The role of interfaces in the high temperature deformation and failure of polycrystalline alumina

Abstract

Numerous studies on high temperature deformation of polycrystalline alumina in compression and bending have yielded stress exponents for deformation of n∼2, where ε^. ∝ σⁿ and ε^. and σ are the strain rate and stress, respectively. Since a stress exponent of ∼2 is typical of superplastic metals, it was anticipated that alumina will exhibit large elongations to failure, in a manner similar to the large strains reported in compression. However, tensile testing of pure alumina has revealed that pure alumina fails prematurely due to extensive cavitation, so that the elongations to failure are typically on the order of only ∼20%. This report examines the role of interfaces in the high temperature deformation and failure of polycrystalline alumina, with a special emphasis on grain boundary mobility and energy. The reported experimental data will be compared with existing theoretical models, and additional factors not considered in theoretical models will be outlined. Furthermore, this report discusses strategies to enhance the tensile ductility of polycrystalline alumina.