Orientation and Temperature Dependence of Superelasticity Caused by Reversible γ-α′ Martensitic Transformations in FeNiCoAlTa Single Crystals

Reversible thermoelastic gamma-alpha' martensite transformations (MTs) have been studied in Fe-28% Ni-17% Co-11.5% Al-2.5% Ta (at. %) single crystals under cooling/heating and loading conditions. It is established that the precipitation of dispersed gamma' phase particles with an average size of d <= 5 nm leads to thermoelastic gamma-alpha' MTs with a small temperature hysteresis (Delta T = 20 K). The [001] oriented crystals favor the attaining of maximum superelasticity (SE) epsilon(SE) = 6.8%, minimum mechanical hysteresis Delta sigma = 130 MPa, and large SE temperature interval Delta T(SE) = 130 K. In contrast, in the [111] oriented crystals, small values of epsilon(SE) = 2.0%, high values of Delta sigma = 350-400 MPa and narrow SE interval Delta T(SE) = 55 K are found.