抄録
For whisker reinforced ceramic composites, many toughening mechanisms are proposed. However, it is not clear yet which mechanism mainly contributes to the toughening. In this paper, we tried to explain the toughening behavior by the pull-out mechanism. A model based on the energy balance of crack propagation and frictional energy during whisker pulling-out was constructed for analyzing experimental results. Seven types of SiC whiskers with various sizes and shapes were used for fabricating SiC whisker/Al2O3 composites. Mechanical properties of these composites such as frature toughness KIC, effective fracture energy γeff and 4-point bending strength σf, were measured as a function of whisker dimension or whisker volume fraction. Fractured surfaces and crack propagation paths in these composites were observed in detail. A linear relationship between γeff and r2/lw was obtained (r: radius of whiskers, lw: length of whiskers). γeff also had a linear relationship with the whisker volume fraction. These results seem to support the whisker pull-out model proposed here. (KIC)2 showed linear relationships with r2/lw and whisker volume fraction as well as γeff. Four-point bending strengths of these composites were not improved in spite of toughening by whisker reinforcement. It is presumed that long whiskers cause to introduce large defects into ceramic matrix.
