Cryston model of formation of α\alpha strain induced martensite

The strain-induced martensite formation is considered as a consequence of carry of a threshold plastic deformation by crystons. The sources of crystons (carriers of shear of a superdislocation type) are caused by interaction of dislocations belonging to systems with intersected slip planes. For crystons (carriers of simple shear) the physical nature of morphological features of a strain-induced martensite crystals and their difference from a case of stressinduced and cooling-induced martensites is discussed. A case of crystal with habits of {hhl} - type is analyzed most explicitly The deloniialions of compression $\epsilon_2$ and tension $\epsilon_1$ along orthogonal axes $$ initiating the Bein strain process are considered as order parameters controlling the austenite stability. The connection between the abnormal orientation relationship for $\alpha'$ martensite crystals formed under tensite loading and the threshold deformation is obtained

Dynamical Lattice State at the Initial Stage of Martensitic Transformation and Possibilities of its Physical Realization

Principles of the physical simulation of conditions at the initial stage of γ-α martensitic transformation are formulated on the basis of the theory which synthesizes conceptions of the heterogeneous nucleation and the wave growth of martensite. The choice of the experimental method available to realize the artificial initiation of transformation is justified. Possible mechanisms of excitation of the hypersonic controlling waves by a single supershort laser pulse are presented. The information about perspectives of using the received results for alloys featuring the shape-memory effect is also presented

Reconstruction of Martensitic Nucleation Process from Morphological Attributes

Within the framework of the concepts of heterogeneous nucleation and wave growth of martensite the refinement of a technique of account of wave normals Nw to expected habits planes are carried out. The technique allows to connect orientations of Nw with definite areas of nucleation of crystals in an elastic field of defects. The specific results are presented for system Cu-Zn. As separate rectilinear dislocations with lines [11-1] and dislocation loops basic elements of which are pieces of these lines are considered here as probable centers of nucleation. It is shown, that the spectrum of Nw can be coordinated with experimentally observable space distribution of normals Ne in a vicinity of a pole [2 11 12]. The similar coordination opens additional opportunities to reconstruct a stage of martensite nucleation from morphological attributes and to transform a distribution of habits in the informative parameter

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

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

Conception of New Phase Dislocation-Based Nucleation at Reconstructive Martensitic Transformations

The role of dislocations and the dynamical mechanism controlling the structural reconstruction in the process of nucleation and wave growth of new phase unit crystals at martensitic transformations in metallic systems are discussed. It has been established that near some rectilinear dislocations with lines and Burgers's vectors typical for the original phase, there are areas where an elastically deformed state is characterized by package of particularities unambiguously corresponding to the well definite morphological attribute set (habit, orientation relationship, macroshear) of the martensite crystal. The distinctiveness of these areas for martensite nucleation is caused by character of strains reducing the magnitude of interphase energetic barrier. The elastic model of the dislocation-based nucleation center of martensitic crystal, allowing to select the dislocations being the most probable for nucleation and to make a martensitic crystal with the morphological attribute specific collection corresponding to each a dislocation, has been proposed. Such dislocations for certain Fe-, Cu- and TiNi-based alloys are indicated. New results for titanium nickel are presented in more detail