Nextel fibers composite system

Domier of Germany developed oxide fiber-reinforced mullite matrix composite systems in the 1980s. The system was based on SMs Nextel 312 fibers and slurry impregnation of a mullite matrix. This composite demonstrated modest levels of strength (120 MPa [17.4 ksi]) and low failure strain (0.2 to 0.3 percent). Several hot gas exhaust nozzles for Dormer s turboprop airerafl were successfully deployed and continue to be used in regular service. 

A potential problem with this type of composite system is the possibility of reaction or sintering between matrix partieles and the fibers at points of contact. Exposure tests of UCSB Nextel 610 composite at 1,200°C (2,192°F) for 100 hours shows reasonable mechanical property retention (Figure 6-11). Similar tests have yet to be performed on Nextel 720 eomposites. Therefore, the data on long-term exposure is insufficient to address the issue of matrix-fiber bonding (Levi et al., 1997). Beeause degradation is likely to be kinetically driven, residual fiber strength will be dictated by time at temperature. 

Ceramic matrix composites are under active consideration for low-observable military applications, where dielectric properties are a key performance factor. The frequency range of interest is the 8-12 GHz microwave range. The composite system must have low electrical conductivity. The SiOC-Nextel 312 system meets that requirement (as compared to ceramic composites made with conductive silicon carbide fibers). 

Fiber reinforced ceramic matrix composites (CMCs) are under active consideration for large, complex high temperature structural components in aerospace and automotive applications. The Blackglas resin system (a low cost polymer-derived ceramic [PDC] technology) was combined with the Nextel 312 ceramic fiber (with a boron nitride interface layer) to produce a sihcon oxycarbide CMC system that was extensively characterized for mechanical, thermal, and electronic properties and oxidation, creep mpture, and fatigue. A gas turbine tailcone was fabricated and showed excellent performance in a 1500-hour engine test. 

This chapter will describe the processing and properties of an oxide fiber reinforced ceramic matrix composite with a silicon oxycarbide matrix based on a PDC technology, introduced by AlliedSignal (now Honeywell International) under the trademark of Blackglas ceramic. The oxide fiber in this CMC system is the Nextel 312 fiber (3M, Inc.) that has been treated to form a boron nitride surface coating. The information that follows was primarily developed from Low Cost Ceramic Matrix Composites (LC ) program funded by DARPA from 1991-1997. 

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