An investigation of the sinter-forging characteristics of alumina-magnesia composites - Implications for superplasticity

It is well known that the addition of a small quantity of magnesia to alumina prevents abnormal grain growth, and the conventional method of producing fully dense alumina with an equiaxed microstructure is to introduce less than 0.1 wt pct magnesia to alumina. In addition to solute drag, grain growth can be limited also by second-phase particles. Superplasticity in alumina-based ceramics can be enhanced by limiting grain growth. Furthermore, the introduction of low-energy interfaces in a two-phase microstructure can also retard early fracture. In the present study on an alumina-10 wt pct magnesia composite, the magnesia reacts with alumina to form a spinel phase. The experimental results indicate that the addition of magnesia retards grain growth and also leads to the formation of low-energy interfaces, both of which are likely to promote superplasticity in the composite. (Author)