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METHOD TO ASSIST SILICON MELT INFILTRATION OF THICK CROSS-SECTION CMC PREFORMS

IP.com Disclosure Number: IPCOM000247852D
Publication Date: 2016-Oct-06
Document File: 6 page(s) / 94K

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention relates to ceramic matric composite (CMC) part production. Specifically, a method to improve melt infiltration of thick cross-section CMC preforms is disclosed.

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METHOD TO ASSIST SILICON MELT INFILTRATION OF THICK CROSS-SECTION CMC PREFORMS

TECHNICAL FIELD

    The invention relates to ceramic matric composite (CMC) part production. Specifically, a method to improve melt infiltration of thick cross-section CMC preforms is disclosed.

BACKGROUND

    Lightweight fiber composites hold great promise for the aircraft industry. Fiber composites provide a significant improvement in specific strength and stiffness over conventional metal alloys. Better specific strength and stiffness translates into weight savings, which leads to fuel savings and lower operating costs.

    A relatively recent development is the formation of parts from ceramic matrix composites (CMCs). One CMC form is a silicon carbide matrix that weighs a third of advanced alloys but reacts to stress like a metal and can perform at higher temperatures. These materials are being used to make aircraft parts such as engine shrouds among others.

    A variety of processing schemes have been developed for the fabrication of CMCs. One process is known as the "prepreg process" and the other is known as the "slurry cast" process. The first step in the "prepreg" process is the application of a fiber coating via chemical vapor deposition (CVD). The fiber coating serves to protect the fibers during composite processing and provides a low-strength fiber-matrix interface, thereby enabling fiber-matrix debonding and fiber pull-out "toughening" mechanisms. CMCs have typically in the past used carbon as the fiber


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coating, but have since incorporated boron nitride or silicon-doped boron nitride for increased oxidation resistance.

    Following fiber coating, the fiber tow is pulled through a slurry containing the preform matrix constituents (SiC and carbon particulate, binders and solvents), and then wound on a drum to form a unidirectional pre-impregnated, i.e., "prepreg," tape. The tape is then dried, removed from the drum, cut to shape, laid-up to give the desired fiber architecture, and laminated to form a green composite preform. Machining of the preform can be done at this stage, which helps to reduce the amount of final machining of the part after densification.

    The slurry casting approach differs from the prepreg approach in that the fibers are first woven or braided into a cloth, which is then laid-up to form the composite preform shape. The fiber coating is then applied to the preform using a chemical vapor infiltration (CVI) process. The remaining porosity in the preform, typically 30-40%, is then partially filled by slurry casting (or slip casting) an SiC particulate into the preform.

    The final densification step in both processes is the silicon meltinfiltration step. The composite preform, containing the coated SiC fibers, SiC and/or carbon particulates, and organic binders (in the prepreg process), is heated above about 1420° C. while in contact with a source of silicon metal. Molten silicon metal readily wets SiC and/or carbon, and therefo...