High-temperature superelasticity and the shape-memory effect in [001] Co-Ni-Al single crystals

Development of thermoelastic B2-Ll0 martensitic transformations (MTs) has been investigated upon cooling/heating and under stress using single crystals of Co40Ni33Al27 and Co35Ni35Al30 (at %), oriented along the [001] direction. It is shown that the temperature intervals of the development of superelasticity TSE and the values of the mechanical (Δσ) and temperature (ΔT) hysteresis are determined by the chemical composition of crystals and the type of deformation (tension or compression) along the longitudinal axis [001]. The effect of the phase and dispersed particles on the development of martensitic transitions, the mechanical stabilization of the stress-induced martensite, and the temperature interval of superelasticity †TSE has been investigated. Conditions necessary for the development of high-temperature superelasticity (at T = 570–580 K) have been determined and a thermodynamic description of the temperature interval of superelasticity has been suggested.