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Mischmetal oxide tbcRelated Patent Categories: Stock Material Or Miscellaneous Articles, Composite (nonstructural Laminate), Of Inorganic Material, Metal-compound-containing Layer, Next To Second Metal-compound-containing LayerMischmetal oxide tbc description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070122658, Mischmetal oxide tbc. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a Divisional of U.S. patent application Ser. No. 10/792,161, filed Mar. 3, 2004, the entire contents of which are incorporated herein by reference in their entirety. FIELD OF THE INVENTION [0002] The present invention relates to thermal barrier coatings for components exposed to high temperatures, such as the hostile thermal environment of a gas turbine engine. More particularly, this invention is directed to thermal barrier coatings comprising mischmetal oxide. BACKGROUND OF THE INVENTION [0003] Higher operating temperatures for gas turbine engines are continuously sought in order to increase their efficiency. However, as operating temperatures increase, the high temperature durability of the components of the engine must correspondingly increase. While significant advances have been achieved with iron, nickel and cobalt-base superalloys, the high-temperature capabilities of these alloys alone are often inadequate for components located in certain sections of a gas turbine engine, such as the turbine, combustor and augmentor. A common solution is to thermally insulate such components in order to minimize their service temperatures. For this purpose, thermal barrier coatings (TBC) formed on the exposed surfaces of high temperature components have found wide use. [0004] To be effective, thermal barrier coatings must have low thermal conductivity and adhere well to the component surface. Various ceramic materials have been employed as the TBC, particularly yttria (Y.sub.2O.sub.3) stabilized zirconia (ZrO.sub.2), commonly known as YSZ. This material is widely employed in the art because it can be readily deposited by plasma spray and vapor deposition techniques. In addition, YSZ has good erosion and impact resistance. An example of the latter is electron beam physical vapor deposition (EB-PVD), which produces a thermal barrier coating having a columnar grain structure that is able to expand with its underlying substrate without causing damaging stresses that lead to spallation, and therefore exhibits enhanced strain tolerance. The component is supported in proximity to an ingot(s) of the ceramic coating material (e.g., YSZ in a vacuum), and an electron beam is projected onto the ingot(s) so as to melt the surface of the ingot and produce a vapor of the coating material that deposits onto the component. Such EB-PVD deposited TBCs are generally deposited to a thickness in the range of about 0.005 inch to about 0.010 inch. Adhesion of the TBC to the component is often further enhanced by the presence of a metallic bond coat, such as a diffusion aluminide or an oxidation-resistant alloy such as MCrAlX, where M is iron, cobalt and/or nickel, and where X is yttria and/or another rare earth oxide [0005] However, the application of a TBC by the EB-PVD process is expensive and time consuming due to the thickness of the coating. Also, maintenance of the EB-PVD apparatus is performed as a function of operation of the apparatus, so fewer parts having a thick coating can be processed in the period of time between maintenance operations. In addition, the thickness of the coating increases the load on the coated part in a high acceleration G-load environment, particularly for TBC coated blades in a high pressure turbine. One of the properties of the TBC that determines the required thickness of the TBC is the thermal conductivity of the TBC, since a coating with lower thermal conductivity does not have to be as thick as a coating with higher thermal conductivity in order to obtain the same thermal protection for the substrate. Developments in the past have led to TBCs with lower thermal conductivity simply by changing the manner in which the TBC is applied using EB-PVD. [0006] One such method is set forth in U.S. Pat. No. 6,620,465 ('465) to Rigney et al. and assigned to the assignee of the present invention. The '465 patent is directed to a method of improving the thermal conductivity of the TBC resulting from an EB-PVD by moving the article to be coated further from the ingot or source of ceramic material. [0007] In view of the above, there is considerable motivation to further reduce the thickness of the TBC through the use of materials that are lower in thermal conductivity. However, limitations of the prior art are often the result of the relatively narrow range of acceptable and readily available materials. Accordingly, new materials for use in the EB-PVD process are continuously being sought for depositing coatings, and particularly ceramic coatings such as TBCs. [0008] What is needed is a new type of material for use in the EB-PVD process that has lower thermal conductivity, better erosion resistance, and/or better impact resistance than presently available TBC materials and is processible for use in TBC materials. In particular, a material is needed that has a lower thermal conductivity, and at least comparable erosion resistance, and/or impact resistance as YSZ. SUMMARY OF THE INVENTION [0009] The present invention is a turbine engine component comprising a superalloy substrate, a bond coat overlying the substrate having a thickness in the range of about 0.0005 inch to about 0.005 inch, a thin alumina scale overlying the bond coat, and a thermal barrier coating (TBC) overlying the thin alumina scale, the TBC having a thickness in the range of about 0.0025 inch to about 0.010 inch, and comprising at least mischmetal oxide. [0010] The present invention is a turbine engine component comprising a superalloy substrate, a bond coat overlying the substrate having a thickness in the range of about 0.0005 inch to about 0.005 inch, a thin alumina scale overlying the bond coat, and a TBC overlying the thin alumina scale, the TBC having a thickness in the range of about 0.0025 inch to about 0.010 inch, and a plurality of layers, wherein at least one of the layers comprises at least mischmetal oxide. [0011] As is known in the art, most rare earth oxides are found in one type of ore, commonly known as mischmetal ore, which, once mined, is cleaned and then smelted to a mixture of rare-earth metals, such as cerium (Ce), lanthanum (La), praseodymium (Pr), and neodymium (Nd), and impurities. This mixture of metals is commonly known as "mischmetal." As used herein the term "mischmetal" refers to clean mischmetal ore as known in the art. As used herein the term "mischmetal oxide" means oxidized