Patent Application
20060239825
The present invention relates generally to turbine components and methods for forming a turbine rotor having a diffusion bonded integral blade ring.
Prior art dual alloy turbine rotors for gas turbine engines have primarily used equiaxed superalloy airfoils. Although single crystal superalloys offer superior high temperature creep strength, it is technically difficult to cast single crystal blade rings for dual alloy turbine rotors. In the past, attempts have been made to cast single crystal dual alloy turbine rotors via radial solidification. These attempts have been abandoned because of the difficulty to produce a radial thermal gradient in the blade ring during solidification. Other attempts may have been made to bi-cast blades into an inner and outer shroud (or rim). However, an oxide scale, formed on the blades during the casting process, prevents diffusion bonding between the blade and the shroud(s).
Attempts have been made in the prior art, for example, U.S. Pat. No. 5,290,143 to Kington, to bi-cast airfoils into at least one of an inner shroud and an outer shroud. However, in the prior art process an oxide scale, e.g., formed during bi-casting, prevents diffusion bonding between the blade and shrouds. The ensuing absence of a metallurgical bond between the blade and shrouds may be advantageous in the case of a stator vane, as disclosed by Kington, but is disadvantageous in the case of a rotor blade.
US Patent Application Publication No. 20050025613 (Strangman) discloses a cast integral blade ring having single crystal airfoils, wherein the blade ring is formed en masse in a single casting process using axial solidification. The viability of production by such axial solidification may rely on relaxed requirements of cast components or production yields significantly above typically attainable production yields (presently about 95%).
As can be seen, there is a need for improved apparatus and methods for forming multi-alloy turbine components.
In one aspect of the present invention, a method for providing a turbine rotor comprises forming a plurality of individual rotor blades; forming an oxidation resistant coating on at least a portion of each of the rotor blades to provide a plurality of coated rotor blades; and bi-casting the coated rotor blades into a blade ring.
In another aspect of the present invention, there is provided a method for providing a turbine rotor comprising casting a plurality of individual rotor blades; coating at least a portion of each of the rotor blades with an oxidation resistant coating to provide a plurality of coated blades; bi-casting the coated blades into at least an inner rim to form an integral blade ring; and diffusion bonding the coated blades to at least the inner rim, wherein the coating step prevents formation of an oxide scale on a surface of the coated blades.
In yet another aspect of the present invention, a method for bi-casting a multi-alloy turbine rotor comprises casting a plurality of individual single crystal rotor blades; coating at least a portion of a surface of each of the rotor blades with an oxidation resistant coating to provide a plurality of coated blades; bi-casting the coated blades into an integral blade ring; diffusion bonding the rotor blades to at least an inner rim of the blade ring; match-machining the blade ring and an alloy disc; and diffusion bonding the blade ring to the disc to provide the multi-alloy turbine rotor. Prior to and during the bi-casting step, the oxidation resistant coating prevents formation of an oxide scale on the surface of the coated blades thereby allowing diffusion bonding of the coated blades to at least the inner rim of the blade ring. The oxidation resistant coating comprises a platinum group metal.
In still another aspect of the present invention, there is provided a method for bi-casting a multi-alloy turbine rotor comprising casting a plurality of individual single crystal rotor blades from a nickel-based superalloy; coating at least a portion of a surface of each of the rotor blades with an oxidation resistant coating to provide a plurality of coated blades; bi-casting the coated blades into at least an inner rim to provide a blade ring; diffusion bonding the coated blades to the blade ring by hot isostatic pressing, wherein prior to and during the bi-casting step, the oxidation resistant coating prevents formation of an oxide scale on the surface of the coated blades, thereby allowing diffusion bonding of the coated blades to at least the inner rim of the blade ring; providing an alloy disc; match-machining the blade ring and the disc; and diffusion bonding the rotor blades and the inner rim to the disc by hot isostatic pressing to provide the multi-alloy turbine rotor. During at least one of the diffusion bonding steps, at least a portion of the oxidation resistant coating diffuses into at least one component selected from: the rotor blades, the inner rim, and the disc. The oxidation resistant coating comprises at least one material such as platinum, palladium, rhodium, ruthenium, osmium, and iridium.
