Regularities and mechanisms of mechanical twinning in TiNi alloys

Microstructure of Mo – 47% Re – 0.4% Zr alloys after rolling at room temperature. II. Peculiarities of mechanical twinning and formation of high-angle boundaries between microbands

“…Therefore, here we shall report but only briefly their potential to describe certain phenomena of plastic deformation and crystal-lattice reorientation, and present one of the atomic models of formation of reorientation bands (50-60)°<110> observed in an bcc-crystal in the present work. To develop the models, the authors of [7,[13][14][15][16][17] used the geometrical theory of martensitic (bcc →fcc and bcc→hcp) transformations (MT) [18], where atomic rearrangements represent combined cooperative atomic shears (shufflings) in close-packed planes of the bcc-lattice and homogeneous deformation of the Bein-type transformation.…”

“…In this version, a direct (bcc→fcc, Fig. 5a) transformation, apart from cooperative displacements of atomic planes (110) along [110 ] and [110 ] not shown here (for details, see, e.g., [13,[15][16][17][18]), involves homogenous deformation transforming these planes into close-packed hcp-phases, in the case where the Nishiyama-Wassermann (N-W) relation is fulfilled.…”

“…Figure 5 presents an example of a bcc→hcp→bcc-transformation resulting in a 60°[110] crystal-lattice reorientation. It was shown in [12,15,17] that in the case where the Kurdyumov-Zaks relation is fulfilled in the course of an MT, the number of alternative systems of reverse transformation is increased, which gives rise to the following versions of reorientations: 10.5°<110>, 49.5°<110>, 60°<110> and 70.5°<110>. Furthermore, multiple direct-plusreverse transformations are very likely to occur and be followed by multiple crystal-lattice reorientations.…”

“…In discussing this phenomenon it is worth mentioning that, as shown in [12][13][14][15][16][17], the main deformation mode of direct-plus-reverse MTs in the course of formation of reorientation bands and deformation twins in bcc-crystals is homogenous transformation deformation of the Bein-type. Note that the defects of sub-structure hardening (dislocations, low-and high-angle fragment and microband boundaries) while suppressing the dislocation activity, do not serve in the least measure effective obstacles either for the carriers of this deformation mode or crystal-lattice reorientation; and the high local internal stresses representative of large plastic deformations stimulate local martensitic transformations rather than hinder them.…”

Stress-induced martensitic transformations in [001] crystals of titanium nickelide and its relation to mechanical twinning in the В2-phase

“…1, whose deformation axis was orientated parallel to the [035] direction (near the [011] pole), rolled in the temperature region of the "stress-induced" В2→В19′ transformation, the formation of low-angle localized strain bands (LSB) with habits close to the habit planes of В19′ martensite and of В2-phase twins has been revealed [2, 3]. A new mechanism of the formation of twins and LSB in austenite by local recoverable В2→В19′→В2 martensitic transformations in stress fields was proposed [2][3][4][5][6]. In this connection, the goal of the present work was to investigate the mechanisms of deformation on compression of TiNi(Fe, Mo) [001] crystals in the interval of temperatures from М on to М d and to find out, for this interval, the role of the mechanical twinning in the В2-phase and its relation to the martensitic transformations that occur under load.…”