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 of removing metallic compositions, such as abradable rub coatings, environmental coatings, bond coats and braze alloys, from the surface of a cobalt-base substrate, such as turbine shrouds and vanes of gas turbine engines. The method is particularly suited for the removal of nickel-base braze alloys and aluminum-containing coatings, the latter of which includes abradable MCrAlY coatings and environmentally-protective diffusion aluminide coatings. The process generally entails contacting such metallic compositions with an aqueous solution containing hydrochloric acid and nitric acid and at a solution temperature of about 130.degree. F. to about 180.degree. F. The solution completely removes nickel-base alloys and aluminum-containing compositions from a cobalt-base substrate without removal or damage to the underlying substrate.

Abstract: A method for repairing a thermal barrier 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 suited for the repair of thermal barrier coatings composed of an aluminide bond coat formed on the surface of an article, and an insulating columnar ceramic layer overlaying the bond coat. Processing steps generally include preparing a powder mixture of a halogen-containing activator and an aluminum-containing material, contacting the ceramic layer with the mixture, and then heating the ceramic layer for a duration sufficient to cause the halogen-containing activator to deteriorate the ceramic layer, while the aluminum-containing constituent of the mixture prevents the bond coat from being attacked or otherwise depleted by the halogen-containing activator. A suitable composition for the mixture is about 0.5 to about 1 weight percent of the halogen-containing activator and about 0.

Abstract: A nickel-base superalloy article has a coating having a composition, in weight percent, of from about 10 to about 20 percent cobalt, from about 14 to about 25 percent chromium, from about 2 to about 12 percent aluminum, from 0 to about 0.2 percent yttrium, from about 0.001 to about 3 percent boron, from about 1 to about 10 percent silicon, balance nickel and incidental impurities. The coating is preferably applied by mixing together two powders, one with a higher solidus temperature and one with a lower solidus temperature, whose net composition is that of the coating. The powder mixture is compacted with a binder, applied to a surface of the article, and heated to a temperature above the lower solidus temperature.

Abstract: A nickel-base superalloy article has a coating having a composition, in weight percent, of from about 10 to about 20 percent cobalt, from about 14 to about 25 percent chromium, from about 2 to about 12 percent aluminum, from 0 to about 0.2 percent yttrium, from about 0.001 to about 3 percent boron, from about 1 to about 10 percent silicon, balance nickel and incidental impurities. The coating is preferably applied by mixing together two powders, one with a higher solidus temperature and one with a lower solidus temperature, whose net composition is that of the coating. The powder mixture is compacted with a binder, applied to a surface of the article, and heated to a temperature above the lower solidus temperature.

Abstract: A process is provided for removing a thermal barrier coating that has been deposited on the surface of an article. Thermal barrier coatings that can be removed by the process of this invention are generally composed of a ceramic layer that is bonded to the surface of an article by a metallic bond layer. The process generally involves heating the article and its thermal barrier coating to a temperature of at least about 870.degree. C., and exposing the thermal barrier coating to a halogen-containing agent for a duration sufficient to deteriorate the bond between the thermal barrier coating and the article to the extent that the coating separates from the article without damaging the underlying surface. The process can be carried out within various types of heated enclosures, including those within which the halogen-containing agent is introduced in a gaseous state, or those in which the halogen-containing agent can be prepared as a powder mixture that changes to a vapor when heated.

Abstract: A nickel-base superalloy article has a coating having a composition, in weight percent, of from about 10 to about 20 percent cobalt, from about 14 to about 25 percent chromium, from about 2 to about 12 percent aluminum, from 0 to about 0.2 percent yttrium, from about 0.001 to about 3 percent boron, from about 1 to about 10 percent silicon, balance nickel and incidental impurities. The coating is preferably applied by mixing together two powders, one with a higher solidus temperature and one with a lower solidus temperature, whose net composition is that of the coating. The powder mixture is compacted with a binder, applied to a surface of the article, and heated to a temperature above the lower solidus temperature.

Abstract: An article with a high temperature superalloy body having a directionally oriented microsuucture and a structural discontinuity, such as a crack, or surface erosion or wear portion, is repaired, to provide a repaired article, using a mixture of Ni base ahoy powders. One powder includes a careful balance of the temperature depressants Si and B. In the one powder, Si is included in the range of about 0.05-2.2 wt. % to provide about 0.02-1.3 wt. % Si in a repaired portion as bonded with the article. In that same powder, B is include in the range of about 0.2-1.2 wt. % to provide about 0.08-0.7 wt. % in that repaired portion. In the repair method, the repaired portion can be provided, when shorter brazing times are used, with improved mechanical properties by diffusing the brazed alloy and aging the repaired structure in the range of about 1600.degree.-1700.degree. F. for a time in the range of about 1-16 hours.

Abstract: An article coated with a thermal barrier coating system for high temperature use, has its thermal cyclic spallation life improved by the application of an aluminide to the outer portion of a bonding coating disposed on a substrate. The bond coating has a surface roughness in the range of about 200-600 microinches Ra prior to application of covering thermal barrier coating.

Abstract: An article is coated with a thermal barrier coating system to increase its thermal cyclic spallation life. A single layer bond coating is applied to the surface of the article to a surface roughness in the range of 200 to 600 microinches RA by low pressure plasma spraying of coarse MCrAlY alloy particles into the surface. A metal selected from aluminum and its alloys is applied to the bond coating by aluminiding and is diffused into the bond coating to provide an aluminum-rich bond coating metal outer surface, while substantially retaining the surface roughness of about 2300 to 600 microinches RA. A metal oxide thermal barrier coating layer is then applied onto the aluminum-rich bond coating outer surface.