WC-Ti(C,N)-Cr₃C₂-Co超微粒超硬合金の引張強度

抄録

The bending strength of ultrafine-grained cemented carbides exceeds that of medium-grained cemented carbides. This was thought to be due to the smaller size of defects within the ultrafine-grained cemented carbides. However, this attribution had not been verified because the specimens broke into numerous small pieces during bending tests. In addition, previous studies on the bending strength of medium-grained cemented carbides reported that there is limiting strength which is a region of not increasing bending strength by reducing the defect size. Therefore, in this study, we conducted the tensile test, which is unlikely to produce many small pieces, and the bending test to determine the cause of the high strength in ultrafine-grained cemented carbides. The ratio of bending strength to tensile strength was comparable between the medium- and ultrafine-grained cemented carbides. The number of fragments produced by fractures were almost same between the medium- and ultrafine-grained cemented carbides in case of the almost same strength. It was clear that the tensile strength of both medium- and ultrafine-grained cemented carbides increased as the defect size decreased with no sign of limiting strength. These results suggest that further strength improvements can be achieved by controlling defect size in ultrafine-grained cemented carbides.