MATERIALS 兴 HIENGE& ENGIEERING ELSEVIER Materials Science and Engineering A 458(2007)11-16 www.elseviercom/locate/msea Relationship between microstructure and mechanical properties of fibrous HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composites Byong-Taek Lee Chi-Woo Lee a, Min-Ho Youn, Ho-Yeon Song a School of Advanced Materials Engineering, Kongju National University, 182 Shinkwan-dong, Kongju Ciry, Chungnam 314-701, South Korea Department of Microbiology, School of Medicine, Soonchunhyang University, 366-1 Ssangyoung-dong. Cheonan Ciry, Chungnam 330-090, South Korea Received 22 September 2006: received in revised form 29 November 2006: accepted 29 November 2006 Abstract The microstructure and mechanical properties of core/shell, fibrous HAp-(t-ZrO2NAl2O3-(m-ZrO2)composites, which were fabricated by the multi-pass extrusion process, were investigated depending on the sintering temperature. In the composite sintered at 1200C, many pores were observed in both HAp-(If-ZrO2)core and Al2O3-(m-ZrO2)shell regions. However, at 1500C, the shell regions showed dense and anisotropic grain growth and the core region were transformed to a-TCP and B-TCP phase. Also, as a minor reaction phase, the CaAl1O1g peaks detected. The values of relative density, hardness, bending strength and fracture toughness increased as the sintering temperature increased, and their maximum values were at 1500C about 890 Hv, 280 MPa and 4. 1 MPam", respectively. The fracture morphology was appeared with homogeneously rough surface, and indentation cracks showed short length due to the crack deflection and microcracking toughening mechanisms 2006 Elsevier B v. All rights reserved. Keywords: Hydroxyapatite; Composite; Microstructure; Mechanical properties 1. ntroduction On the other hand, for the application of bioimplant, Al2O3, ZrOz and their composite ceramics have been considered as a Because of the excellent biocompatibility and bioactive matrix as well as reinforcement phases due to their excellent characteristics, calcium phosphate based ceramics have been oxidation resistance, good biocompatibility and wear resistance received attention for the application of bone substitutes, scaf- [7-14. Shen et al. reported that the bending strength and the olds for tissue engineering and drug delivery system [1-3]. fracture toughness of HAp-50 vol %o ZrOz composite had high The most widely used calcium phosphate based bioceramics with 440 MPa and 2.5 MPam", respectively [15]. Kim et al are hydroxyapatite(HAp, Ca3(PO4)6(OH)2)and p-tricalcium made HAp-ZrO2 composite by pressureless sintering using cal phosphate(B-TCP, Ca3(PO4)2). Especially, the composition cium fluoride( CaF2)sintering additive and the values of bending of HAp is similar to the inorganic part of the natural bone strength and fracture toughness were achieved about 180 MPa and stable in body fluid. However, for the application of load and 2.3 MPam, respectively [16]. In general, the HAp crys- bearing part, it has been limited due to its inherent low mechan- talline phase can be easily transformed to B-TCP when the ical properties. Unfortunately, the fracture toughness of the HAp compact body was sintered at over 1200C. However, monolithic HAp ceramic does not exceed I MPam 2 that is no found the detailed reports on the microstructure change and compared with 2-12 MPam for human bone[4]. However, to fracture behavior properties of HAp and B-TCP-Al2O3-ZrO2 improve the mechanical properties of HAp ceramic, there were sintered bodies. Recently, the fibrous composites have been eas many approaches on the microstructure control of HAp sintered ily controlled using the novel fibrous monolithic process, which body [5]. Using the MgO-P2Os sintering additives, the fracture is frequently called multi-pass extrusion process, and also the toughness was not improved although the relative density was mechanical properties such as fracture toughness and strength remarkably increased 6] were remarkably improved due to the multi toughening mecha In this work, the fibrous HAp-(t-ZrO2)/Al2O3-(m-ZrO2 Corresponding author. Tel: +82 41 850 8677: fax: +82 41 858 2939 composite was fabricated to improve the mechanical proper E-mail address: Ibt @kongju ac kr(B.