Two-Way Shape Memory Effect Induced by High-Temperature Isothermal Training in [001]-Oriented Heterophase Single Crystals of Ni49Fe18Ga27Co6 Alloy

Results of investigations of the two-way shape memory effect (TWSME) and its stability during stress-free thermal cycling of [001]-oriented Ni49Fe18Ga27Co6 single crystals after high-temperature isothermal training (100 loading/unloading cycles at a temperature of 373 K) in superelasticity (SE) conditions during L21–L10 martensitic transformations (MT) are presented. A maximal reversible strain of single crystals aged at 673 K for 4 h with 3.8% TWSME has been obtained. For crystals after stress-free aging at 673 K for 4 h, the TWSME is 2.2%. It has been established that on the one hand, the high-temperature training at 373 K, in comparison with analogous training at a low temperature of 295 K of stress-assisted aged crystals causes the maximal TWSME to decrease by 1.7%, and on the other hand, it promotes the increase of the cyclic stability of TWSME during reversible strain. The influence of the isothermal training temperature on the TWSME mechanism and on its degradation during stress-free cooling/heating cycles is discussed.