Methods for Applying Thermal Barrier Coatings

Abstract

A method for coating a substrate includes suspension plasma spraying of a size distribution of a ceramic powder of essentially uniform chemical composition to form a first ceramic layer. The size distribution has a trough spanning a transition size for powder behavior of gas-flow trajectories of smaller particles and ballistic trajectories of larger particles.

What is claimed is: 
     
         1 . A method for coating a substrate, the method comprising suspension plasma spraying of a bimodal size distribution of a ceramic powder of essentially uniform chemical composition to form a first ceramic layer, the bimodal size distribution having a trough spanning a transition size for powder behavior of gas-flow trajectories of smaller particles and ballistic trajectories of larger particles. 
     
     
         2 . The method of  claim 1  wherein:
 the bimodal distribution is in a common body of powder. 
 
     
     
         3 . The method of  claim 1  wherein:
 the first layer has a thickness of 50 micrometers to 1000 micrometers. 
 
     
     
         4 . The method of  claim 1  wherein the bimodal distribution comprises by weight:
 at least 42.9% at or below 0.818 micrometer; 
 at least 13.5% above 1.156 micrometer; and 
 no more than 27.2% between 0.818 micrometer and 1.156 micrometer. 
 
     
     
         5 . The method of  claim 1  wherein the bimodal distribution comprises by weight:
 at least 45.7% at or below 0.818 micrometer; 
 at least 21.0% above 1.156 micrometer; and 
 no more than 24.6% between 0.818 micrometer and 1.156 micrometer. 
 
     
     
         6 . The method of  claim 1  further comprising:
 applying a bond coat to the substrate prior to said spraying. 
 
     
     
         7 . The method of  claim 1  further comprising:
 applying a top coat after said spraying. 
 
     
     
         8 . The method of  claim 1  further comprising:
 applying at least one additional ceramic layer to the substrate prior to said spraying. 
 
     
     
         9 . The method of  claim 8  wherein:
 the applying at least one additional ceramic layer is of a unimodal distribution. 
 
     
     
         10 . The method of  claim 8  wherein:
 the applying at least one additional ceramic layer is of a lesser D50 than a D50 of the bimodal size distribution. 
 
     
     
         11 . The method of  claim 10  wherein:
 the applying the at least one additional ceramic layer is before the suspension plasma spraying; and 
 the applying is also by suspension plasma spraying. 
 
     
     
         12 . The method of  claim 10  wherein:
 the at least one additional ceramic layer is characterized by higher porosity than the ceramic layer. 
 
     
     
         13 . The method of  claim 1  further comprising pre-blending the ceramic powder from at least two different size distributions. 
     
     
         14 . The method of  claim 1  wherein:
 the substrate has an airfoil, the airfoil having a leading edge, a trailing edge, a pressure side, and a suction side. 
 
     
     
         15 . A method for coating a substrate, the method comprising:
 blending two or more ceramic powders including a first powder and a second powder of different size distribution from each other but essentially like chemical composition to form a blend; and   suspension plasma spraying of the blend.   
     
     
         16 . The method of  claim 15  wherein the blending and the suspension plasma spraying are performed iteratively to balance powder behavior of gas-flow trajectories of smaller particles and ballistic trajectories of larger particles and limit sensitivity to compositional variations. 
     
     
         17 . The method of  claim 15  wherein the blending is a blending of suspensions of the respective powders or a blending of the respective powders prior to forming the suspension. 
     
     
         18 . A method for coating a substrate, the method comprising:
 suspension plasma spraying of a ceramic powder of size distribution of:
 at least 42.9% at or below 0.818 micrometer; 
 at least 13.5% above 1.156 micrometer; and 
 no more than 27.2% between 0.818 micrometer and 1.156 micrometer. 
   
     
     
         19 . The method of  claim 18  wherein:
 the ceramic powder is of essentially uniform chemical composition. 
 
     
     
         20 . The method of  claim 18  wherein:
 the distribution has a trough spanning a transition size for powder behavior of gas-flow trajectories of smaller particles and ballistic trajectories of larger particles.