Structure and chemistry of grain boundaries in yttria doped aluminas

Abstract

The structure and chemistry of grain boundaries (GBs) are investigated by CTEM, HREM and EDXS in polycrystalline aluminas doped with yttria or codoped with magnesia and yttria. Yttrium is the major segregant element, in agreement with a driving force energy resulting from elastic interaction. Yttrium level is maximum in GBs whose plane is parallel to (0112) plane in one grain. A segregation of silicon occurs in most GBs of an Y-doped large-grained sample. It is higher than yttrium content in GBs whose plane is parallel to the basal (0001) plane. An epitaxial growth of a Si-rich compound is proposed to interpret this preferential silicon segregation on alumina basal plane. Finally, a segregation of yttrium occurs on GB dislocations, in agreement with the strengthening effect of this element during high temperature deformation of alumina.