Hi-Nicalon Type

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. 

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). 

Takeda, M. 1996. Mechanical and structural analysis of silicon carbide fiber Hi-Nicalon types. Ceramic Engineering and Science Proceedings 17(4-5) 35 2. 

FIGURE 7. Typical transverse thermal conductivity curves for thin panels with CMC systems N22, N24-A, and N24-C. Effect of fiber conductivity is shown by curve for the N22 system with the lower conductivity Hi-Nicalon Type-S fiber type. 

FIGURE 10. Typical room-temperature stiess-strain curves for the N22 CMC system with Sylramic and Hi-Nicalon Type-S fibers, and for the N24-B CMC system with Sylramic-iBN fibers before and after combustion gas exposure ofthe systems in a low-pressure burner rig at -800°C for -100 hours. The fibers in the N22 systems each had carbon on their surfaces before BN interphase deposition. 

The three major constituents of any continuous fiber ceramic matrix composite are the reinforcing fibers, the matrix and a fiber-matrix interphase, usually included as a coating on the fibers. HiPerCompTM composites can be processed with various monofilament and multifilament fibers, such as the SCS family of monofilament SiC from Specialty Materials, Inc. CG-Nicalon and Hi-Nicalon Type S from Nippon Carbon Company Tyranno ZE , Tyranno ZMl and Tyranno S A from Ube Industries and Sylramic fiber from COl Ceramics. However, the composites described in this paper all utilize Hi-Nicalon SiC fiber from Nippon Carbon Company. A companion paper, in this book, by Jim DiCarlo [11] from NASA gives the properties of slurry cast composites reinforced with Sylramic and Sylramic-iBN fibers. 

The creep rate of Hi-Nicalon type fibers is significantly lowered when the fibers are heat treated at 1400-1600°C in argon prior to the creep tests (also performed in argon). Further, fibers which are heat treated at 1600°C exhibit a steady state creep domain at Tt = 1500°C, whereas the untreated fibers do not creep when tested at Tj = 1500°C [32]. The creep resistance of heat treated fibers at 1400°C in air is higher than that of the untreated fibers [87]. 

Nippon Carbon has obtained a near-stoichiometric fibre, the Hi-Nicalon Type S, from a PCS cured, in a hydrogen rich environment, by electron irradiation using a modified Hi-Nicalon process . It is claimed that the excess carbon is reduced from C/Si = 1.39 for the Hi-Nicalon to 1.05 for the Hi-Nicalon Type S. 

Fit . 9. Fraefure morphology of the Hi-Nicalon Type S libre after a creep test at I400 C. 

The Hi-Nicalon Type S, near-stoichiometric fibre from Nippon Carbon shows the greatest stability of the three fibres and Fig. 9 reveals its fracture morphology at I400°C, which is unchanged in appearance to that obtained at room temperature. The fracture surface is noticeably less granular in appearance than the other two near-stoichiometric fibres, which is due to a smaller average grain size of around 50 nm. 

The Young moduli of the near-stoichiometric fibres are 375 GPa for the Hi-Nicalon Type S, 330 GPa for the Tyranno SA and 390 GPa for the Sylramic fibre. Fig. 12 shows that they retain their strengths to higher temperatures than the earlier generations of fibres. The Hi-Nicalon Type S fibre shows little or no loss of strength even at 1400°C. 

As can be seen from Fig. 13 the creep rate of the Hi-Nicalon Type S fibre is one order of magnitude lower than that of the other two near-stoichiometric fibres because of the lack of sintering aids which facilitate creep at high temperatures. Growth of a... 

Fig. 15 shows the silica layer formed at the surface of a Hi-Nicalon Type S fibre after creep at 1400°C... 

Trade name Nicalon Hi-Nicalon Hi-Nicalon type S Tyranno Lox M Tyranno ZMI Tyranno SA Sylramic SCS/Ultra scs... 

The interphase degradation of unidirectional Hi-Nicalon Type-S/CVI-SiC composites with a PyC monolayer or a PyC/SiC multilayer, which is measurable but not so dramatic, did not compromise the overall mechanical performance of the composites. PyC/SiC multilayer composites exhibit comparably higher interfacial shear stresses than monolayer composites even after neutron irradiation. The effect of the irradiation temperature seems very minor at <1000°C for both interphase types [47]. 

SiC fibers, e.g., Hi-Nicalon Type-S or Tyranno-SA SiC fibers are considered the reference nuclear-grade SiCf/SiC composites because of their perceived radiation tolerance and chemical compatibility of the high-purity, stoichiometric SiC matrix with various harsh environments. 

Y. Katoh, T. Nozawa, C.H. Shih, K. Ozawa, T. Koyanagi, W. Porter, L.L. Snead, High-dose neutron irradiation of Hi-Nicalon Type S silicon carbide composites. Part 2 mechanical and physical properties, J. Nucl. Mater. 462 (2015) 450—457. 

Continuous SiC fibers contribute to the toughening of ceramics as the interface in SiC/SiC composites works effectively. Furthermore, continuous SiC fibers are formed into the SiC fiber preform composed of multidimensional woven and braided structures (two-dimensional woven cloth, three-dimensional woven fabric, complex braids shaped as the desired component and so on). The shape of the SiC fiber preform mostly determines the final shape of the SiC/SiC composites. High-performance SiC fibers supplied by Nippon Carbon Co., Ltd., Japan (Nicalon, Hi-Niealon, Hi-Nicalon Type S) (Ichikawa, Okamura, Seguchi, 1995 Takeda,... 

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