Abstract: A method for removing sand particles from a substrate is described. The method includes the step of treating the substrate with an acid solution comprising HxAF6, wherein A is selected from the group consisting of Si, Ge, Ti, Zr, Al, and Ga; and wherein HxAF6 is present at a concentration in the range from about 5 weight percent to about 40 weight percent.

Abstract: A slurry coating composition is described, which is very useful for enriching the surface region of a metal-based substrate with aluminum. The composition includes colloidal silica and particles of an aluminum-based powder, and is substantially free of hexavalent chromium. The slurry may include colloidal silica and an alloy of aluminum and silicon. Alternatively, the slurry includes colloidal silica, aluminum or aluminum-silicon, and an organic stabilizer such as glycerol. The slurry exhibits good thermal and chemical stability for extended periods of time, making it very useful for industrial applications. Related methods and articles are also described.

Abstract: The present invention provides a method for sealing pinholes in an electroless metal coating, said method comprising: (a) coating a substrate with an electroless metal coating layer to provide a coated article comprising an electroless metal coating in contact with the surface of the substrate, said electroless metal coating being characterized by the presence of pinhole imperfections which allow fluid communication between the substrate and the environment; (b) applying a layer of a curable epoxy sealant over the electroless metal coating layer and filling the pinhole imperfections; (c) curing the curable epoxy sealant to provide a cured epoxy overcoating layer; and (d) removing a substantial portion of the cured epoxy overcoating layer to provide an article comprising an electroless metal coating which is substantially free of pinhole imperfections allowing fluid communication between the substrate and the environment.

Abstract: A slurry suitable for forming facecoats, facecoats formed by such a slurry, and processes using such facecoats. The slurry is formed of a particulate refractory material, an aqueous suspension containing a particulate inorganic binder, a thixotropic organic binder, a dispersant, and possibly optional constituents excluding particulate refractory materials and inorganic binders. The particulate refractory material constitutes at least about 60 weight percent of the slurry and consists essentially of yttria. The aqueous suspension containing the particulate inorganic binder constitutes at most about 35 weight percent of the facecoat slurry. The dispersant is present in the slurry in an amount sufficient to stabilize the slurry at a pH of up to about 10, and has the general formula Hx[N(CH2)yOH]z, where x has a value of 0, 1 or 2, y has a value of 1 to 8, and z=3?x.

Abstract: Disclosed herein is a method for aluminiding an internal passage of a metal substrate comprising injecting a slurry composition that comprises a powder comprising aluminum, a binder selected from the group consisting of colloidal silica, an organic resin, and a combination thereof, into the internal passage; applying compressed air to the internal passage to facilitate distribution of the slurry composition throughout the internal passage; and, heat treating the slurry composition under conditions sufficient to remove volatile components from the composition, and to cause diffusion of aluminum into a surface of the internal passage.

Abstract: Formation of a silicon-modified aluminide coating on the under platform region of a superalloy gas turbine engine blade for improved corrosion and oxidation resistance. The coating is formed from a slurry composition including colloidal silica and aluminum-based powder and is substantially free of hexavalent chromium. The coating provides aluminum and silicon content in the outer 25% of a coating thickness of at least about 20% by weight aluminum and about 3% by weight silicon.

Abstract: A method for storing hydrogen is described. The hydrogen is infused into hollow spheres. The spheres are made from a polymer which has a tensile strength sufficient to contain hydrogen under selected internal pressure conditions; and has a permeation coefficient which can be adjusted under variable humidity conditions. Adjustment of the humidity level after the hydrogen is infused results in the walls of the spheres becoming impermeable to hydrogen. The hydrogen stored in the spheres can then be released at a desired time by readjusting the humidity level. The released hydrogen can be directed to any type of equipment which is fueled by hydrogen or otherwise uses the gas. Related articles and systems are also described.

Abstract: Slurry coating process for selectively enriching surface regions of a metal-based substrate, for example, the under-platform regions of a turbine blade, with chromium. The process employs a slurry coating composition containing metallic chromium, optionally metallic aluminum in a lesser amount by weight than chromium, and optionally other constituents. The composition further includes colloidal silica, and may also include one or more additional constituents, though in any event the composition is substantially free of hexavalent chromium and sources thereof. The coating composition is applied to a surface region to form a slurry coating, which is then heated to remove any volatile components of the coating composition and thereafter cause diffusion of chromium from the coating into the surface region to form a chromium-rich diffusion coating.

Abstract: A method for removing a metallic material from the surface of a casted substrate includes the step of contacting the metallic material with an aqueous composition which comprises an acid having the formula HxAF6, or precursors to said acid. “A” in the formula is selected from the group consisting of Si, Ge, Ti, Zr, Al, and Ga; and x is 1-6.

Abstract: A method for manufacturing a casted article is presented. The method includes steps of forming a casted article by a liquid metal cooled directional solidification process, removing a metallic material from a surface of the casted article and inspecting the surface of the casted article. The surface of the casted article is inspected for the presence of the metallic material by exposing the surface to a visualization reagent. A system for manufacturing the casted article is also presented.

Abstract: A method and aqueous composition are provided for removing at least a portion of a coating from the surface of a substrate. The coating comprises an insulative material, and is contacted with an aqueous composition. The aqueous composition comprises dimethyl formamide.

