Is there diffusion creep in alumina?

Abstract

Although early studies on polycrystalline alumina attributed creep to diffusional processes, a re-analysis of the data and additional experimental results indicated that the creep behavior was non-linear, with a stress exponent of n - 2, where ε^. ∝ σⁿ and ε^. and σ are the strain rate and stress, respectively. Recently, there has been renewed interest in characterizing the mechanical properties of alumina-based ceramics, in view of the possibility of obtaining superplastic-like large elongations in such materials. However, the occurrence of concurrent grain growth and extensive cavitation has precluded a complete characterization of the mechanisms of tensile flow. This paper reviews some of the earlier studies, and then describes results from recent experimental results on alumina doped with 300 ppm magnesia. The mechanical testing was accompanied by detailed microstructural investigations on grain growth, changes in grain shape and cavitation. These experimental results and appropriate analysis are used to critically examine the possibility of diffusion creep in polycrystalline alumina.