Abstract
Fracture toughness has been recently considered to be one of the important mechanical properties in the same way as transverse-rupture strength for sintered hard materials such as ceramics, cermets and cemented carbides. The measuring method of fracture toughness was established according to JISR1607 in 1990 for fine ceramics, but it has not been established for cermets and cemented carbides. Therefore, fracture toughness of TiC-TiN based cermets, K-grade and P-grade cemented carbides with different metal binder content or WC grain size were measured by SEPB method according to JISR1607 for comparing with that of ceramics. And also, the effects of various notches for inducing precrack on fracture toughness and the relations between groove width of anvil and load for inducing precrack or length of precrack were investigated. Fracture toughness of cermets and cemented carbides increased with increasing metal binder content or WC grain size. With the same metal binder content, the amplitude of the fracture toughness showed the following order : K-grade cemented carbides > P-grade cemented carbides > cermets. These results were discussed from the standing point of mean free path of metal binder phase and young's modulus of the alloy.
