In the present study the superelasticity (SE) under tension/compression was investigated in the oligocrystals of Fe42.5Mn34Al15Ni7.5Ti1 (1% Ti), Fe42Mn34Al15Ni7.5Ti1.5 (1.5% Ti) and Fe41.5Mn34Al15Ni7.5Ti2 (2% Ti) (at %) alloys undergoing alpha (bcc)-gamma' (fcc) martensitic transformation. It was optically established that, first, with a growth in the Ti concentration from 1 to 2% the average and maximum grain sizes increase. Second, the optimal Ti concentration necessary to suppress the precipitation of the gamma-phase particles during quenching is no more than 1.5%. SE strain studied at room temperature depends on the Ti concentration, heat treatment and stress state-tension/compression. In the quenched state the SE with value of 6% was observed only in 1% Ti oligocrystal under compression. Quenched oligocrystals was brittle and broke at the yield stress under tension. Aging at 473 K for 3 h leads to an increase in the SE value to 6.8% in 1% Ti oligocrystal under compression, observation of the SE of 3.1% in 1.5% Ti oligocrystal and suppression of brittle fracture at the yield stress under tension. The SE strain in aged 1% Ti and 1.5% Ti oligocrystals under tension was epsilon(SE)(1% Ti) = 1.2% and epsilon(SE)(1.5% Ti) = 2%, respectively. SE was not found in a 2% Ti oligocrystal under tension/compression.

Two-way shape memory effect (TWSME) and its stability under cooling/heating cycling through the martensitic transformation (MT) temperatures in stress-free condition were investigated in mono-phase [001]-oriented single crystals of the ferromagnetic Co49Ni21Ga30 (at %) alloy. TWSME is induced by thermomechanical training cooling under different external compressive stress and subsequent stress-free heating. It is shown that the TWSME strain cTwsmE depends on the applied stress in the training cycle. The maximum of the cTwsmE equal to 4.2(+/- 0.2)% is achieved after training under sigma(ext) = 125 MPa and then decreases with increase of sigma(ext). The value of epsilon(TWSME) = 4.2(+/- 0.2)% is equal to the theoretical transformation strain for [001]-orientation at B2-L1(0) MT in compression. In crystals after training under sigma(ext) = 125 MPa with maximum epsilon(TWSME), the stability of the TWSME strain and martensitic start temperature MS is observed up to 150 cooling/heating cycling. From 150 to 300 thermocycle, TWSME strain decreases from 4.1(+/- 0.2)% to 3.5(+/- 0.2)%, and the M-S temperature decreases from 251 to 242 K.

The effect of gamma'-phase particles on the mechanical behaviour was studied in single crystals of the fcc CoCrFeNiAl0.3 (at %) high-entropy alloy (HEA) under tensile strain. It was shown that ageing of the CoCrFeNiAl0.3 HEA single crystals at a temperature of 823 K for 150 hours and at 893 K for 50 hours, results in the precipitation of gamma'-phase particles of size d < 5 nm, with L1(2)-type ordering. In the [<(1)over bar>11]-oriented crystals, precipitation of gamma'-phase particles leads to an increase in critical shear stresses tau(cr) by 25-30 MPa in the temperature range T = 77-873 K, a decrease in the strain hardening coefficient Theta = d sigma/d epsilon and an increase in plasticity of 11-14% relative to the initial crystals without particles. The decrease in Theta = d sigma/d epsilon and the increase in plasticity are associated with the influence of the gamma'-phase particles on the localization of the deformation, predominantly in one system.

For [001]-oriented single crystals of Fe-28Ni-17Co-11.5Al-2.5Ti (at %) alloy in tension, it was shown that particles of the gamma'-phase with a size of 4-6 nm lead to the appearance of superelasticity, with a strain of epsilon(SE) = 4.5% and a shape memory effect of epsilon(SME) = 5.9%. Increasing the particle size to 10-12 nm reduces epsilon(SE) to 3.6% and epsilon(SME) to 3.5%. The paper discusses the causes of the influence of particle size on the reversible strain.