M.L. Antti et al. Journal of the European Ceramic Society 24(2004)565-578 but some of them showed incomplete infiltration(see The fracture surface of the +450 material and after Fig 9c and d) for 100 h at 1100C is shown in Fig Overviews of the microstructure after heat-treatment As mentioned above, at room temperature the samples for 100 h at 1000 and 1 100oC are shown in Figs. 10a separated without bundle breakage, failing by inter- and b, respectively. The heat-treatment caused an laminar shear of the matrix(Fig 5b). After heat-treat- opening of some of the shrinkage cracks and coarsening ment bundle fracture occurred with no fibre bundle of the macropores. Characterisation of the porosity is pull-out giving a brittle impression(Fig. 12) presented in Section 4.4. No fibre bundle fractures were found. The response of +450 material was identical to 4.4. Density and porosity measurements that of the 0/90 material Evidence for shear damage was sought on micro- The density, porosity and microhardness measure- graphs of the LW surfaces of fractured samples of as- ments are summarised in Table 4. The overall dimen received 0/90 material. Damage in the form of crack sions and the weight of the samples and consequently networks in the matrix that could well be attributed to their overall density did not change significantly with shear deformation was observed in zones stretching thermal exposure. Similarly no significant change in the diagonally from the holes in several samples open porosity was detected. However, there was a sig- SEM fractographs of selected fracture surfaces of 0/ nificant change in the nature of the macroporosity; the 90 samples are shown in Fig. 11. The as-received macropores tended to grow larger and some matrix material exhibited considerable fibre pull-out. The cracks opened during exposure(cf Figs. 9, 10a and b) pulled out fibres were smooth and free of attached The macroporosity was therefore characterised quanti matrix consistent with a low ratio of interface debond- tatively on TW sections, defining macropores as all ing energy to fibre fracture energy. After heat-treat- pores with a diameter larger than 22 um or, in the case ment at 1000C, fibre pull-out was still extensive but of elongated pores and cracks, lengths greater than 44 significantly reduced in comparison with that of the as- um. It was found (table 4) that the volume fraction of received material. Moreover traces of matrix material macropores increased with thermal exposure and at sticking to fibre surfaces could be observed as well as 1100oC their average size also increased. An obvious groups of fibres sintered together. Evidence of increased interpretation of these results is that the matrix densified matrix sticking could also be seen in the samples tested by sintering. Instead of leading to overall shrinkage of at high temperature (i.e. after very short thermal expo- the composite which was constrained dimensionally by sure). After heat-treatment for 100 h at 1100C the the fibre skeleton, the densification occurred internally material exhibited negligible fibre pull-out(Fig. 11 c). by growth of existing macropores and matrix cracks Very short pull-out of sintered bundles could be found SEM observation did indicate a reduction in the micro- ig. 11 d) porosity in the matrix from about 30 to 10 vol. but 器 你多;标小 包 Fig. 10. Microstructures of material heat-treated for 100 h ures of 1000C(a)and 1100C(b), respectively (LT surface sections of 0/90 samples).(a) After 100 h at 1000C.(b) After 100 h at 1100but some of them showed incomplete infiltration (see Fig. 9c and d). Overviews of the microstructure after heat-treatment for 100 h at 1000 and 1100
C are shown in Figs. 10a and b, respectively. The heat-treatment caused an opening of some of the shrinkage cracks and coarsening of the macropores. Characterisation of the porosity is presented in Section 4.4. No fibre bundle fractures were found. The response of 45
material was identical to that of the 0/90 material. Evidence for shear damage was sought on micro￾graphs of the LW surfaces of fractured samples of as￾received 0/90 material. Damage in the form of crack networks in the matrix that could well be attributed to shear deformation was observed in zones stretching diagonally from the holes in several samples. SEM fractographs of selected fracture surfaces of 0/ 90 samples are shown in Fig. 11. The as-received material exhibited considerable fibre pull-out. The pulled out fibres were smooth and free of attached matrix consistent with a low ratio of interface debond￾ing energy to fibre fracture energy. After heat-treat￾ment at 1000
C, fibre pull-out was still extensive but significantly reduced in comparison with that of the as￾received material. Moreover traces of matrix material sticking to fibre surfaces could be observed as well as groups of fibres sintered together. Evidence of increased matrix sticking could also be seen in the samples tested at high temperature (i.e. after very short thermal expo￾sure). After heat-treatment for 100 h at 1100
C the material exhibited negligible fibre pull-out (Fig. 11 c). Very short pull-out of sintered bundles could be found (Fig. 11 d). The fracture surface of the 45
material and after heat-treatment for 100 h at 1100
C is shown in Fig. 12. As mentioned above, at room temperature the samples separated without bundle breakage, failing by inter￾laminar shear of the matrix (Fig. 5b). After heat-treat￾ment bundle fracture occurred with no fibre bundle pull-out giving a brittle impression (Fig. 12). 4.4. Density and porosity measurements The density, porosity and microhardness measure￾ments are summarised in Table 4. The overall dimen￾sions and the weight of the samples and consequently their overall density did not change significantly with thermal exposure. Similarly no significant change in the open porosity was detected. However, there was a sig￾nificant change in the nature of the macroporosity; the macropores tended to grow larger and some matrix cracks opened during exposure (cf. Figs. 9, 10a and b). The macroporosity was therefore characterised quanti￾tatively on TW sections, defining macropores as all pores with a diameter larger than 22 mm or, in the case of elongated pores and cracks, lengths greater than 44 mm. It was found (Table 4) that the volume fraction of macropores increased with thermal exposure and at 1100
C their average size also increased. An obvious interpretation of these results is that the matrix densified by sintering. Instead of leading to overall shrinkage of the composite which was constrained dimensionally by the fibre skeleton, the densification occurred internally by growth of existing macropores and matrix cracks. SEM observation did indicate a reduction in the micro￾porosity in the matrix from about 30 to 10 vol.% but Fig. 10. Microstructures of material heat-treated for 100 h at temperatures of 1000
C (a) and 1100
C (b), respectively (LT surface sections of 0/90
samples). (a) After 100 h at 1000
C. (b) After 100 h at 1100
C. M.-L. Antti et al. / Journal of the European Ceramic Society 24 (2004) 565–578 573