Patent Application
20130323074
The present invention relates to gas turbine engines, and in particular, to turbine disks for use in turbine sections of gas turbine engines.
Gas turbine engines include various sections and components which can be subjected to very high temperatures. For example, a turbine section of a gas turbine engine is positioned downstream of a combustor section. Consequently, certain components in the turbine section can experience some of the highest temperatures in a gas turbine engine. However, not all components are subjected to the same temperatures. Similarly, certain components can be subjected to high loads, but not all components need to withstand the same loads.
Gas turbine engines are typically designed with systems designed to cool certain components. It can also be desirable to design components using materials capable of withstanding high temperatures. However, certain high temperature materials can be undesirably expensive. Moreover, such materials can be challenging to use in certain manufacturing operations.
According to the present invention, an assembly for use in a turbine of a gas turbine engine includes a turbine disk and a shaft. The turbine disk comprises a superalloy. The shaft is friction welded to the turbine disk at a shaft interface substantially adjacent the turbine disk.
Another embodiment of the present invention includes a method of fabricating a turbine disk assembly. The method includes creating a forging of superalloy material having a diameter at least twice its thickness, machining a turbine disk from the forging, and friction welding a shaft to the turbine disk at a shaft interface substantially adjacent a hub of the turbine disk.
A series of shafts 36A-36G connect and support compressor 12 and turbine 16. Shaft 36C is connected to shafts 36B and 36D via curvic couplings 38A and 38B, respectively. Shafts 36E and 36F are spacer shafts connected via curvic coupling 38C. In the illustrated embodiment, no other curvic coupling exists between turbine disk 26 and turbine disk 30. Shafts 36E and 36F connect and provide spacing between turbine disk 26 and turbine disk 30. Shaft 36G is an aft shaft having bearing interface section 40 which supports bearing 42. Seal 44, which limits air flow between opposite sides of seal 44, is also positioned on shaft 36G. Tie-bolt 45 is positioned radially inward of shafts 36A-36G and is put in tension so as to hold compressor 12 to turbine 16.
In operation, air flows from inlet 46 to compressor 12, where it is compressed and passed to combustor 14. Compressed air in combustor 14 is mixed with fuel to form a blended gas which is combusted and passed to turbine 16. As the combusted gas is forced over turbine blades 24 and 28 of turbine 16, turbine 16 and compressor 12 are forced to rotate about centerline axis CL. The gas then flows from turbine 16 to outlet 48.
Spacer shaft 36F is a substantially annular shaft that has curvic coupling interface 62 for connecting spacer shaft 36F to spacer shaft 36E (shown in
Spacer shaft 36F is friction welded to turbine disk 30. In one method of friction welding, inertia welding (also known as spin welding), can be used to connect spacer shaft 36F to turbine disk 30. Either spacer shaft 36F or turbine disk 30 is held in place while the other is rotated. Then spacer shaft 36F and turbine disk 30 are moved closer together such that front shaft interface 58 and disk interface 64 come into contact, which creates friction that causes heat generation at the point of contact and effectively welds spacer shaft 36F to turbine disk 30. This creates friction weld joint 72, which provides a relatively strong and economical connection between spacer shaft 36F and turbine disk 30. Aft shaft 36G can be friction welded to turbine disk 30 in a similar manner to create friction weld joint 74. In alternative embodiments, friction weld joints 72 and 74 can be created via another friction welding technique, such as linear friction welding.
