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K. Yoshida et al. / Composites Science and Technology 61(2001)1323-1329 Hi-Nicalon fibers were deformed since fibers were in um, AKP-50, Sumitomo Chemical, Japan), Y2O3(aver direct contact with each other because of insufficient age particle size: 2-3 um, 99.9%, High Purity Chemical impregnation by the Sic slurry between each fiber, Japan) and Cao(99.9%, Kanto Chemical, Japan), and resulting in low mechanical properties [19] some organics were used for the fabrication of the SiC In order to form the matrix between the fibers and to green sheet. The green sheet was prepared using labora- improve the mechanical properties of the SiC/SiCr com- tory-scale doctor-blade equipment (DP150, Tsugawa posite, polycarbosilane (PCS)-impregnated Hi-Nicalon Seiki, Japan). Two kinds of green sheets with different cloths were used for the reinforcement instead of Sic thickness were prepared by adjusting the blade height to slurry-impregnated Hi-Nicalon cloths. It is expected that 0.5-0.7 mm and at a carrier film speed of 10 cm/min the SiC matrix can be formed between fibers by the use of These sheets were dried at room temperature. The thick a liquid precursor. In addition, increase of fiber volume nesses of the green sheets were 105-125 and 220-285 um fraction should also be effective in improving the respectively. Details of the composition, organics in the mechanical properties of the SiC/SiCr composite. PCs green sheet, and the fabrication process were described impregnation into SiC filaments was already employed elsewhere [19]. The green sheet was cut to 35 mmx35 by Nakano et al. [21], but they fabricated only one- mm. dimensional SiC/SiCr composites by a filament winding method 2. 2. Fabrication of the SiC/Sicr composite In this study, two kinds of composites with a different olume fraction of fibers were fabricated by hot-pressing Schematic illustration of the fabrication process of the from green SiC sheet with sintering additives and PCs- Sic/SiCr composite is shown in Fig. 1. In this study, impregnated Hi-Nicalon cloth. The effects of fiber volume two-dimensionally (0/90)plain-woven BN-coated Hi fraction and sintering temperature on mechanical proper- Nicalon(Nippon Carbon, Japan) fiber cloth was used as ties of the SiC/SiCr composite at room temperature were the reinforcement. The thickness of the BN-coating was evaluated 0.4 um. The cloth was cut to 35 mmx 35 mm Polycarbosilane(PCs, NIPUSI-Type S Car. bon, Japan) was used for the impregnation into Hi 2. Experimental procedure Nicalon fiber cloth. pcs is a mixture of two molecular components, -CH3- and-(CH3)2SIiCH2-Den- 2.1. Fabrication of green sheet sity, melting point and average molecular weight of PCS powder used in this study were 1.10 g/cm, 242-249oC In this study, an Al2O3-Y2O3-CaO system was cho- and 1470-24400C, respectively. PCS powder was dissolved n for the fabrication of the SiC/SiCr composite as in toluene at 80C and the cloths were impregnated with sintering additives because of their low liquidus tem- PCS-toluene solution under reduced pressure peratures [22] The sizing agent was removed prior to polycarbosilane Submicron B-Sic powders(ultrafine, average particle impregnation. The PCS-impregnated cloths were dried at size: 0.28 Hm, Ibiden, Japan), sintering additives (20 130 C. The green sheets and the PCs-impregnated cloths mass% in total) using Al,O3(average particle size: 0.18 were stacked alternately and heat-treated at 300 C for 24 20 kPa -Sic green sheet thickness:(a)220-285 u m, (b)105-125 u m I PCS- impregnated Hi-Nicalon cloth Heat-treatment Hot-pressing 1650C,1700Cand1750°C 300C,24h, 1h in Ar, 40MPa In air 2D SiC/SiCt composite Fiber volume fraction: ( a)40 vol% Fig. 1. Schematic illustration of the fabrication process of the SiC/SiCr compositeHi-Nicalon fibers were deformed since fibers were in direct contact with each other because of insufficient impregnation by the SiC slurry between each fiber, resulting in low mechanical properties [19]. In order to form the matrix between the fibers and to improve the mechanical properties of the SiC/SiCf composite, polycarbosilane (PCS)-impregnated Hi-Nicalon cloths were used for the reinforcement instead of SiC slurry-impregnated Hi-Nicalon cloths. It is expected that the SiC matrix can be formed between fibers by the use of a liquid precursor. In addition, increase of fiber volume fraction should also be effective in improving the mechanical properties of the SiC/SiCf composite. PCS impregnation into SiC filaments was already employed by Nakano et al. [21], but they fabricated only onedimensional SiC/SiCf composites by a filament winding method. In this study, two kinds of composites with a different volume fraction of fibers were fabricated by hot-pressing from green SiC sheet with sintering additives and PCSimpregnated Hi-Nicalon cloth. The effects of fiber volume fraction and sintering temperature on mechanical properties of the SiC/SiCf composite at room temperature were evaluated. 2. Experimental procedure 2.1. Fabrication of green sheet In this study, an Al2O3–Y2O3–CaO system was chosen for the fabrication of the SiC/SiCf composite as sintering additives because of their low liquidus temperatures [22]. Submicron b-SiC powders (ultrafine, average particle size: 0.28 mm, Ibiden, Japan), sintering additives (20 mass% in total) using Al2O3 (average particle size: 0.18 mm, AKP-50, Sumitomo Chemical, Japan), Y2O3 (average particle size: 2–3 mm, 99.9%, High Purity Chemical, Japan) and CaO (99.9%, Kanto Chemical, Japan), and some organics were used for the fabrication of the SiC green sheet. The green sheet was prepared using laboratory-scale doctor-blade equipment (DP150, Tsugawa Seiki, Japan). Two kinds of green sheets with different thickness were prepared by adjusting the blade height to 0.5–0.7 mm and at a carrier film speed of 10 cm/min. These sheets were dried at room temperature. The thicknesses of the green sheets were 105–125 and 220–285 mm, respectively. Details of the composition, organics in the green sheet, and the fabrication process were described elsewhere [19]. The green sheet was cut to 35 mm35 mm. 2.2. Fabrication of the SiC/SiCf composite Schematic illustration of the fabrication process of the SiC/SiCf composite is shown in Fig. 1. In this study, two-dimensionally (0/90) plain-woven BN-coated HiNicalon (Nippon Carbon, Japan) fiber cloth was used as the reinforcement. The thickness of the BN-coating was 0.4 mm. The cloth was cut to 35 mm35 mm. Polycarbosilane (PCS, NIPUSI-Type S, Nippon Carbon, Japan) was used for the impregnation into HiNicalon fiber cloth. PCS is a mixture of two molecular components, –CH3SiHCH2– and –(CH3)2SiCH2–. Density, melting point and average molecular weight of PCS powder used in this study were 1.10 g/cm3 , 242–249C and 1470–2440C, respectively. PCS powder was dissolved in toluene at 80C and the cloths were impregnated with PCS-toluene solution under reduced pressure. The sizing agent was removed prior to polycarbosilaneimpregnation. The PCS-impregnated cloths were dried at 130C. The green sheets and the PCS-impregnated cloths were stacked alternately and heat-treated at 300C for 24 Fig. 1. Schematic illustration of the fabrication process of the SiC/SiCf composite. 1324 K. Yoshida et al. / Composites Science and Technology 61 (2001) 1323–1329