PRIMARY RECRYSTALLIZATION MECHANISMS IN CERAMIC MATERIALS

Data on the mechanisms of primary recrystallization in covalent type c eramics under temperature-and-pressure treatment are generalized and d iscussed. There are three types of structural transformations governin g nucleation during primary recrystallization. I. Formation of intragr ain boundaries. As a result of plastic shears boundaries appear to be kinked due to dislocation pile-ups (materials bared on 2H BN, 6H SiC). With deformation by total dislocations the boundaries arise as a resu lt of dynamic recovery due to rebuilding of dislocation pile-ups (AIN, beta-Si3N4, TiB2). II. Twinning. This structural transformation promo tes the formation of recrystallization nuclei in the following cares: a),vith insertion of lattice dislocations into the boundaries of strai n-induced twins, b) with formation of annealing twins, c) with develop ment of multiple twinning near grain boundaries (3C BN). Ill. Structur al transformations in migrating boundaries: a) splitting of boundaries and ternary junctions (3C BN); b) local bulging of boundaries (3C BN) , c) generation of high-angle and platelet twins (3C BN); d) plastic r otation of material microvolumes near grain boundaries (3C BN, SiC).