The effect of post-creep thermal treatment on cavitation damage

Abstract

Small-angle neutron scattering measurements have shown that nucleation and growth of grain boundary cavities occurs, in many ceramics, during the early stages of creep. Subsequent failure generally transpires by cavity coalescence to form cracks, followed by growth of the cracks. The effect on creep cavity populations of thermal treatment, both with and without pressure, has been investigated by comparing cavity distributions obtained from small-angle scattering measurements performed before and after the thermal treatments. The results of these measurements indicate that creep cavities can be removed if sufficient temperature and pressure are applied. From the results obtained on a sintered alumina and a hot-pressed silicon carbide, it appears that hydrostatic pressures approximately equal to the creep stress are required to afford substantial cavity sintering. The use of insufficient pressure not only fails to sinter the cavities formed during prior creep but has also been shown to lead to the nucleation of additional cavities, thus, apparently, increasing the level of damage.