ALN plastic deformation between room temperature and 800 degrees C - I. Dislocation substructure observations

摘要

Dislocations substructures in aluminium nitride (AlN) ceramics have been studied by transmission electron microscopy for samples plastically deformed under a high stress in the temperature range 20-800 degrees C. The activation of basal slip 1/3 [11 (2) over bar 0](0001) as well as of the first-kind prismatic slip 1/3 [11 (2) over bar 0]{1 (1) over bar 00} have been observed. In the basal plane, dislocations configurations attest to the role of the Peierls forces along the screw orientation. It is easier for a dislocation to cross-slip in the prismatic plane than to lie in the basal plane along an orientation other than the screw direction. In the basal plane as well as in the prismatic plane, no dissociation of dislocations has been resolved under weak-beam imaging conditions. Cross-slip is favoured by numerous pinning points on screw dislocations, giving rise to dipole dragging. From 20 to 500 degrees C, AlN deformation proceeds by dislocation glide in the basal and the prismatic planes and frequent cross-slip between these two planes. At higher temperature (800 degrees C), a change in the mobility of edge dislocations has been evidenced in the prismatic plane which may result from lattice friction operating on the (0001) orientation or from a possible dislocation dissociation out of the glide plane. [References: 12]