Patent Application
20120231295
The present invention is directed to manufactured components and processes of fabricating manufactured components. More specifically, the present invention relates beam-brazed components and processes of fabricating beam-brazed components.
In general, turbine blades can be coupled to a central hub that is attached to a driven shaft with the blades radially disposed with respect to the axis of the hub and shaft. The blades can include an airfoil that imparts a rotational energy rotating the shaft. Some gas turbine blades have shrouds at the outer extremities of the associated airfoils. The blade shrouds are nested in close proximity to each other. Many turbine blade shrouds have a mechanical interlocking feature in the form of a notch that allows each blade to be physically interlocked at its shroud with an adjacent blade.
There are a variety of mechanisms that may cause wear in the mechanical interlocking feature. For example, during operation of the turbine there may be vibration of adjacent blades with respect to each other and the hub. The aforementioned interlocking feature can facilitate mitigation of airfoil vibration such that the stresses induced within the blades during operation are in turn mitigated. The close tolerances of the interlocking features may increase wear in the vicinity of the interlocking features as the adjacent notches rub against each other.
Further, during starting operations, as the temperatures of the shrouds, airfoils, and hub (as well as all other components that interface with hot gases) vary within each individual component and with respect to other adjacent components, and the turbine is accelerated to an operating speed, the blades and shrouds can twist such that the notches at times contact each other and attain an interlocked condition. Also, during stopping operations variation in component temperatures can be substantially reversed from the variations associated with startup as well as turbine deceleration such that the blades and shrouds can twist so that the notches do not contact each other and attain a non-interlocked condition.
Many shroud materials do not have the surface wear resistance characteristics to resist the long-term cumulative effects of contact and rubbing.
A component and a process of fabricating a component that do not suffer from one or more of the above drawbacks would be desirable in the art.
In an exemplary embodiment, a method of fabricating a component includes beam brazing a pre-sintered preform or a flexible tape to the component to form a beam-brazed portion.
In another exemplary embodiment, a method of fabricating a component includes preparing at least a portion of the component for receiving a sintered preform, forming a pre-sintered preform, positioning the sintered preform on the component, and beam brazing the sintered preform to at least a portion of the component.
In another exemplary embodiment, a component includes a non-brazed portion and an beam-brazed portion formed by a pre-sintered preform.
Provided is an exemplary beam-brazed component and exemplary processes of fabricating a beam-brazed component. Embodiments of the present disclosure mitigate long-term cumulative effects of contact and rubbing, prevent maintenance shutdowns and repairs resulting from twisting and vibration of components, include increased wear resistance and/or hardness, decrease susceptibility to wear, and combinations thereof.
The beam-brazed component is any suitable component formed by a pre-sintered preform (PSP). Suitable components include gas turbine components (for example, surfaces on shrouds, blades or bucket surfaces, interlocking features, or hardfacing surfaces) or any other suitable metal or metal-composite component.
The component includes a substrate formed of, for example, a superalloy material. In one embodiment, the substrate has a composition, by weight, of about 14% chromium, about 9.5% cobalt, about 3.8% tungsten, about 1.5% molybdenum, about 4.9% titanium, about 3.0% aluminum, about 0.1% carbon, about 0.01% boron, about 2.8% tantalum, and a balance of nickel. In one embodiment, the substrate has a composition, by weight, of about 9.75% chromium, about 7.5% cobalt, about 3.5% titanium, about 4.2% aluminum, about 6.0% tungsten, about 1.5% molybdenum, about 4.8% tantalum, about 0.08% carbon, about 0.009% zirconium, about 0.009% boron, and a balance of nickel. In one embodiment, the substrate has a composition, by weight, of about 7.5% cobalt, about 7.0% chromium, about 6.5% tantalum, about 6.2% aluminum, about 5.0% tungsten, about 3.0% rhenium, about 1.5% molybdenum, about 0.15% hafnium, about 0.05% carbon, about 0.004% boron, about 0.01% yttrium, and a balance of nickel. In one embodiment, the substrate has a composition, by weight, of about 9.75% chromium, about 7.5% cobalt, about 4.2% aluminum, about 3.5% titanium, about 1.5% molybdenum, about 6.0% tungsten, about 4.8% tantalum, about 0.5% niobium, about 0.15% hafnium, about 0.05% carbon, about 0.004% boron, and a balance of nickel. In one embodiment, the substrate has a composition, by weight, of about 8.35% chromium, about 9.50% cobalt, about 5.50% aluminum, about 0.75% titanium, about 9.50% tungsten, about 0.50% molybdenum, about 3.05% tantalum, 0.09% carbon, about 1.50% hafnium, and a balance of nickel. In one embodiment, the substrate has a composition, by weight, of about 0.06% carbon, about 9.80% chromium, about 7.50% cobalt, about 1.50% molybdenum, about 4.20% aluminum, about 3.50% titanium, about 4.80% tantalum, about 6.00% tungsten, about 0.50% niobium, about 0.15% hafnium, and a remainder 62% nickel.
In one embodiment, the substrate includes a superalloy that is capable of resisting creep at high temperatures, for example, temperatures of a hot gas path in a gas turbine. For example, in one embodiment, a first portion of the substrate maintains creep strength above a first/higher temperature, for example, about 1000° F., about 1250° F., about 1500° F., about 2000° F., or about 3000° F., and a second portion of the substrate is resistant to heat above a second/lower temperature, for example, between 800° F. and 1250° F., about 800° F., about 1000° F., about 1250° F., about 1500° F., or about 2000° F. In one embodiment, additional heating is provided, for example, by an induction heater (not shown).
