High-temperature deformation of polycrystalline magnesium oxide

The mechanical behaviour of two types of polycrystalline MgO was studied in compression over the temperature range 1200–1400°C. Differences in behaviour between hot-pressed specimens and specimens which were hot-pressed, then annealed, were attributed to differences in the structure of the grain boundary regions. Results indicate that creep in the hot-pressed specimens was controlled by a grain boundary sliding mechanism characterized by the movement of dislocations along grain boundaries, with a stress exponent n = l·8 and an apparent activation energy for the process of ∼70 kcal/mol. Creep in the specimens which were also annealed was found to be controlled by a dislocation climb mechanism within the grains, with a stress exponent n = 7 and an apparent activation energy of ∼110 kcal/mol.