Solute and defect segregation at the space charge layers of Fe-doped fine-grained Al2O3: Effect on the creep rate

Compressive creep in air of vacuum hot-pressed undoped alumina and 0.5 at.% iron doped alumina materials was investigated. The dark green colour of doped alumina accounted for the presence of iron as Fe2+ species at first. Also, iron rich precipitates were observed and identified as FeAl2O4 spinel. During the tests, Fe2+ species underwent oxidation during creep. The space charge concept is developed to account for the data and the interaction between the space charge and the extrinsic defect species. The observed iron segregation is proposed in the subgrain boundary region. Iron spinel precipitates were observed interacting with grain boundaries. Oxidation of Fe2+ resulted in Fe3+, which segregated into the grain boundaries. This segregation produced creep resistance of alumina.