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

Abstract

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% 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 % 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.