Dynamic mechanism of lateral growth of thin-lamellar martensite crystals in iron-nickel alloys under external tensile stress

Within the framework of the dynamic theory of martensitic transformations, the possibility of cooperative growth of the faces of the resulting crystal is discussed using the example of the formation of a layer parallel to the habit plane. This growth is comparable to the lateral crystal growth typical of shape memory alloys, but not typical of α-martensite in iron alloys upon simple cooling. However, under conditions of external tensile stress, rapid lateral growth of thin-lamellar α-martensite crystals was observed. It is shown that the formation of a layer parallel to the habit plane is similar to the formation of the original crystal. The functions of the dislocation nucleation center (DNC*) for this layer are performed by a dislocation loop framing the habit plane with the Burgers vector b*, and b* is specified by the macroshift in the initial crystal. An example of a crystal with a habit close to (3 14 9) is considered. The results of calculation of the elastic field of the DNC* loop are presented using data on the elastic moduli of the Fe–31.5%Ni alloy at a temperature Ms = 239 K. In the approximation of longitudinal waves for a pair of relatively long-wave components in the control wave process, the practical coincidence of the layer habit with the initial habit is demonstrated. The value of b* has been estimated.