clean mischmetal ore as known in the art that is obtained by oxidizing clean mischmetal. The specific combination of rare earth metals in the mischmetal ore varies depending on the mine and vein from which the ore was extracted. Mischmetal generally has a composition, based on 100% of weight, of about 30% to about 70% Ce by weight, about 19% to about 56% La by weight, about 2% to about 7% Pr by weight and from about 0% to about 20% Nd by weight, and impurities. Mischmetal is often refined to its individual rare-earth metals constituents. The present invention uses mischmetal, which has not been separated and refined into its individual metal constituents, as a source of oxides for the deposition of TBC by EB-PVD, such that the TBC comprises the rare earth oxides present in mischmetal. [0012] The present invention is also a method for the application of a mischmetal oxide TBC to a superalloy turbine engine component including the steps of providing an electron beam physical vapor deposition apparatus, providing a turbine engine component comprising a surface to be coated, providing a first mischmetal ingot, and providing a second ingot comprising another oxide material selected from the group consisting of yttria-stablized zirconia, zirconia, yttria, hafnia, at least one other rare earth oxide, and combinations thereof. The component and the ingots are placed in to the apparatus as known in the art. Melt pools are formed on the ingots by the electron beam as known in the art. The mischmetal is then oxidized by bleeding a small controlled amount of oxygen into the EB-PVD apparatus. Mischmetal oxide vapors and other oxide vapors are then dispersed as known in the art. The mischmetal oxide vapors and the yttria-stabilized vapors are then deposited onto the surface to be coated. The deposition process forms a TBC having a thickness in the range of about 0.0025 inch to about 0.010 inch. Thicker TBCs provide enhanced thermal protection. [0013] As is known in the art, thermal conductivity is calculated by the following equation:k=.alpha..rho.C.sub.p [0014] where k is thermal conductivity (W/m/K), .alpha. is thermal diffusivity (cm.sup.2/s), .rho. is density (g/cm.sup.3), and C.sub.p is specific heat (Ws/g/K). The higher the thermal conductivity of a TBC material, the thicker the TBC has to be, as the purpose of the TBC is to resist heat transfer of heat from the hot gases of combusting into the underlying superalloy substrate. Preferably, the thermal conductivity of the TBC should be lower so that a thinner TBC layer may be used. The TBC formed that includes the mischmetal oxide has a lower thermal conductivity than does YSZ. [0015] The present invention is also a method for the application of oxide TBC that includes a mischmetal oxide to a superalloy turbine engine component including the steps of providing an electron beam physical vapor deposition apparatus, providing a turbine engine component comprising a surface to be coated, providing a first ingot that includes mischmetal oxide, and providing an second ingot comprising another oxide material selected from the group consisting of yttria-stablized zirconia, zirconia, yttria, hafnia, at least one other rare earth oxide, and combinations thereof. The component and the ingots are placed in the EB-PVD apparatus as known in the art. Melt pools are formed on the ingots as known in the art. Mischmetal oxide vapors and other oxide vapors are then dispersed as known in the art. The mischmetal oxide vapors and other oxide vapors are then deposited onto the surface to be coated. The deposition process forms a TBC having a thickness in the range of about 0.0025 inch to about 0.010 inch. [0016] The present invention is also a method for the application of an oxide TBC that includes a mischmetal oxide to a superalloy turbine engine component including the steps of providing an electron beam physical vapor deposition apparatus, providing a turbine engine component comprising a surface to be coated, and providing an ingot that includes a mischmetal oxide. The component and the ingot are placed in the apparatus as known in the art. Melt pools are formed on the ingot as known in the art. Mischmetal oxide vapors are then dispersed as known in the art. The mischmetal oxide vapors are then deposited onto the surface to be coated. The deposition process forms a TBC having a thickness in the range of about 0.0025 inch to about 0.010 inch. [0017] The present invention is also a method for the application of a TBC that includes a mischmetal oxide to a superalloy turbine engine component including the steps of providing an electron beam physical vapor deposition apparatus, providing a turbine engine component comprising a surface to be coated, and providing an ingot that includes mischmetal oxide and another oxide material selected from the group consisting of yttria-stablized zirconia, zirconia, yttria, hafnia, at least one other rare earth oxide, and combinations thereof. The component and the ingot are placed in the EB-PVD apparatus as known in the art. Melt pools are formed on the ingot by the electron beam as known in the art. Mischmetal oxide vapors and other oxide vapors are then dispersed as known in the art. The mischmetal oxide vapors and other oxide vapors are then deposited onto the surface to be coated. The deposition process forms a TBC having a thickness in the range of about 0.0025 inch to about 0.010 inch. [0018] An advantage of the present invention is that the use of the rare earth oxides in the mischmetal oxide, which have lower thermal conductivity than yttria-stabilized zirconia, reduces the conductivity of the TBC, allowing a thinner TBC layer to be applied to the turbine engine component. [0019] Another advantage of the present invention is erosion resistance of the TBC layer is improved through the use of the rare earth oxides in the mischmetal, which are believed to have at least comparable erosion resistance compared to yttria-stabilized zirconia. [0020] Another advantage of the present invention is that the impact resistance of the TBC layer is improved through the use of the rare earth oxides in the mischmetal, which are believed to have at least comparable impact resistance compared to yttria-stabilized zirconia. [0021] Another advantage of the present invention is that using a mischmetal or a mischmetal oxide ingot separate along with another oxide ingot permits intermittent co-evaporation, which allows the deposition of a TBC comprising a plurality of layers with different properties. Continue reading about Mischmetal oxide tbc... Full patent description for Mischmetal oxide tbc Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Mischmetal oxide tbc patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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