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1326 K. Yoshida et al. / Composites Science and Technology 61(2001)1323-1329 case of PCS-impregnated Hi-Nicalon cloths, sufficient fibers hot-pressed at 1650, 1700 and 1750C was about formation of the SiC matrix between fibers could be 2.3, 1.2 and 0.5 kJ/m, respectively achieved and round shape of the fiber was maintained Fig. 6 shows the maximum bending strength of the after hot-pressing. In this fabrication process, PCS- SiC/SiCr composites measured at room temperature. In impregnation into Hi-Nicalon cloths is an effective way the case of the composites with slurry-impregnated Hi to form SiC matrix between the fibers. Therefore all of Nicalon cloths, maximum strength decreased with low the following results were obtained for the composites ering sintering temperature, and the values were 130- with PCS-impregnated cloths 220 MPa Maximum strength of the composites with 52 Fig 3 shows the change in bulk density of the SiC SiCr composites with sintering temperature. Bulk den a)40 vol% of fibers sity of the composites with 40 vol. of fibers decreased with lowering sintering temperature and the relative density was about 89-97%. The composites with 52 vol. of fibers did not show much difference in bulk density regardless of sintering temperature and the relative density was about 93-94% 1700°C 1650°c 3.2. Mechanical properties (b)52 vol% of fibe ers The typical load-displacement curves of the SiC/SiCe 1700° ites with 40 and 52 vol. of fibers in three-point bending test at room temperature are shown in Fig 4 For comparison, the load-displacement curves of the composites with slurry-impregnated Hi-Nicalon cloths fabricated by hot-pressing at 1650 and 1750Care 1650°C shown in Fig. 5 [20]. In the case of the composite with 100 slurry-impregnated Hi-Nicalon cloths, the composites hot-pressed at 1700 C (not shown in Fig. 4)or 1750C displayed completely brittle fracture behavior, whereas the composites obtained in this study showed non-brit- tle fracture behavior. The load-displacement curves spread more widely with lowering sintering temperature 0.2 independent of fiber volume fraction. Fracture energy Displacement(mm) increased with lowering sintering temperature in both Fig 4. Typical load-displacement curves of the SiC/SiCr composites cases of fiber volume fraction, and larger values were with about(a)40)voL. and(b)52 vol. of fibers fabricated by hot- measured for the composite with higher fiber content pressing at various sintering temperature Fracture energy of the composites with 52 vol. of 200 3.4r 1750 oo-40vol%of fibers H52vol%of fibers 0.2 0.4 0.6 1650 1750 Displacement(mm) Sintering temperature(C) Fig. 5. Typical load-displacement curves of the Sic/SiCr composites vith slurry-impregnated Hi-Nicalon cloths fabricated by hot-pressing Fig. 3. Bulk density of the SiC/SiCr composites fabricated by hot at various sintering temperature. Fiber volume fraction of the com- posite is about 40 voL%case of PCS-impregnated Hi-Nicalon cloths, sufficient formation of the SiC matrix between fibers could be achieved and round shape of the fiber was maintained after hot-pressing. In this fabrication process, PCSimpregnation into Hi-Nicalon cloths is an effective way to form SiC matrix between the fibers. Therefore, all of the following results were obtained for the composites with PCS-impregnated cloths. Fig. 3 shows the change in bulk density of the SiC/ SiCf composites with sintering temperature. Bulk density of the composites with 40 vol.% of fibers decreased with lowering sintering temperature and the relative density was about 89–97%. The composites with 52 vol.% of fibers did not show much difference in bulk density regardless of sintering temperature and the relative density was about 93–94%. 3.2. Mechanical properties The typical load-displacement curves of the SiC/SiCf composites with 40 and 52 vol.% of fibers in three-point bending test at room temperature are shown in Fig. 4. For comparison, the load-displacement curves of the composites with slurry-impregnated Hi-Nicalon cloths fabricated by hot-pressing at 1650 and 1750C are shown in Fig. 5 [20]. In the case of the composite with slurry-impregnated Hi-Nicalon cloths, the composites hot-pressed at 1700C (not shown in Fig. 4) or 1750C displayed completely brittle fracture behavior, whereas the composites obtained in this study showed non-brittle fracture behavior. The load-displacement curves spread more widely with lowering sintering temperature independent of fiber volume fraction. Fracture energy increased with lowering sintering temperature in both cases of fiber volume fraction, and larger values were measured for the composite with higher fiber content. Fracture energy of the composites with 52 vol.% of fibers hot-pressed at 1650, 1700 and 1750C was about 2.3, 1.2 and 0.5 kJ/m2 , respectively. Fig. 6 shows the maximum bending strength of the SiC/SiCf composites measured at room temperature. In the case of the composites with slurry-impregnated HiNicalon cloths, maximum strength decreased with lowering sintering temperature, and the values were 130– 220 MPa. Maximum strength of the composites with 52 Fig. 3. Bulk density of the SiC/SiCf composites fabricated by hotpressing at various sintering temperature. Fig. 4. Typical load-displacement curves of the SiC/SiCf composites with about (a) 40) vol.% and (b) 52 vol.% of fibers fabricated by hotpressing at various sintering temperature. Fig. 5. Typical load-displacement curves of the SiC/SiCf composites with slurry-impregnated Hi-Nicalon cloths fabricated by hot-pressing at various sintering temperature. Fiber volume fraction of the composite is about 40 vol.%. 1326 K. Yoshida et al. / Composites Science and Technology 61 (2001) 1323–1329