S042023 Effect of the magnification of optics on the fracture toughness of silicon carbide measured by indentation fracture (IF) method

Abstract

A round robin with 13 laboratories was conducted to evaluate the reproducibility of indentation fracture toughness, K_<IFR> of silicon carbides sintered with B and C. K_<IFR> varied widely from 3.43 to 4.43 MPa・m^<1/2> when the crack length was measured with an optical microscope at a low magnification of 〜 100x, while those obtained by powerful microscopy with both an objective lens of 40x and a traveling stage exhibited a consistent value of 3.23 ± 0.10 MPa・m^<1/2>. The crack lengths of the returned samples were also measured by the authors and compared with the reported values from each participant to clarify the origin of the variation of K_<IFR>. The wide scatter of K_<IFR> for the former measurements was explained by the misreading of the crack length which ranged from 55 to 115μm. It was revealed that the high resolving power of the objective lens of 40x enabled to find exact crack tips easier, which resulted in the good matching of K_<IFR> between laboratories for the latter case.