C. Lee et al / Materials Letters 61(2007)405-408 Fig 3. TEM micrographs of HAp-(t-ZrO2)Al2Or-(m-ZrO2)composite sintered at 1400C;(a)core region and (b)shell region. Fig 4. SEM fracture surfaces of 3rd passed HAp-(t-ZrO2VAl2O3-(m-zrO2)bodies sintered at different temperatures; (a)1200C,(b)1400C. microstructure was clearly observed without any processing defects bright and dark contrast(Fig. 3(a)) corresponds to HAp and t-zrO2 such as large cracks or shrinkage cavities. The core was about 35 um in phases, respectively. The fine t-zrO2 phase, less than 400 nm in diameter and the shell was 4.5 um thick. In the enlarged SEM images diameter, was homogeneously dispersed in the HAp matrix On the (b, c), which were sintered at 1200C and 1400C, respectively, the HAp-(t-ZrO2) core and AlO3(m-zrO2) shell regions were clearly observed In the sample sintered at 1200C, HAp-(t-zrO2)and Al2O3- HAp (m-zrO2) regions appeared with a porous microstructure due to the loy sintering temperature. However, at 1400C, the Al2O3-(m-zrO2) shell was comprised of a dense, fine microstructure due to the higher density. On the other hand, the HAp-(t-zrO2)core region showed some porous structure due to decomposition of the HAp phase. Also, the grain size was larger compared with the sample sintered at 1200C. Furthermore the t-ZrO2 and m-ZrO, phases were homogeneously dispersed in the HAp and AlO3 matrices, respectively. In the longitudinal orientation (Fig. 1(d)), the continuous fibrous microstructure was well controlled Fig. 2 shows the XRD profiles of HAp-t-ZrO2VAI2O3-m-zrO2 composites, depending on the sintering temperature. In the samples sintered at(a)1000C and (b), 1200C, a HAp phase was detected well as t-ZrO2, Al2O3, and m-zrO2 phases. However, after sintering at (c)1400C, it was found that most of HAp phase was transformed to B-tricalcium phosphate(B-TCP) Fig 3 shows TEM micrographs of the cross-sections of(a)core and Fig. 5. TEM images of crack propagation of 3rd passed HAp-(t-ZI02)core (b) shell regions of fibrous HAp composite sintered at 1400C. The region sintered at 1400C.microstructure was clearly observed without any processing defects such as large cracks or shrinkage cavities. The core was about 35 μm in diameter and the shell was 4.5 μm thick. In the enlarged SEM images (b, c), which were sintered at 1200 °C and 1400 °C, respectively, the HAp-(t-ZrO2) core and Al2O3-(m-ZrO2) shell regions were clearly observed. In the sample sintered at 1200 °C, HAp-(t-ZrO2) and Al2O3- (m-ZrO2) regions appeared with a porous microstructure due to the low sintering temperature. However, at 1400 °C, the Al2O3-(m-ZrO2) shell was comprised of a dense, fine microstructure due to the higher density. On the other hand, the HAp-(t-ZrO2) core region showed some porous structure due to decomposition of the HAp phase. Also, the grain size was larger compared with the sample sintered at 1200 °C. Furthermore, the t-ZrO2 and m-ZrO2 phases were homogeneously dispersed in the HAp and Al2O3 matrices, respectively. In the longitudinal orientation (Fig. 1(d)), the continuous fibrous microstructure was well controlled with white and gray colors, respectively. Fig. 2 shows the XRD profiles of HAp-(t-ZrO2)/Al2O3-m-ZrO2 composites, depending on the sintering temperature. In the samples sintered at (a) 1000 °C and (b), 1200 °C, a HAp phase was detected as well as t-ZrO2, Al2O3, and m-ZrO2 phases. However, after sintering at (c) 1400 °C, it was found that most of HAp phase was transformed to β-tricalcium phosphate (β-TCP). Fig. 3 shows TEM micrographs of the cross-sections of (a) core and (b) shell regions of fibrous HAp composite sintered at 1400 °C. The bright and dark contrast (Fig. 3(a)) corresponds to HAp and t-ZrO2 phases, respectively. The fine t-ZrO2 phase, less than 400 nm in diameter, was homogeneously dispersed in the HAp matrix. On the Fig. 3. TEM micrographs of HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composite sintered at 1400 °C; (a) core region and (b) shell region. Fig. 4. SEM fracture surfaces of 3rd passed HAp-(t-ZrO2)/Al2O3-(m-ZrO2) bodies sintered at different temperatures; (a) 1200 °C, (b) 1400 °C. Fig. 5. TEM images of crack propagation of 3rd passed HAp-(t-ZrO2) core region sintered at 1400 °C. C. Lee et al. / Materials Letters 61 (2007) 405–408 407