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

Sintered and hot-pressed AlN was tested in compression at high tempera ture (1500-1650-degrees-C) either in creep or constant strain rate exp eriments. The mechanical behaviour can be described with low stress ex ponents (1 < n < 2) and large apparent activation energies (greater th an or similar to 600 kJ/mol). Microstructural observations point to pr edominant intergranular deformation mechanisms, cavitation being espec ially important. Increased dislocation activity was seen in the grains when strain increased. Dislocations have basal Burgers vectors but gl ide in prismatic planes as well. Easy cross-slip is consistent with th e observation of non-dissociated dislocations. At large stresses, scre w dislocations are dominant.