Abstract: A gas turbine airfoil has an external surface and an internal passage therethrough. The internal passage is selectively coated by providing a source of a flowable precursor coating material in contact with the internal passage of the airfoil, and providing a coating prevention structure overlying at least a portion of the external surface. The flowable precursor coating material is flowed from the source of the flowable precursor coating material and through the internal passage of the airfoil. The coating prevention structure prevents contact of the flowable precursor coating material with the external surface of the airfoil.

Abstract: Apparatus and method to improve vapor phase diffusion coating of articles. The apparatus provides a barrier to segregate the portion of the article requiring coating from the portion of the article not requiring coating. The fixture is reusable, being unaffected by the coating gases. The fixture reduces the exposure of the coating gases with the portion of the article not requiring coating. By use of an optional seal, the portion of the article not requiring coating can be isolated from the coating gases.

Abstract: A thermal barrier coating system and a method for forming the coating system on an article designed for use in a hostile thermal environment. The method is particularly directed to a coating system that includes a plasma-sprayed MCrAlY bond coat on which a thermal-insulating APS ceramic layer is deposited, in which the oxidation resistance of the bond coat and the spallation resistance of the ceramic layer are substantially increased by vapor phase aluminizing the bond coat. The bond coat is deposited to have a surface area ratio of at least 1.4 and a surface roughness of at least 300 &mgr;inch Ra in order to promote the adhesion of the ceramic layer. The bond coat is then overcoat aluminized using a vapor phase process that does not alter the surface area ratio of the bond coat. This process is carried out at relatively low temperatures that promote inward diffusion of aluminum relative to outward diffusion of the bond coat constituents, particularly nickel and other refractory elements.

Abstract: A method for imparting an aluminide coating to an alloy gas turbine engine component, heat treating the component, and quenching the component. The component is exposed to a source of aluminum at an elevated temperature in a coating furnace to deposit an aluminum-based oxidation barrier on the component, heated in the coating furnace to a temperature of at least the solution temperature of the alloy, and quenched by flowing a chilled inert gas around the component in the coating furnace to cool the component from the temperature of at least the solution temperature of the alloy to a temperature at which a gamma′ phase of the alloy is set in the alloy in less than about 10 minutes.

Abstract: A thermal barrier coating system and a method for forming the coating system on a component designed for use in a hostile thermal environment, such as superalloy turbine, combustor and augmentor components of a gas turbine engine. The method is particularly directed to a thermal barrier coating system that includes a thermal insulating ceramic layer and a diffusion aluminide bond coat on which an aluminum oxide scale is grown to protect the underlying surface of the component and to chemically bond the ceramic layer. The bond coat is formed to contain an additive metal of platinum, palladium, rhodium, chromium and/or silicon, and an additive element of yttrium and/or zirconium, with possible additions of hafnium. The bond coat may be formed by codepositing aluminum with the active element, or by depositing the additive metal and active element on the surface of the component, and then aluminizing to form the diffusion aluminide bond coat.

Abstract: A thermal barrier coating system and a method for forming the coating system on a component designed for use in a hostile thermal environment, such as superalloy turbine, combustor and augmentor components of a gas turbine engine. The coating system includes a diffusion aluminide bond coat whose oxide growth rate is significantly reduced to improve the spallation resistance of a thermal barrier layer by forming the bond coat to include a dispersion of aluminum, chromium, nickel, cobalt and/or platinum group metal oxides. The oxides preferably constitute about 5 to about 20 volume percent of the bond coat. A preferred method of forming the bond coat is to initiate a diffusion aluminizing process in the absence of oxygen to deposit a base layer of diffusion aluminide, and then intermittently introduce an oxygen-containing gas into the diffusion aluminizing process to form within the bond coat the desired dispersion of oxides.

Abstract: A method for imparting an aluminide coating to an alloy gas turbine engine component, heat treating the component, and quenching the component. The component is exposed to a source of aluminum at an elevated temperature in a coating furnace to deposit an aluminum-based oxidation barrier on the component, heated in the coating furnace to a temperature of at least the solution temperature of the alloy, and quenched by flowing a chilled inert gas around the component in the coating furnace to cool the component from the temperature of at least the solution temperature of the alloy to a temperature at which a gamma′ phase of the alloy is set in the alloy in less than about 10 minutes.

Abstract: A process for forming a diffusion aluminide coating on a substrate, such as a component for a gas turbine engine. The process generally entails placing the substrate in a suitable coating chamber, flowing an inert or reducing gas into and through the coating chamber, and then aluminizing the substrate using an aluminizing technique with a substantially constant aluminum activity, such as a vapor phase deposition process. During the aluminizing process, the amount of unreacted aluminum within the coating chamber is controlled by altering the flow rate of the gas through the coating chamber so that a portion of the unreacted aluminum is swept from the coating chamber by the gas. The amount of unreacted aluminum swept from the coating chamber is regulated by metering the gas flow rate in order to control the aluminizing rate and aluminum content of the resulting aluminide coating.

Abstract: A gas turbine airfoil has an external surface and an internal passage therethrough. The internal passage is selectively coated by providing a source of a flowable precursor coating material in contact with the internal passage of the airfoil, and providing a coating prevention structure overlying at least a portion of the external surface. The flowable precursor coating material is flowed from the source of the flowable precursor coating material and through the internal passage of the airfoil. The coating prevention structure prevents contact of the flowable precursor coating material with the external surface of the airfoil.

