Dynamic growth mechanism of martensite crystal faces with {110} habits

Abstract

The dynamic theory of martensitic transformations (MT) considers the formation of habit planes of martensitic crystals as a result of the propagation of controlling wave process (CWP) CWP is generated by the occurrence of an initial excited state (IES) of the oscillatory type in the elastic fields of defects. The general ideology allows, by comparing the observed habits with the calculations of the dislocation loops elastic fields, to identify dislocation nucleation centers. In a number of cases (In-Tl alloys, Ni<inf>50</inf> Mn<inf>50</inf> alloys, Heusler alloys…) during MT in alloys with shape memory, habits {110} are observed (in the basis of the initial cubic phase), which often have a fine twin structure with the same type orientations of twin boundaries. In this case, the formation of martensite crystals is associated with a CWP containing longitudinal waves (both relatively long-wave (ℓ) and short-wave (s)) propagating along the 4th-order symmetry axes. The habits {110} of the initial martensite crystal are associated with the rectilinear sections of dislocation loops with directions Λ along <001> and Burgers vectors along <010> (or <110>), orthogonal to Λ. It is shown that the elastic field of a dislocation loop framing the habit plane of the formed crystal can initiate lateral crystal growth described by the same universal dynamic model. It is noted that similar conclusions can be made with respect to the growth of other crystal faces. © 2025, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.