Hi-Nicalon

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. 

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

The multifilament fiber (10-20 xm diameter) as commercially produced consists of a mixture of /3-SiC, free carbon and SiOj. The properties of this fiber are summarized in Table 6.5. The properties of Nicalon start to degrade at temperatures above about 600°C because of the thermodynamic instability of composition and microstructure. A ceramic grade of Nicalon, called Hi Nicalon, having low oxygen content is also available Yet another version of a multifilament silicon carbide fiber is Tyranno, produced by Ube Industries, Japan. This is made by pyrolysis of poly (titano carbosilanes) and contains between 1.5 and 4wt% titanium. 

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 6.27 Comparison of the creep behavior of Nicalon, Hi-Nicalon and CVD SiC fiber. Note the superior performance of the CVD fiber, which is attributable to stoichiometric /3-SiC (after Dicarlo, 1994)...

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.)... 

Gouadec, G., Colomban, R, and Bansal, N.R, Raman study of Hi-nicalon fiber reinforced celsian composites. Rart I Distribution and nanostructure of different phases, J. Am. Ceram. Soc., 84, 1129, 2001. 

FIGURE 18.10 Flow scheme for the preparation of Nicalon and Hi Nicalon fibers. " ... 

Nicalon and Hi-Nicalon are trademarks of Nippon Carbon Co., Tokyo, Japan. Y. Nakaido, Y. Otani, N. Kozakai, S.Otani, Chem. Lett., 705 (1987). 

H. Lin and M. Singh, Evaluation of Lifetime Performance of Hi-Nicalon Fiber-reinforced Melt-infiltrated SiC Ceramic Composites, Ceram. Trans., 144, 207-20(2002). 

The electrical conductivity for SiC/SiC is strongly affected by the matrix conductivity and in the fiber direction, it is usually dominated by conduction through the PyC (Pyrolitic Carbon) interphase By 2-probe DC (direct current) and AC (alternating current) and 4-probe DC methods, Youngblood et al measured the EC-values of 2D Hi-Nicalon S/PyC interphase/ICVI SiC matrix composites, and composites with the PyC interphase layer removed by oxidation (in plane) at temperatures up to 500 "C. It was found that by removing the PyC interphase, in plane EC of the composites decreased 30%. 

R. Yamada, N. Igawa, and T. Taguchi, Thermal DifFusivity/Conductivity of Tyranno SA fiber and Hi-Nicalon Type S Fiber-reinforced 3-D SiC/SiC Composites, J, Nucl. Mater., 329-333, 497-501 (2004). 

Figure 7.3 Creep curves for Sic libers (Hi Nicalon ) at 1400 and 1450 C in argon at a stress of 140 MPa. The inelastic deformation shows only the presence of primary creep. (From Rugg and Tressler, 1997, reproduced courtesy of The American Ceramic Society, Westerville, OH.)...

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