In a further aspect of the present invention, there is provided a turbine rotor prepared by a process comprising casting a plurality of individual single crystal rotor blades; coating at least a portion of the surface of each of the rotor blades with an oxidation resistant coating to provide a plurality of coated blades; bi-casting the coated blades into a blade ring comprising an inner rim; diffusion bonding the rotor blades to the inner rim of the blade ring; and diffusion bonding the blade ring to an alloy disc to provide the turbine rotor.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawings, description, and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Broadly, the present invention provides apparatus and methods for making turbine rotor components for gas turbine engines, which may be used in vehicles, such as fixed wing aircraft, rotorcraft, and land vehicles, as well as for industrial power generation, and the like. The methods of this invention may provide turbine rotor components comprising single crystal rotor blades. As used herein, the term “single crystal” may be used to describe a cast component, such as a rotor blade, in which the component has a single crystallographic orientation throughout at least 95% of the load bearing portions of the component, in the absence of high angle grain boundaries.
Turbine components of the invention may be formed by bi-casting individually cast rotor blades into a blade ring, and diffusion bonding the rotor blades to at least one other component of the blade ring and/or to a rotor disc, wherein at least a portion of each rotor blade may be coated with an oxidation resistant coating prior to diffusion bonding the rotor blades to the blade ring. The oxidation resistant coating may prevent oxide scale formation on the rotor blade surface, thereby allowing diffusion bonding of the rotor blades to the blade ring. According to the invention, individually cast rotor blades may be inspected, and any sub-standard rotor blades may be eliminated prior to bi-casting the rotor blades into the blade ring. The individually cast rotor blades may be single crystal blades comprising various nickel-based superalloys. In contrast, prior art processes lack a step of applying an oxidation resistant coating to the airfoils during the manufacturing process, and/or form the bladed ring en masse in a single casting process using axial solidification of the superalloy, CMSX-486 (see, for example, US Patent Application Publication No. 20050025613). In contrast to the invention, in which the oxidation resistant coating prevents oxide scale formation on the rotor blades, in prior art processes for bi-casting turbine components, an aluminide coating applied to the airfoils results in the formation of an oxide scale during bi-casting, thereby preventing diffusion bonding between the airfoils and shrouds.
Blade ring 10 may be formed by individually casting the plurality of rotor blades 30; coating at least a portion of the surface 31 of each rotor blade 30 to provide a plurality of coated blades 30′ (see,
In some embodiments of the present invention, oxidation resistant coating 36 may be applied to the entire surface of blade 30. Alternatively, in other embodiments oxidation resistant coating 36 may be selectively applied to selected regions of blade 30. As a non-limiting example, oxidation resistant coating 36 may be selectively applied to one or both of first and second blade tips 32a, 32b. Blade 30 may typically comprise a single crystal nickel-based superalloy, such as a member of the CMSX family of superalloys. In alternative embodiments, rotor blade 30 may comprise equiaxed superalloy material.
Again with reference to
Again with reference to
Each of the plurality of rotor blades formed in step 102 may comprise a single crystal nickel-based superalloy. Each of the individually cast rotor blades may be inspected, for example, using techniques such as macroscopic visual inspection, application of fluorescent penetrant, and X-ray diffraction, to identify any sub-standard rotor blades, which may be discarded prior to step 104. Such inspection techniques are well known in the art for inspecting airfoils and other turbine components.
During or after casting the rotor blades in step 102, oxide scale may form on the rotor blades. Accordingly, prior to step 104, any oxide scale may be removed from the surface of the rotor blades, e.g., using an acid, and thereafter the rotor blades may be cleaned, e.g., with surfactant and/or acid.
Step 104 may involve coating each of the rotor blades, over at least a portion of its surface, with an oxidation resistant coating, wherein the oxidation resistant coating may prevent formation of an oxide scale on the rotor blade surface. In the absence of such an oxidation resistant coating, oxide scale may be formed on the rotor blade surface prior to and during step 106 following exposure of the rotor blades to an oxidizing environment. The oxidation resistant coating applied in step 104 may comprise a platinum group metal, e.g., platinum, palladium, rhodium, ruthenium, osmium, and iridium, or a mixture thereof. The oxidation resistant coating may be applied to each rotor blade to a thickness sufficient to protect the rotor blade from oxidation and oxide scale formation thereon until such time as the rotor blades have been diffusion bonded to the blade ring (steps 106 and/or 108, infra). Furthermore, the oxidation resistant coating may be applied to each rotor blade to a thickness sufficiently thin such that at least about 50% of the oxidation resistant coating may dissipate by diffusion into other rotor components of the turbine rotor during steps 106, 108, and 114. The oxidation resistant coating may typically be applied to the rotor blades to a thickness of up to about 0.0030 inches (ca. 12 μm), and usually up to about 0.0015 inches (ca. 6 μm).
