December 2003 Crack-Healing Behavior of Al,O, Toughened by sic Whiskers 2145 a Vickers indentation 50um 5 um (a b SiC whisker Oxide 5 um (b) c) Oxide 5um OHn Fig. 3. SEM micrographs of the fracture surface of crack-healed A,O, -healed at 1300C for I h in air, JB=90 MPa: (a)crack profile tail of crack-healed zone shown by A in(a); (c)detail of outside k-healed zone shown by B in(a) Fig. 2. SEM m f specimen surfaces after heat treatment in a for A1,O/SiC-W following heat-treatment conditions: (a)1100.C lh;(b)1200°C 1300°C.Ih ould be detected. Therefore, the oxidation products in Fig. 2 are presumed to be the phase consisting of Sio, glass and alumino- urred, forming an aluminosilicate glass and crystalline mullin silicate glass formed by the reaction of SiO, and AL, O,. Chou et w,4and SiC-particle-reinforced Al,0,(AL Oy/SiC-P)sic. the crack-healing of Al 2O /SiC-P after heat treatment at 1300C Similar oxidation behaviors have been pointed out in Al,O,/S Chiu investigated the healing behaviors of thermal-shock for 2 h in air. On the basis of the present observation, it is clear that induced cracks in Al,O,SiC-w. They reported that the shock urface cracks were filled and bonded by the oxidation products nduced cracks were filled by oxidation products after heat formed on the crack surfaces(Fig. 3(b). The bend treatment at 1450%C for 2 h in air. Chou et al. 2 studied the healing cracked specimens after heat treatment in air recovered to a value of indent cracks and subsequent strength behavior of Sic-particle imilar to that of heat-treated smooth specimens due to a substan- reinforced Al2O3 nanocomposites. They pointed out that, after heat tial increase in the bonding force acting across the crack surfaces specimens recovered almost to the value of the unindented strength (4) Effect of Testing Temperature on the Bending Strength of the nanocomposite of Crack-Healed Specimens We examined the oxidation products on the specimen su Figure 4 shows the effect of testing temperature on gB of by X-ray diffraction. However, only crystalline Al,O, and crack-healed specimens Crack-healing was conducted at 1300oCoccurred, forming an aluminosilicate glass and crystalline mullite.7 Similar oxidation behaviors have been pointed out in Al2O3/SiC￾W11,34 and SiC-particle-reinforced Al2O3 (Al2O3/SiC-P).35,36 Chiu34 investigated the healing behaviors of thermal-shock￾induced cracks in Al2O3/SiC-W. They reported that the shock￾induced cracks were filled by oxidation products after heat treatment at 1450°C for 2 h in air. Chou et al. 12 studied the healing of indent cracks and subsequent strength behavior of SiC-particle￾reinforced Al2O3 nanocomposites. They pointed out that, after heat treatment at 1300°C for 2 h in air, the bending strength of indented specimens recovered almost to the value of the unindented strength of the nanocomposites. We examined the oxidation products on the specimen surface by X-ray diffraction. However, only crystalline Al2O3 and SiC could be detected. Therefore, the oxidation products in Fig. 2 are presumed to be the phase consisting of SiO2 glass and alumino￾silicate glass formed by the reaction of SiO2 and Al2O3. Chou et al. 12 reported similar results of X-ray diffraction in their study on the crack-healing of Al2O3/SiC-P after heat treatment at 1300°C for 2 h in air. On the basis of the present observation, it is clear that surface cracks were filled and bonded by the oxidation products formed on the crack surfaces (Fig. 3(b)). The bending strength of cracked specimens after heat treatment in air recovered to a value similar to that of heat-treated smooth specimens due to a substan￾tial increase in the bonding force acting across the crack surfaces. (4) Effect of Testing Temperature on the Bending Strength of Crack-Healed Specimens Figure 4 shows the effect of testing temperature on
B of crack-healed specimens. Crack-healing was conducted at 1300°C Fig. 2. SEM micrographs of specimen surfaces after heat treatment in air for Al2O3/SiC-W for the following heat-treatment conditions: (a) 1100°C, 1 h; (b) 1200°C, 1 h; (c) 1300°C, 1 h. Fig. 3. SEM micrographs of the fracture surface of crack-healed Al2O3/ SiC-W, 2c 100 m, crack-healed at 1300°C for 1 h in air,
B 903 MPa: (a) crack profile; (b) detail of crack-healed zone shown by A in (a); (c) detail of outside the crack-healed zone shown by B in (a). December 2003 Crack-Healing Behavior of Al2O3 Toughened by SiC Whiskers 2145