In the illustrated embodiment, aft shaft 36G is connected to turbine disk 30 and is free of curvic couplings. No curvic coupling is positioned between bearing interface section 40 and hub 52. No curvic coupling is positioned between bearing interface section 40 and seal 44. Also in the illustrated embodiment, spacer shaft 36F is free of curvic couplings internally (that is, spacer shaft 36F does not have any curvic couplings between disk interface 64 and curvic coupling interface 62); but spacer shaft 36F does, of course, have curvic coupling interface 62 at an upstream end which is part of curvic coupling 38C (shown in
In the illustrated embodiment, disk interface 64 and front shaft interface 58 are both angled with respect to a radial direction, which is a direction that extends radially outward from centerline axis CL (shown in
Similarly, in the illustrated embodiment, disk interface 66 is also angled with respect to the radial direction. Aft shaft interface 60 is aligned substantially parallel to the radial direction. Consequently, in the illustrated embodiment, disk interface 66 and aft shaft interface 60 are not shaped to have flat, abutting contact with one-another. During friction welding, however, disk interface 66 and/or aft shaft interface 60 can plasticize and then harden together so as to have a substantially uniform and solid friction weld. In an alternative embodiment, disk interface 66 and/or aft shaft interface 60 can be angled by about 3° to about 10° from the radial direction. In further alternative embodiments, the angled frusto-conical shape of disk interface 66 can be complimentary to the angled frusto-conical shape of aft shaft interface 60, similar to those of disk interface 64 and front shaft interface 58. In further alternative embodiments, disk interface 64, front shaft interface 58, disk interface 66, and aft shaft interface 60 can have different angles and alternative shapes, so long as those angles and shapes are suitable for friction welding in the particular application.
Turbine disk 30 can be made of a superalloy known as DA-718 (also known as direct age 718). Spacer shaft 36F and aft shaft 36G can be made of a superalloy known as Inconel-718. DA-718 and Inconel-718 are chemically similar nickel and chromium based superalloys. Inconel-718 is subjected to a process that includes first receiving thermo-mechanical work, next receiving a first heat treatment, and then receiving a second heat treatment. Unlike Inconnel-718, DA-718 does not receive the first heat treatment as a separate step. Instead, DA-718 is subjected to a process that includes first receiving thermo-mechanical work and then receiving the second heat treatment. For DA-718, the first heat treatment is, effectively, performed simultaneously with the step or receiving thermo-mechanical work. This differing process allows DA-718 to achieve improved material properties, including improved creep and fatigue properties. Use of friction welding allows for turbine disk 30 to be made of DA-718 and be integrally connected to shafts 36F and 36G made of Inconel-718. In alternative embodiments, turbine disk 30, spacer shaft 36F, and aft shaft 36G can be made of other superalloys suitable for a particular application, such as other nickel based superalloys or cobalt based super alloys. Turbine disk 30 can be made of a superalloy different from that of spacer shaft 36F and/or aft shaft 36G. For example, turbine disk 30 can be made of Waspaloy 718+ or Powder IN-100. Spacer shaft 36F and/or aft shaft 36G can be made of Steel 15-5 PH. In a further alternative embodiment, turbine disk 30, spacer shaft 36F, and aft shaft 36G can be made of a common superalloy.
Turbine disk 26 (shown in
In some of the above-described embodiments, friction welding shafts 36F and/or 36G to turbine disk 30 can have certain benefits. Friction welding can allow shafts 36F and 36G to be connected to turbine disk 30 without use of curvic couplings that can be expensive and time-consuming. Friction welding can allow shafts 36F and 36G to be made of a different superalloy than that of turbine disk 30, thus allowing turbine disk 30 to be made of a relatively expensive superalloy without requiring shafts 36F and 36G to be made of the same superalloy. This can be beneficial in applications where turbine disk 30 needs to withstand higher temperature and/or strength requirements than the requirements needed of shafts 36F and 36G. Friction welding can further allow shafts 36F and 36G to be integrally connected to turbine disk 30, without requiring shafts 36F and 36G to be part of the same forging as that of turbine disk 30. This can allow turbine disk 30 to be made of a forging having a shape (such as a pancake shape) conducive to achieving improved material properties using DA-718 superalloy material. This is in contrast to having to use another shape (such as a spherical shape) that would allow shafts 36F and 36G to be part of the forging, but that may be less conducive to creating a suitable forging of DA-718 superalloy material. Further, by using a forging sized and shaped for a turbine disk without one or more attached shafts, a common forging can be used for turbine disks used in different engines, even if those disks attach to shafts having different sizes.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. For example, gas turbine engine 10 need not be constructed exactly as illustrated, but could instead be another type of gas turbine engine.
