Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Utility Patent
1999-06-10
2001-01-02
Mai, Ngoclan (Department: 1742)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C416S095000
Utility Patent
active
06168871
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for manufacturing components that must operate at high temperatures. More particularly, this invention relates to a process for forming superalloy components, such as blades and vanes of gas turbine engines, produced by a powder metallurgy technique and components formed thereby.
BACKGROUND OF THE INVENTION
Components of gas turbine engines, such as blades (buckets), vanes (nozzles) and combustors, are typically formed of nickel, cobalt or iron-base superalloys characterized by desirable mechanical properties at turbine operating temperatures. Because the efficiency of a gas turbine engine is dependent on its operating temperatures, there is a demand for components, and particularly turbine blades and vanes, that are capable of withstanding higher temperatures. As the material requirements for gas turbine engine components have increased, various processing methods and alloying constituents have been used to enhance the mechanical, physical and environmental properties of components formed from superalloys. For example, turbine blades and vanes are often cast to have single-crystal (SX) or directionally-solidified (DS) microstructures, characterized by a crystal orientation or growth direction in a selected direction, are typically employed for more demanding applications.
In general, advancements in such technologies have been such that the maximum local metal temperatures of components formed from these superalloys are approaching the alloy melting temperatures. Accordingly, in terms of high temperature capability, it is generally necessary that gas turbine engine components have internal cooling passages through which cooling air is routed to lower the surface temperature of the component. Typical cooling schemes include one or more interior cooling passages having possibly a circuitous route through the airfoil section, with bleed air being forced through the cooling passages and discharged through openings at the surface of the component in order to transfer heat from the component. Considerable cooling air is often required to sufficiently lower the surface temperature of a blade or vane. However, the casting process and the cores required to form the cooling passages limit the complexity of the cooling scheme that can be formed within a component, and therefore limits the rate at which heat can be transferred to the cooling air.
In view of the above, it would be advantageous if high-temperature components such as gas turbine engine blades and vanes could be produced to have a more efficient internal cooling scheme. One such approach has been to fabricate blades and vanes with double walls which form a plenum that is supplied by cooling air through multiple cooling channels. This type of cooling scheme enables a more uniform supply of cooling air near the surface of such components, which significantly reduces surface temperatures. Techniques for fabricating double-walled blades and vanes have included the use of brazed foils, low pressure plasma spraying (LPPS), and electron beam physical vapor deposition (EBPVD). However, each of these processes has disadvantages. For example, the brazed foil technique requires forming the exterior shell of a component from an alloy that can be readily worked to form a suitably thin foil. As a result, the types of alloys that can be used to form the foil are extremely limited. Plasma sprayed shells inherently have a relatively high oxygen content and must be densified to eliminate porosity. Furthermore, the plasma spray process is inefficient in the use of powders, since much of the sprayed powder misses the deposit surface. Finally, the EBPVD process cannot be sufficiently controlled to be practical for production.
Therefore, it would be desirable if an improved method were available for mass producing high-temperature components with more efficient internal cooling schemes that include a double-walled shell structure.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a method for forming an exterior superalloy surface for a high-temperature component, such as a blade or vane of a gas turbine engine. The method entails forming an exterior shell of the component by a powder metallurgy technique that yields an airfoil whose composition can be readily tailored for the particular service conditions of the component. The shell can be produced as a free-standing article or produced directly on a mandrel that subsequently forms the interior structure of the component. By forming the shell in this manner, the component can be configured to have double walls that form a plenum supplied by cooling air, thereby increasing the temperature at which the component may operate by more efficiently and uniformly transferring heat from the component surface.
According to this invention, the method generally entails providing a pair of inner and outer mold members that form a cavity therebetween. A metallic powder is then placed in the cavity, and the powder consolidated within the cavity at an elevated temperature and pressure in a non-oxidizing atmosphere. Thereafter, at least the outer mold member is removed to expose the consolidated powder structure. By appropriately shaping the mold members, the consolidated powder can have the desired shape for the exterior shell of a component, such that subsequent processing of the component does not require substantially altering the configuration or shape of the exterior shell.
According to this invention, the inner mold member may be removed along with the outer mold member, such that the shell is a free-standing member that can be subsequently assembled with and secured to an interior structure of the component, such as a spar of a gas turbine engine blade or vane. Alternatively, an interior structure of the component can be used as the inner mold member, such that the shell is formed in situ during consolidation. To tailor the mechanical, physical and/or environmental properties of the shell, multiple powders having different compositions may be placed in the cavity between the inner and outer mold members. The powders may all be superalloy compositions, or one or more powders may be formulated to yield a composite region in the shell. For this purpose, powders may be used that contain fiber materials, wire materials, particulate materials, and compositions that react in situ to form fiber, wire and/or particulate materials.
In view of the above, it can be seen that forming the exterior shell of a high-temperature component in the manner described above allows the interior structure of the component to be more readily configured to have a complex cooling scheme, including a double-walled configuration that provides plenum cooling near the surface of the component. In this manner, the temperature of the component can be more readily reduced by more efficient heat transfer and/or the amount of cooling air flow through the component can be considerably reduced. Furthermore, the mechanical, physical and environmental properties of various regions of a component can be tailored by selectively using different powder compositions to form certain regions of the component shell. As a result, alloys, alloying constituents and compositions that promote certain mechanical, physical or environmental properties can be used in limited regions of the component where their effect will be most beneficial, which will often promote service life while also potentially lowering component weight and material costs.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
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patent: 5304039 (1
Dupree Paul Leonard
Jackson Melvin Robert
Ritter Ann Melinda
Wemple, Jr. Donald Norman
Cusick Ernest G.
General Electric Company
Johnson Noreen C.
Mai Ngoclan
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