C. Lee et al. Materials Letters 61(2007)405-408 HAp(t-ZrO Fig. 1. SEM micrographs of 3rd passed(a)cross-sectional HAp-(t-ZrO2)AlO3(m-ZrO2) bodies and ( b),(c), enlarged images sintered at 1200C and 1400C. respectively,(d) longitudinal sectional images. respectively. HAp/t-ZrO2(volume fraction 80: 20)and Al2O3/ scattered electron scanning microscope(BSE-SEM, JEOL-JSM m-zrO2(volume fraction 75: 25) were homogeneously mixed in 5410)and transmission electron microscope (TEM, JEM-2010, ethanol by ball milling using Al2O3 milling media. After JEOL, Japan) techniques. The crystal phases were analyzed by mixing, each composition was dried on a hot plate while being X-ray diffraction (XRD, D/MAX-250, Rigaku, Japan)using stirred. The Al,O3/m-zrO2, EVA, and stearic acid(volume Cu-Ka of 0. 1542. nm. fraction 60: 30: 10) were homogeneously mixed using a shear mixer(Shina Platec Co., Korea). The shear-mixed materials 3. Results and discussion were used to produce a hollow tube or shell by warm pressing To make the core rod, HAp/t-ZrO2 powders, EVA, and stearic Fig. 1 shows SEM micrographs of the 3rd pass fibrous HAp- acid(volume fraction 50: 40: 10)were mixed using a shear (20 voL %o t-ZrO2)Al203-(25 voL %m-ZrO2) composites. In cross- mixer. These core and shell were assembled to make a feedrod section, low magnification images(Fig. 1(a)), the core-shell and extruded in a heated die to make the lst pass filaments, which were about 3.5 mm in diameter. The lst pass filaments mZrO2·HAp, were then cut and loaded into a steel die and extruded to make the 2nd pass filaments. The 3rd pass filaments were produced in the same way, using the 2nd pass filaments. To remove the eVA binder, the burn-out process was carried out in a tube furnace with a heating rate(45C/h)up to 700C for 2 h under a N mosphere [15]. The samples were densified by pressureless sintering at1200°C-1400°for2 h in air The relative density was measured by the Archimedes method in an immersion medium of water. The average Vickers hardness was measured randomly by indenting with a load of 2.5 kg(10 pointssample)in core and shell regions. To prepare the bending test samples, 3.4 mm in diameter, the as sintered bulk samples were cut 35 mm in length and measured by a 4- oint bending method using 5 specimens with a crosshead speed fo I mm/min, using a universal testing machine(Unitech M,R Fig. 2. XRD profiles of raw powders and HAp(t-ZrO2MA1203-(m-z102 and B, Korea). Microstructures were examined using back- composites sintered at(a)1000C(b)1200C and(c)1400C.respectively. HAp/t-ZrO2 (volume fraction 80:20) and Al2O3/ m-ZrO2 (volume fraction 75:25) were homogeneously mixed in ethanol by ball milling using Al2O3 milling media. After mixing, each composition was dried on a hot plate while being stirred. The Al2O3/m-ZrO2, EVA, and stearic acid (volume fraction 60:30:10) were homogeneously mixed using a shear mixer (Shina Platec. Co., Korea). The shear-mixed materials were used to produce a hollow tube or shell by warm pressing. To make the core rod, HAp/t-ZrO2 powders, EVA, and stearic acid (volume fraction 50:40:10) were mixed using a shear mixer. These core and shell were assembled to make a feedrod and extruded in a heated die to make the 1st pass filaments, which were about 3.5 mm in diameter. The 1st pass filaments were then cut and loaded into a steel die and extruded to make the 2nd pass filaments. The 3rd pass filaments were produced in the same way, using the 2nd pass filaments. To remove the EVA binder, the burn-out process was carried out in a tube furnace with a heating rate (45 °C/h) up to 700 °C for 2 h under a N2 atmosphere [15]. The samples were densified by pressureless sintering at 1200 °C–1400 °C for 2 h in air. The relative density was measured by the Archimedes method in an immersion medium of water. The average Vickers hardness was measured randomly by indenting with a load of 2.5 kg (10 points/sample) in core and shell regions. To prepare the bending test samples, 3.4 mm in diameter, the as sintered bulk samples were cut 35 mm in length and measured by a 4- point bending method using 5 specimens with a crosshead speed of 0.1 mm/min, using a universal testing machine (Unitech™, R and B, Korea). Microstructures were examined using back￾scattered electron scanning microscope (BSE-SEM, JEOL-JSM 5410) and transmission electron microscope (TEM, JEM-2010, JEOL, Japan) techniques. The crystal phases were analyzed by X-ray diffraction (XRD, D/MAX-250, Rigaku, Japan) using Cu–Kα of 0.1542 nm. 3. Results and discussion Fig. 1 shows SEM micrographs of the 3rd pass fibrous HAp- (20 vol.% t-ZrO2)/Al2O3-(25 vol.% m-ZrO2) composites. In cross￾section, low magnification images (Fig. 1(a)), the core–shell Fig. 1. SEM micrographs of 3rd passed (a) cross-sectional HAp-(t-ZrO2)/Al2O3-(m-ZrO2) bodies and (b), (c), enlarged images sintered at 1200 °C and 1400 °C., respectively, (d) longitudinal sectional images. Fig. 2. XRD profiles of raw powders and HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composites sintered at (a) 1000 °C (b) 1200 °C and (c) 1400 °C. 406 C. Lee et al. / Materials Letters 61 (2007) 405–408