Patent Application
20130017071
The present invention relates to manufactured components and processes of manufacturing components. More specifically, the present invention relates to metallic foams and process of fabricating metallic foams.
Manufactured components are increasingly subjected to difficult environments. For example, gas turbine components are subjected to thermally, mechanically and chemically hostile environments. For example, in the compressor portion of a gas turbine, atmospheric air is compressed to 10-25 times atmospheric pressure, and adiabatically heated to about 800° F. to about 1250° F. in the process. This heated and compressed air is directed into a combustor, where it is mixed with fuel. The fuel is ignited, and the combustion process heats the gases to very high temperatures, in excess of about 3000° F. These hot gases pass through the turbine, where airfoils fixed to rotating turbine disks extract energy to drive the fan and compressor of the turbine, and the exhaust system, where the gases provide sufficient energy to rotate a generator rotor to produce electricity. Tight seals and precisely directed flow of the hot gases provides operational efficiency. To achieve such tight seals in turbine seals and precisely directed flow can be expensive.
Traditionally, foam structures have not been used in such harsh environments. It has been believed that only high alloy honeycomb materials were capable of withstanding such types of environments. Likewise, foam structures have not been used in other environments due to what were believed to be similar limitations.
A foam structure, and a method of fabricating a foam structure, and a turbine including a foam structure that are capable of operating within the above conditions would be desirable in the art.
In an embodiment, a foam structure includes a cast metallic foam having pores and a gel within at least a portion of the pores.
In another embodiment, a process of fabricating a foam structure includes providing a cast metallic foam having pores and infusing at least a portion of the pores with a gel.
In another embodiment, a turbine includes a rotating portion and a turbine seal. The turbine seal includes a foam structure. The foam structure includes a cast metallic foam having pores and a gel positioned within at least a portion of the pores.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.
Provided is a lower-cost turbine seal and method of fabricating a turbine seal capable of operating within the above conditions. Embodiments of the present disclosure permit use of less expensive materials in hot gas path regions, permit simpler and/or less expensive assembly and/or repair of turbine seals, permit improved operational efficiency of gas turbines, permit increased oxidation resistance, and combinations thereof.
The predetermined thickness 114 corresponds to a predetermined thickness 116 of the groove 108. For example, in one embodiment, the predetermined thickness of the edge 112 is slightly smaller than the predetermined thickness of the groove 108 and/or is formed by rotating the rotating portion 102 to abrade the turbine seal 104 to form the groove 108. In one embodiment, the predetermined thickness 116 of the groove 108 is between about ¼ inch and about ¾ inch, between about ¼ inch and about ½ inch, about ¼ inch, or about ½ inch. In one embodiment, the difference between the predetermined thickness 114 of the edge 112 and the predetermined thickness 116 of the groove 108 permits the rotating portion 102 to rotate without contacting the turbine seal 104 but provides a seal that reduces or eliminates the amount of the hot gas path 106 traveling between the turbine seal 104 and the rotating portion 102.
The turbine seal 104 is any suitable geometry.
The turbine seal 104 includes a metallic foam 118 positioned along the hot gas path 106. Referring to
The metallic foam 118 is secured to a position along the hot gas path 106. The securing is to a backing plate 120 and/or sidewalls 202. In one embodiment, the metallic foam 118 is secured by brazing or welding the metallic foam 118 to the backing plate 120 (see
In another embodiment, the metallic foam 18 is secured by mechanically securing to the backing plate 120 and/or the sidewalls 202. The mechanical securing is by any suitable mechanism, including, but not limited to, a fastener 122 such as a bolt (see
Referring to
Referring to
In one embodiment, the metallic foam 118 is additionally or alternatively mechanically secured by the latch 702 to the backing plate 120 and/or the sidewalls 202. Referring to
In one embodiment, the metallic foam 118 is additionally or alternatively mechanically secured by the interlocking feature 902 (such as a tongue and groove feature) to the backing plate 120 and/or the sidewalls 202. Referring to
Referring to
The metallic foam 118 is any suitable alloy or metal. In one embodiment, the metallic foam 118 includes stainless steel. In another embodiment, the metallic foam 118 includes a nickel-based alloy. Other suitable alloys include, but are not limited to, cobalt-based alloys, chromium-based alloys, carbon steel, and combinations thereof. Suitable metals include, but are not limited to, titanium, aluminum, and combinations thereof. As will be appreciated by those skilled in the art, the selection of the alloy or metal in the metallic foam 118 corresponds with the desired operational temperatures. However, less expensive alloys and/or metals may be selected based upon increased operational capabilities resulting from a gel infusion/impregnation treatment described below. Additionally or alternatively, the gel increases oxidation resistance of the metallic foam 118.
