Cl. Hu et Mn. Rahaman, SIC-WHISKER-REINFORCED AL2O3 COMPOSITES BY FREE SINTERING OF COATED POWDERS, Journal of the American Ceramic Society, 76(10), 1993, pp. 2549-2554
SiC whiskers were coated with a thick cladding of fine-grained Al2O3 p
owder by controlled heterogeneous precipitation in a concentrated susp
ension of whiskers. After calcination, the coated whiskers were compac
ted by cold isostatic pressing and sintered at a constant heating rate
of 5-degrees-C/min in a helium atmosphere. The parameters which contr
ol the coating process and the sintering characteristics of the consol
idated powders are reported. Starting with an initial matrix density o
f 40-45% of the theoretical, composites containing up to almost-equal-
to 20 vol% whiskers (aspect ratio almost-equal-to 15) were sintered fr
eely to nearly theoretical density below 1800-degrees-C. By comparison
, a similar composite formed by mechanical mixing of the whiskers and
the precipitated Al2O3 powder reached a density of only 68% of the the
oretical after sintering under identical conditions. For a fixed whisk
er content, the sinterability of the composites formed from the coated
whiskers shows a fairly strong dependence on the whisker aspect ratio
.