Coating methods and coated articles

Abstract

One aspect of the present invention includes a method. The method includes combusting a fuel and an oxidant in a combustion chamber of a thermal spray gun to form a combustion stream. The method further includes injecting a liquid and a feedstock material into the combustion stream in the combustion chamber to form an entrained feedstock stream, wherein the feedstock material includes a plurality of cermet particles having a median particle size of less than about 5 microns. The method further includes directing the entrained feedstock stream on a surface of a substrate to form a coating, wherein a temperature of the plurality of cermet particles in the entrained feedstock stream is less than a melting temperature of the plurality of cermet particles. Coated articles are also presented.

1 . A method, comprising:
 combusting a fuel and an oxidant in a combustion chamber of a thermal spray gun to form a combustion stream;   injecting a liquid and a feedstock material into the combustion stream in the combustion chamber to form an entrained feedstock stream, wherein the feedstock material comprises a plurality of cermet particles having a median particle size of less than about 5 microns; and   directing the entrained feedstock stream on a surface of a substrate to form a coating,   wherein a temperature of the plurality of cermet particles in the entrained feedstock stream is less than a melting temperature of the plurality of cermet particles.   
     
     
         2 . The method of  claim 1 , wherein maintaining the temperature of the plurality of cermet particles in the entrained feedstock stream to be less than the melting temperature of the plurality of cermet particles is effected substantially by the liquid. 
     
     
         3 . The method of  claim 1 , further comprising injecting the liquid in an amount sufficient to provide a thermal barrier for the plurality of cermet particles in the entrained feedstock stream. 
     
     
         4 . The method of  claim 1 , wherein the temperature of the plurality of cermet particles in the entrained feedstock stream is maintained to be less than the melting temperature of the plurality of cermet particles without the addition of an external coolant. 
     
     
         5 . The method of  claim 1 , wherein a temperature of the plurality of cermet particles in the entrained feedstock stream is less than about 0.9 times the melting temperature of the plurality of cermet particles. 
     
     
         6 . The method of  claim 1 , wherein injecting the liquid and the feedstock material into the combustion stream comprises injecting a feedstock mixture comprising the feedstock material disposed in the liquid through a liquid injection port disposed in the thermal spray gun. 
     
     
         7 . The method of  claim 1 , wherein the liquid and the feedstock material are injected into the combustion stream through a coaxial injection tube port disposed in the thermal spray gun. 
     
     
         8 . The method of  claim 7 , wherein the feedstock material is injected into the combustion stream through an inner tube of the coaxial injection port, and the liquid is injected into the combustion stream through an outer tube of the coaxial injection port. 
     
     
         9 . The method of  claim 1 , wherein the thermal spray gun comprises a high velocity air fuel (HVAF) spray gun or a high velocity oxygen fuel (HVOF) spray gun. 
     
     
         10 . The method of  claim 1 , wherein the liquid comprises water, alcohol, an organic combustible liquid, an organic incombustible liquid, or combinations thereof. 
     
     
         11 . The method of  claim 1  wherein the plurality of cermet particles comprise a ceramic phase comprising carbides, nitrides, or combinations thereof. 
     
     
         12 . The method of  claim 1 , wherein the plurality of cermet particles comprise a metallic phase comprising cobalt, chromium, nickel, tungsten, or combinations thereof. 
     
     
         13 . The method of  claim 1 , wherein the plurality of cermet particles are present in the feedstock mixture at a concentration in a range from about  1  weight percent to about 50 weight percent of the feedstock mixture. 
     
     
         14 . The method of  claim 1 , wherein the plurality of cermet particles have a median particle size in a range from about 500 nanometers to about 3 microns. 
     
     
         15 . The method of  claim 1 , wherein the substrate comprises a component of a steam turbine. 
     
     
         16 . The method of  claim 1 , wherein the substrate comprises a component of a gate valve. 
     
     
         17 . A method, comprising:
 combusting a fuel and an oxidant in a combustion chamber of a thermal spray gun to form a combustion stream;   injecting a liquid into the combustion stream in the combustion chamber through an outer tube of a coaxial injection port disposed in the thermal spray gun;   injecting a feedstock material into the combustion stream in the combustion chamber through an inner tube of a coaxial injection port disposed in the thermal spray gun to form an entrained feedstock stream, wherein the feedstock comprises a plurality of cermet particles having a median particle size of less than about 5 microns; and   directing the entrained feedstock stream on a surface of a substrate to form a coating,   wherein a temperature of the plurality of cermet particles in the entrained feedstock stream is less than a melting temperature of the plurality of cermet particles.   
     
     
         18 . An article, comprising:
 a substrate and a coating disposed on the substrate,   wherein the coating comprises a plurality of cermet particles bonded along their prior particle boundaries, wherein the plurality of cermet particles have a median particle size less than about 5 microns, and   wherein less than 25 percent of the plurality of cermet particles comprise melted and re-solidified particles.   
     
     
         19 . The article of  claim 18 , wherein at least 99% of the plurality of cermet particles have an aspect ratio less than about 5. 
     
     
         20 . The article of  claim 18 , wherein the coating is substantially free of lamellae. 
     
     
         21 . The article of  claim 18 , wherein the plurality of cermet particles comprise a ceramic phase comprising carbides, nitrides, or combinations thereof. 
     
     
         22 . The article of  claim 18 , wherein the plurality of cermet particles comprise a metallic phase comprising cobalt, chromium, nickel, tungsten, or combinations thereof. 
     
     
         23 . The article of  claim 18 , wherein a density of the coating is greater than about 99 percent of the theoretical density. 
     
     
         24 . The article of  claim 18 , wherein the coating is hermetic. 
     
     
         25 . The article of  claim 18 , wherein the coating has a thickness in a range from about 100 nanometers too about 1000 microns. 
     
     
         26 . A gate valve, comprising:
 a first component;   a second component; and   a hermetic coating interposed between the first component and the second component, wherein the coating comprises a plurality of cermet particles bonded along their prior particle boundaries, wherein the plurality of cermet particles have a median particle size less than about 5 microns,   wherein less than 25 percent of the plurality of cermet particles comprise melted and re-solidified particles.   
     
     
         27 . The gate valve of  claim 26 , wherein the plurality of cermet particles comprise a ceramic phase comprising carbides, nitrides, or combinations thereof. 
     
     
         28 . The gate valve of  claim 26 , wherein the plurality of cermet particles comprise a metallic phase comprising cobalt, chromium, nickel, tungsten, or combinations thereof. 
     
     
         29 . The gate valve of  claim 26 , wherein the coating is substantially free of a polymer sealant. 
     
     
         30 . The gate valve of  claim 26 , wherein a density of the coating is greater than about 99 percent of the theoretical density. 
     
     
         31 . The gate valve of  claim 26 , wherein the first component comprises a seat and the second component comprises a gate.