This study was carried out to clarify the relationship between microstructures and mechanical properties of SiC sintered with Al2O3 additive (1960°C for 2h and 1980°C for 4h) and with B and C additives. Fracture surface energy, γi, for crack initiation and work of fracture surface energy, γwof, for crack propagation were selected as suitable parameters for screening the mechanical properties. γi was measured by both indentation fracture (IF) and Chevron notch three-point bend methods. The Chevron notch method was also performed to measure γwof·γi measured by the IF method depended on the applied load and the relationship between the load and γi differed among specimens with different microstructures. It was found that the γi measured at a high load is about the same as that measured by the Chevron notch method for all the specimens. Both γi and γwof of SiC sintered with Al2O3 additive were higher than those of SiC sintered with B and C additives. γi and γwof of SiC sintered with B and C were about the same, while γwof of SiC sintered with Al2O3 additive was higher than γi. Sintering aids, grain size and morphology affected the crack propagation behavior.
