V. A. Kirillov

Orientational dependence of shape memory effects and superelasticity in CoNiGa, NiMnGa, CoNiAl, FeNiCoTi, and TiNi single crystals

The dependence of deforming stresses, shape memory effect (SME), and superelasticity (SE) on the orientation of the single crystal axis, test temperature, and disperse particle size is examined for CoNiGa, NiMnGa, CoNiAl, FeNiCoTi, and TiNi single crystals. The orientational dependence of SME, SE, and temperature interval of the development of martensitic transformations (MT) under loading and SE is established. The influence of disperse particles on magnitudes of SME, SE, and mechanical hysteresis is discussed.

Orientation and temperature dependence of superelasticity caused by reversible γ-α′ martensitic transformations in FeNiCoAlTa single crystals

Reversible thermoelastic γ-α′ 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 γ′ phase particles with an average size of d ≤ 5 nm leads to thermoelastic γ-α′ MTs with a small temperature hysteresis (ΔT = 20 K). The [001] oriented crystals favor the attaining of maximum superelasticity (SE) ɛSE = 6.8%, minimum mechanical hysteresis Δσ = 130 MPa, and large SE temperature interval ΔTSE = 130 K. In contrast, in the [111] oriented crystals, small values of ɛSE = 2.0%, high values of Δσ = 350–400 MPa and narrow SE interval ΔTSE = 55 K are found.

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.