B -T Lee et al. / Materials Science and Engineering A 458(2007)11-16 SEM micrographs of (a) third passed longitudinal section HAp-(t-ZrO2)Al2O3-(m-ZrO2) bodies sintered at 1500C and (b)enlarged images of core and regions. fibrous HAp composites dramatically increased. To investigate +a-TCP..p-TCP-ZrO, CaAln O the main reason for showing the high fracture toughness the fracture surfaces and crack propagation, which were made by 4-point bending test and Vickers indentation, respectively, were observed by SEM and TEM techniques. Fig. 7 shows the SEM fracture surfaces of (a) third passed fibrous HAp composite sintered at 1500.C and enlarged image (b). In the low magnification image(a), the fracture surface was appeared with homogeneous structure although the pull outing phenomenon off In the enlarged image(b), the dense Al2O3-(m-zrO2) shell region showed mixed fracture mode with intergranular and trans- granular fracture corresponding with rough and flat surfaces respectively, and also, most of shell regions showed locally Fig.4. XRD profiles of HAp-(I-ZrO2MAl2O3-(m-ZrO2)bodies depending on oriented fracture surface due to the existence of anisotropic the sintering temperatures: (a)1200"C, (b)1500C. grain growth as shown in Fig. 2(b). On the other hand, the HAp-(t-ZrO2)core regions were appeared with severely rough surface although some pores also remained. Especially, many 4.5 1200 P Relative density 豆 Bending strength 4.0 o Vickers hardness 250. Fracture tou 1000 1200 Sintering temperature(C) Sintering temperature(C) 5. Relative density and Vickers hardness of third passed HAp-(I- Fig. 6. Bending strength and fracture toughness of third passed HAp-(14 B.-T. Lee et al. / Materials Science and Engineering A 458 (2007) 11–16 Fig. 3. SEM micrographs of (a) third passed longitudinal section HAp-(t-ZrO2)/Al2O3-(m-ZrO2) bodies sintered at 1500 ◦C and (b) enlarged images of core and shell regions. Fig. 4. XRD profiles of HAp-(t-ZrO2)/Al2O3-(m-ZrO2) bodies depending on the sintering temperatures; (a) 1200 ◦C, (b) 1500 ◦C. Fig. 5. Relative density and Vickers hardness of third passed HAp-(t￾ZrO2)/Al2O3-(m-ZrO2) composites depending on sintering temperature. fibrous HAp composites dramatically increased. To investigate the main reason for showing the high fracture toughness, the fracture surfaces and crack propagation, which were made by 4-point bending test and Vickers indentation, respectively, were observed by SEM and TEM techniques. Fig. 7 shows the SEM fracture surfaces of (a) third passed fibrous HAp composite sintered at 1500 ◦C and enlarged image (b). In the low magnification image (a), the fracture surface was appeared with homogeneous structure although the pull￾outing phenomenon of fibrous microstructure was not observed. In the enlarged image (b), the dense Al2O3-(m-ZrO2) shell region showed mixed fracture mode with intergranular and trans￾granular fracture corresponding with rough and flat surfaces, respectively, and also, most of shell regions showed locally oriented fracture surface due to the existence of anisotropic grain growth as shown in Fig. 2(b). On the other hand, the HAp-(t-ZrO2) core regions were appeared with severely rough surface although some pores also remained. Especially, many Fig. 6. Bending strength and fracture toughness of third passed HAp-(t￾ZrO2)/Al2O3-(m-ZrO2) composites depending on sintering temperature