Formation of α-Martensite Crystals with Habits (hhl) in Cryston Model

Abstract
The mechanisms of formation of martensite with habit planes of the {hhl}-type are discussed for Fe-based alloys which undergo a γ-α (fcc-bcc) martensitic transformation. The relaxation of the lattice is interpreted in the framework of the "cryston" model. A "cryston" is the combination of dislocations of one or two slip systems which play the role of quasiparticles among the dislocation association on the mesoscale level. A number of cryston models of simple shear are presented. A possibility of the limiting transition to the cryston wave model is noted. Using the lath martensite as an example, it has been shown that using the cryston model allows to interpret morphological features of separated martensite crystals such as non-equivalence of parallel faces of lath crystals, deflection of orientation relationships from the ideal ones, the high residual density of dislocations. It is emphasized that the choice of prismatic dislocation loops as probable centers of martensite nucleation is a promising idea.