Viscous cavity growth in ceramics under compressive loads

Abstract

The cavity growth behavior of liquid phase sintered ceramics containing a continuous, amorphous grain boundary phase and subjected to compressive loads is examined. Based on the assumption that under compressive loads the creep-induced cavities nucleate and grow on grain boundaries which are approximately parallel to the loading axis, it is deduced that the local tensile stress which drives cavity growth in the viscous grain boundary film is likely induced as the result of sliding in the adjacent grain boundaries and, for compatibility reasons, controlled by the constraints and creep behavior of the matrix. On this basis, a viscous cavity growth model is developed by extending the analysis of Raj and Dang to compressive loading conditions through the incorporation of Raj and Ashby's grain boundary sliding analysis and Dyson's concept of constrained cavity growth. The present model is used to predict the sizes and shapes of evolving cavities as a function of creep strain. The predicted results are discussed and compared with small-angle neutron scattering measurements of hot-pressed SiC.