Temperature dependent transparent optical coatings for high temperature reflection

Abstract

A gas turbine engine component having a coating with a temperature dependent transparency is disclosed. The component includes a substrate having an optically reflective surface and a coating disposed over the substrate that has a transparency that is temperature dependent. At temperatures below the glass transition temperature, the coating has a low transparency to incident radiation, while at higher temperatures, the coating has a high transparency to incident radiation. As a result of the increased transparency at high temperatures, incident radiation passes through the coating and is reflected off of the optically reflective surface of the substrate underlying the coating. At low temperatures, when the coating has a low transparency, incident radiation is absorbed by the component, resulting in lower reflectivity.

1 . A component for use in an elevated temperature environment having temperature dependent reflectivity comprising: 
 a substrate having an optically reflective surface; and    a coating disposed over and in contact with the optically reflective surface of the substrate, wherein the coating has a glass transition temperature, the coating having a transparency to incident radiation of less than about 50% below the coating glass transition temperature and greater than about 50% above the coating glass transition temperature, whereby below the glass transition temperature the component absorbs incident radiation and converts it to heat and above the glass transition temperature, the component reflects incident radiation from the optically reflective surface of the substrate.    
   
   
       2 . The component of  claim 1  wherein the substrate comprises a metallic material.  
   
   
       3 . The component of  claim 1  wherein the substrate comprises a superalloy selected from the group consisting of nickel-based, cobalt-based, iron-based and combinations thereof.  
   
   
       4 . The component of  claim 1  wherein the substrate comprises a ceramic matrix composite and the optically reflective surface comprises an optically reflective metal overlying the ceramic matrix composite.  
   
   
       5 . The component of  claim 1  wherein the coating comprises a glass selected from the group consisting of borosilicate glass, lithium silicate glass, potassium germinate glass, barium germinate glass, arsenic germinate glass, and combinations thereof.  
   
   
       6 . The component of  claim 1  wherein the coating includes a pigment.  
   
   
       7 . The component of  claim 6  wherein the pigment comprises a material selected from the group of consisting of a metal, a metal fluoroide, a metal oxide or combinations thereof.  
   
   
       8 . The component of  claim 6  wherein the pigment comprises a material selected from the group consisting of barium fluoride, calcium fluoride, strontium fluoride, magnesium fluoride, silicon/silicon monoxide and combinations thereof.  
   
   
       9 . The component of  claim 1  wherein the coating is at least about 10 mils thick.  
   
   
       10 . The component of  claim 1  wherein the coating is about 20 mils thick.  
   
   
       11 . The component of  claim 1  wherein the coating absorbs at least about 60% of incident radiation at a temperature below the glass transition temperature and wherein the transparency of the coating to incident radiation is at least about 90% at and above the coating glass transition temperature.  
   
   
       12 . The component of  claim 1  wherein the component has a surface roughness of about 0.5 to about 20 RA.  
   
   
       13 . The component of  claim 12  wherein the component has a surface roughness of less than about 8 RA.  
   
   
       14 . A gas turbine engine component having temperature dependent reflectivity comprising: 
 a substrate having an optically reflective surface; and    a coating disposed over and in contact with the optically reflective surface of the substrate, wherein the coating comprises a material having a glass transition temperature and wherein the coating has a transparency to incident radiation of less than 50% below the glass transition temperature and a transparency to incident radiation of at least about 90% at temperatures above the glass transition temperature.    
   
   
       15 . The component of  claim 14  wherein the coating includes pigment.  
   
   
       16 . The component of  claim 14  wherein the component is selected from the group consisting of an exhaust nozzle, a nozzle liner, a combustor liner, an exhaust strut, a seal, and a flap.  
   
   
       17 . A method for optically tailoring a surface of a gas turbine engine component to control heat transfer comprising the steps of: 
 providing a component of a gas turbine engine having an optically reflective surface;    coating the optically reflective surface of the component with a material having a glass transition temperature, wherein the material has a higher transparency to incident radiation above the glass transition temperature than below the glass transition temperature; and    providing cooling to a surface of the component opposite the optically reflective surface.    
   
   
       18 . The method of  claim 17  wherein the provided component of the gas turbine engine comprises a superalloy selected from the group consisting of nickel-based, cobalt-based, iron-based and combinations thereof.  
   
   
       19 . The method of  claim 17  wherein the provided component comprises a ceramic matrix composite and the optically reflective surface comprises an optically reflective metal overlying the ceramic matrix composite.  
   
   
       20 . The method of  claim 17  wherein the provided component is selected from the group consisting of an exhaust nozzle, a nozzle liner, a combustor liner, an exhaust strut, a seal, and a flap.  
   
   
       21 . The method of  claim 17  wherein the coating includes pigment.  
   
   
       22 . The method of  claim 17  wherein the transparency of the coating is less than about 50% below the coating glass transition temperature.  
   
   
       23 . The method of  claim 17  wherein the step of providing a component of a gas turbine engine having a reflective surface further includes the additional steps of: 
 providing a component of a gas turbine engine; and    applying a layer of reflective material to a surface of the gas turbine engine component.    
   
   
       24 . The method of  claim 23  wherein the reflective material comprises at least one material selected from the group consisting of gold, platinum, palladium, rhodium, aluminum and combinations thereof.  
   
   
       25 . A gas turbine engine component having temperature dependent reflectivity comprising: 
 a substrate;    a thermal barrier coating system overlying and in contact with a first surface of the substrate, the thermal barrier coating system comprising a bond coat, the bond coat in contact with the substrate and a ceramic coat overlying the bond coat;    a layer of optically reflective material overlying and in contact with the thermal barrier coating system; and    a coating disposed over and in contact with the layer of optically reflective material, wherein the coating comprises a material having a glass transition temperature and wherein the coating has a transparency to incident radiation of less than 50% below the glass transition temperature and a transparency to incident radiation of at least about 95% at temperatures at or above the glass transition temperature.    
   
   
       26 . The component of  claim 25  wherein the ceramic coat of the thermal barrier coating system is polished.  
   
   
       27 . The component of  claim 25  wherein the ceramic coat of the thermal barrier coating system is yttrium-sustained zirconia.