Vickers indentation crack analysis of solid-phase-sintered silicon carbide ceramics

Solid-phased-sintered silicon carbide ceramics were prepared by traditional process with carbon and boron carbide as additives. The crack initiation and the profiles of the samples after Vickers indentation were observed in order to analyze the crack system. The typical characterizations of Vickers indentation, crack length c and diagonal 2a were used to determine the crack system. The surface cracks appear when the indentation load surpasses 0.1–0.2 N or the indentation diagonal length is over 3 μm. Clear and typical half-penny cracks formed after 10 N or above indentations. Within the 3–10 N range, the expected radial crack was not observed; but the relation between the crack length and indentation load told that the crack system after 3–10 N indentation is still half-penny. As to the critical c/a value for crack system transition, if it exists, it does not exceed 2.2. The fact that the toughness by IF method after 3–10 N strongly differs from that after 10–100 N may suggest that the determination of fracture toughness by indentation fracture method is not related to crack system. In addition, it is found that a more precise fracture toughness test of SSiC ceramics by IF method requires an indentation force larger than 10 N.