HIGH-TEMPERATURE COMPRESSIVE TESTS OF ALUMINUM NITRIDE - MECHANICAL-PROPERTIES AND MICROSTRUCTURE

Sintered and hot-pressed AlN was tested in compression at high temperature (1500-1650-degrees-C) either in creep or constant strain rate experiments. The mechanical behaviour can be described with low stress exponents (1 < n < 2) and large apparent activation energies (greater than or similar to 600 kJ/mol). Microstructural observations point to predominant intergranular deformation mechanisms, cavitation being especially important. Increased dislocation activity was seen in the grains when strain increased. Dislocations have basal Burgers vectors but glide in prismatic planes as well. Easy cross-slip is consistent with the observation of non-dissociated dislocations. At large stresses, screw dislocations are dominant.