Where and when are dislocations induced by thermal cycling in Ti–Ni shape memory alloys?

Orientation Dependence of B19’-Martensite Reorientation Stress and Yield Stress in TiNi Single Crystals

“…A V-shaped microstructure is formed (Figure 9), which was repeatedly observed in the deformed thin TiNi wire with the [111]B2 texture [28]. The microstructure of plastically deformed TiNi wire consists of a high density of the {114}B2 austenite twins that often form wedges-like twins inside strongly dislocated austenite phase [28]. The analysis of structure shows that there is a mix of B2-and B19'-phases in the [111]B2-oriented 50.4Ni single crystals deformed in martensite and heated to room temperature.…”

“…In [111] B2 -oriented single crystals the morphology of deformation structure differs from the morphology of the [001] B2 -oriented single crystals after the plastic deformation above the B19'-martensite yield stress to ε g = 12.0-15.5% with followed by heating to room temperature. A V-shaped microstructure is formed (Figure 9), which was repeatedly observed in the deformed thin TiNi wire with the [111] B2 texture [28]. The microstructure of plastically deformed TiNi wire consists of a high density of the {114} B2 austenite twins that often form wedges-like twins inside strongly dislocated austenite phase [28].…”

“…The two twin-related variants constitute the correspondent variants pair (CVP). The CVPs form a self-accommodating structure of martensite and define an invariant habit plane {0.89 0.40 0.22} [7,[26][27][28][29][30][31]. Type It is well known that at M d temperature, the critical stress for the stress-induced martensite formation and B2-austenite yield stress are equal to each other [2,5,[8][9][10].…”

“…The two twin-related variants constitute the correspondent variants pair (CVP). The CVPs form a self-accommodating structure of martensite and define an invariant habit plane {0.89 0.40 0.22} [7,[26][27][28][29][30][31]. Type II <011> B19' and the type I {111} B19' are the preferred twinning modes required to obtain the lattice invariant strain and the habit plane at the B2-B19' MT in the quenched TiNi alloys [7].…”

Cyclic Stability of Two-Way Shape Memory Effect in Aged Ni50.3Ti32.2Hf17.5 Polycrystals after Various Thermomechanical Treatments

“…In polycrystals after training, a microstructure consisting of a large number of dislocations and residual martensite was formed, which induced the formation of various intersecting variants of martensite, as shown in Figure 5 b,c. In [ 20 , 21 ], the appearance of a large number of dislocations near the residual martensite during thermal cycling was detected on Ni-rich NiTi alloys. The main part of the dislocations formed during the reverse movement of the interphase boundary.…”