Flaw‐Tolerance and R ‐Curve Behavior of Liquid‐Phase‐Sintered Silicon Carbides with Different Microstructures

β‐SiC powder containing 6 wt% A1 2 O 3 and 4 wt% Y 2 O 3 as sintering additives was pressureless sintered at 2000°C for 1 h (AYE‐SiC) and 3 h (AYP‐SiC). AYE‐SiC consisted of an equiaxed grain structure and AYP‐SiC exhibited a micro‐structure with platelike grains as a result of grain growth related to β→α phase transformation during sintering, R ‐curve behavior and flaw tolerance for these silicon carbides were evaluated by the indentation‐strength technique. For comparison, the R ‐curve behavior of conventional sintered, boron‐ and carbon‐doped SiC (SS‐SiC) was evaluated. AYE‐SiC and AYP‐SiC exhibited rising R ‐curve behavior with toughening exponents of m = 0.042 and m = 0.135, respectively. AYP‐SiC exhibited better flaw tolerance and more sharply rising R ‐curve behavior than AYE‐SiC. The more sharply rising R ‐curve behavior and the better flaw tolerance of AYP‐SiC were attributed mainly to grain bridging of crack faces by platelike grains. Because of the high degree of transgranular fracture, SS‐SiC exhibited a flat R ‐curve despite a microstructural feature with platelike grains.