Abstract: A method for promoting the environmental resistance of nickel, iron and cobalt-base superalloys of the type alloyed to develop a protective oxide scale. The method entails a technique for removing sulfur during or subsequent to the casting operation. The method generally includes casting a superalloy article in a mold cavity, and then heat treating the article while surfaces of the article are in contact with a compound containing a sulfide and/or oxysulfide-forming element, such as yttria, calcium oxide, magnesia, scandia, ceria, hafnia, zirconia, titania, lanthana, alumina and/or silica. The heat treatment is performed at a temperature sufficient to cause sulfur within the superalloy article to segregate to the surfaces of the article and react with the sulfide-forming element, thereby forming sulfides at the interface with the compound.

Abstract: A nickel-base superalloy substrate includes a surface region having an integrated aluminum content of from about 18 to about 24 percent by weight and an integrated platinum content of from about 18 to about 45 percent by weight, with the balance components of the substrate. The substrate is preferably a single-crystal advanced superalloy selected for use at high temperatures. The substrate may optionally have a ceramic layer deposited over the platinum-aluminide region, to produce a thermal barrier coating system. The platinum-aluminide region is produced by diffusing platinum into the substrate surface, and thereafter diffusing aluminum into the substrate surface.

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 coating system and method for forming the coating system on an article designed for use in a hostile environment, such as the superalloy turbine, combustor and augmentor components of a gas turbine engine. The method employs a nitrided zone in the surface of the superalloy substrate to inhibit the formation of deleterious topologically-close packed (TCP) phases in the substrate when protected by an aluminum-rich coating and optionally a thermal insulating ceramic layer. Superalloys of particular interest are those containing significant levels of TCP phase-forming elements, such as tungsten, rhenium, tantalum, molybdenum and chromium.

Abstract: A nickel-base superalloy substrate has an overlying protective coating including a modified aluminum-containing protective layer. The modified aluminum-containing protective layer is formed of nickel, aluminum, calcium in an amount of from about 50 to about 300 parts per million by weight, and, optionally, elements interdiffused into the modified aluminum-containing protective layer from the substrate. Magnesium or barium may be used instead of or in addition to the calcium. A ceramic layer may overlie the modified aluminum-containing protective layer.

Abstract: A coated article is prepared by furnishing an nickel-base article substrate having a free sulfur content of more than 0 but less than about 1 part per million by weight. A protective layer is formed at a surface of the article substrate. The protective layer includes a platinum aluminide diffusion coating. The protective layer may be substantially yttrium-free, or have a controlled amount of yttrium. A ceramic layer may overlie the protective layer.

Abstract: A coated article is prepared by furnishing an nickel-base article substrate having a free sulfur content of more than 0 but less than about 1 part per million by weight. A protective layer is formed at a surface of the article substrate. The protective layer includes a platinum aluminide diffusion coating. The protective layer may be substantially yttrium-free, or have a controlled amount of yttrium. A ceramic layer may overlie the protective layer.

Abstract: A coated article is prepared by furnishing an nickel-base article substrate having a free sulfur content of more than 0 but less than about 1 part per million by weight. A protective layer is formed at a surface of the article substrate. The protective layer includes a platinum aluminide diffusion coating. The protective layer may be substantially yttrium-free, or have a controlled amount of yttrium. A ceramic layer may overlie the protective layer.

Abstract: A nickel-base superalloy substrate includes a surface region having an integrated aluminum content of from about 18 to about 24 percent by weight and an integrated platinum content of from about 18 to about 45 percent by weight, with the balance components of the substrate. The substrate is preferably a single-crystal advanced superalloy selected for use at high temperatures. The substrate may optionally have a ceramic layer deposited over the platinum-aluminide region, to produce a thermal barrier coating system. The platinum-aluminide region is produced by diffusing platinum into the substrate surface, and thereafter diffusing aluminum into the substrate surface.

Abstract: A coating for use on a superalloy substrate comprising a diffusion barrier as an intermediate layer overlying the substrate and underlying a protective coating having a high aluminum content. The diffusion barrier layer is characterized by having low solubility for aluminum from either the substrate or the protective coating. Further, the diffusion barrier layer has low interdiffusivity for elements from the substrate and the coating, a minimal impact on the mechanical properties of the article which is coated, a minimal thermal expansion mismatch with both the substrate and the high aluminum content protective coating, and can be applied readily using existing coating application techniques. The diffusion barrier is preferably a single phase alloy or intermetallic compound.

Abstract: A tumble medium for surface treatment of an article having a first radiographic signature comprises material having a second radiographic signature different from the first radiographic signature sufficient to enable radiographic detection of the material as distinct from the article. The tumble medium is used in a method for treatment of a surface of an article including there through openings communicating with an interior of the article. After tumbling, the article is inspected by radiography to detect any tumble medium within the interior of the article.

