The formation of martensite crystals with a degenerate structure of transformation twins

摘要

The dynamic theory of martensitic transformation explains the phenomenon of initiation of fine structure of transformation twins as the result of coordinated action of relatively long-wave displacements (?-waves) with more short-wave displacements (s-waves). Being a part of controlling wave process, ?-waves provide habit formation, whereas s-waves play the leading part in initiation of the main component of twin structure (TS). It was shown that the dynamic theory allows consideration of degenerate TS (DTS) formation as a private case of TS when twin component volume is converted to zero. In this work the case of DTS is discussed by the example of crystals with habits {110}. The peculiarity of this variant consists in the fact that in order to describe the morphology of transformation it’s enough to consider only longitudinal waves running along axes as a part of controlling wave process. In particular, habit (101) may be matched with a pair of ?-waves with velocities along [100] and [001] and a pair of s-waves with velocities along [100] and [010]. At the same time, the condition ds = λs/4, where λs is wavelength of s-waves, and ds is transversal (in directions [100] and [010]) size of initial exited (oscillatory) s- ?- cell with longitudinal size ds ?d? <λ?/2, conforms DTS formation. For martensite transformations FCC-BCT, BCC-FCT, FCC-FCT, the transition to finish deformations and the connection of the values of tetragonality of martensite and volume effect with one of characteristic main values of deformation tensor are discussed.