Fracture surface energy and microstructure of silicon carbides with different additives

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