Influence of microstructural variation on fracture toughness of LPS-SiC ceramics

The influence of microstructural variations obtained by different
powder compositions and sintering times on the fracture toughness of
liquid phase sintered (LPS)-SiC has been investigated. SiC ceramics
were obtained by normal sintering in flowing nitrogen at 2080degreesC
for 1 h using 10 wt% of AIN and Y2O3 mixtures as additives, at molar
ratios of 80:20 and 40:60, respectively. In order to modify the
microstructures some samples of each composition were further
heat-treated at 2000 degreesC for 4 h to promote grain growth.
It has been found that the AIN rich composition resulted in a
microstructure with more elongated, platelet like grains and therefore
increased fracture toughness. Grain growth resulted also in higher
fracture toughness especially because the mechanism of crack-deflection
is more pronounced. AIN rich samples sintered at 2080 degreesC for I h
and heat-treated at 2000 degreesC for 4 h showed fracture toughness of
6.7 Wav rootm (determined by the SENVB method).