Atomic models of the nucleation of dislocations and mechanical twinning in fcc crystals

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

“…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.…”

“…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.…”

“…Here belong initiation of partial and complete dislocations in fcc-nanocrystals [19,20], non-polar mechanisms of mechanical twinning in these materials [19,20], deformation twinning in the planes with different indices in TiNi alloys [14,15], formation of localized strain bands with crystal lattice reorientations at ≈ 35°<110> and 60°<110> in austenite steels [13,14,16] and, finally, the reorientation bands (50-60)°<110> in bcc-alloys discussed in [12].…”

“…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.…”

Mechanisms of deformation localization and mechanical twinning under the conditions of phase instability of a crystal in stress fields

“…First of all this refers to strain localization bands (SLB's) with the crystal lattice reoriented by large (tens of degrees) angles [5][6][7][8][9][10] and to deformation twins formed in planes of composite index [6,8,[11][12][13][14][15]. The lack of adequate physical and structural models of their formation is, in our opinion, due to the fact that the cooperative modes of deformation and reorientation of a crystal lattice cannot be reduced to dislocation modes.…”