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A Porous Ceramic Interphase for SiC / Si 3 N 4 Composites
| Content Provider | Semantic Scholar |
|---|---|
| Copyright Year | 2009 |
| Abstract | A suitable Interphase material for non-oxide ceramic-matrix composites must be resistant to oxidation. This means it must exhibit a slow rate of oxidation, and its oxidation product must be such as to ensure that the system survives oxidation when it does occur. Because the current benchmark interphase materials, carbon and boron nitride, lack these qualities, a porous fiber coating was developed to satisfy both the mechanical and oxidative requirements of an interphase for the SiC/SiC and SiC/S~N. composites that are of interest to NASA. This report presents the interphase microstructure achieved and the resulting characteristics of fiber push-out from a matrix of reaction-bonded silicon nitride (RBSN), both as-fabricated and after substantial annealing and oxidation treatments. Introduction The mechanical funcbon of the fiber-matrix interface in brittle composites IS to assure load transfer from matrix to fiber, and enhance damage control through the diversion of matrix cracks away from the fiber. The diversion assures fiber debond from the matrix and hence -graceful(as opposed to catastrophic) failure of the composite. N. present, carbon (C) or boron nitride (BN) is used at the interface in developmental nonoxide ceramic-matrix composites (CMCs) because, in their turbostratic forms, these materials exhibit high compliance for load transfer, and low strength that permits fiber debond when intersected by a crack. However, C and BN pose unacceptable oxidation problems: When exposed to the atmosphere (by an open matrix crack, for instance), they oxidize rapidly. If the interface layer IS thicker than -1 ~m (1), the oxidation leaves behind a corresponding cylindrical void around the fiber Qn the case of carbon), which prevents load transfer and may act as a flaw in the composite; and if It IS thin «0.1 ~m)(1) the void fills up with silica from oxidizing fiber and matrix (and hence a borosilicate glass, in the case of BN), which embrittles the CMC below the glass transition temperature. These problems make it necessary to seek an altemative interfacial material that is slow to oxidize, and in a form that enhances the oxidation survival of the system. Strictly from the stand-pOint of the mechanical function, a ceramic interphase with a high volume fraction of finely- |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960007957.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
