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

Abstract 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 2080 °C for 1 h using 10 wt% of AlN 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 °C for 4 h to promote grain growth. It has been found that the AlN 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. AlN rich samples sintered at 2080 °C for 1 h and heat-treated at 2000 °C for 4 h showed fracture toughness of 6.7 MPa m (determined by the SENVB method).