The effects of heat treatment on the stress-induced B2-B19' martensitic transformations in the Ni_51.0Ti_36.5Hf_12.5 single crystals oriented along [236] direction are studied. It is shown that in the annealed at 1323K for 4 h crystals, the temperature range of superelasticity increase almost twofold from 75K up to 135K as compared to the as-grown single crystal contained disperse particles of H-phase. The [236]-oriented Ni_51.0Ti_36.5Hf_12.5 single crystals are characterized with high levels of applied compressive stress up to 1700 MPa in the as-grown state and 1900 MPa in annealed crystals for the completely reversible stress- induced B2-B19' martensitic transformation with reversible strain up to |ε_SE| =1.4%.

For the first time, a study of the two-way shape memory effect (the TWSME) for the quenched and aged at 673 K for 0.5 h [001]-oriented Co35 Ni 35Al30 single crystals in compression was carried out. In the quenched CoNiAl crystals, the TWSME with a reversible strain of (-3.1 ± 0.3) % was induced by training procedure in the superelasticity temperature range. The physical reason of the TWSME is the creation of internal stress fields due to the formation of dislocations next to γ-phase particles, and an interface between the B2-matrix and the γ-phase in the quenched crystals. It was experimentally shown that aging at 673 K for 0.5 h under a compressive stress of 100 MPa along the [110] direction creates the conditions necessary for observing the TWSME, without additional training with a reversible strain of (+2.2 ± 0.3) %. The conditions for observing the TWSME are determined by the action of the internal stress fields of 25 MPa created by the oriented arrangement of the dispersed particles in the stress-assisted aged crystals. The TWSME is not observed in the stress-free aged crystals with non-oriented precipitation of particles, both before and after training.

The orientation dependence of the two-way shape memory effect (TWSME) in stress-induced martensite aged Co₃₅Ni₃₅Al₂₈Fe₂ (B2 + γ') single crystals has been studied. Aging leads to the stabilization of the oriented L1₀-martensite, which helps to induce the TWSME. By orientation variation of the single crystal, one can stabilize the twinned or detwinned martensite, which determines the regularities of the TWSME manifestation. In the aged [001] crystals, the twinned L1₀-martensite variant is stabilized. The TWSME in the [001] crystals develops with a large (−2.4%) reversible strain in the temperature range of 57–60 K and with a narrow (45 K) hysteresis, while the stabilization of the detwinned L1₀-martensite variant during aging in [110] crystals facilitates the development of a smaller TWSME value (−1.6%) in narrow ranges of 3–9 K, with a wide (79 K) hysteresis.