Method of Protecting a Component Against Hot Corrosion

Abstract

A method of protecting a component against hot corrosion comprising the steps: (a) applying a chromium diffusion coating to the component; and (b) applying a further coating to selected regions of the chromium diffusion coating, the selected regions being chosen dependent on subsequent use of the component.

1 - 20 . (canceled)  
   
   
       21 . A turbine blade comprising: 
 an aerofoil;    a shroud arranged at a first end of the aerofoil;    a platform arranged at a second end of the aerofoil;    a root arranged adjacent the platform; and    a protective coating system for protecting the turbine blade against hot corrosion, wherein the coating system has: 
 a first layer with a chromium diffusion coating applied to the turbine blade, and  
 a second layer arranged on top of the first layer having an aluminium diffusion coating applied to the aerofoil, the shroud, the platform and the root, wherein the second layer covers the root only in part.  
   
   
   
       22 . The turbine blade according to  claim 21 , wherein the first layer covers the entire turbine blade.  
   
   
       23 . The turbine blade according to  claim 21 , wherein the chromium diffusion coating comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.  
   
   
       24 . The turbine blade according to  claim 21 , wherein the turbine blade is a nickel based superalloy turbine blade.  
   
   
       25 . A turbine blade comprising: 
 an aerofoil;    a shroud arranged at a first end of the aerofoil;    a platform arranged at a second end of the aerofoil, the platform comprising a top face arranged adjacent the aerofoil;    a protective coating system for protecting the turbine blade against hot corrosion, wherein the coating system comprises: 
 a first layer, the first layer comprising a chromium diffusion coating applied to the turbine blade, and  
 a second layer, the second layer arranged on top of the first layer and comprising a MCrAlY overlay coating, wherein M is selected from the group consisting of Ni, Co and a combination of Ni and Co, and the overlay coating is applied only to the aerofoil, the shroud and the top face of the platform.  
   
   
   
       26 . The turbine blade according to  claim 25 , wherein the first layer covers the entire turbine blade.  
   
   
       27 . A turbine blade according to  claim 25 , wherein the turbine blade comprises a third layer, wherein the third layer is an aluminium diffusion coating, arranged on top of the second layer.  
   
   
       28 . The turbine blade according to  claim 25 , wherein the MCrAlY overlay coating comprises: 
 30 to 70 weight % Nickel,    30 to 50 weight % Cobalt,    15 to 25 weight % Chromium,    5 to 15 weight % Aluminium, and    up to 1 weight % Yttrium.    
   
   
       29 . The turbine blade according to  claim 25 , wherein the MCrAlY overlay coating additionally includes at least one element selected from the group consisting of rhenium, silicon and hafnium.  
   
   
       30 . The turbine blade according to  claim 25 , wherein the chromium diffusion coating comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.  
   
   
       31 . The turbine blade according to  claim 25 , wherein the turbine blade is a nickel based superalloy turbine blade.  
   
   
       32 . A method of protecting a turbine blade against hot corrosion, comprising: 
 providing the turbine blade comprising: 
 an aerofoil,  
 a shroud arranged at a first end of the aerofoil,  
 a platform arranged at a second end of the aerofoil, and  
 a root arranged adjacent the platform;  
   applying a first layer comprising a chromium diffusion coating to the turbine blade; and    applying a second layer comprising an aluminium diffusion coating to the aerofoil, the shroud, the platform and the root, wherein the second layer covers the root only in part.    
   
   
       33 . The method according to  claim 32 , wherein the chromium diffusion coating comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.  
   
   
       34 . The method according to  claim 32 , wherein the turbine blade is a nickel based superalloy turbine blade.  
   
   
       35 . A method of protecting a turbine blade against hot corrosion, comprising: 
 providing the turbine blade, wherein the turbine blade comprises: 
 an aerofoil,  
 a shroud arranged at a first end of the aerofoil, and  
 a platform arranged at a second end of the aerofoil, the platform comprising a top face arranged adjacent the aerofoil;  
   applying a first coating layer including a chromium diffusion coating to the turbine blade; and    applying a second coating layer on top of the first coating layer to the aerofoil, the shroud and the top face of the platform, wherein the second layer is an MCrAlY overlay coating, and wherein M is selected from the group consisting of Ni, Co and a combination of Ni and Co.    
   
   
       36 . The method according to  claim 35 , further comprising applying a third coating layer on top of the MCrAlY coating, wherein the third coating is an aluminium diffusion coating.  
   
   
       37 . The method according to  claim 35 , wherein the MCrAlY coating comprises: 
 30 to 70 weight % Nickel;    30 to 50 weight % Cobalt;    15 to 25 weight % Chromium;    5 to 15 weight % Aluminium; and    up to 1 weight % Yttrium.    
   
   
       38 . The method according to  claim 35 , wherein the MCrAlY overlay coating includes at least one element selected from the group consisting of rhenium, silicon and hafnium.  
   
   
       39 . A method according to  claim 35 , wherein the chromium diffusion coating comprises 15 to 30 weight % chromium and is 5 to 25 microns thick.  
   
   
       40 . A method according to  claim 35 , wherein the turbine blade is a nickel based superalloy turbine blade.