TL Wong et aL. /Journal of Materials Processing Technology 63(1997)399-404 A/w/p blends could not be extruded with the 3 mm diameter die, so a 6 mm diameter die had to be used. The use of a die with a small diameter for the a/p blend increases its time inside the heated barrel of the compounder. Thus, more Fe will be taken up from the barrel Table 5 Wt% of ceramic constituents of injection moulded samples 838483.6584.8585.34 85 84, 84.94 (0.08)* vol% SiCw, (B)1 *Standard deviation mounding. D)is the length distribution of the as-received whiskers Usually, the loss of Fe from the barrel will increase with content. However, it seems that this effect do not apply to the compounded A/w/P blends(see Fig. 5 curve A), since the Fe content did not increase significantly with whisker content. It might be due to the fact that the screw and barrel of the compounder had been significantly hardened by the manufacturer. For the A/w/p blends after injection moulding the tendency of increasing Fe content with whisker content can be observed since the screw and the barrel were prepared fo plastic injection moulding and so were not hardened to significant extent. 3. 4. Whisker length degrad The whisker length distribution of the a/w/p blends with 5 15 and 30 vol of SiCw after compounding are shown in Fig. 6. The longest whisker length measured from the as-received SiC Fig. 7. Variation of whisker length distribution of ceramic is 70 mm, while in the twin-screw compounded A/w/P blend polymer blend with(A)5 vol% SiCw,(B)15 vol% SiCw and(C) the longest measured whisker length is 40 mm. The mean 30 vol SiCw after injection moulding. D)is the length whisker length of the as-received SiCw was 13.8 mm. distribution of the as-received whiskers However, the mean whisker length of the compounded A/W/P blends ranged from 4 to 5 mm. Obviously, the overall whisker length of the A/w/p blends after compounding were seriousl decreased. Also, it seems that the degree of degradation of the whisker length of the compounded A/W/P blends did not Fig. 7 shows the whisker length distribution of the A/W/P increase with the whiskers content, as all the compounded blends after injection moulding with mean whisker between 3.5 A/w/P blends had nearly the same mean whisker length and 4.5 There is no significant damage on the me whisker length due to an increase in whisker content. Fig. 8 nows the optical micrographs for the as-received SiCw, A/W/P blends with 15 vol% SiCw after compounding and after injection moulding. It can be seen from the micrographs that the whisker lengths of the as-received SiCw are definitely longer than those of the whiskers after compounding or after injection moulding Moreover, the whiskers after compounding and after injection moulding have similar lengths. This observation showed that the decrease in whisker length was mainly due According to Frangen et al [12], as the whiskers are injection moulded, they interact with the alumina powder, the polymer whisker content/volz melt or the whiskers themselves. Such interaction may lead to bending force acting perpendicular to the whisker length. The whisker will be broken at some critical bending force whick Fig. 5. Variation of Fe content in the ceramic/polymer blends depends on the length and diameter of the whisker. During with whisker content(A)after compounding and (B)after compounding(or injection moulding), the whiskers continue to break until the bending force acting on the whiskers fall belowT.L. Wong et al.!Journal of Materials Processing Technology 63 (1997) 399-404 403 A/WIP blends could not be extruded with the 3 mm diameter die, so a 6 mrn diameter die had to be used. The use of a die with a small diameter for the AlP blend increases its time inside the heated barrel of the compounder. Thus, more Fe will be taken up from the barrel. Table 5 Wt% of ceramic constituents of injection moulded samples Ceramic blend A152 5SC 15SC 30SC Sample 1 83.95 83.50 84.97 85.57 Sample 2 83.84 83.65 84.85 85.34 Sample 3 83.80 84.38 84.97 85.36 Sample 4 83.83 83.57 85.12 85.16 Sample 5 83.72 84.44 84.78 85.08 Mean 83.83 83.91 84.94 85.30 (0.08)* (0.46)* (0.13)* (0.19)* *Standard deviation Usually, the loss of Fe from the barrel will increase with increasing SiCw content. However, it seems that this effect does not apply to the compounded A/W/P blends (see Fig. 5 curve A), since the Fe content did not increase significantly with whisker content. It might be due to the fact that the screw and barrel of the compounder had been significantly hardened by the manufacturer. For the A/W/P blends after injection moulding, the tendency of increasing Fe content with whisker content can be observed since the screw and the barrel were prepared for plastic injection moulding and so were not hardened to a significant extent. 3.4. Whisker length degradation The whisker length distribution of the A/W/P blends with 5, 15 and 30 vol % of SiCw after compounding are shown in Fig. 6. The longest whisker length measured from the as-received SiCw is 70 mm, while in the twin-screw compounded A/WIP blends the longest measured whisker length is 40 mm. The mean whisker length of the as-received SiCw was 13.8 mm. However, the mean whisker length of the compounded A/WIP blends ranged from 4 to 5 mm. Obviously, the overall whisker length of the A/WIP blends after compounding were seriously decreased. Also, it seems that the degree of degradation of the whisker length of the compounded A/WIP blends did not increase with the whiskers content, as all the compounded A/W/P blends had nearly the same mean whisker length. 3 '" I'~=~ o L....:0-~-:5-~.,..10=--~-:"15=--~--=2::-0~--:2'="5~--:3'::-O whisker content / vol7- Fig. 5. Variation of Fe content in the ceramic/polymer blends with whisker content (A) after compounding and (B) after injection moulding. 100 '" 90 """- v 80 0 c 70 v " 60 0- 50 v 40 0- 2 30 E" 20 0" 10 , 0 20 30 40 50 60 70 80 whisker length / /-lm Fig. 6. Variation of whisker length distribution of aluminal whisker/polymer blend with (A) 5 vol% SiCw , (B) 15 vol% SiCw and (C) 30 vol % SiCw after compounding. (D) is the length distribution of the as-received whiskers. '""""- v 80 0 c 70 0 v " 60 0- J:' 50 v 40 0- 0 30 E" 20 U" 10 10 20 30 40 50 60 70 80 whisker length / /-lm Fig. 7. Variation of whisker length distribution of ceramicl polymer blend with (A) 5 vol % SiCw, (B) 15 vol % SiCw and (C) 30 vol % SiCw after injection moulding. (D) is the length distribution of the as-received whiskers. Fig. 7 shows the whisker length distribution of the A/W/P blends after injection moulding with mean whisker between 3.5 and 4.5 !-lm. There is no significant damage on the mean whisker length due to an increase in whisker content. Fig. 8 shows the optical micrographs for the as-received SiCw , A/WIP blends with 15 vol % SiCw after compounding and after injection moulding. It can be seen from the micrographs that the whisker lengths of the as-received SiCw are definitely longer than those of the whiskers after compounding or after injection moulding. Moreover, the whiskers after compounding and after injection moulding have similar lengths. This observation showed that the decrease in whisker length was mainly due to the compounding process. According to Frangen et al [12], as the whiskers are injection moulded, they interact with the alumina powder, the polymer melt or the whiskers themselves. Such interaction may lead to a bending force acting perpendicular to the whisker length. The whisker will be broken at some critical bending force which depends on the length and diameter of the whisker. During compounding (or injection moulding), the whiskers continue to break until the bending force acting on the whiskers fall below