Abstract: A gas turbine airfoil has an external surface and an internal passage therethrough. The internal passage is selectively coated by providing a source of a flowable precursor coating material in contact with the internal passage of the airfoil, and providing a coating prevention structure overlying at least a portion of the external surface. The flowable precursor coating material is flowed from the source of the flowable precursor coating material and through the internal passage of the airfoil. The coating prevention structure prevents contact of the flowable precursor coating material with the external surface of the airfoil.

Abstract: A process for forming a diffusion aluminide-hafnide coating on an article, such as a component for a gas turbine engine. The process is a vapor phase process that generally entails placing the article in a coating chamber containing a halide activator and at least one donor material. The donor material collectively consists essentially of at least 0.5 weight percent hafnium and at least 20 weight percent aluminum with the balance being chromium and/or cobalt.

Abstract: A process for forming a diffusion aluminide coating on an article, such as a component for a gas turbine engine. The process is a vapor phase process that generally entails placing the article in a coating chamber containing an aluminum donor material, without any halide carrier or inert filler present. The aluminum donor material consists essentially of about 20 to about 70 weight percent aluminum, with the balance being chromium or cobalt. While the article is held out of contact with the donor material, coating is initiated in an inert or reducing atmosphere by heating the article and the donor material to vaporize the aluminum constituent of the donor material, which then condenses on the surface of the article and diffuses into the surface to form a diffusion aluminide coating on the article.

Abstract: A process for reclaiming aluminum alloy donor from a vapor phase deposition process used to form a diffusion aluminide coating on a component, such as the high-temperature superalloy components of gas turbine engines. The process generally entails recycling a particulate aluminum alloy donor material that, as a result of having been used as the donor material for depositing a diffusion aluminide coating on an article by vapor phase deposition, particles of the donor material comprise an aluminum alloy core encased in an aluminum-depleted shell. The process generally entails tumbling the donor material in a manner that removes the aluminum-depleted shell, followed by sieving the donor material to remove shell fragments and undersized particles.

Abstract: Apparatus and method to improve vapor phase diffusion coating of articles. The apparatus provides a barrier to segregate the portion of the article requiring coating from the portion of the article not requiring coating. The fixture is reusable, being unaffected by the coating gases. The fixture reduces the exposure of the coating gases with the portion of the article not requiring coating. By use of an optional seal, the portion of the article not requiring coating can be isolated from the coating gases.

Abstract: A method of removing a diffusion aluminide coating on a component designed for use in a hostile environment, such as superalloy turbine, combustor and augmentor components of a gas turbine engine. The method selectively removes an aluminide coating by stripping aluminum from the coating without causing excessive attack, alloy depletion and gross thinning of the underlying superalloy substrate. Processing steps generally include contacting the coating with a mixture that contains a halogen-containing activator and a metallic powder containing an aluminide-forming metal constituent, such as by pack cementation-type process. The mixture is then heated to a temperature sufficient to vaporize the halogen-containing activator and for a duration sufficient to cause the halogen-containing activator to provide a transfer mechanism for the removal of aluminum from at least a portion of the diffusion aluminide coating, while the metallic powder absorbs the removed aluminum.

Abstract: A thermal barrier coating system and a method for forming the coating system on a component designed for use in a hostile thermal environment, such as superalloy turbine, combustor and augmentor components of a gas turbine engine. The coating system includes a diffusion aluminide bond coat whose oxide growth rate is significantly reduced to improve the spallation resistance of a thermal barrier layer by forming the bond coat to include a dispersion of aluminum, chromium, nickel, cobalt and/or platinum group metal oxides. The oxides preferably constitute about 5 to about 20 volume percent of the bond coat. A preferred method of forming the bond coat is to initiate a diffusion aluminizing process in the absence of oxygen to deposit a base layer of diffusion aluminide, and then intermittently introduce an oxygen-containing gas into the diffusion aluminizing process to form within the bond coat the desired dispersion of oxides.

Abstract: A process for simultaneously vapor phase aluminizing nickel-base and cobalt-base superalloys within a single process chamber using the same aluminum donor and activator, to yield diffusion aluminide coatings of approximately equal thickness. The process entails the use of an aluminum donor containing about 50 to about 60 weight percent aluminum, and an aluminum fluoride activator present in an amount of at least 1 gram per liter of coating chamber volume. Nickel-base and cobalt-base superalloys are simultaneously vapor phase aluminized for 4.5 to 5.5 hours at a temperature of about 1900.degree. F. to about 1950.degree. F. in an inert or reducing atmosphere. With these materials and process parameters, diffusion aluminide coatings are developed on both superalloys whose thicknesses do not differ from each other by more than about 30%.

Abstract: A high temperature vapor coating container, including a hollow interior, resists distortion and cracking at a vapor coating temperature of at least about 1700.degree. F. as a result of making the container of a nonmetallic material having a coefficient of thermal expansion of less than about 4.5.times.10.sup.-6 at the vapor coating temperature, the material being nonreactive with the coating vapor at the vapor coating temperature.

Abstract: A method for preventing clouding of a lens employed in a high-temperature oxidizing environment, an example of which is a lens of a pyrometer used to sense exhaust gas temperature (EGT) of a gas turbine engine. Clouding is prevented by inhibiting the generation of volatile oxide species that react with high-temperature lens materials, forming deposits including oxides of chromium, molybdenum and other elements having volatile oxide species. The method is particularly directed to a pyrometer whose lens is formed of sapphire (alumina) or silica, and is mounted within a structure formed of a material containing chromium and/or molybdenum, such as a superalloy or stainless steel. The method entails forming an alumina scale-forming barrier coating such as a diffusion aluminide on surfaces of the structure that are subject to oxidation and high temperatures.