Abstract: A tumble medium for surface treatment of an article having a first radiographic signature comprises material having a second radiographic signature different from the first radiographic signature sufficient to enable radiographic detection of the material as distinct from the article. The tumble medium is used in a method for treatment of a surface of an article including there through openings communicating with an interior of the article. After tumbling, the article is inspected by radiography to detect any tumble medium within the interior of the article.

Abstract: A tumble medium for surface treatment of an article having a first radiographic signature comprises material having a second radiographic signature different from the first radiographic signature sufficient to enable radiographic detection of the material as distinct from the article. The tumble medium is used in a method for treatment of a surface of an article including there through openings communicating with an interior of the article. After tumbling, the article is inspected by radiography to detect any tumble medium within the interior of the article.

Abstract: A thermal barrier coating system and a method for forming the coating system which yields a thermal barrier coating having good adhesion to a bond coat overlying a metal superalloy substrate. The adhesion of the bond coat and the thermal barrier coating is enhanced by forming a mature .alpha.-alumina (Al.sub.2 O.sub.3) scale at the bond coat-TBC interface. The desired mature .alpha.-alumina scale can be obtained by utilizing one or more of the following steps: preoxidation of the bond coat at certain minimum temperatures and durations; inoculation of the surface of the bond coat; surface doping or alloying of the bond coat surface; and the addition of noble metals to the bond coat. Each of these steps promotes the formation of .alpha.-alumina and avoids the formation of the .gamma., .delta. and .theta.-alumina phases which undergo phase transformations at elevated temperatures, with the result that a more spallation-resistant thermal barrier coating system is obtained.

Abstract: A nickel-base superalloy substrate includes a surface region having an integrated aluminum content of from about 18 to about 24 percent by weight and an integrated platinum content of from about 18 to about 45 percent by weight, with the balance components of the substrate. The substrate is preferably a single-crystal advanced superalloy selected for use at high temperatures. The substrate may optionally have a ceramic layer deposited over the platinum-aluminide region, to produce a thermal barrier coating system. The platinum-aluminide region is produced by diffusing platinum into the substrate surface, and thereafter diffusing aluminum into the substrate surface.

Abstract: A method and apparatus for forming a multilayer thermal barrier coating such that the coating is composed of substantially homogeneous layers of different ceramic materials. The method entails supporting an article within a coating apparatus and in proximity to ceramic ingots of the different ceramic materials, and then simultaneously directing electron beams at both ingots so as to maintain a portion of each ingot in a molten state. According to a particular aspect of this invention, vapors of both ceramic materials coexist within the coating apparatus, yet each ceramic material is sequentially deposited onto the article by sequentially interrupting exposure of surfaces of the article to the vapors, such that the vapors form homogeneous successive layers on the surface. Exposure of the article to one or more of the vapors can be interrupted with a baffle, such that the vapor of only one of the ceramic ingots is directly deposited on a given surface of the article at any instant.

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.

Abstract: A thermal barrier coating and a method for forming the coating on an article designed for use in a hostile thermal environment, such as turbine, combustor and augmentor components of a gas turbine engine. The method is particularly directed to increasing the spallation resistance of a thermal barrier coating system that includes a thermal insulating ceramic layer. The coating system of this invention generally includes a nickel aluminide alloy on which an aluminum oxide layer is formed, over which a ceramic layer is deposited so as to overlie and contact the aluminum oxide layer. The coating system does not include a bond coat, such as a diffusion aluminide or MCrAlY coating known in the prior art. The nickel aluminide alloy may be a binary NiAl alloy consisting essentially of nickel and aluminum in stoichiometric amounts, or may contain one or more oxygen-active elements.

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, such as superalloy turbine, combustor and augmentor components of a gas turbine engine. The coating system includes a carburized zone at the surface of a component on which a thermal barrier coating system is to be formed. An aluminum-rich bond coat is then formed on the carburized surface, followed by oxidation of the bond coat to form an aluminum oxide layer. A thermal insulating ceramic layer is then formed on the oxide layer, so as to be chemically bonded thereto. According to the invention, appropriately carburizing the surface of a component serves to form carbides that tie up refractory metals present in the underlying superalloy substrate of the component, and thereby prevents the detrimental effects of these metals on the bond coat-oxide layer interface.

Abstract: A method for removing an environmental coating on an article intended for use in a hostile environment, such as turbine, combustor and augmentor components of a gas turbine engine. The method is particularly suited for the repair of diffusion aluminide coatings covered by a protective oxide scale, which may further include a thermal insulating ceramic outer layer. Processing steps generally include peening the environmental coating at a temperature below the ductile-to-brittle transition temperature of the diffusion coating, such that cracks are formed in the diffusion coating. Thereafter, the diffusion coating is subjected to an acidic solution that penetrates the cracks and interacts with the coating diffusion zone, resulting in the diffusion coating being chemically stripped from its underlying substrate.