Basic Study on the Toughening of Ceramics

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As abasic study on the improvement of the brittleness in ceramic materials,(1) Studies on manufactural processing of toughend ceramics, and (2) Reconsidering studies on the evaluation of fracture toughness K_<IC> for brittle materials, were investigated.Sic wisker reinforced MgO or AlN ceramics were hot-pressed. K_<IC> values of thise ceramics were a little larger than those of hot-pressed MgO or AlN without wisker at lower temperature. On the otherhand, the values increased remarkably at the temperature range above 1000C and 1400C for MgO and AlN composite respectivery, due mainly to wisker pull-out mechanisum.K_<IC> of stractural ceramics such a sAl_2O_3,Si_3N_4 Sic was evaluated by SEPB technique. The values obtained from each measurment showed a good reproducibillity for Al_2O_3 and SiC. Si_3N_4, however, the values scattered a little. The causes of the scattering were discussed on the observation of inclined precrack front and deflected fracture surface.The fracture mechanics for toughened ceramics such as refractory materials were remarked. K_<IC> derived from linear fracture mechanics rcipe may be meanless for the toughened ceramics, bacause there might be a considerable difference between the fracture resistances for crack initiation and propagation. Some experimental techniques were tried to some refractories and castable composit.