A Cr:YAG sintered body including Al, Y, Cr, Ca, Mg, Si, and O, and component contents in the sintered body satisfying conditional expressions of 1) to 3) below, provided in the Conditional expression, each chemical symbol represents a component content (atppm).

|(Y+Ca)/(Al+Cr+Si+Mg)−0.6|<0.001;  1)

0≤(Ca+Mg)−(Cr+Si)≤50 atppm; and  2)

50≤Si≤500 atppm  3)

The embodiment of the present invention is to provide a Cr:YAG sintered body which exhibits high transparency and has a high Cr.sup.4+ conversion ratio, and its production method.

A method for making a component includes the steps of providing a preform formed of carbon fibers. A first densification is performed forming a carbon composite. A first hardening of the carbon composite is performed. The method machines the carbon composite to form a shape. The method then performs a second densification and a second hardening. The method then final machines the carbon composite to form a final shape of the component.

A method of processing a CMC component includes applying a surface formulation comprising a resin and/or a preceramic polymer to a fiber preform. The surface formulation is cured to form a surface coating, which is then pyrolyzed to convert the resin to carbon and/or the preceramic polymer to silicon carbide. After pyrolysis, the fiber preform is infiltrated with a melt comprising silicon to form a CMC component. During melt infiltration, the carbon reacts with the silicon to form silicon carbide, and the silicon carbide prevents unreacted silicon from accessing a surface region of the CMC component. Thus, after melt infiltration, a concentration of free silicon in the surface region is a low amount of about 5 vol. % or less. Upon assembling the CMC component with a metal component, diffusion between the components is inhibited or prevented by the low amount of free silicon in the surface region.

A ceramic matrix composite article includes a melt infiltration ceramic matrix composite substrate comprising a ceramic fiber reinforcement material in a ceramic matrix material having a free silicon proportion, and a chemical vapor infiltration ceramic matrix composite outer layer comprising a ceramic fiber reinforcement material in a ceramic matrix material having essentially no free silicon proportion disposed on an outer surface of at least a portion of the substrate.

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 of manufacture for a carbon/carbon part including a method to remove contamination from an intermediate product of the carbon/carbon part and furnace utilizing a gaseous reducing agent hydrogen gas to reduce the contaminates, thereby causing the contaminates to transition to a gaseous state at relatively lower temperatures. A method to remove contamination from an intermediate product of the carbon/carbon part and furnace utilizing hydrogen gas to reduce the contaminates, thereby causing the contaminates to transition to a gaseous state at relatively lower temperatures.

A method of processing a CMC component includes preparing a fiber preform having a predetermined shape, and positioning the fiber preform with tooling having holes facing one or more surfaces of the fiber preform. After the positioning, a clamping pressure is applied to the tooling to force portions of the one or more surfaces of the fiber preform into the holes, thereby forming protruded regions of the fiber preform. During the application of the clamping pressure, the fiber preform is exposed to gaseous reagents at an elevated temperature, and a matrix material is deposited on the fiber preform to form a rigidized preform including surface protrusions. After removing the tooling, the rigidized preform is infiltrated with a melt for densification, and a CMC component having surface bumps is formed. When the CMC component is assembled with a metal component, the surface bumps may reduce diffusion at high temperatures.

In one example, a method for forming an environmental barrier coating (EBC) on a substrate. The method may include heating the substrate before and/or during deposition of EBC on the substrate using an external burner and/or resistive electrical heating. Additionally, or alternatively, the as-deposited EBC may be heat treated using an external burner and/or resistive electrical heating. In some examples, the techniques of the disclosure are configured to increase or otherwise tailor the amount of crystalline phase in the EBC.

A method of altering a surface of a ceramic matrix composite to aid in nodule removal is described. A fiber preform comprising a framework of ceramic fibers is heated to a temperature at or above a melting temperature of silicon. During the heating, the fiber preform is infiltrated with a molten material comprising silicon. After the infiltration, the fiber preform is cooled, and the infiltrated fiber preform is exposed to a gas comprising nitrogen during cooling. Silicon nitride may be formed by a reaction of free (unreacted) silicon at or near the surface of the infiltrated fiber preform with the nitrogen. Thus, a ceramic matrix composite having a surface configured for easy nodule removal is formed. Any silicon nodules formed on the surface during cooling may be removed without machining or heat treatment.

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.