Transient cavity growth in ceramics under compression

The transient cavity growth behaviour of liquid phase-sintered ceramics subject to compressive loads is examined. Three possible sources of transient behaviour are suggested, and their ranges of applicability evaluated. By considering the values of the characteristic time for individual transient modes, it has been determined that transient cavity growth in ceramics probably originates from transient grain-boundary sliding. Assuming that the creep-induced cavities nucleate and grow on grain boundaries that are parallel to the loading axis, a transient cavity growth model is developed on the basis that the local stress which drives cavity growth is induced by transient sliding of adjacent grain boundaries. Results of the proposed model are compared with small-angle neutron scattering measurements of a hot-pressed silicon carbide and a liquid phase-sintered alumina, both of which contain a continuous, amorphous grain-boundary phase. The different cavity growth behaviours observed in these ceramics are discussed in conjunction with transient grain-boundary sliding.