During step 104, the oxidation resistant coating may be applied to the surface of the rotor blades by various deposition techniques, such as one or more methods selected from: electroplating, chemical vapor deposition, and ion plating. In some embodiments, step 104 may involve applying the oxidation resistant coating sequentially in a series of layers. The various layers may have the same or different compositions, and may be applied using various deposition techniques, to form an oxidation resistant coating, having suitable thickness, adhesion to the superalloy rotor blade substrate, and composition, for preventing oxide scale formation on the coated rotor blades. Step 104 may involve applying the oxidation resistant coating to the entire surface of each rotor blade. In alternative embodiments, the oxidation resistant coating may be selectively applied to each rotor blade, for example, to one or both of first and second blade tips (see, for example,
Step 106 may involve bi-casting the individually cast, coated blades into an integral blade ring. The blade ring may include at least an inner rim. In some embodiments, the blade ring may further include an outer rim. The rotor blades may extend radially outward from the inner rim towards the outer rim. Each of the inner and outer rims may comprise a nickel- or cobalt-based superalloy. Each rotor blade may have a first blade tip disposed within the outer rim and a second blade tip disposed within the inner rim (see, for example, FIGS. 1A-B). During the bi-casting of step 106, the first and second blade tips may be diffusion bonded to the outer and inner rims, respectively. Diffusion bonding of the rotor blades to the outer and inner rims may take place in part during step 106, and in further part during a subsequent heat treatment procedure (e.g., step 108, infra).
Step 108 may comprise a heat treatment step in which the first and second blade tips may be further diffusion bonded to the outer and inner rims of the blade ring. As an example, step 108 may involve hot isostatic pressing (HIP) of the blade ring. Step 108 may be performed at a temperature typically in the range of from about 2000 to 2350° F., and at a pressure of from about 15 to 30 ksi for about 2 to 8 hours, and usually from about 2100 to 2300° F. at a pressure of from about 20 to 30 ksi for about 2 to 6 hours.
During diffusion bonding (e.g., step 108), constituents of the rotor blades may diffuse into the inner and outer rims, and vice versa, as is well known in the art. In addition, during step 108, at least a portion of the oxidation resistant coating may dissipate, for example, due to diffusion of constituents of the oxidation resistant coating from the coated blades into the inner and outer rims. Typically, during step 108 the proportion of the oxidation resistant coating that may diffuse into the inner and outer rims may be in the range of from about 50-100%, usually about 70-100%, and often about 80 to 100%.
Step 110 may involve providing an alloy disc for the blade ring. As a non-limiting example, the disc may be a powder metallurgy superalloy disc, such discs for turbine rotors being well known in the art. Alternatively, the disc provided in step 110 may be forged. A high temperature powder metallurgy superalloy is disclosed in commonly assigned, co-pending US Patent Application Publication No. 20050047953, the disclosure of which is incorporated by reference herein in its entirety.
Step 112 may involve match-machining the disc and the blade ring preparatory to diffusion bonding the disc to components of the blade ring during step 114. Step 114 may involve diffusion bonding components of the blade ring to the disc to form the turbine rotor. Thus, during step 114 the disc may be diffusion bonded to the rotor blades at the inner rim/disc interface, and the inner rim may be diffusion bonded to the disc at the blade/disc interface (see, for example, FIGS. 3A-B). Step 114 may involve a further heat treatment, such as hot isostatic pressing of the turbine rotor. Thus, during step 114, further diffusion bonding of the rotor blades to the inner and outer rims may occur.
Although the invention has been described primarily with respect to turbine components for aircraft gas turbine engines, the present invention may also find applications for making components for other types of apparatus and systems.
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
