Round robin on indentation fracture resistance of silicon carbide ceramics by using a powerful optical microscope

Reproducibility of indentation fracture resistance, KIFR of silicon carbides sintered with B and C was evaluated by a round robin with ten laboratories. When the crack length was measured with an optical microscope at a low magnification of ∼100×, KIFR varied widely from 3.43 to 4.20 MPa m1/2, whereas those obtained by a powerful microscopy with both an objective lens of 40× and a traveling stage exhibited a consistent value of 3.20±0.12 MPa m1/2. The wide scatter of KIFR for the former measurements was attributed mainly to the variation in misreading of the crack length. It was revealed that the high resolving power of the objective lens of 40× enabled to find exact crack tips easily, which resulted in the good matching of KIFR between laboratories for the latter case. It was suggested that the observation of indentations with powerful optics was effective for improving the reproducibility of the IF method.