D.-S. Lim et al./Wea225-2291999868-873 al to hot pressing direction(conventional H P) o. parallel to tape casting direction(tape casting -+-normal to tape casting direction(tape casting --V--surface normal to lamination direction( tape casting) m260226k0-sx 989 Whisker content(vol% Fig. 3. Wear of the alumina-SiC whisker composite samples and the balls EUl 28kU prismatic plane, respectively) were 20.9 and 27.03 GPa. It also interesting to note that the width of the ridge KIMM 的e2kU5x4,8B日 determined by projection length of the whisker normal to the direction of motion. It implies that whiskers were held strongly by the matrix. It was understood that SiC whiskers did not provide the weak grain boundaries for improving the fracture toughness. This is quite different from some other ceramic composite materials where cracks propa gated through weak grain boundary and the fracture tough ness increased [9]. Ceramic composites with weak grain boundary were reported not to exhibit good wear resis tance in spite of the high fracture toughness [10]. In fact unlike the composites with weak boundary, a significant portion of the reinforcements(which were whiskers in this were present within the matrix grains(alumina s). So, SiC whiskers in the sample were thought to protect the surface and formed ridges which, however KIMM 包白28kU5μmx4;88 ere thought to increase the surface roughness and friction coefficient Fig. 4. SEM micrographs of etched surface of w10 and W20 sample with Fig. 3 shows wear of the samples and the balls (wear w20 can be seen. The samples were thermally etched for 0.5 h at 1723K scar diameter). Sample W10 exhibited higher wear rate870 D.-S. Lim et al.rWear 225–229 1999 868–873 ( ) Fig. 2. SEM micrographs of wear track on sample A a and sample W10 Ž . Ž . b . prismatic plane, respectively were 20.9 and 27.03 GPa. It . is also interesting to note that the width of the ridge was determined by projection length of the whisker normal to the direction of motion. It implies that whiskers were held strongly by the matrix. It was understood that SiC whiskers did not provide the weak grain boundaries for improving the fracture toughness. This is quite different from some other ceramic composite materials where cracks propa￾gated through weak grain boundary and the fracture tough￾ness increased 9 . Ceramic composites with weak grain w x boundary were reported not to exhibit good wear resis￾tance in spite of the high fracture toughness 10 . In fact, w x unlike the composites with weak boundary, a significant portion of the reinforcements which were whiskers in this Ž case were present within the matrix grains alumina . Ž grains . So, SiC whiskers in the sample were thought to . protect the surface and formed ridges which, however, were thought to increase the surface roughness and friction coefficient. Fig. 3 shows wear of the samples and the balls wear Ž scar diameter . Sample W10 exhibited higher wear rate . Fig. 3. Wear of the alumina–SiC whisker composite samples and the balls. Fig. 4. SEM micrographs of etched surface of W10 and W20 sample with aligned whiskers; smaller grain size of sample W20 than that of sample W20 can be seen. The samples were thermally etched for 0.5 h at 1723 K in Ar environment