M. Kotani et al. / Composites Science and Technology 62(2002)2179-2188 2183 should be completed below 700 K. Curing processing Fig. 6(b), the break of a product into fibers was caused prior to consolidation might be effective for densifica- by squeeze of slurry from fiber preform. Successive tion of a body because effective volumetric yield of a consolidation was accomplished under the pressure of 1 precursor was improved [see Formula(1)]. If the poly- 5 and 10 MPa. Similar profiles were shown as a function mer was cured up to 600 and 700 K, it could be of curing temperature under these pressures;i.e.con- improved by almost twice. Also, further densification tinuous change and particular high density could be might be possible by crushing pores with appropriate presented. It was considered that the green bodies were pressure, because the polymer continuously underwent efficiently consolidated owing to well-balanced relation viscous liquid and plastic solid in this range of tem- ship between the physical characteristics of a precursor perature. At that time, a precursor impregnated into and pressure in these conditions. As pressure was fibrous body had to be soft enough for plastic defor- increased, curing temperature at which the particular mation under external forces. In addition, heating rate high relative density appeared rose, and those values during the first pyrolysis should be slow so as not only was increased. It nsidered that this increase of to control crack initiation and dilatation but to improve relative density was owing to the improvement of effec ceramic yield. These requirements have to be fully taken tive yield of a precursor. In this optimization, relative into consideration for process development density could attain to 70% in the condition of (623, 10) Fig. 7 shows apparent densities of the consolidated 3. 2. Optimization of consolidation conditions bodies under various conditions. Apparent density defined in this work provides useful information about 3.2.1. Curing temperature and pressure microstructure, because it depends on the ratio of the As thermosetting of PVS from viscous liquid to solid occurred in very short range between 583 and 663 K curing temperature was precisely controlled with the interval of 20 K. Fig. 5 shows relative densities of the consolidated bodies under various conditions between curing temperature and pressure. Clear effects of the process conditions on relative density could be identi- fied. Fig. 6(a) and(b) exhibits representative appear ances of the samples consolidated in the conditions of g (583, 0) and(603, 20) respectively, showing extreme. 551 cases related with pressure. As a noticeable feature of Fig 5, the results of 0 MPa are notably inferior to those of other pressure. Many large pores among inhomo- geneously distributed fibers and bundles could be seen in Fig. 6(a). This figure indicates that pressure was very important for appropriate fiber distribution and densi- fication, though the fabrication process of a composite without pressurization is very attractive to develop near-net shape production of complicated-shaped com- K ponents. On the contrary, excessive pressure also gave a Fig. 5. Relative densities of as-consolidated bodies under various negative influence for microstructure. As shown in conditions between curing temperature and pressure (b) Fig. 6. Optical micrographs of as-consolidated bodies under the conditions of (a)(583, 0)and(b)(623, 15)should be completed below 700 K. Curing processing prior to consolidation might be effective for densifica￾tion of a body because effective volumetric yield of a precursor was improved [see Formula (1)]. If the poly￾mer was cured up to 600 and 700 K, it could be improved by almost twice. Also, further densification might be possible by crushing pores with appropriate pressure, because the polymer continuously underwent viscous liquid and plastic solid in this range of tem￾perature. At that time, a precursor impregnated into a fibrous body had to be soft enough for plastic defor￾mation under external forces. In addition, heating rate during the first pyrolysis should be slow so as not only to control crack initiation and dilatation but to improve ceramic yield. These requirements have to be fully taken into consideration for process development. 3.2. Optimization of consolidation conditions 3.2.1. Curing temperature and pressure As thermosetting of PVS from viscous liquid to solid occurred in very short range between 583 and 663 K, curing temperature was precisely controlled with the interval of 20 K. Fig. 5 shows relative densities of the consolidated bodies under various conditions between curing temperature and pressure. Clear effects of the process conditions on relative density could be identi- fied. Fig. 6(a) and (b) exhibits representative appear￾ances of the samples consolidated in the conditions of (583, 0) and (603, 20) respectively, showing extreme cases related with pressure. As a noticeable feature of Fig. 5, the results of 0 MPa are notably inferior to those of other pressure. Many large pores among inhomo￾geneously distributed fibers and bundles could be seen in Fig. 6 (a). This figure indicates that pressure was very important for appropriate fiber distribution and densi- fication, though the fabrication process of a composite without pressurization is very attractive to develop near-net shape production of complicated-shaped com￾ponents. On the contrary, excessive pressure also gave a negative influence for microstructure. As shown in Fig. 6(b), the break of a product into fibers was caused by squeeze of slurry from fiber preform. Successive consolidation was accomplished under the pressure of 1, 5 and 10 MPa. Similar profiles were shown as a function of curing temperature under these pressures; i. e. con￾tinuous change and particular high density could be presented. It was considered that the green bodies were efficiently consolidated owing to well-balanced relation￾ship between the physical characteristics of a precursor and pressure in these conditions. As pressure was increased, curing temperature at which the particular high relative density appeared rose, and those values was increased. It was considered that this increase of relative density was owing to the improvement of effec￾tive yield of a precursor. In this optimization, relative density could attain to 70% in the condition of (623,10). Fig. 7 shows apparent densities of the consolidated bodies under various conditions. Apparent density defined in this work provides useful information about microstructure, because it depends on the ratio of the Fig. 5. Relative densities of as-consolidated bodies under various conditions between curing temperature and pressure. Fig. 6. Optical micrographs of as-consolidated bodies under the conditions of (a) (583, 0) and (b) (623, 15). M. Kotani et al. / Composites Science and Technology 62 (2002) 2179–2188 2183