Single phase platinum aluminide bond coat

Abstract

A thermal barrier coating system having an improved life as a result of a preoxidation treatment applied to a single phase platinum aluminide bond coat. After coating the substrate to form a diffusion platinum aluminum bond coat, the surface finish of the bond coat was grit blasted with an inert grit of preselected size at a preselected pressure to achieve a predetermined surface finish. After the grit blasting, but before application of the ceramic top coat of yttria-stabilized zirconia (YSZ), the coating was preoxidized to form a thin alumina scale by heat treating the diffusion platinum aluminide bond coat at an elevated temperature at a preselected partial pressure of oxygen.

1 - 18 . (canceled)  
     
     
         19 . A gas turbine component having at least a portion of an outer surface coated with a ceramic thermal barrier system that has a single phase platinum aluminide coating with a pure alumina layer formed with a method comprising the steps of: 
 providing a gas turbine component for use at high temperatures;    applying a thin layer of platinum to at least a portion of a surface of the component;    forming a single phase platinum aluminide on the surface of the component by exposing the thin layer of platinum to a source of aluminum for a preselected time; then,    producing a surface of the single phase platinum aluminide having a surface finish between about 16 microinches R a  and 125 microinches R a ;    cleaning the single phase platinum aluminide to provide a surface free of oxides, contaminants and local gradients of nickel, aluminum and platinum; then,    preoxidizing the single phase platinum aluminide by heating the component in a preselected partial pressure of oxygen, wherein the preoxidation is accomplished by heating the component to a preselected temperature at a preselected rate so as to form a thin layer of pure alumina over the single phase platinum aluminide; followed by,    applying a ceramic top coat over the thin layer of pure alumina.    
     
     
         20 . The gas turbine component of  claim 19 , wherein the step of forming a single phase platinum aluminide by exposing the thin layer of platinum to a source of aluminum for a preselected time includes exposing the thin layer of platinum to a source of vapor phase aluminum for sufficient time and at a sufficiently high temperature to form a single phase platinum aluminide.  
     
     
         21 . The gas turbine component of  claim 19  wherein the step of preoxidizing the single phase platinum aluminide is accomplished by heating the component in a vacuum furnace at a partial pressure of oxygen between 1000 Mbar and 10 −5  mbar.  
     
     
         22 . The gas turbine component of  claim 20  wherein the step of preoxidizing the single phase platinum aluminide is accomplished by heating the component in a vacuum furnace at a partial pressure of oxygen between 1000 Mbar and 10 −5  mbar.  
     
     
         23 . The gas turbine component of  claim 19  wherein the pure alumina layer is formed at a preselected temperature is in the range of about 1800° F. to about 2100° F.  
     
     
         24 . The gas turbine component of  claim 20  wherein the pure alumina layer is formed at a preselected temperature is in the range of about 1800° F. to about 2000° F.  
     
     
         25 . The method of  claim 19  wherein the step of applying a ceramic top coat uses a PVD technique over the thin layer of pure alumina by applying the ceramic top coat within a preselected temperature range includes applying a yttria-stabilized zirconia using EB-PVD.  
     
     
         26 . A gas turbine component comprising: 
 a superalloy substrate having a surface;    a single phase platinum aluminide bond coat having a surface on at least a portion of the surface of the substrate, the platinum aluminide bond coat having a surface, the bond coat surface being free of contaminants and local gradients of nickel, aluminum and platinum;    a pure alumina layer having a compact microstructure overlying the surface of the platinum aluminide bond coat, the bond coat surface being free of oxides other than the pure alumina; and    a ceramic top coat overlying the pure alumina layer.    
     
     
         27 . The gas turbine component of  claim 26 , wherein the bond coat surface has a roughness in the range of about 16 microinches R a  and about 125 microinches R a .  
     
     
         28 . The gas turbine component of  claim 26 , wherein the superalloy is a nickel-based superalloy.  
     
     
         29 . The gas turbine component of  claim 26 , wherein the superalloy is René N5.  
     
     
         30 . The gas turbine component of  claim 26 , wherein a diffusion barrier is imposed between the superalloy substrate and the bond coat.  
     
     
         31 . The gas turbine component of  claim 27 , wherein the superalloy is a nickel-based superalloy.  
     
     
         32 . The gas turbine component of  claim 27 , wherein the superalloy is René N5.  
     
     
         33 . A gas turbine component having at least a portion of an outer surface coated with a ceramic thermal barrier system that has a single phase platinum aluminide coating with a pure alumina layer formed with a method comprising the steps of: 
 providing a gas turbine component for use at high temperatures;    applying a thin layer of platinum to at least a portion of a surface of the component;    forming a single phase platinum aluminide on the surface of the component by exposing the thin layer of platinum to a source of aluminum for a preselected time;    grit blasting the single phase platinum aluminide using a grit of preselected size at a preselected pressure for a time sufficient to achieve a preselected surface finish;    preoxidizing the single phase platinum aluminide by heating the component in a partial pressure of oxygen between 10 −5  mbar and 1000 Mbar, wherein the preoxidation is accomplished by heating the component to a preselected temperature at a preselected rate so as to form a thin layer of pure alumina over the single phase platinum aluminide; followed by,    applying a ceramic top coat over the thin layer of pure alumina.    
     
     
         34 . The gas turbine component of  claim 33 , wherein the step of forming a single phase platinum aluminide by exposing the thin layer of platinum to a source of aluminum for a preselected time includes exposing the thin layer of platinum to a source of vapor phase aluminum for sufficient time and at a sufficiently high temperature to form a single phase platinum aluminide.  
     
     
         35 . The gas turbine component of  claim 33 , wherein the step of grit blasting the single phase platinum aluminide using a grit of preselected size at a preselected pressure includes selecting an alumina grit having a size classification from about #60 to about #120.  
     
     
         36 . The gas turbine component of  claim 35 , wherein the step of grit blasting the single phase platinum aluminide using a grit of preselected size at a preselected pressure includes selecting an alumina grit having a size classification of about #80.  
     
     
         37 . The gas turbine component of  claim 33 , wherein the step of preoxidizing the single phase platinum aluminide by heating includes heating the component in a partial pressure of oxygen of about 10 −4  mbar.  
     
     
         38 . The gas turbine component of  claim 35 , wherein the step of preoxidizing the single phase platinum aluminide by heating includes heating the component in a partial pressure of oxygen of about 10 −4  mbar.  
     
     
         39 . A method for coating a gas turbine component with a thermal barrier coating system by a controlled preoxidation heat treatment, comprising the steps of: 
 providing a gas turbine component for use at high temperatures;    applying a thin layer of platinum to at least a portion of a surface of the component;    forming a single phase platinum aluminide on the surface of the component by exposing the thin layer of platinum to a source of aluminum for a preselected time;    grit blasting the single phase platinum aluminide using a grit of preselected size at a preselected pressure for a preselected period of time to achieve a preselected surface finish; then,    preoxidizing the single pahse platinum aluminide by heating the component in at a preselected partial pressure of oxygen between 10 −5  mbar and 1000 Mbar, wherein the preoxidation is accomplished by heating the component to a preselected temperature at a preselected rate so as to form a thin layer of pure alumina over the single phase platinum aluminide; followed by,    applying a ceramic top coat over the thin layer of pure alumina.    
     
     
         40 . The method of  claim 39 , wherein the step of preoxidizing the single phase platinum aluminide the component at a preselected partial pressure of oxygen between 10 −5  mbar and 1000 Mbar includes heating the component at a preselected partial pressure of oxygen of about 10 −4  mbar.