TBC material, which is costly and time consuming. Often in the past cooling passages have been formed in superalloy engine components 239, after TBC layer application by laser ablation, such as shown in progression of
Potential damage to thermal barrier coating (“TBC”) layer(s) 276 during subsequent cooling passage 270 formation is mitigated by creation of a partially completed or formed cooling passage 264 in the superalloy, turbine engine component 260, and prior to application of the TBC layer 276 on the same surface, as shown in
In practicing the TBC damage mitigation method of embodiments of the invention, the partially completed cooling passage 264 is formed by any previously known cutting/or ablation method within the component surface, but beneficially such partially completed cooling passages 264 are formed in some embodiments by use of the projecting ceramic post, ceramic inserts 130 of the type shown in
A partially completed cooling passage 264 is formed in a first surface of a wall of a superalloy engine component 260 for a combustion turbine engine. The partially formed or partially completed cooling passage 264 has an entrance 266 formed in the component substrate 262 first surface, which corresponds to a cooling passage inlet or outlet. The partially completed cooling passage 264 has a skewed passage path within the component wall substrate 262, having a terminus 268 that is laterally offset from the passage entrance 266, and distal the component first surface. The laterally offset passage entrance 266 and terminus 268 have an overhanging shield layer 269 of superalloy material in the wall that is interposed between the passage terminus 266 and the component first surface proximate the laterally offset passage entrance 266. While the cooling passage 270 and the partially completed or partially formed passage 264 are shown in
A thermal barrier coating 276 is applied over the component substrate 262 first surface and the partially completed or formed passage entrance 266. The thermal barrier coating 276 comprises a known composition, thermally sprayed, or vapor deposited, or solution/suspension plasma sprayed thermal barrier coat that is applied directly to the component substrate 262 surface, or that is applied over an intermediate bond coat layer 274 that was previously applied over the component substrate surface.
An ablation apparatus, such as a pulsed laser 246 or an electric discharge machine, is used for ablating the thermal barrier coating 276 and the superalloy material in the substrate 262. The laser 246 or other ablation device is aligned with the entrance 266 of the partially completed or formed passage 264, and ablates thermal barrier coating material 276 from the partially completed or formed passage, reaching the passage terminus 268.
In
As described in the aforementioned, International Application No. PCT/US15/16318, filed Feb. 18, 2015, and entitled “TURBINE COMPONENT THERMAL BARRIER COATING WITH CRACK ISOLATING ENGINEERED GROOVE FEATURES”, in some embodiments, referring to
Although various embodiments that incorporate the invention have been shown and described in detail herein, others can readily devise many other varied embodiments that still incorporate the claimed invention. The invention is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted”, “connected”, “supported”, and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical, mechanical, or electrical connections or couplings.
This application claims priority to International Application No. PCT/US15/16318, filed Feb. 18, 2015, and entitled “TURBINE COMPONENT THERMAL BARRIER COATING WITH CRACK ISOLATING ENGINEERED GROOVE FEATURES”, the entire contents of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/018215 | 2/17/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2015/016318 | Feb 2015 | US |
| Child | 15548267 | US |
