PSI - Issue 69

Nadezhda M. Kashchenko et al. / Procedia Structural Integrity 69 (2025) 89–96

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6. Due to austenite's metastability, the habit plane formed at low threshold deformations maintains its orientation throughout subsequent atomic transitions to final deformation states. 7. The kinematic and deformation descriptions in the threshold regime require consistent habit plane orientations, enabling us to establish a relationship between wave velocity ratios and the deformation ratios governing tension and compression. 8. Martensite crystals exhibit not only characteristic macroscopic morphology but also an internal dislocation structure, often accompanied by transformation twinning. The dynamic theory accounts for these structural features by incorporating relatively short-wavelength displacements within the (CWP), which cooperate with the long-wavelength displacements responsible for habit plane formation. Notably, only through inclusion of short-wavelength components can we properly describe the initiation of three-dimensional Bain deformation. 9. The region undergoing instability during atomic rearrangement lacks elastic properties, suggesting that the strain ratio determined by the threshold CWP configuration remains preserved during rapid transformation. This principle enables crystal formation control extending to final strain states. 10. The generation of dislocations corresponds to the transition to a degenerate twin structure, when the thickness of the twin component becomes close to the lattice parameter. 11. During martensitic transformations in metals and alloys, significant chemical potential and temperature gradients develop in the interphase region during rapid growth. Under conditions of intense electron flows, the processes of amplification and generation of elastic waves by nonequilibrium electrons (phonon maser effect) are possible. 12. Considering electronic structure characteristics helps explain observed magnetic field effects on martensitic transformation, including single crystal orientation phenomena and magnetic field influence on austenite's critical grain size. 13. The dynamic theory of (MT) has elucidated the existence of multiple discrete M s temperatures under varying austenite quenching rates. 3. Extension of the dynamic theory of MT to the process of formation of SM crystals, including lateral growth The fundamental concept for understanding the dynamic process of cooperative crystal face growth (particularly lateral growth) involves the formation of rectangular dislocation loops. These loops envelop specific facets of the developing martensite crystal and perform dislocation nucleation center (DNC) functions analogous to those described in Section 2. It is important that the role of the Burgers vector b* is performed by the macroshear. It is assumed that the visually recorded relatively small values of the face growth rates are, in fact, fast jump-like processes alternating with long pauses between jumps. Then it is the stage of the fast jump that ends with the formation of the DNC*. The elastic field of the rectangular dislocation loop (DNC*), which initiates lateral crystal growth with a (112) habit plane, was calculated using a cylindrical coordinate system (Fig. 6a). The elastic moduli (in TPa) were chosen according to Haush and Warlimont (1973) for the Fe-31%-Ni composition: C 44 ≈ 0.112, C ′ = (C 11 -C 12 )/2 ≈ 0.027, C L = (C 11 +C 12 +2C 44 )/2 ≈ 0.218. Fig. 6(b) shows the calculation data for the elastic field of the DNC on a scale convenient for perception. Note that of the two maxima of the shear S 1 , selecting the normal N ║ n 2 + ӕ n 1 in (1), preference is given to the maximum at θ ≈ -15º, since the γ-α MT occurs with an increase in the specific volume δ, and this maximum corresponds to a larger value of δ > 0.

Fig. 6. To the calculation of the elastic field of the DNC: (a) – cylindrical coordinate system (Λ 1 , Λ 2 are the directions of the DNC loop segments, Λ 1 ║[1 1" 0], Λ 2 ║[11 2" ], Z axis ║Λ 1 , the angle θ is measured from the plane of the loop, b║ [0 1" 1]); (b) – dependence of the magnitude of the shift