B.-T. Lee et al. Materials Science and Engineering A 458(2007)11-16 Fig. 7. SEM fracture surfaces of (a) third passed HAp-(t-ZrO2MAl2O3-(m-ZrO2)bodies sintered at 1500C temperature and(b),(c)enlarged images of core and shell regions. fine t-ZrO2 particles were observed on the fracture surface Some crack bridging and branching were observed due to the of core region, and this observation is a typical evidence of anisotropic grain growth, when a crack propagated perpendicu microcracking lar into Al2O3-(m-Zro2shell region(c). At the HAp-(t-ZrO2) e. Fig. 8 shows the crack propagation made by Vickers inden- core region, the crack was propagated with deflection due to on in the third passed fibrous HAp composite sintered at the homogeneously dispersion of t-ZrO2 particles On the other 1500C. In the low magnification SEM image(a), the marked hand, Fig. 8(d) shows TEM image of crack tip zone which r indicates an indentation site and cracks were shortly prop- was taken from the HAp-(t-ZrO2)region. The t-zrO2 and HAp agated from four corner of an indentation site. In the enlarged phases were appeared with dark and gray contrasts, respectivel images(b, c), which were respectively taken from the longitudi- The main crack was straightly propagated into HAp matrix with nal and perpendicular direction of the fibrous microstructure, the transgranular fracture mode. However, an important observation rack propagation was clearly observed as indicated with arrow- was that when the crack met the t-ZrO2 particles, a remarkable heads. In the longitudinal direction(b), the crack was propagated crack deflection behavior was observed at the interfaces between along the AlO3(m-zrO2)shell region with heavy deflection. HAp and t-ZrO2, which may be formed due to the mismatching To pm 200nm Crack propagation of third passed HAp-(t-ZrO2)AlzO3-(m-ZrOzcomposites: (a) low SEM magnification,(b),(c)enlarged images of (a) and (d), TEM ore regionB.-T. Lee et al. / Materials Science and Engineering A 458 (2007) 11–16 15 Fig. 7. SEM fracture surfaces of (a) third passed HAp-(t-ZrO2)/Al2O3-(m-ZrO2) bodies sintered at 1500 ◦C temperature and (b), (c) enlarged images of core and shell regions. fine t-ZrO2 particles were observed on the fracture surface of core region, and this observation is a typical evidence of microcracking. Fig. 8 shows the crack propagation made by Vickers inden￾tation in the third passed fibrous HAp composite sintered at 1500 ◦C. In the low magnification SEM image (a), the marked “I” indicates an indentation site and cracks were shortly prop￾agated from four corner of an indentation site. In the enlarged images (b, c), which were respectively taken from the longitudi￾nal and perpendicular direction of the fibrous microstructure, the crack propagation was clearly observed as indicated with arrow￾heads. In the longitudinal direction (b), the crack was propagated along the Al2O3-(m-ZrO2) shell region with heavy deflection. Some crack bridging and branching were observed due to the anisotropic grain growth, when a crack propagated perpendicu￾lar into Al2O3-(m-ZrO2) shell region (c). At the HAp-(t-ZrO2) core region, the crack was propagated with deflection due to the homogeneously dispersion of t-ZrO2 particles. On the other hand, Fig. 8(d) shows TEM image of crack tip zone which was taken from the HAp-(t-ZrO2) region. The t-ZrO2 and HAp phases were appeared with dark and gray contrasts, respectively. The main crack was straightly propagated into HAp matrix with transgranular fracture mode. However, an important observation was that when the crack met the t-ZrO2 particles, a remarkable crack deflection behavior was observed at the interfaces between HAp and t-ZrO2, which may be formed due to the mismatching Fig. 8. Crack propagation of third passed HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composites; (a) low SEM magnification, (b), (c) enlarged images of (a) and (d), TEM images of core regions