Creep of Zr-doped alumina at very low creep rates

Fine-grain high-purity alumina doped by small amounts of Zr was tested by a high strain-sensitivity creep technique at temperatures from 1273 to 1423 K and stresses from 4.2 to 35 MPa. Stress exponents close to 1 and apparent activation energies of about 235 kJ/mol were observed at lower temperatures, while both values become higher at 1423 K. Quasi-periodic instabilities in creep flow were observed in all creep tests at temperatures lower than 1423 K. Attempts to attribute it to some measuring artifacts caused by external influences were not successful. Nevertheless, more experiments are needed to ensure that they belong to the creep deformation process. The origin of their observation remains unclear.