Preparation of fibre reinforced Si 800 (I)The products with high volume fraction of fibre can be obtained easily. Since both the polymer rheology and the thermosetting nature are similar to 600 organic thermosetting resin(c g. epoxide phenolic 兰旨400 resin), the FRP's fabrication process can be applied to the shaping process of PCPI.(2) To densify the matrix, shrinkage of the whole material, including 200 /SNC /SNC reinforcement, is not necessary in PCPI. While in the hot-pressing method, UD composites could be densified easily because the degree of freedom of shrinkage is two. However, 2D composites could not 0.4 0. 8 1.2 be well-densified because the degree of freedom of Displacement(mm) shrinkage is only one(the direction of thickness) Fig. 6. Stress-deflection curves of 2D composites In high temperature flexural tests, the strengths at room temperature are maintained to 1250C Fig. 8). There is no obvious difference in strength Thus, the high strengths of UD composites are between the SNF composite and SNBF composite, due to improved interaction between coating on because both fibres(SnF, SnBF) do not degrade the fibre and adequate matrix at the present manufacturing temperature and pressure. In the fibre evaluation, SNBF has better 3. 2 2D (Cross-ply composites) properties at elevated temperatures than SNF. Therefore, SNBF is expected to be applied as the Polished cross-sections of cross-ply composites are reinforcement of CMCs(target temperature shown in Fig. 7. The contrast of the fibre/matrix 1500C or above) interface and microcracks. attributed to the back scattered-electron intensity, are observed. From repetition of the impregnation and firing process, 4 CONCLUSION dense products are obtained. The properties of the samples are shown in Table 3. The excellent flexural By the PCPI method, dense SNF and SnbF rein strength(= 600 MPa) is obtained in samples of both forced silicon nitride composites were obtaincd SNF composite and SNBF composite. The stress- Three-point flexural strengths of the UD and 2D deflection curve is shown in Fig. 6. The fracture sur- (cross-ply) composites were shown to be as high as face shows a non-brittle failure with fibre pull-out, as 1000 and 600 MPa, respectively. This resulted from in the UD composites. The apparent effectiveness of improved interaction between the coating on the fibre strength in 2D composites is also extremely fibre and an adequate matrix. Using SNC as the high. This would be due to the following reasons: matrix precursor to fabricate these composites has 10m (b) ig. 7. Backscatterd electron image(composition)of polished cross-section SNBF reinforced composite, (a)Low magnifi ation,(b) high magnificaticPreparation of jibre reinforced Si3N4 composites 183 0 0.4 0.8 1.2 Displacement (mm) Fig. 6. Stress-deflection curves of 2D composites. Thus, the high strengths of UD composites are due to improved interaction between coating on the fibre and adequate matrix. 3.2 20 (Cross-ply composites) Polished cross-sections of cross-ply composites are shown in Fig. 7. The contrast of the fibrelmatrix interface and microcracks, attributed to the back￾scattered-electron intensity, are observed. From repetition of the impregnation and firing process, dense products are obtained. The properties of the samples are shown in Table 3. The excellent flexural strength (zz 600 MPa) is obtained in samples of both SNF composite and SNBF composite. The stress￾deflection curve is shown in Fig. 6. The fracture sur￾face shows a non-brittle failure with fibre pull-out, as in the UD composites. The apparent effectiveness of fibre strength in 2D composites is also extremely high. This would be due to the following reasons: (I) The products with high volume fraction of fibre can be obtained easily. Since both the polymer rheology and the thermosetting nature are similar to organic thermosetting resin (e.g. epoxide phenolic resin), the FRP’s fabrication process can be applied to the shaping process of PCPI. (2) To densify the matrix, shrinkage of the whole material, including reinforcement, is not necessary in PCPI. While in the hot-pressing method, UD composites could be densified easily because the degree of freedom of shrinkage is two. However, 2D composites could not be well-densified because the degree of freedom of shrinkage is only one (the direction of thickness). In high temperature flexural tests, the strengths at room temperature are maintained to 1250°C (Fig. 8). There is no obvious difference in strength between the SNF composite and SNBF composite, because both fibres (SNF, SNBF) do not degrade at the present manufacturing temperature and pressure. In the fibre evaluation, SNBF has better properties at elevated temperatures than SNF. Therefore, SNBF is expected to be applied as the reinforcement of CMCs (target temperature is 1500°C or above). 4 CONCLUSION By the PCPI method, dense SNF and SNBF rein￾forced silicon nitride composites were obtained. Three-point flexural strengths of the UD and 2D (cross-ply) composites were shown to be as high as 1000 and 600 MPa, respectively. This resulted from improved interaction between the coating on the fibre and an adequate matrix. Using SNC as the matrix precursor to fabricate these composites has (4 - 10pm P) - lpm Fig. 7. Backscatterd electron image (composition) of polished cross-section of 2D SNBF reinforced composite. (a) Low magnifi￾cation, (b) high magnification