Cmas- resistant thermal barrier coatings

Abstract

A coating including a CMAS-resistant layer with a rare earth oxide. The CMAS-resistant layer is essentially free of zirconia and hafnia, and may further include at least one of alumina, silica, and combinations thereof.

What is claimed is: 
     
         1 . An article comprising:
 a substrate comprising at least one of a superalloy, a ceramic, or a ceramic matrix composite; and   a coating comprising a CMAS-resistant layer over the substrate, wherein the CMAS-resistant layer comprises free rare earth oxide, free silica, and an alkali oxide and is essentially free of zirconia and hafnia, wherein the CMAS-resistant layer is the outermost layer of the coating, and wherein the CMAS-resistant layer comprises at least 10 mol. % free rare earth oxide.   
     
     
         2 . The article of  claim 1 , wherein the CMAS-resistant layer further comprises alumina. 
     
     
         3 . The article of  claim 2 , wherein the CMAS-resistant layer comprises up to 90 mol. % of a combination of the alumina and the free silica, between 0.1 mol. % and 50 mol. % of the alkali oxide, and a balance of the free rare earth oxide, with a total of 100 mol. %. 
     
     
         4 . The article of  claim 2 , wherein the CMAS-resistant layer comprises 10 mol. % to 90 mol. % of the free rare earth oxide, 10 mol. % to 90 mol. % of a combination of the alumina and the free silica, and between 0.1 mol. % and 50 mol. % of the alkali oxide, with a total of 100 mol. %. 
     
     
         5 . The article of  claim 2 , wherein the CMAS-resistant layer comprises 20 mol. % to 80 mol. % of the free rare earth oxide, between 0.1 mol. % and 50 mol. % of the alkali oxide, and 20 mol. % to 80 mol. % of a combination of the alumina and the free silica, with a total of 100 mol. %. 
     
     
         6 . The article of  claim 2 , wherein the CMAS-resistant layer comprises between about 10 mol. % and about 90 mol. % of the free rare earth oxide, between about 10 mol. % and about 90 mol. % of a combination of the alumina and the free silica, and between about 0. 1 mol. % and about 50 mol. % of a mixture of the alkali oxide and an additive component selected from the group consisting of Ta 2 O 5 , alkaline earth oxides, and combinations thereof 
     
     
         7 . The article of  claim 1 , wherein the free rare earth oxide is selected from the group consisting of oxides of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and combinations thereof. 
     
     
         8 . The article of  claim 1 , wherein the CMAS-resistant layer is between about 0.1 mil and about 60 mil thick. 
     
     
         9 . The article of  claim 1 , further comprising a bond coat layer disposed between the substrate and the CMAS-resistant layer, wherein the bond coat layer comprises at least one of a MCrAlY alloy, wherein M is selected from Ni, Co, and NiCo; a β-NiAl alloy; a γ-Ni+γ′-Ni 3 Al alloy; silicon; or mullite. 
     
     
         10 . The article of  claim 9 , wherein the bond coat layer comprises the β-NiAl alloy, and wherein the β-NiAl alloy further comprises at least one of Pt, Cr, Hf, Zr, Y, Si, and combinations thereof. 
     
     
         11 . The article of  claim 9 , wherein the bond coat layer comprises the γ-Ni+γ′-Ni 3 Al alloy, and wherein the γ-Ni+γ′-Ni 3 Al alloy further comprises at least one of Pt, Cr, Hf, Zr, Y, Si, and combinations thereof. 
     
     
         12 . The article of  claim 1 , further comprising a transitional layer, wherein the transitional layer is between the substrate and the CMAS-resistant layer. 
     
     
         13 . The article of  claim 12 , wherein the transitional layer is between an environmental barrier coating layer and the CMAS-resistant layer, wherein the environmental barrier layer is between the substrate and the transitional layer, and wherein the environmental barrier coating layer comprises a rare earth silicate. 
     
     
         14 . The article of  claim 13 , wherein the transitional layer comprises the rare earth silicate, free rare earth oxide, the free silica, and the alkali oxide. 
     
     
         15 . A method comprising:
 forming a CMAS-resistant layer over a substrate comprising at least one of a superalloy, a ceramic, or a ceramic matrix composite, wherein the CMAS-resistant layer comprises free rare earth oxide, free silica, and an alkali oxide and is essentially free of zirconia and hafnia, wherein the CMAS-resistant layer is the outermost layer, and wherein the CMAS-resistant layer comprises at least 10 mol. % of the free rare earth oxide.   
     
     
         16 . The method of  claim 15 , wherein the CMAS-resistant layer further comprises alumina. 
     
     
         17 . The method of  claim 16 , wherein the CMAS-resistant layer comprises between about 10 mol. % and about 90 mol. % of the free rare earth oxide, between about 10 mol. % and about 90 mol. % of a combination of the alumina and the free silica, and between about 0.1 mol. % and about 50 mol. % of a mixture of the alkali oxide and an additive component selected from the group consisting of Ta 2 O 5 , alkaline earth oxides, and combinations thereof. 
     
     
         18 . The method of  claim 15 , further comprising forming a bond coat layer on the substrate, wherein forming the CMAS-resistant layer over the substrate comprises forming the CMAS-resistant layer over the bond coat layer, wherein the bond coat layer comprises at least one of a MCrAlY alloy, wherein M is selected from Ni, Co, and NiCo; a β-NiAl alloy; a γ-Ni+γ′-Ni 3 Al alloy; silicon; or mullite. 
     
     
         19 . The method of  claim 18 , further comprising forming an environmental barrier coating layer over the bond coat layer, wherein forming the CMAS-resistant layer over the bond coat layer comprises forming the CMAS-resistant layer over the environmental barrier coating layer, and wherein the environmental barrier coating layer comprises a rare earth silicate. 
     
     
         20 . The method of  claim 19 , further comprising forming a transitional layer on the CMAS-resistant layer, wherein forming the CMAS-resistant layer over the environmental barrier coating layer comprises forming the CMAS-resistant layer over the transitional layer, and wherein the transitional layer comprises the rare earth silicate, free rare earth oxide, the free silica, and the alkali oxide.