010 Deformed particulate composite (50%Qtz,50%CAS) J24-QA Mean grain size: 44.5ocm LOWER (010) J24-QA Q OWER Mean aspect ratio: 2.0 Fig. 11. Crystallographic preferred orientation( CPO)of CAS from a CAs layer shortened to 52%. Foliation(horizontal line) is perpendicular to the compression direction(o1). Notice that the whole sphere, rather than a hemisphere, is necessary to represent the distribution of the positive ions. Projections of [00 1], [010) and [100] on the upper(a)and (b) hemispheres. (c) Lower hemisphere projections of poles to 1)(0 10) and(100). Stereonets are equal-area plots. One hundred thirty measurements are used 1.2 and have undergone the same type and magnitude of strain he addition of Qtz into the CAs matrix appears to have two separate but antagonist effects on CAS texture. On the Fig. 12. Grain size distribution of quartz in a particulate composite ne hand, rigid Qtz clasts cause complex flow in adjacent (24-QA)containing equal volume fractions of quartz and CAs, shortened axially at 300 MPa, 1373 K, 10-5s-I and 23%strain Measurements were CAS matrix, producing deflected foliation and local varia- tions in the texture around the Qtz clasts and accordingly diffusing the overall pattern of the texture and attenuating the texture intensity of CAS. On the other hand, the CAs (ie,(0 10)[100] with less mobile forest dislocations(e.g has to undergo nearly twice as much strain to accomplish (010)10011(00 1)[100] and(1 1o)(oolD and by the in- teraction between gliding dislocations and mechanical twins deformed in the particulate composites; such a strong strain The planar zones of high dislocation densities indicate that partitioning tends to increase the texture intensity of CAS. the(0 10)plane is a main slip plane under the conditions of a combination of the above effects results that the addition nvestigation. Furthermore, the deformed CAs developed of rigid Qtz grains does not cause a discernible change in strongly sutured grain boundaries with neograins bulging either the CPO pattern or the CPo intensity of CAs om regions with very high dislocation densities to areas TEM observations show that CAS grains from the pure with low dislocation densities. No well-developed sub- CAS aggregates, particulate composites or the CAS layers of grain boundaries or dislocation walls have been observed Qtz--CAS layered composites have very similar microstruc tural characteristics. The CAs grains display variable dis- location densities with very high densities(5x 1014 m-2)5.Discussion in relict grains and very low densities(5-8X in recrystallized neograins(Fig. 13). Even within the grains 5.1. Flow strengt with very high dislocation densities, the distribution of dis- locations is heterogeneous. with dislocations clustered alons One of the major problems with the high temperature narrow planar zones that are generally parallel to(0 10) structural applications of pure CAs aggregates is their rel- planes, forming so-called cells. 3.14 The cells could be atively low flow strength at high temperatures. The present formed by the interaction of more active glide dislocations study provides one way of overcoming this problem by308 S. Ji et al. / Journal of the European Ceramic Society 25 (2005) 301–311 Fig. 11. Crystallographic preferred orientation (CPO) of CAS from a CAS layer shortened to 52%. Foliation (horizontal line) is perpendicular to the compression direction (σ1). Notice that the whole sphere, rather than a hemisphere, is necessary to represent the distribution of the positive directions. Projections of [0 0 1], [0 1 0] and [1 0 0] on the upper (a) and lower (b) hemispheres. (c) Lower hemisphere projections of poles to (0 0 1), (0 1 0) and (1 0 0). Stereonets are equal-area plots. One hundred and thirty measurements are used. and have undergone the same type and magnitude of strain. The addition of Qtz into the CAS matrix appears to have two separate but antagonist effects on CAS texture. On the one hand, rigid Qtz clasts cause complex flow in adjacent CAS matrix, producing deflected foliation and local varia￾tions in the texture around the Qtz clasts and accordingly diffusing the overall pattern of the texture and attenuating the texture intensity of CAS. On the other hand, the CAS has to undergo nearly twice as much strain to accomplish the same total strain of sample because Qtz is almost un￾deformed in the particulate composites; such a strong strain partitioning tends to increase the texture intensity of CAS. A combination of the above effects results that the addition of rigid Qtz grains does not cause a discernible change in either the CPO pattern or the CPO intensity of CAS. TEM observations show that CAS grains from the pure CAS aggregates, particulate composites or the CAS layers of Qtz–CAS layered composites have very similar microstruc￾tural characteristics. The CAS grains display variable dis￾location densities with very high densities (>5 × 1014 m−2) in relict grains and very low densities (5 − 8 × 1011 m−2) in recrystallized neograins (Fig. 13). Even within the grains with very high dislocation densities, the distribution of dis￾locations is heterogeneous, with dislocations clustered along narrow planar zones that are generally parallel to (0 1 0) planes, forming so-called cells.13,14 The cells could be formed by the interaction of more active glide dislocations Deformed particulate composite (50% Qtz, 50% CAS) 0 10 20 30 40 50 60 Grain size, ∝m Number of measurements 0 10 20 30 40 50 60 70 80 90 100 N=265 Mean grain size: 44.5 ∝m J24-QA Qtz 0 10 20 30 40 50 60 Aspect ratio Number of measurements 0 1.2 2.4 3.6 4.8 6.0 7.2 N=265 Mean aspect ratio: 2.0 J24-QA Qtz (a) (b) Fig. 12. Grain size distribution of quartz in a particulate composite (J24-QA) containing equal volume fractions of quartz and CAS, shortened axially at 300 MPa, 1373 K, 10−5 s−1 and 23% strain. Measurements were made from optical photomicrographs. (i.e., (0 1 0)[1 0 0]) with less mobile forest dislocations (e.g., (0 1 0)[0 0 1], (0 0 1)[1 0 0] and (1 1 0)[0 0 1]) and by the in￾teraction between gliding dislocations and mechanical twins. The planar zones of high dislocation densities indicate that the (0 1 0) plane is a main slip plane under the conditions of investigation. Furthermore, the deformed CAS developed strongly sutured grain boundaries with neograins bulging from regions with very high dislocation densities to areas with low dislocation densities.30 No well-developed sub￾grain boundaries or dislocation walls have been observed. 5. Discussion 5.1. Flow strength One of the major problems with the high temperature structural applications of pure CAS aggregates is their rel￾atively low flow strength at high temperatures. The present study provides one way of overcoming this problem by