B -T Lee et al. / Materials Science and Engineering A 458(2007)11-16 of their thermal expansion coefficients. Also, the strong strain References field contrast was observed at HAp matrix. However, at the crack process and tip zones, no found remarkable twin defects in the t- [1 W Suchanek, M. Yoshimura, J Mater Res 13(1998)94-117 ZrO2 grains, which are expected due to the stress-induced phase (21 P Ducheyne, Q Qiu, Biomaterials 20(1999)2287-2303 transformation [3]LL. Hench,J,Am. Ceran.Soc.81(7)(1998)1705-1728 [4 W. Suchanek, M. Yashima, M. Kakihana, M. Yashima, Biomaterials 18 (1997)923-933 4. Conclusion [5 B T Lee, N.Y. Shin, JK Han, H.Y. Song, Mater. Sci Eng. A 429(2006) 348-352. The relationship between microstructure and material prop- [6] S.J. Kalita, D. Rokusek, S. Bose, H.L. Hosick, A. Bandyopadhyay, J erties of the fibrous HAp-(1-ZrO2)Al203-(m-ZrO2)composites (7B.T. Lee, L.C. Kang. I. Am. Ceram Soc. 88(2005)2262-2266 were investigated depending on the sintering temperature. In the [8]BT.Lee, S.K. Sarkar, A.K. Gain, S JYim, H.Y. Song, Mater. Sci Eng.A ample sintered at 1200C, HAp-(t-ZrO2)core and Al2O3-(m- 432(2006)317-323 ZrO2)shell showed the porous structure. However at 1500C, 191A K Gain, B.T. Lee, Mater. Sci Eng- A 419(2006)269-275 the shell was appeared with dense and anisotropic grain grow [10] B.T. Lee, D H Jang, l.C. Kang, C.w. Lee, J. Am. Ceram Soc. 88(2005) 2874-2878 and the HAp core regions were transformed to a and p-ICP [11 M.C. Heisel. M.M. Silva, M T P. Schmalzried, J Bone Joint Surg. 85(2003) phases. The maximum values of hardness, bending strength and 1366-1379 fracture toughness were obtained at 1500C, and their values [12]SG. Huang, J. Vleugels, L Li, O.V. Biest, PL. Wang, J.Eur. Ceram. Soc. were about 890 Hv, 280 MPa and 4. I MPam, respectively 25(2005)3109-3115 The increasing of fracture toughness was basically due to the [13 M. Uo, G. Sjoren, A Sundh, E. Watari, M. Bergman, U. Lerner, Dent crack deflection toughening mechanism, which was occurred [14] P. Christel, A. Meunier, M. Heller, J. P. Torre, B. Cales, C.N. Peille. J at the Al2O3-(m-ZrO2)shell and HAp-(t-ZrO2) core regions, Biomed Mater Res. 23(1989)45-61 [15] Z Shen, E. Dolfasson, M. Nygren, L Gao, H Kawaoka, K Niihara, Ad Mater.1302001)214-216 Acknowledgement [16]H W. Kim, Y.J. Noh, Y.H. Koh, H.E. Kim, H.M. Kim, Biomaterials 23 (2002)4113-4121 [17] B.T. Lee, K.H. Kim, J K. Han, J Mater Res 19(2004)3234-3241 This work was supported by NRL research program of the [18]B T. Lee, C W. Lee. A K Gain, H.Y. Song, J. Eur. Ceram Soc. 27(200 orean Ministry of Science and Technology 157-163.16 B.-T. Lee et al. / Materials Science and Engineering A 458 (2007) 11–16 of their thermal expansion coefficients. Also, the strong strain field contrast was observed at HAp matrix. However, at the crack process and tip zones, no found remarkable twin defects in the t￾ZrO2 grains, which are expected due to the stress-induced phase transformation. 4. Conclusion The relationship between microstructure and material prop￾erties of the fibrous HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composites were investigated depending on the sintering temperature. In the sample sintered at 1200 ◦C, HAp-(t-ZrO2) core and Al2O3-(m￾ZrO2) shell showed the porous structure. However at 1500 ◦C, the shell was appeared with dense and anisotropic grain growth and the HAp core regions were transformed to α and -TCP phases. The maximum values of hardness, bending strength and fracture toughness were obtained at 1500 ◦C, and their values were about 890 Hv, 280 MPa and 4.1 MPa m1/2, respectively. The increasing of fracture toughness was basically due to the crack deflection toughening mechanism, which was occurred at the Al2O3-(m-ZrO2) shell and HAp-(t-ZrO2) core regions, respectively. Acknowledgement This work was supported by NRL research program of the Korean Ministry of Science and Technology. References [1] W. Suchanek, M. Yoshimura, J. Mater. Res. 13 (1998) 94–117. [2] P. Ducheyne, Q. Qiu, Biomaterials 20 (1999) 2287–2303. [3] L.L. Hench, J. Am. Ceram. Soc. 81 (7) (1998) 1705–1728. [4] W. Suchanek, M. Yashima, M. Kakihana, M. Yashima, Biomaterials 18 (1997) 923–933. [5] B.T. Lee, N.Y. Shin, J.K. Han, H.Y. Song, Mater. Sci. Eng. A 429 (2006) 348–352. [6] S.J. Kalita, D. Rokusek, S. Bose, H.L. Hosick, A. Bandyopadhyay, J. Biomed. Mater. Res. 71 (2004) 35–44. [7] B.T. Lee, I.C. Kang, J. Am. Ceram. Soc. 88 (2005) 2262–2266. [8] B.T. Lee, S.K. Sarkar, A.K. Gain, S.J. Yim, H.Y. Song, Mater. Sci. Eng. A. 432 (2006) 317–323. [9] A.K. Gain, B.T. Lee, Mater. Sci. Eng. A. 419 (2006) 269–275. [10] B.T. Lee, D.H. Jang, I.C. Kang, C.W. Lee, J. Am. Ceram. Soc. 88 (2005) 2874–2878. [11] M.C. Heisel, M.M. Silva, M.T.P. Schmalzried, J. Bone Joint Surg. 85 (2003) 1366–1379. [12] S.G. Huang, J. Vleugels, L. Li, O.V. Biest, P.L. Wang, J. Eur. Ceram. Soc. 25 (2005) 3109–3115. [13] M. Uo, G. Sjoren, A. Sundh, F. Watari, M. Bergman, U. Lerner, Dent. Mater. 19 (2003) 487–492. [14] P. Christel, A. Meunier, M. Heller, J.P. Torre, B. Cales, C.N. Peille, J. Biomed. Mater. Res. 23 (1989) 45–61. [15] Z. Shen, E. Dolfasson, M. Nygren, L. Gao, H. Kawaoka, K. Niihara, Adv. Mater. 13 (2001) 214–216. [16] H.W. Kim, Y.J. Noh, Y.H. Koh, H.E. Kim, H.M. Kim, Biomaterials 23 (2002) 4113–4121. [17] B.T. Lee, K.H. Kim, J.K. Han, J. Mater. Res. 19 (2004) 3234–3241. [18] B.T. Lee, C.W. Lee, A.K. Gain, H.Y. Song, J. Eur. Ceram. Soc. 27 (2007) 157–163.