Nicalon® fiber

As can be seen from this figure, the heat-resistance was remarkably improved by the drastic changes in the microstructure from amorphous to polycrystalline structure. Another type of SiC-based fiber, SA fiber (2), has a sintered SiC polycrystalline structure and includes very small amounts of aluminum. This fiber exhibits outstanding high temperature strength, coupled with much improved thermal conductivity and thermal stability compared with the Nicalon and Hi-Nicalon fibers. The fabrication cost of the SA fiber is also reduced to near half of that of the Hi-Nicalon Type S [ 17]. The SA fiber makes SiC/SiC composites even more attractive to the many applications [18]. In the next section, the production process, microstructure and physical properties of the SA fiber are explained in detail. 

SiC monofilaments produced by the CVD process is generally superior to Nicalon SiC fibers in mechanical properties because of its almost 100% 6-SiC purity while Nicalon is a mixture of SiC, Si02 and free carbon. Representative properties of SiC monofilaments and Nicalon fibers are given in Table 5.15. 

Sun, E.Y., Nutt, S.R. and Brennan, J.J. (1994). Interfacial microstructure and chemistry of SiC/BN dual-coated Nicalon-fiber reinforced glass-ceramic matrix composites. J. Am. Ceram. Soc. 77, 1329-1239. 

Figure 5.111 The strengths of three commercially available Nicalon fibers as a function of temperature. Reprinted, by permission, from A. Kelly, ed.. Concise Encyclopedia of Composite Materials, p. 256, revised edition. Copyright 1994 by Elsevier Science Pubhshers, Ltd.

Development has been conducted to fabricate SiC-based matrix/Si-C-based fiber composites by polymer infiltration. Nicalon fibers are used, and various polymers such as polysilazanes, polysiloxanes, and polycarbosilanes are used to yield matrices of SiCO, SiNC, and SiC. As with CVI of SiC/SiC composites, carbon acts as an interface layer but does not result in stability at high temperatures. 

Chemical and phase purity are critical issues that drive precursor design because optimal mechanical properties are achieved only with high purity. For example, ceramics grade Nicalon fibers, with a chemical composition of ca SiCi 45O0 36 and densities 17,9... 

SEM micrograph of BN-coated Hi-Nicalon fiber for use as a reinforcement of a SiC/SiC-composite. (Source Nippon Carbon Co Ltd Japan). 

Boccaccini, A.R., Strutt, A.J., Vecchio, A.S., Mendoza, D., Chawla, K.K., Ponton, C.B., Pearce, D.H. (1998), Behaviour of Nicalon -fiber-reinforced glass-matrix composites under thermal cycling conditions , Composites, 29A, 1343-1352. 

Chawla, N., Chawla, K.K., Koopman, M., Patel, B., Coffin, C., Eldridge, J.I. (2001), Thermal-shock behaviour of a Nicalon-fiber-reinforced hybrid glass-ceramic composite , Comp. Sci. Tech., 61, 1923-1930. 

Fareed, A.S., Sonuparlak, B., Lee, C.T., Fortini, A.J., Schiroky, G.H. (1990), Mechanical properties of 2-D Nicalon fiber-reinforced LANXIDE aluminum oxide and aluminum nitride matrix composites , Ceram. Eng. Sci. Proc., 11(7-8), 782-794. 

SiC is an excellent nonoxide ceramic with high-temperature stability and suitable mechanical properties. Since silicon-containing polymers are generally used for preparing nonoxide ceramics, various polymeric precursors with different structures have been designed. Preceramic polycarbosilane (PCS), used for preparing commercial Nicalon fiber,... 

Fig. 1.21 In situ strength distributions measured for Nicalon fibers on three CMCs, using the fracture mirror approach.

Table 8.1 Flexural (three-pt loading) properties of BMAS matrix/SiC/BN/Nicalon fiber composites24...

E. Y. Sun, S. R. Nutt, and J. J. Brennan, Interfacial Microstructure and Chemistry of SiC/BN Dual-Coated Nicalon Fiber Reinforced Glass-Ceramic Matrix Composites, J. Am. Ceram. Soc., 77[5], 1329-1339 (1994). 

The structure of Nicalon fiber has been studied by many researchers. Figure... 

Figure 6.25 Topographic views of the surface of (a) Nicalon and (b) Hi-Nicalon fiber (courtesy of N. Chawla). Note the nodular surface in both cases.

FIGURE 12.14 (a) Plot of the wave number and bandwidth (full width at half height) of the C-C raman peaks for different SiC fibers after various thermal treatment in air or in nonoxidizing atmospheres, (b) Comparison between ultimate tensile strength and sp peak FWHH as a function of thermal treatment for SiC Hi Nicalon fibers. (Adapted from Colomban, P., Raman microscopy and imaging of ceramic fibers in CMCs and MMCs, Ceramic Trans., 103, 517, 2000. With permission.)... 

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