Characteristics of hot-pressed fiber-reinforced ceramics with SiC matrix
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INTRODUCTION
THE purpose of this report is to clarify the effects of fiber reinforcements in the silicon carbide matrix composite, especially those on fracture toughness. Improvement of those composites in fracture toughness is a key technology for the application of ceramics instead of metals as structural components in high-temperature environments. In recent years, research and development of fiberreinforced ceramics have accelerated, together with the development and availability of high-performance fiberform reinforcement materials. The most significant reinforcing materials are SiC continuous fibers derived from organosilicon polymer precursors, t~,2j SiC whiskers, [3,4] and SiC monofilaments obtained via the chemical vapor deposition (CVD) process. Glass or glass-ceramic matrix composites [5,6,7]reinforced by Nicalon fiber (Nippon Carbon Company, Japan), which is made from polycarbosilane, have proven to be very tough materials. These composites have an advantage of relatively low processing temperatures. In contrast to them, several refractory Si3N 4 matrix composites have been studied. For example, SiC monofilament-reinforced reaction-bonded Si3N4 composites, which exhibit high work-of-fracture, are reported, t8] SiC monofilament-reinforced Si3N 4 m a trix composites with relatively high fracture toughness have been fabricated by slurry coating and the filamentwinding process, followed by hot pressing, tg} The authors have reported the effect of a C coating layer on the SiC monofilament on the filament pullout at fracture and the increase in the fracture toughness of SiC monofilament/Si3N4 matrix composite. [l~ It was confumed that the fracture toughness increases with filamentmatrix interfacial frictional stress in the case of the TADAHIKO MIYOSHI and SHIROO IIJIMA, Senior Researchers, and HIRONORI KODAMA, HIROSHI SAKAMOTO, and AKIHIRO GOTOH, Researchers, are with the Hitachi Research Laboratory, Hitachi, Ltd., 4026 Kuji-cho, Hitachi-shi, Ibaraki-ken 319-12, Japan. Manuscript submitted September 26, 1988. METALLURGICAL TRANSACTIONS A
composites, which experience filament pullout at fracture, but when the frictional stress becomes too large for the filament to be pulled out, the fracture toughness does not increase significantly over monolithic ceramics. However, few studies have been reported on SiC matrix composites, which are expected to be the most promising candidate materials for high-temperature use. In the present study, a CVD SiC monofilament or carbon filament made from PAN resin is used for the reinforcement of SiC matrix composites in order to investigate the reinforcing effect of the fibers in a highly refractory SiC matrix. The filament diameter of the former is considerably larger than those of SiC whiskers and SiC fibers derived from organosilicon polymer precursors. So, it is relatively easy to handle the filament to realize a desired filament arrangement in composites. The latter is chosen because of its higher refractoriness compared with Nicalon fiber. Whiskers are not used becaus
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