-T. Lee) ties using the multi-pass extrusion process. In addition, we 0921-5093/S-see front matter 2006 Elsevier B v. All rights reservedMaterials Science and Engineering A 458 (2007) 11–16 Relationship between microstructure and mechanical properties of fibrous HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composites Byong-Taek Lee a,∗, Chi-Woo Lee a, Min-Ho Youn a, Ho-Yeon Song b a School of Advanced Materials Engineering, Kongju National University, 182 Shinkwan-dong, Kongju City, Chungnam 314-701, South Korea b Department of Microbiology, School of Medicine, Soonchunhyang University, 366-1 Ssangyoung-dong, Cheonan City, Chungnam 330-090, South Korea Received 22 September 2006; received in revised form 29 November 2006; accepted 29 November 2006 Abstract The microstructure and mechanical properties of core/shell, fibrous HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composites, which were fabricated by the multi-pass extrusion process, were investigated depending on the sintering temperature. In the composite sintered at 1200 ◦C, many pores were observed in both HAp-(t-ZrO2) core and Al2O3-(m-ZrO2) shell regions. However, at 1500 ◦C, the shell regions showed dense and anisotropic grain growth and the core region were transformed to -TCP and -TCP phase. Also, as a minor reaction phase, the CaAl12O19 peaks detected. The values of relative density, hardness, bending strength and fracture toughness increased as the sintering temperature increased, and their maximum values were at 1500 ◦C about 890 Hv, 280 MPa and 4.1 MPa m1/2, respectively. The fracture morphology was appeared with homogeneously rough surface, and indentation cracks showed short length due to the crack deflection and microcracking toughening mechanisms. © 2006 Elsevier B.V. All rights reserved. Keywords: Hydroxyapatite; Composite; Microstructure; Mechanical properties 1. Introduction Because of the excellent biocompatibility and bioactive characteristics, calcium phosphate based ceramics have been received attention for the application of bone substitutes, scaf￾folds for tissue engineering and drug delivery system [1–3]. The most widely used calcium phosphate based bioceramics are hydroxyapatite (HAp, Ca3(PO4)6(OH)2) and -tricalcium phosphate (-TCP, Ca3(PO4)2). Especially, the composition of HAp is similar to the inorganic part of the natural bone and stable in body fluid. However, for the application of load bearing part, it has been limited due to its inherent low mechan￾ical properties. Unfortunately, the fracture toughness of the monolithic HAp ceramic does not exceed 1 MPa m1/2 that is compared with 2–12 MPa m1/2 for human bone [4]. However, to improve the mechanical properties of HAp ceramic, there were many approaches on the microstructure control of HAp sintered body [5]. Using the MgO–P2O5 sintering additives, the fracture toughness was not improved although the relative density was remarkably increased [6]. ∗ Corresponding author. Tel.: +82 41 850 8677; fax: +82 41 858 2939. E-mail address: lbt@kongju.ac.kr (B.-T. Lee). On the other hand, for the application of bioimplant, Al2O3, ZrO2 and their composite ceramics have been considered as a matrix as well as reinforcement phases due to their excellent oxidation resistance, good biocompatibility and wear resistance [7–14]. Shen et al. reported that the bending strength and the fracture toughness of HAp-50 vol.% ZrO2 composite had high with 440 MPa and 2.5 MPa m1/2, respectively [15]. Kim et al. made HAp-ZrO2 composite by pressureless sintering using cal￾cium fluoride (CaF2) sintering additive and the values of bending strength and fracture toughness were achieved about 180 MPa and 2.3 MPa m1/2, respectively [16]. In general, the HAp crys￾talline phase can be easily transformed to -TCP when the HAp compact body was sintered at over 1200 ◦C. However, no found the detailed reports on the microstructure change and fracture behavior properties of HAp and -TCP-Al2O3–ZrO2 sintered bodies. Recently, the fibrous composites have been eas￾ily controlled using the novel fibrous monolithic process, which is frequently called multi-pass extrusion process, and also the mechanical properties such as fracture toughness and strength were remarkably improved due to the multi toughening mecha￾nisms [17,18]. In this work, the fibrous HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composite was fabricated to improve the mechanical proper￾ties using the multi-pass extrusion process. In addition, we 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.11.155