Method step 208 includes positioning a preform 402 (for example, the sintered preform or a first and second pre-sintered preform) on the component or the portion of the component to be beam-brazed (for example, the interlocking feature 110). In one embodiment, the portion of the component to be beam-brazed is heated to a predetermined temperature, for example, between about 2100° F. and about 2225° F. As shown in
In one embodiment, the pre-sintered preform (PSP) has a composition, by weight, of about 27.00% to about 30.00% molybdenum, about 16.50% to about 18.50% chromium, up to about 1.50% iron, up to about 1.50% nickel, up to about 0.15% oxygen, up to about 0.08% carbon, up to about 0.03% phosphorus, up to about 0.03% sulfur, and a balance of cobalt. In one embodiment, the PSP has a composition, by weight, of about 0.70% to about 1.00% carbon, about 26.00% to about 30.00% chromium, about 1.00% silicon, about 4.00% to about 6.00% nickel, about 3.00% iron, about 1.25% vanadium, about 0.10% boron, about 18.00% to about 21.00% tungsten, and a balance of cobalt. In one embodiment, the PSP has a composition, by weight, of about 22.00% to about 24.74% chromium, about 9.00% to about 11.00% nickel, about 6.50% to about 7.60% tungsten, about 3.00% to about 4.00% tantalum, about 2.60% to about 3.16% boron, about 0.55% to about 0.65% carbon, about 0.30% to about 0.60% zirconium, about 0.15% to about 0.30% titanium, up to about 1.30% iron, up to about 0.40% silicon, up to about 0.10% manganese, up to about 0.02% sulfur, and a balance of cobalt. In one embodiment, the PSP has a composition, by weight, of about 17.00% nickel, about 19.00% chromium, about 4.00% tungsten, about 0.40% carbon, about 0.80% boron, about 8.00% silicon, and a balance of cobalt.
In a further embodiment, the composition includes a mixture of one or more compositions, for example, about 80% a first composition and about 20% a second composition, about 60% a first composition and about 40% a second composition, about 50% a first composition and about 50% a second composition, or any other suitable composition selected for providing desired properties.
The PSP is a suitable predetermined geometry or corresponding geometries. Suitable geometries include a substantially planar geometry (for example, a flat plate), a tape-like geometry (for example, a flexible tape capable of being rolled, a flexible tape capable of bending at a right angle without mechanical forces, or a flexible tape having a predetermined length), a substantially consistent thickness geometry (for example, about 0.030 inches, about 0.160 inches, or between about 0.020 inches and about 0.080 inches), a rigid tape, a varying thickness geometry (for example, having a thickness of about 0.010 inches in a first region and having a thickness of about 0.020 inches in a second region or having a thickness of about 0.020 inches in a first region and having a thickness of about 0.030 inches in a second region), or combinations thereof. In one embodiment having the first PSP and the second PSP, the first PSP and the second PSP include a substantially identical geometry. In another embodiment, the first PSP and the second PSP have different geometries (for example, the first PSP having thicker regions corresponding to thinner regions in the second PSP).
In one embodiment, a flexible tape is used in addition to or alternative to the PSP. The flexible tape is formed by combining a first composition with a second composition along with a binder and then rolling the mixture to form tape-like or rope-like structures. The flexible tape is capable of being bent to several geometries, includes a predetermined thickness, for example, about 0.020 inches to about 0.125 inches, and is capable of being cut to a predetermined length.
Method step 210 includes beam brazing the component or the portion of the component (for example, beam brazing the preform 402 to the mating surface 114). In one embodiment, the beam brazing of step 210 includes a heating cycle sub-step and a cooling cycle sub-step. The heating cycle sub-step includes placing the shroud 108, with the preform 402 tack welded to the interlocking features 110, into an electron beam welding chamber (not shown) at a predetermined temperature (for example, at room temperature or about 70° F.). To facilitate the brazing process, a non-oxidizing atmosphere within the electron beam welding chamber is provided (for example, by evacuating the electron beam welding chamber). In one embodiment, the evacuated electron beam welding chamber is evacuated to a predetermined pressure (for example, 0.067 Pa or less).
A portion of the component is locally heated by the beam at a predetermined rate (for example, about 250° F. per minute) by a defocused electron beam, for example, the beam being selectively positioned or oscillated to spread heat over a predetermined region of the combustion turbine component 100. The predetermined region may be defined by a predetermined path for on the portion of the component. In one embodiment, the defocused electron beam provides substantially uniform heating of the predetermined region. Additionally or alternatively, in one embodiment, the defocused electron beam is formed by having increased deflection in comparison to a focused beam that may be used for electron beam welding. Upon reaching the predetermined temperature, the predetermined temperature is maintained for a predetermined period of time (for example, between about 2 and about 5 minutes) and the predetermined region is sequentially heated to a brazing temperature by the defocused electron beam. In one embodiment, the predetermined region is increased to a higher temperature (for example, about 1800° F.) at a predetermined rate (for example, 250° F. per minute) and maintained for a predetermined period (for example, 5 minutes). In this embodiment, the predetermined region is next increased to the brazing temperature (for example, about 2200° to 2225° F.) at a predetermined rate (for example, 350° F. per minute) and maintained for a predetermined period of time (for example, about 5 minutes).
Method step 212 includes machining the beam-brazed component or a beam-brazed portion of the component. For example, minor machining (for example, of hardfacing preform 402 shown in
While the invention has been described with reference to a preferred embodiment, 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 embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
