Gd. Zhan et al., Effect of beta-to-alpha phase transformation on the microstructural development and mechanical properties of fine-grained silicon carbide ceramics, J AM CERAM, 84(5), 2001, pp. 945-950
Ultrafine beta -SiC powders mixed with 7 wt% Al2O3, 2 wt% Y2O3, and 1.785 w
t% CaCO3 were hot-pressed and subsequently annealed in either the absence o
r the presence of applied pressure. Because the beta -SiC to (beta -SiC pha
se transformation is dependent on annealing conditions, the novel processin
g technique of annealing under pressure can control this phase transformati
on, and, hence, the microstructures and mechanical properties of fine-grain
ed liquid-phase-sintered SiC ceramics. In comparison to annealing without p
ressure, the application of pressure during annealing greatly suppressed th
e phase transformation from beta -SiC to alpha -SiC. Materials annealed wit
h pressure exhibited a fine microstructure with equiaxed grains when the ph
ase transformation from beta -Sic to alpha -SiC was < 30 vol%, whereas mate
rials annealed without pressure developed microstructures with elongated gr
ains when phase transformation was > 30 vol%. These results suggested that
the precise control of phase transformation in SiC ceramics and their mecha
nical properties could be achieved through annealing with or without pressu
re.