Abstract:
Slurry coating composition for selectively enriching surface regions of a metal-based substrate, for example, the under-platform regions of a turbine blade, with chromium. The slurry coating composition contains 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 can be used in a process that entails applying the coating composition to a surface region to form a slurry coating, and then heating the coating 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 fabricating an electrically insulating coating on a surface is disclosed comprising coating the surface with a metal, and reacting the metal coated surface with a nonmetal so as to create a film on the metal-coated surface. Alternatively, the invention provides for a method for producing a noncorrosive, electrically insulating coating on a surface saturated with a nonmetal comprising supplying a molten fluid, dissolving a metal in the molten fluid to create a mixture, and contacting the mixture with the saturated surface. Lastly, the invention provides an electrically insulative coating comprising an underlying structural substrate coated with an oxide or nitride compound
Abstract:
A substrate material to be coated with either a nitride, carbide, or oxide contains a small percent of a specific reactive element, like titanium, which forms very stable nitrides, carbides, or oxides. The material also contains larger percentages of elements, such as chromium, which form less-stable nitrides, carbides, or oxides. When the substrate material is immersed in a process medium which contains reactants, such as nitrogen, carbon, or oxygen, at a chosen elevated temperature and concentration, the less-stable nitrides, carbides, or oxides are reduced and cannot form a coating on the material surface. Thus, only a very stable nitride, carbide, or oxide can form a strong, adherent coating. As such, a stable compound forms on the surface, the surface concentration of the specific reactive element atoms (example: titanium) is depleted in relation to the atom concentration in the bulk material, and a concentration gradient results which causes more of the specific reactive element atoms to diffuse to the surface and react with the reactant in the process medium until a coating of the desired thickness is formed.
Abstract:
A process for chemical and thermal treatment of steel workpieces accompanied by the formation thereon of a coating includes diffusive precipitation onto the base metal of the workpiece of an intermetallic compound from a melt of a low-melting-point metal, such as sodium or lithium, at a temperature of from 720.degree. to 820.degree. C. for a duration of time necessary for obtaining a coating layer of required thickness.
Abstract:
A method of producing multicomponent diffusion coatings on metal articles mprises the steps of separately dissolving in a transport melt the alloying elements at temperature T equalling 0.5 to 0.8 of their respective melting points, and saturating with these alloying elements by diffusion the surface of a metal article at temperature T.sub.1 equalling 0.3 to 0.5 of the melting point of the material of this article, with the difference T-T.sub.1 being at least 50.degree. C. To perform this method, the apparatus comprises a central chamber for accommodating the transport melt and the metal article to be coated, and two (in one embodiment) peripheral chambers for accommodating the transport melt and the respective individual alloying elements, communicating via ducts. All the chambers and ducts have heating elements arranged thereon.
Abstract:
Steel product in coil form such as sheet steel is uncoiled, then preheated, continuously transported through a lead bath containing chromium, then cooled, and finally recoiled. When the coiled steel does not have titanium, titanium is included in the bath in order to improve the corrosion resistance of the final product.
Abstract:
A method of diffusing a metallic coating into a metallic substrate using molten lead, in some embodiments, as the transport medium for the metal being deposited. Has particular utility for depositing chromium on a ferrous base substrate to form a relatively high chromium content surface layer thereon. Also quite useful in providing aluminum containing surface zones. Further directed to diffusion alloying with the stabilization of ferritic phase or other means of reducing undesirable surface layer carbide formation.