Fracture toughness studies on ceramics and ceramic particulate composites at different temperatures

The fracture toughness of alumina, zirconia, silicon nitride, and silicon carbide ceramics as well as silicon nitride and silicon carbide particulate composites were studied by the single edge V-notched beam (SEVNB) method over a wide temperature range. Manual and mechanical procedures for V-notch polishing-out and three- and four- point flexure tests were developed. Load-deflection diagrams for V-notched specimens contributed to better understanding of the deformation behavior of ceramics at room temperature and 1300 - 1400 degreesC. SENB (single edge notched beam) and SEPB (single edge precracked beam) as well as micro-Raman spectroscopy data were used to analyze the SEVPB results. The ratio between SEVNB and SENB results is about 0.6 for elastic materials and over 0.9 for inelastic ones. The results for zirconia, in the case of a V-notch root radius less than 5-7 mum, are in good agreement with SEPB results. The polishing-out of a V-notch does not lead to the tetragonal-monoclinic phase transformation in these materials.