A method for producing an alumina sintered body, including: a step of applying an alkaline earth metal compound onto a surface of an alumina raw material which is an unsintered alumina compact or an alumina sintered body; and a step of subjecting the alumina raw material to which the alkaline earth metal compound has been applied to heat treatment at a temperature of 1200 C. or more for 5 minutes or more and 300 minutes or less.

A method for producing an alumina sintered body, including: a step of applying an alkaline earth metal compound onto a surface of an alumina raw material which is an unsintered alumina compact or an alumina sintered body; and a step of subjecting the alumina raw material to which the alkaline earth metal compound has been applied to heat treatment at a temperature of 1200 C. or more for 5 minutes or more and 300 minutes or less.

A ceramic matrix composite (CMC) component includes at least one seal surface, the at least one seal surface disposed adjacent an interfacing surface for providing a seal therebetween; and a coating disposed on the seal surface. The coating includes an aluminum oxide and/or a silicon dioxide.

A ceramic matrix composite (CMC) component includes at least one seal surface, the at least one seal surface disposed adjacent an interfacing surface for providing a seal therebetween; and a coating disposed on the seal surface. The coating includes an aluminum oxide and/or a silicon dioxide.

A coating includes: at least 34.9 percent by mass silicon dioxide; at least 9.1 percent by mass aluminum oxide; and at least 16.1 percent by mass yttrium oxide.

A coating includes: at least 34.9 percent by mass silicon dioxide; at least 9.1 percent by mass aluminum oxide; and at least 16.1 percent by mass yttrium oxide.

A blade outer air seal has at least one internal surface and a layer atop the at least one internal surface. The layer has: a matrix comprising at least one of hafnium silicate (HfSiO.sub.4) and zirconium silicate (ZrSiO.sub.4), ytterbium disilicate (Yb.sub.2Si.sub.2O.sub.7); and barium magnesium alumino silicate (BMAS) or other alkaline earth aluminosilicate.

A blade outer air seal has at least one internal surface and a layer atop the at least one internal surface. The layer has: a matrix comprising at least one of hafnium silicate (HfSiO.sub.4) and zirconium silicate (ZrSiO.sub.4), ytterbium disilicate (Yb.sub.2Si.sub.2O.sub.7); and barium magnesium alumino silicate (BMAS) or other alkaline earth aluminosilicate.

Coating systems are provided for use on a CMC substrate, that can include: a bond coat on a surface of the CMC substrate; a first rare earth silicate coating on the bond coat; a sacrificial coating of a reinforced rare earth silicate matrix on the at least one rare earth silicate layer; a second rare earth silicate coating on the sacrificial coating; and an outer layer on the second rare earth silicate coating. The first rare earth silicate coating comprises at least one rare earth silicate layer, and the second rare earth silicate coating comprises at least one rare earth silicate layer. The sacrificial coating has a thickness of about 4 mils to about 40 mils. Methods are also provided for tape deposition of a sacrificial coating on a CMC substrate.

Coating systems are provided for use on a CMC substrate, that can include: a bond coat on a surface of the CMC substrate; a first rare earth silicate coating on the bond coat; a sacrificial coating of a reinforced rare earth silicate matrix on the at least one rare earth silicate layer; a second rare earth silicate coating on the sacrificial coating; and an outer layer on the second rare earth silicate coating. The first rare earth silicate coating comprises at least one rare earth silicate layer, and the second rare earth silicate coating comprises at least one rare earth silicate layer. The sacrificial coating has a thickness of about 4 mils to about 40 mils. Methods are also provided for tape deposition of a sacrificial coating on a CMC substrate.