Thermal barrier coating systems and materials

Abstract

A new family of ceramic materials is identified having particular utility as thermal insulating or thermal barrier coatings on metallic substrates. The ceramic materials have a pyrochlore structure and are typified by the composition A 2 B 2 O 7 where A and B are various ions and O is oxygen. A may have a positive charge of 3 + or 2 + and B may have a positive charge of 4 + or 5 + . These materials are characterized by having chemical stability, thermal stability and thermal insulating properties superior to those of currently used thermal barrier ceramics. An example pyrochlore material is lanthanum zirconate.

I claim:  
     
         1 . A metallic article comprising a metallic substrate, said substrate having a ceramic coating on its surface wherein said ceramic coating has a cubic pyrochlore structure.  
     
     
         2 . An article as in    claim 1    wherein said metallic substrate is selected from the group consisting of steels, superalloys, titanium alloys and copper alloys.  
     
     
         3 . An article as in    claim 1    wherein said pyrochlore has the formula A 2 B 2 O 7  and the A and B species ionic radii fall approximately within the cubic field in FIG. 2.  
     
     
         4 . An article as in    claim 1    wherein the B constituent comprises Hf, Ti, Zr, and single phase mixtures thereof.  
     
     
         5 . An article as in    claim 1    wherein the A constituent comprises La, Gd, Zr, and single phase mixtures thereof.  
     
     
         6 . An article as in    claim 1    wherein said coated article is adopted to be used in environments where the free surface of the pyrochlore coating will be heated and the free surface of the substrate will be cooled, whereby the pyrochlore coating will reduce heat flow.  
     
     
         7 . An article as in    claim 1    wherein said pyrochlore has a columnar microstructure.  
     
     
         8 . A metallic article as in    claim 1    wherein said metallic article has an oxide scale on its outer surface, said oxide consisting essentially of alumina, and whereas said cubic pyrochlore ceramic coating is bonded to said oxide scale.  
     
     
         9 . An article as in    claim 8    wherein said metallic substrate is selected from the group consisting of steels, superalloys, titanium alloys and copper alloys.  
     
     
         10 . An article as in    claim 8    wherein said pyrochlore has the formula A 2 B 2 O 7  and the A and B species ionic radii fall approximately within the cubic field in FIG. 2.  
     
     
         11 . An article as in    claim 8    wherein the B constituent comprises Hf, Ti, Zr, and single phase mixtures thereof.  
     
     
         12 . An article as in    claim 8    wherein the A constituent comprises La, Gd, Zr, and single phase mixtures thereof.  
     
     
         13 . An article as in    claim 8    wherein said coated article is adopted to be used in environments where the free surface of the pyrochlore coating will be heated and the free surface of the substrate will be cooled, whereby the pyrochlore coating will inhibit heat flow.  
     
     
         14 . A metallic article comprising a metallic substrate, said substrate having an alumina forming coating on its surface and a pyrochlore coating bonded to said alumina forming coating.  
     
     
         15 . An article as in    claim 14    wherein said substrate coating comprises an alumina forming metallic overlay coating.  
     
     
         16 . An article as in    claim 14    wherein said substrate coating comprises a diffusion aluminide coating.  
     
     
         17 . An article as in    claim 14    wherein the B constituent comprises Hf, Ti, Zr, and single phase alloys thereof.  
     
     
         18 . An article as in    claim 14    wherein the A constituent comprises La, Gd, Zr, and single phase alloys thereof.  
     
     
         19 . An article as in    claim 14    wherein said coated article is adopted to be used in environments where the free surface of the pyrochlore coating will be heated and the free surface of the substrate will be cooled, whereby the pyrochlore coating will inhibit heat flow.  
     
     
         20 . An article as in    claim 14    wherein said pyrochlore has a columnar microstructure.  
     
     
         21 . In a superalloy gas turbine component which operates in an environment with gas temperatures in excess of 1,000°C., said component having internal cooling passages, the improvement which comprises a coating of a ceramic having a pyrochlore crystal structure, said coating being located to reduce heat flow into said component.  
     
     
         22 . A method of thermally insulating a metallic substrate which comprises: applying a cubic pyrochlore ceramic coating to at least a portion of said substrate by electron beam physical vapor deposition.  
     
     
         23 . A method as in    claim 22    wherein said substrate is selected from the group consisting of steels, superalloys, titanium alloys and copper alloys.  
     
     
         24 . An article as in    claim 22    wherein said pyrochlore has the formula A 2 B 2 O 7  and the A and B species ionic radii fall approximately within the cubic field in FIG. 2.  
     
     
         25 . An article as in    claim 22    wherein the B constituent comprises Hf, Ti, Zr, and single phase alloys thereof.  
     
     
         26 . An article as in    claim 22    wherein the A constituent comprises La, Cd, Zr, and single phase alloys thereof.  
     
     
         27 . An article as in    claim 22    wherein said coated article is adopted to be used in environments where the free surface of the pyrochlore coating will be heated and the free surface of the substrate will be cooled, whereby the pyrochlore coating will inhibit heat flow.  
     
     
         28 . An article as in    claim 22    wherein said pyrochlore has a columnar microstructure.  
     
     
         29 . A metallic article as in    claim 22    wherein said metallic article has an oxide scale on its outer surface, said oxide consisting essentially of alumina, and wherein said pyrochlore ceramic coating is bonded to said oxide scale.  
     
     
         30 . A method of thermally insulating a metallic substrate which comprises: applying a cubic pyrochlore ceramic coating to at least a portion of said substrate by thermal spray deposition.  
     
     
         31 . An article as in    claim 30    wherein said metallic substrate is selected from the group consisting of steels, superalloys, titanium alloys and copper alloys.  
     
     
         32 . An article as in    claim 30    wherein said pyrochlore has the formula A 2 B 2 O 7  and the A and B species ionic radii fall approximately within the cubic field in FIG. 2.  
     
     
         33 . An article as in    claim 30    wherein the B constituent comprises Hf, Ti, Zr, and single phase alloys thereof.  
     
     
         34 . An article as in    claim 30    wherein the A constituent comprises La, Gd, Zr, and single phase alloys thereof.  
     
     
         35 . An article as in    claim 30    wherein said coated article is adopted to be used in environments where the free surface of the pyrochlore coating will be heated and the free surface of the substrate will be cooled, whereby the pyrochlore coating will inhibit heat flow.  
     
     
         36 . An article as in    claim 30    wherein said pyrochlore has a columnar microstructure.  
     
     
         37 . A metallic article as in    claim 30    wherein said metallic article has an oxide scale on its outer surface, said oxide consisting essentially of alumina, and wherein said pyrochlore ceramic coating is bonded to said oxide scale.  
     
     
         38 . A gas turbine engine component which comprises a superalloy substrate having a layer consisting essentially of lanthanum zirconate on at least a portion of it's external surface.