Dynamic fatigue behaviors of structural ceramics were investigated in both air and vacuum (10-5 Torr) at room temperature. Experimental results were summarized as follows:
(1) The slow crack growth was observed in oxide ceramics and in non-oxide ceramics with oxide additives. Those ceramics did not show the slow crack growth in vacuum. In reaction bonded ceramics and ceramics with non-oxide additives and small oxygen contents, the slow crack growth was not observed in air.
(2) In air, the fatigue parameter of nonoxide ceramics which shows the slow crack growth decreased with increasing oxygen content.
(3) The slow crack growth originated from surface flaw predominated in air.
It is concluded that (1) the slow crack growth of ceramics at room temperature results from the stress corrosion induced by water vapour in air and it occurs within glassy phase at polycrystalline grain boundaries and (2) the oxygen content affects the fatigue parameter of non-oxide ceramics with oxide additives.
