Thermal barrier coating for turbine bucket platform side faces and methods of application

Abstract

Grooves are formed along portions of the side edges of a turbine bucket platform and open through the side edges of the surface of the platform exposed to the hot gas path of the turbine. A bond coat is applied to the groove followed by a thermal barrier coating which is preferably plasma sprayed onto the bond coat. The thermal barrier coating thickness protects the coating beyond the surface of the bare metal of the platform side and is then abraded or ground to lie flush with the bare metal surface. Thus, the side faces of the platform have a thermal barrier coating to reduce oxidation.

1 . A bucket for a turbine comprising: 
 an airfoil, a root and a platform intermediate said airfoil and said root, said platform having generally circumferentially facing side faces for registration with generally corresponding side faces of adjacent buckets;    each of said platform side faces having a groove therein opening circumferentially outwardly through said side faces; and    a thermal barrier coating in said grooves and exposed along the side faces of the platform.    
   
   
       2 . A bucket according to  claim 1  including a bond coat between the side faces of said platform and the thermal barrier coating to facilitate adherence of the thermal barrier coating and the platform side faces to one another.  
   
   
       3 . A bucket according to  claim 1  wherein said thermal barrier coating lies generally flush with remaining portions of the side faces.  
   
   
       4 . A bucket according to  claim 1  wherein a surface of the platform forming part of a hot gas path through the turbine includes a thermal barrier coating, the thermal barrier coating on the surface and side faces forming continuations of one another.  
   
   
       5 . A bucket according to  claim 1  wherein the groove opens outwardly through said surface of the platform.  
   
   
       6 . A method of protecting side faces of a platform of a turbine bucket comprising the steps of: 
 forming a groove along a side face of the platform opening circumferentially outwardly through said side faces;    applying a bond coat to the groove;    applying a thermal barrier coating to the bond coating; and    removing a portion of the thermal bond coating along said side face to render side face portions having the applied thermal barrier coating thereon and bare metal to lie flush with one another.    
   
   
       7 . A method according to  claim 6  wherein the step of removing includes abrading the thermal barrier coating.  
   
   
       8 . A method according to  claim 6  including applying the bond coating and the thermal barrier coating to the platform surface to form a continuous thermal barrier coating surface along the platform surface and at least portions of the side faces.  
   
   
       9 . A method according to  claim 6  including applying the thermal bond coating to a thickness wherein a portion thereof projects beyond uncoated remaining portions of said platform side face, and removing said projected portion to leave a thermal bond coating surface substantially flush with said uncoated remaining portions of the platform side face.