Articles for high temperature service and methods for their manufacture

Abstract

An article for use in aggressive environments is presented. In one embodiment, the article comprises a substrate and a self-sealing and substantially hermetic sealing layer comprising an alkaline-earth aluminosilicate disposed over the bondcoat. The substrate may be any high-temperature material, including, for instance, silicon-bearing ceramics and ceramic matrix composites.

1 . An article comprising:
 a substrate; and   a self-sealing and substantially hermetic sealing layer disposed over the substrate, wherein the sealing layer comprises an alkaline-earth aluminosilicate.   
     
     
         2 . The article of  claim 1 , wherein the alkaline-earth aluminosilicate comprises at least one alkaline-earth element selected from the group consisting of strontium and barium. 
     
     
         3 . The article of  claim 2 , wherein the sealing layer comprises barium strontium aluminosilicate. 
     
     
         4 . The article of  claim 1 , wherein the alkaline-earth aluminosilicate comprises up to about 80 mole % silica. 
     
     
         5 . The article of  claim 1 , wherein the alkaline-earth aluminosilicate comprises up to about 60 mole % alumina. 
     
     
         6 . The article of  claim 1 , wherein the alkaline-earth aluminosilicate comprises up to about 50 mole % alkaline-earth oxide. 
     
     
         7 . The article of  claim 1 , wherein the alkaline-earth aluminosilicate has a composition in the range bounded by a region in alumina/silica/alkaline-earth oxide compositional space defined by a first line connecting a first composition point at about (22.5 mole % alumina, 55 mole % silica, 22.5 mole % alkaline-earth oxide) with a second composition point at about (43.8 mole % alumina, 44.6 mole % silica, 11.6 mole % alkaline-earth oxide);
 a second line connecting the second composition point with a third composition point at about (49.3 mole % alumina, 29.6 mole % silica, 21.1 mole % alkaline-earth oxide);   a third line connecting the third composition point with a fourth composition point at about (38.4 mole % alumina, 23.6 mole % silica, 38.0 mole % alkaline-earth oxide);   a fourth line connecting the fourth composition point with a fifth composition point at about (19.3 mole % alumina, 46.5 mole % silica, 34.2 mole % alkaline-earth oxide); and   a fifth line connecting the fifth composition point with the first composition point.   
     
     
         8 . The article of  claim 1 , wherein the alkaline-earth aluminosilicate has a composition in the range bounded by a region in alumina/silica/alkaline-earth oxide compositional space defined by
 a first line connecting a first composition point at about (25 mole % alumina, 50 mole % silica, 25 mole % alkaline-earth oxide) with a second composition point at about (33.7 mole % alumina, 47.5 mole % silica, 18.8 mole % alkaline-earth oxide);   a second line connecting the second composition point with a third composition point at about (45.5 mole % alumina, 36.4 mole % silica, 18.2 mole % alkaline-earth oxide);   a third line connecting the third composition point with a fourth composition point at about (39.6 mole % alumina, 38.0 mole % silica, 22.4 mole % alkaline-earth oxide);   a fourth line connecting the fourth composition point with a fifth composition point at about (31.5 mole % alumina, 37.0 mole % silica, 31.5 mole % alkaline-earth oxide);   a fifth line connecting the fifth composition point with a sixth composition point at about (19.3 mole % alumina, 46.5 mole % silica, 33.9 mole % alkaline-earth oxide); and   a sixth line connecting the sixth composition point with the first composition point.   
     
     
         9 . The article of  claim 1 , wherein the sealing layer is substantially free of any additional material disposed within internal surfaces of the sealing layer. 
     
     
         10 . The article of  claim 1 , wherein the substrate comprises silicon. 
     
     
         11 . The article of  claim 1 , wherein the substrate comprises at least one material selected from the group consisting of silicon nitride, molybdenum disilicide, and silicon carbide. 
     
     
         12 . The article of  claim 11 , wherein the substrate comprises a ceramic matrix composite material. 
     
     
         13 . The article of  claim 12 , wherein the composite comprises a matrix phase and a reinforcement phase, and wherein the matrix phase and the reinforcement phase comprise silicon carbide. 
     
     
         14 . The article of  claim 1 , wherein the article comprises a component of a gas turbine assembly. 
     
     
         15 . The article of  claim 1 , further comprising a bondcoat disposed between the substrate and the sealing layer. 
     
     
         16 . The article of  claim 15 , wherein the bondcoat comprises silicon. 
     
     
         17 . The article of  claim 15 , wherein the bondcoat comprises at least one material selected from the group consisting of elemental silicon and a silicide. 
     
     
         18 . The article of  claim 1 , further comprising a topcoat disposed over the sealing layer. 
     
     
         19 . The article of  claim 18 , wherein the topcoat comprises a ceramic material. 
     
     
         20 . The article of  claim 19 , wherein the ceramic material is selected from the group consisting of silicates, aluminosilicates, and yttria-stabilized zirconia. 
     
     
         21 . The article of  claim 19 , wherein the topcoat comprises at least one material selected from the group consisting of a rare earth monosilicate and a rare earth disilicate. 
     
     
         22 . The article of  claim 21 , wherein the topcoat comprises an outer layer of rare earth monosilicate and an inner layer of rare earth disilicate. 
     
     
         23 . The article of  claim 15 , further comprising an intermediate layer disposed between the sealing layer and the bondcoat, wherein the intermediate layer comprises a barrier material that is substantially inert with respect to silica. 
     
     
         24 . The article of  claim 23 , wherein the barrier material comprises a rare-earth disilicate. 
     
     
         25 . The article of  claim 24 , wherein the barrier material comprises yttrium disilicate. 
     
     
         26 . An article comprising:
 a substrate comprising silicon;   a bondcoat disposed over the substrate, the bondcoat comprising silicon;   a self-sealing and substantially hermetic sealing layer disposed over the bondcoat, the sealing layer comprising an alkaline-earth aluminosilicate having a composition in the range bounded by a region in alumina/silica/alkaline-earth oxide compositional space defined by
 a first line connecting a first composition point at about (11.8 mole % alumina, 76.1 mole % silica, 12.1 mole % alkaline-earth oxide) with a  225497 - 2  second composition point at about (58.6 mole % alumina, 29.8 mole % silica, 11.6 mole % alkaline-earth oxide); 
 a second line connecting the second composition point with a third composition point at about (44.3 mole % alumina, 8.2 mole % silica, 47.5 mole % alkaline-earth oxide); 
 a third line connecting the third composition point with a fourth composition point at about (13.6 mole % alumina, 43.8 mole % silica, 42.6 mole % alkaline-earth oxide); and 
 a fourth line connecting the fourth composition point with the first composition point; 
   an intermediate layer disposed between the sealing layer and the bondcoat, wherein the intermediate layer comprises a barrier material that is substantially inert with respect to silica; and   a topcoat disposed over the sealing layer.