D.-S. Lim et al./Wea225-2291999868-873 than sample A. Cho et al. [11] reported that alumina with tained in the direction normal to tape casting direction on larger grains was vulnerable to intergranular damage due tape surface and highest in the direction normal to the to the residual stress and accumulated deformation. The lamination direction as shown in Fig. 1. Miyoshi and higher wear rate of sample w10 than that of sample A was Buckley [12] reported that the friction coefficient of single thought to be due to larger matrix grain size. Wear scar crystal SiC against the spherical diamond indenter was diameters on the ball were measured. The diameter on the lowest on the basal plane and highest in the direction ball worn against sample a was similar to that against parallel to the c-axis. They also reported that the wear sample W10. When whisker content increased from 10 groove width was smallest on the basal plane and largest vol. to 20 vol % the friction coefficient decreased from in the direction parallel to the c-axis. Their friction coeffi 0.91 to 0.67. Less wear of sample W20 than that of sample cient measurements showed a different tendency from the 10 shown in Fig 3 was explained by smaller matrix results of this study shown in Fig. I due to the fact that not grain growth, retarded by the whiskers(Fig. 4). However, only SiC whiskers but also the alumina matrix was present ear of sample w20 was still larger than sample a due to in the current samples. The friction coefficient parallel to rger matrix grains. Grain size of the ceramic exerted a tape casting direction was similar to that normal to thelam- strong influence on the wear behavior. ination direction. This was due to the fact that the projec- Fig 5 shows optical micrographs of the wear track of tion lengths of the whiskers normal to the direction of amples with 10 vol. whiskers. Whiskers were randomly motion that was parallel to the tape casting direction and oriented in sample w10. The whiskers of sample T10 were normal to lamination direction were similar to each other aligned in the tape casting direction. Sliding on sample Friction coefficients in the two directions were also close 10 was carried out in three directions with respect to the to the friction coefficient of W10. The friction coefficient whisker orientation, but the whiskers were well aligned as was lower in the direction normal to the tape casting shown in Fig. 5(b)-(d). Sample T10 showed different direction on the tape surface. As already mentioned, the friction coefficients depending on the orientation and sur- friction coefficient depended on the contact surface condi- face of the test. The lowest friction coefficient was ob- tions. Sliding in the two directions (i.e, parallel to the tape Sliding direction (b) (d),餐 5. Optical micrographs of wear track on the samples; (a)sample W10, (b) sample T1O-sliding parallel to the whisker length direction, (c) ple T10-sliding normal to the whisker length direction, and (d)sample T10-sliding normal to lamination direction; bright contrast represents theD.-S. Lim et al.rWear 225–229 1999 868–873 ( ) 871 than sample A. Cho et al. 11 reported that alumina with w x larger grains was vulnerable to intergranular damage due to the residual stress and accumulated deformation. The higher wear rate of sample W10 than that of sample A was thought to be due to larger matrix grain size. Wear scar diameters on the ball were measured. The diameter on the ball worn against sample A was similar to that against sample W10. When whisker content increased from 10 vol.% to 20 vol.%, the friction coefficient decreased from 0.91 to 0.67. Less wear of sample W20 than that of sample W10 shown in Fig. 3 was explained by smaller matrix grain growth, retarded by the whiskers Fig. 4 . However, Ž . wear of sample W20 was still larger than sample A due to larger matrix grains. Grain size of the ceramic exerted a strong influence on the wear behavior. Fig. 5 shows optical micrographs of the wear track of samples with 10 vol.% whiskers. Whiskers were randomly oriented in sample W10. The whiskers of sample T10 were aligned in the tape casting direction. Sliding on sample T10 was carried out in three directions with respect to the whisker orientation, but the whiskers were well aligned as shown in Fig. 5 b – d . Sample T10 showed different Ž. Ž. friction coefficients depending on the orientation and sur￾face of the test. The lowest friction coefficient was ob￾tained in the direction normal to tape casting direction on tape surface and highest in the direction normal to the lamination direction as shown in Fig. 1. Miyoshi and Buckley 12 reported that the friction coefficient of single w x crystal SiC against the spherical diamond indenter was lowest on the basal plane and highest in the direction parallel to the c-axis. They also reported that the wear groove width was smallest on the basal plane and largest in the direction parallel to the c-axis. Their friction coeffi￾cient measurements showed a different tendency from the results of this study shown in Fig. 1 due to the fact that not only SiC whiskers but also the alumina matrix was present in the current samples. The friction coefficient parallel to tape casting direction was similar to that normal to thelam￾ination direction. This was due to the fact that the projec￾tion lengths of the whiskers normal to the direction of motion that was parallel to the tape casting direction and normal to lamination direction were similar to each other. Friction coefficients in the two directions were also close to the friction coefficient of W10. The friction coefficient was lower in the direction normal to the tape casting direction on the tape surface. As already mentioned, the friction coefficient depended on the contact surface condi￾tions. Sliding in the two directions i.e., parallel to the tape Ž Fig. 5. Optical micrographs of wear track on the composite samples; a sample W10, b sample T10-sliding parallel to the whisker length direction, c Ž. Ž. Ž. sample T10-sliding normal to the whisker length direction, and d sample T10-sliding normal to lamination direction; bright contrast represents the Ž . whiskers