Surface Cracks of Solid-phase-sintered Silicon Carbide Ceramics and Their Influences on Material Strength

The effects of surface cracks on bending strength of Solid-phase-sintered Silicon Carbide Ceramic (SSiC) were systematically investigated in aspects of crack size and inclined angle. The relation between the surface cracks and material strength revealed that the Vickers crack size is about 10 μm after 0.5 N indentation load that begins to dominant the fracture of SSiC test bars. Vickers cracks no larger than 3 μm are safe and do not harm to the general bending strength. It is found that inclined Knoop crack after 5 N or above is easier to deflect from the original direc- tion and dominates the sample fracture process. And the relationship between the flexure strength σ and inclined angle θ is found to correspond with σ∝(sinθ) -1/2 . When the indentation load is smaller than 1-2 N, Knoop crack plays a similar effect as intrinsic defect that they randomly dominate the sample fracture process; and this randomness makes