A compound is generally provided that has the formula: Ln.sub.3-xB.sub.xM.sub.5-yB.sub.yO.sub.12, where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; x is 0 to about 1.5; M comprises Ga, In, Al, Fe, or a combination thereof; y is 0 to about 2.5; and x+y is greater than 0. A composition is also provided that includes a silicon-containing material (e.g., silicon metal and/or a silicide) and the boron-doped refractory compound having the formula described above, such as about 0.001% to about 85% by volume of the boron-doped refractory compound.

A compound is generally provided that has the formula: Ln.sub.3-xB.sub.xM.sub.5-yB.sub.yO.sub.12, where Ln comprises Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof; x is 0 to about 1.5; M comprises Ga, In, Al, Fe, or a combination thereof; y is 0 to about 2.5; and x+y is greater than 0. A composition is also provided that includes a silicon-containing material (e.g., silicon metal and/or a silicide) and the boron-doped refractory compound having the formula described above, such as about 0.001% to about 85% by volume of the boron-doped refractory compound.

A ceramic component is generally provided that includes a silicon-based layer comprising a silicon-containing material (e.g., a silicon metal and/or a silicide) and about 0.001% to about 85% of a Ga-containing compound. For example, the silicon-based layer can be a bond coating directly on the surface of the substrate. Alternatively or additionally, the silicon-based layer can be an outer layer defining a surface of the substrate, with an environmental barrier coating on the surface of the substrate. Gas turbine engines are also generally provided that include such a ceramic component.

A ceramic component is generally provided that includes a silicon-based layer comprising a silicon-containing material (e.g., a silicon metal and/or a silicide) and about 0.001% to about 85% of a Ga-containing compound. For example, the silicon-based layer can be a bond coating directly on the surface of the substrate. Alternatively or additionally, the silicon-based layer can be an outer layer defining a surface of the substrate, with an environmental barrier coating on the surface of the substrate. Gas turbine engines are also generally provided that include such a ceramic component.

A method for forming a high temperature coating includes applying carbon powder to a surface of a carbon/carbon (C/C) composite substrate to force the carbon powder into one or more surface voids of the surface of the C/C composite substrate. The carbon powder has a substantially same composition and morphology as a surface portion of the C/C composite substrate. The method includes applying a metal slurry to the surface of the C/C composite substrate following the application of the carbon powder and reacting a metal of the metal slurry with carbon of the carbon powder and carbon of the surface portion of the C/C composite substrate to form a metal-rich antioxidant layer of a metal carbide on the C/C composite substrate.

A component includes a component body in which at least one cavity is formed, wherein a wall surface of the component body, which wall surface delimits the cavity, is at least partially coated with a coating. The design of the component is based on a porous preform made in one or more parts from an inorganic matrix (M1), the preform having the cavity and a porous pre-coating made from an inorganic matrix (M2), the pre-coating coating at least part of a wall surface of the preform that delimits the cavity The porous preform and the porous pre-coating are infiltrated with an inorganic infiltrate (M3). The infiltrated preform forms the component body, and the infiltrated pre-coating forms the coating. A method for producing the component, wherein the preform and the pre-coating are infiltrated so as to produce the component body comprising the coating is also disclosed.

A method of forming a -SiC material or coating by mixing SiO.sub.2 with carbon and heating the mixture in vacuum wherein the carbon is oxidized to CO gas and reduces the SiO.sub.2 to SiO gas and reacting a carbon material with the SiO gas at a temperature in the range of 1300 to 1600 C. resulting in a SiC material or a SiC coating on a substrate. Also disclosed is the related SiC material or coating prepared by this method.

A method of forming a -SiC material or coating by mixing SiO.sub.2 with carbon and heating the mixture in vacuum wherein the carbon is oxidized to CO gas and reduces the SiO.sub.2 to SiO gas and reacting a carbon material with the SiO gas at a temperature in the range of 1300 to 1600 C. resulting in a SiC material or a SiC coating on a substrate. Also disclosed is the related SiC material or coating prepared by this method.

A manufacturing process for the synthesis of environmental barrier coating system (EBC) which protect Si-based Ceramic Matrix Composite (CMC) material against oxidation and volatilization at high temperatures is disclosed. The manufacturing process is carried out in vacuum and includes steps of depositing a silicon bond coat and an oxygen containing barrier coating. The process is supported by plasma, preferably through and arc discharge, which lead to full dissociation of the gas precursors such as silane. Plasma is as well used for pre-treatment of substrates in an uninterrupted process chain. A deposition system with essential vacuum and plasma components is disclosed as well as EBC coatings manufactured by the process.

An article comprises a substrate comprising a ceramic matrix composite; a first layer disposed over the substrate, the first layer comprising an interconnected first silicide, and a second phase; and a second layer disposed over the first layer, the second layer comprising a second silicide in mass transfer communication with the first silicide.