Primary recrystallization mechanisms in ceramic materials

Abstract

Data on the mechanisms of primary recrystallization in covalent type ceramics under temperature-and-pressure treatment are generalized and discussed. There are three types of structural transformations governing nucleation during primary recrystallization. I. Formation of intragrain boundaries. As a result of plastic shears boundaries appear to be kinked due to dislocation pile-ups (materials based on 2H BN, 6H SiC). With deformation by total dislocations the boundaries arise as a result of dynamic recovery due to rebuilding of dislocation pile-ups (AlN, β-Si3N4, TiB2). II. Twinning. This structural transformation promotes the formation of recrystallization nuclei in the following cases: a) with insertion of lattice dislocations into the boundaries of strain-induced twins; b) with formation of annealing twins; c) with development of multiple twinning near grain boundaries (3C BN). III. Structural 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 rotation of material microvolumes near grain boundaries (3C BN, SiC).