Y Hua et al. Materials Science and Engineering A 428(2006)346-350 30 HArdness Relative density (% Fig. 3. Fracture tough ss value as a function of relative density of 25% SiC w/SiC composi can be concluded that the CVI path in the whisker preforms is expedite 3. 2. Microstructure and mechanical propertie Fracture toughness and micro-hardness values. determined by means of vickers indentation method with a load of 196N are shown in Fig. 3. Fracture toughness and micro-hardness value increase insignificantly with increasing the relative density from 84. 30% to 87.95%6. while the fracture toughness increases significantly with increasing the relative density from 87.95%o to 88.72%o Micro-hardness value increases significantly with V8. 5mm x5, 0Ok SE increasing the relative density from 87. 95% to 88.40%o, but ther increases slowly. Fracture toughness and micro-hardness value depend on the relative density significantly when it is higher than 87.95%0 he pores among whisker clusters of the composites with rel- ative density of 84.30%0, namely the pores at the triple-junction pockets, are larger than those with relative density of 87.95%0 and 88.72%. The pores at the triple-junction pockets contribute to the relative density mainly(see Fig 4). There are small pores in whisker clusters of the composites with relative density of 84.30%0, and there are no pores in the whisker clusters of the composites with relative density of 87.95% and 88. 72%0. Micro- hardness is determined by vickers indentation method within the clusters of the composites. The pores in the clusters dominate the micro-hardness, the fewer the pores, the higher the hardness (see Fig. 5). The pores can shield the main cracks, and contribute to the increase of fracture toughness [21 ]. The effect of pores posites with the relative density: (a)84.30%, (b)87.95%and(c)88.72% on fracture toughness is secondary compared to the role of SiC Fig. 4. Typical microstructure of cross-section surface of 25% SiCw/SiC composites with the relative density:(a)84.30%,(b)87.95% and (c)88.72%348 Y. Hua et al. / Materials Science and Engineering A 428 (2006) 346–350 Fig. 3. Fracture toughness and micro-hardness value as a function of relative density of 25% SiCW/SiC composites. can be concluded that the CVI path in the whisker preforms is expedite. 3.2. Microstructure and mechanical properties Fracture toughness and micro-hardness values, determined by means of Vickers indentation method with a load of 196 N, are shown in Fig. 3. Fracture toughness and micro-hardness value increase insignificantly with increasing the relative density from 84.30% to 87.95%, while the fracture toughness increases significantly with increasing the relative density from 87.95% to 88.72%. Micro-hardness value increases significantly with increasing the relative density from 87.95% to 88.40%, but then increases slowly. Fracture toughness and micro-hardness value depend on the relative density significantly when it is higher than 87.95%. The pores among whisker clusters of the composites with rel￾ative density of 84.30%, namely the pores at the triple-junction pockets, are larger than those with relative density of 87.95% and 88.72%. The pores at the triple-junction pockets contribute to the relative density mainly (see Fig. 4). There are small pores in whisker clusters of the composites with relative density of 84.30%, and there are no pores in the whisker clusters of the composites with relative density of 87.95% and 88.72%. Micro￾hardness is determined by Vickers indentation method within the clusters of the composites. The pores in the clusters dominate the micro-hardness, the fewer the pores, the higher the hardness (see Fig. 5). The pores can shield the main cracks, and contribute to the increase of fracture toughness [21]. The effect of pores on fracture toughness is secondary compared to the role of SiC Fig. 5. Typical microstructure of cross-section surface of 25% SiCW/SiC com￾posites with the relative density: (a) 84.30%, (b) 87.95% and (c) 88.72%. Fig. 4. Typical microstructure of cross-section surface of 25% SiCW/SiC composites with the relative density: (a) 84.30%, (b) 87.95% and (c) 88.72%