High temperature plastic deformation of aluminium nitride with a lower-oxygen content

Aluminium nitride (AlN) ceramics with a low oxygen content were deformed up to 10% strain in compression at elevated temperatures (1823–1923 K) under constant stress in the range 150–250 MPa. Stationary creep rates are lower by an order magnitude than those previously measured in AlN with higher oxygen content. All dislocations imaged by transmission electron microscopy (TEM) look undissociated, which clearly relates the formerly observed wide dissociation to oxygen in excess. The temperature dependence of the stationary creep rate is characterized by an activation energy of ∼8.25 eV and the stress exponent is ∼2.8, both quantities being significantly higher than in previous work. The observed constitutive phenomenology significantly departs from current models of diffusional creep, suggesting that dislocation climb could be the rate-limiting process.