Abstract: A method for evaluating the thermal exposure of a selected metal component which has been exposed to changing temperature conditions is described. The voltage distribution on a surface of the metal component, or on a metallic layer which lies over the component, is first obtained. The voltage distribution usually results from a compositional change in the metal component. The voltage distribution is then compared to a thermal exposure-voltage model which expresses voltage distribution as a function of exposure time and exposure temperature for a reference standard corresponding to the metal component. In this manner, the thermal exposure of the selected component can be obtained. A related device for evaluating the thermal exposure of a selected metal component is also described.

Abstract: Process for roughening a surface of a base metal substrate includes contacting the surface with an aqueous solution comprising oxalic acid, sulfuric acid, and hydrogen peroxide at a temperature and for a period of time effective to roughen the surface to an average roughness greater than 60 Ra, removing a modest amount of base material, and generating no narrow and deep crevices at all. The surface is roughened prior to application of an electroless coating onto the substrate.

Abstract: A method of protecting an article from a high temperature environment, the method includes providing a substrate comprising silicon, forming a slurry coating composition, wherein the composition comprises a metallic silicon powder, a rare-earth oxide, an alkaline earth metal oxide, an aluminum oxide, or a combination comprising at least one of the foregoing, and a binder effective to chemically stabilize the slurry coating, applying a layer of the slurry coating over the substrate, and heat-treating the slurry coating under conditions sufficient to oxidize the metallic silicon powder and form an alkaline earth metal aluminosilicate, a rare-earth silicate, an aluminum silicate, or a combination comprising at least one of the foregoing bonded to the substrate.

Abstract: Multiple layers of nickel phosphorous coatings are formed by electroless plating onto a base metal substrate such as a turbine component. In one embodiment, a first nickel layer metallurgical bonded by a heat treatment process to a surface of the base metal substrate, the first nickel layer containing about 4 to about 6 weight percent phosphorous with the balance being essentially nickel; and a second nickel layer deposited onto the first layer, the second nickel layer containing about 8 to about 12 weight percent phosphorous with the balance being essentially nickel, wherein the first and second layers are formed by electroless plating. In this manner, adhesion is maximized without degrading the properties of the second layer such as corrosion resistance and ductility. Also disclosed are processes for forming the multilayered nickel phosphorus coatings.

Abstract: A method for selectively removing an aluminum-poor overlay coating from a substrate of a component, which as a result of its low aluminum content is highly resistant to a selective stripping solution. The method entails diffusing aluminum into the overlay coating to form an aluminum-infused overlay coating having an increased aluminum level in at least an outer surface thereof. The diffusion step is carried out so that the increased aluminum level is sufficient to render the aluminum-infused overlay coating removable by selective stripping. The outer surface of the aluminum-infused overlay coating is then contacted with an aqueous composition to remove the aluminum-infused overlay coating from the substrate. The aqueous composition includes at least one acid having the formula HxAF6, and/or precursors thereof, wherein A is Si, Ge, Ti, Zr, Al, and/or Ga, and x is from 1 to 6.

Abstract: A process for chemically stripping a metallic coating on an external surface of a substrate without attacking an internal surface defined by an internal passage within the substrate. Processing steps include depositing within the internal passage a thermally-decomposable wax having a melting temperature above 75° C. so as to mask the internal surface of the substrate, and then treating the substrate with an aqueous solution containing an acid having the formula HxAF6 where A is silicon, germanium, titanium, zirconium, aluminum, or gallium, and x has a value of one to six. The aqueous solution is at a temperature below the melting temperature of the wax and substantially removes the metallic coating from the external surface of the substrate, while the wax is substantially unreactive with the aqueous solution and prevents the aqueous solution from contacting the internal surface of the substrate. Thereafter, the substrate is heated to thermally decompose the wax without producing hazardous byproducts.

Abstract: An aluminizing composition includes an aluminum-based powder, an inert organic pyrolysable thickener, and a binder selected from the group consisting of colloidal silica, at least one organic resin, and combinations thereof. A method for aluminizing an internal passage of a metal substrate comprises injecting the organic-based aluminizing composition into the internal passage, heat treating the composition under conditions sufficient to remove volatile components from the composition, to cause diffusion of aluminum into surface regions of the internal passage, and to cause decomposition of at least some pyrolysable thickener particles, and burnishing excess material from the internal passage.

Abstract: Formation of a silicon-modified aluminide coating on the under platform region of a superalloy gas turbine engine blade for improved corrosion and oxidation resistance. The coating is formed from a slurry composition including colloidal silica and aluminum-based powder and is substantially free of hexavalent chromium. The coating provides aluminum and silicon content in the outer 25% of a coating thickness of at least about 20% by weight aluminum and about 3% by weight silicon.

Abstract: Braze compositions containing flux compositions and processes for using such braze compositions, such as for use in the manufacturing, coating, repair, and build-up of superalloy components. The braze composition contains an aqueous binder system, multiple inorganic compounds, titanium hydride, and a metallic braze alloy. The braze composition is useful when brazing superalloys that are prone to oxidation at elevated brazing temperatures.