C. Xu/Journal of the European Ceramic Sociery 25 (2005)605-611 咄画 1.7m I.n (d) Fig. 4. Fracture morphology of As15T15 ceramic material at 1780.C x 60 min(a)accidented fracture surface; (b)crack bridging, (c)grain pulling-out; (d) brittle cleavage Microstructural morphology of the material under TEM of the material but also to the increase in the fracture tough- is shown in Fig. 5. Both the two dispersed phases SiC and ness of the material which is similar, to a certain extent, to Ti(C, N), distributed uniformly in the matrix, bond well with the toughening mechanism found in the whisker toughened Al2O3 at the interface with fine grain size. SiC particles ceramic material. I8 are usually dispersed uniformly in the matrix, but few of Dislocations have also been observed in the SiC/TI(C, N)/ them with the sub-micron meter grain size, nearly less than Al2O3 ceramic material. Typical morphology is given in 200 nm, can be observed to exist inside the alumina grains Fig 5c. Most of the dislocations originate from the interface (Fig. 5a). These existing sub-micron meter sized Sic par- under the action of the residual thermal stresses and then ticles inside the alumina grains can improve the flexural propagate into the grains On the one side, the elastic strain strength and the fracture toughness of the material with the energy can be deposited in the dislocations On the other similar toughening mechanism of intergranular fracture hap. side. when the crack reaches. the dislocations can absorb pened frequently in ceramic nanocomposites. 16. 7 On the parts of the energy of fracture through their own deforma- other hand, the twin sub-structure can be observed clearly tion. The propagating crack will be pinned and the fracture no matter inside large or small SiC grains among which the toughness is resultedly increased. At a matter of fact, the twin sub-structure with the orientation angle of 60o is dis- dislocation toughening, which is similar to the microcrack covered(Fig 5b). The formation of twins will absorb the toughening, can cause the regional blunting effect in the tip energy of fracture at the interface of Al2 O3/SiC so that the area of the extending crack and it will have the KR-curve addition of Sic can contribute not only to the reinforcement behavior. 9.20 The interlaced dislocation lines are seemed608 C. Xu / Journal of the European Ceramic Society 25 (2005) 605–611 Fig. 4. Fracture morphology of AS15T15 ceramic material at 1780 ◦C × 60 min (a) accidented fracture surface; (b) crack bridging; (c) grain pulling-out; (d) brittle cleavage . Microstructural morphology of the material under TEM is shown in Fig. 5. Both the two dispersed phases SiC and Ti(C,N), distributed uniformly in the matrix, bond well with Al2O3 at the interface with fine grain size. SiC particles are usually dispersed uniformly in the matrix, but few of them with the sub-micron meter grain size, nearly less than 200 nm, can be observed to exist inside the alumina grains (Fig. 5a). These existing sub-micron meter sized SiC par￾ticles inside the alumina grains can improve the flexural strength and the fracture toughness of the material with the similar toughening mechanism of intergranular fracture hap￾pened frequently in ceramic nanocomposites.16,17 On the other hand, the twin sub-structure can be observed clearly no matter inside large or small SiC grains among which the twin sub-structure with the orientation angle of 60◦ is dis￾covered (Fig. 5b). The formation of twins will absorb the energy of fracture at the interface of Al2O3/SiC so that the addition of SiC can contribute not only to the reinforcement of the material but also to the increase in the fracture tough￾ness of the material which is similar, to a certain extent, to the toughening mechanism found in the whisker toughened ceramic material.18 Dislocations have also been observed in the SiC/Ti(C,N)/ Al2O3 ceramic material. Typical morphology is given in Fig. 5c. Most of the dislocations originate from the interface under the action of the residual thermal stresses and then propagate into the grains. On the one side, the elastic strain energy can be deposited in the dislocations. On the other side, when the crack reaches, the dislocations can absorb parts of the energy of fracture through their own deforma￾tion. The propagating crack will be pinned and the fracture toughness is resultedly increased. At a matter of fact, the dislocation toughening, which is similar to the microcrack toughening, can cause the regional blunting effect in the tip area of the extending crack and it will have the KR-curve behavior.19,20 The interlaced dislocation lines are seemed