Referring to
The cast metallic foam is formed from any suitable cast metal alloy. For example, in one embodiment, the cast metallic alloy is a nickel-based alloy having a compositional range, by weight, of up to about 15% chromium, up to about 10% cobalt, up to about 4% tungsten, up to about 2% molybdenum, up to about 5% titanium, up to about 3% aluminum, and up to about 3% tantalum. In a further embodiment, the cast metallic alloy 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% aluminum, about 0.1% carbon, about 0.01% boron, about 2.8% tantalum, and a balance of nickel.
The gel is any suitable slurry capable of being infused within the metallic foam 118. For example, one suitable gel is a gel aluminide slurry. The gel includes a metallic component, a halide activator, and a binder. The composition of the gel provides a consistency permitting application to the turbine seal 104 by spraying, dipping, brushing, or injection.
The composition of the gel is, by weight, between about 10% and about 90% solids (the metallic component and the halide activator) with a balance being the binder. In further embodiments, with the remainder being the binder, the halide activator, and impurities, the metallic component is, by weight between about 35% and about 65%, between about 45% and about 60%, between about 50% and about 55%, or any subrange within. In these embodiments, with the remainder being the metallic component, the halide activator, and impurities, the binder is, by weight, between about 25% and about 60%, between about 25% and about 50%, between about 35% and about 40%, or any subrange within. In these embodiments, with the remainder being the binder, the metallic component, and impurities, the halide activator is, by weight, between about 1% and about 25%, between about 5% and about 25%, between about 10% and about 15%, or any subrange within.
In one embodiment, the gel has a predetermined melting point. The melting point of the gel exceeds the melting point of metallic foam 118, for example, about 1220° F. for aluminum. As such, by infusing the metallic foam 118 with the gel, the melting point of the resulting structure (for example, the seal structure) is increased.
The gel is devoid of particles larger than a predetermined size. For example, in one embodiment, the gel is devoid of particles larger than about 74 micrometers. In another embodiment, the gel is devoid of particles larger than about 149 micrometers.
The metallic component of the gel includes any suitable metal or alloy capable of forming a slurry with the halide activator and the binder. The metallic component is an alloying agent having a sufficiently high melting point so as not to deposit during a diffusion process. The metallic component serves as an inert carrier of a metal, for example, aluminum.
In one embodiment, the metallic component is metallic aluminum alloyed with chromium, for example, having a composition, by weight, of about 56% chromium and about 44% aluminum, with any remainder being aluminum and/or incidental impurities. Other suitable compositions, include but are not limited, about 30% chromium and about 70% aluminum, about 70% chromium and about 30% aluminum, about 40% chromium and about 60% aluminum, about 60% chromium and about 40% aluminum, and about 50% chromium and about 50% aluminum. In another embodiment, the metallic component includes a metallic aluminum alloyed with cobalt. In another embodiment, the metallic component includes metallic aluminum alloyed with iron.
The halide activator corresponds to the selected metallic component of the gel and/or composition of the metallic foam 118. In one embodiment, the halide activator is in the form of a fine powder. Suitable halide activators include, but are not limited to, ammonium halides, such as, ammonium chloride, ammonium fluoride, ammonium bromide, and combinations thereof. Suitable halide activators are capable of reacting with the selected metal in the metallic component, for example, aluminum, to form a volatile aluminum halide, for example AlCl3 or AlF3. In one embodiment, the halide activator is encapsulated to inhibit absorption of moisture, such as when a water-based binder is used.
The binder corresponds to the selected metallic component and the halide activator. Suitable binders include, but are not limited to, alcohol-based organic polymers, water-based organic polymers, and combinations thereof. The binder is capable of being burned off entirely and cleanly at temperatures below that required to vaporize and react the halide activator, with the remaining residue being in the form of an ash that is easily removed, for example, by forcing a gas, such as air, over the surface of the metallic foam 118. Suitable alcohol-based organic polymer binders include, but are not limited to, low molecular weight polyalcohols (polyols), such as polyvinyl alcohol. In one embodiment, the binder also includes a cure catalyst or accelerant such as hypophosphite. In another embodiment, the binder is an inorganic polymeric binder.
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.
