Stress-induced thermoelastic martensitic transformations and functional properties in [011]-oriented NiTiHfPd single crystals

The stress-induced martensitic transformation in the [011]-oriented Ni45.3Ti29.7Hf20Pd5 (at. %) single crystals in as-grown, homogenized and aged states were investigated in compression. It is experimentally shown that heat treatments of single crystals result in increase in martensitic transformation temperatures, two-fold decrease in reversible strain and increase in strain-hardening coefficient. As-grown single crystals demonstrate large temperature range of superelasticity (up to 140 K), large reversible strain (up to 4.3%) and large work output in comparison with homogenized and aged crystals

Orientation dependence of superelasticity in quenched high-nickel Ti51.8Ni single crystals

The orientation dependence of the functional and mechanical properties of quenched Ti-51.8at.%Ni single crystals, undergoing a strain-glass transition upon cooling/heating was investigated. It was found that a compressive stress above 800 MPa leads to the B2-B190 martensitic transformation (MT), regardless of orientation. In the high-strength [0 0 1]-orientation, superelasticity (SE) was observed at 203–248 K, with a reversible strain of 2.3%. Degradation of SE at deforming stresses r > 1000 MPa was associated with the formation of {1 1 3}B2 twins during the reverse MT. In the low-strength 1 1 1-orientation, the formation of stress-induced B190 -martensite occurred simultaneously with the plastic deformation of the B2-phase (due to the formation of reorientation bands and dislocation slip) and a reversible strain was not observed

Stress-induced thermoelastic martensitic transformations and functional properties in [011]-oriented NiTiHfPd single crystals

The stress-induced martensitic transformation in the [011]-oriented Ni45.3Ti29.7Hf20Pd5 (at. %) single crystals in as-grown, homogenized and aged states were investigated in compression. It is experimentally shown that heat treatments of single crystals result in increase in martensitic transformation temperatures, two-fold decrease in reversible strain and increase in strain-hardening coefficient. As-grown single crystals demonstrate large temperature range of superelasticity (up to 140 K), large reversible strain (up to 4.3%) and large work output in comparison with homogenized and aged crystals

Effect of one family of Ti3Ni4 precipitates on shape memory effect, superelasticity and strength properties of the B2 phase in high-nickel [001]-oriented Ti-51.5 at.%Ni single crystals

Abstract. In this study, we investigated the effect of the number of Ti3Ni4 particle variants (obtained via stress-free and stress-assisted aging at 823 K for 1 hour) on the shape memory effect, superelasticity, and strength properties of the B2-phase in high-nickel [001]-oriented Ti-51.5 at.% Ni single crystals. Four crystallographically equivalent variants of lenticular Ti3Ni4 particle with the {111}B2 habit plane and a diameter of 250–300 nm were obtained via stress-free aging. Aged under an applied compressive stress of 150 MPa along the direction, single crystals contain predominantly one variant of Ti3Ni4 particle, forming plane-parallel plates with lengths from 1 to 5 μm. The oriented arrangement of semi-coherent Ti3Ni4 particles leads to the formation of long-range stress fields, an increase of 23 K in the martensitic transformation (MT) starting temperature Ms, the induction of a two-way shape memory effect, and a decrease of 200 MPa in the stress required to obtain the maximum reversible strain (1.5–1.7%) during cooling/heating cycles compared to stress-free aged single crystals. The number of variants of Ti3Ni4 particle determines the mechanism of the formation of B19'-martensite and the strength properties of the B2-phase (1600 MPa in stress-assisted aged crystals and 2100 MPa in stress-free aged crystals)

Shape memory effect in TiNi single crystals with thermal-induced martensite transformation or strain glass transition

In present work, we investigated the thermoelastic B2-B19' martensitic transformations in thermocycles under constant stress, σapp, (ε(Т) curves) and in loading/unloading cycles (σ(ε) curves) in quenched [001]-oriented single crystals of Ti-50.7 at%Ni and Ti-51.7 at%Ni alloys. Single crystals undergo either thermal-induced В2-В19' martensitic transformation (Ti-50.7 at%Ni) or strain glass transition (Ti-51.7 at%Ni), depending on their chemical composition. The transformation type defines the morphology of a martensite during cooling under stress. In Ti-50.7 at%Ni alloys during stress-assisted cooling the morphology is the mix of self-accommodation martensite and oriented martensite. In opposite, in Ti-51.7 at%Ni alloys the morphology consists of oriented martensite only. The following parameters in stress-assisted cooling/heating cycles are determined by transformation type and morphology of a martensite: the minimal stress, σmin, for oriented martensite formation; the coefficient dεfor/dσ that defines the strain dependence on stress, εfor(σapp), and the presence of additional stage in the dependence Msσ(σapp). Similar in loading/unloading cycles the transformation type defines the energy barrier that should be overcome in order to start the stress-induced martensitic transformation, and, so, the stress level, σcr(Ms0)

Temperature dependence of martensite variant reorientation in stress-induced martensite aged Ni49Fe18Ga27Co6 single crystals

In the present study, the temperature dependence of martensite variant reorientation in stress-induced martensite aged at 423 K along the [110] B2 [100] L10 -direction Ni 49 Fe 18 Ga 27 Co 6 single crystals was inves- tigated in compression. This martensite aging induces a rubber-like behavior with a reversible strain of up to –16.0% along the [001] B2 -direction in the temperature range from 248 K to 344 K, which is caused by L 1 0 -martensite variant reorientation. At higher temperatures between the forward and reverse trans- formation from 344 K to 382 K, the stress-induced martensite aged crystals demonstrate a two-stage stress-strain response with a reversible strain of up to –13.5%. The first stage is characterized by low critical stresses of σcr1 ≈1 –15 MPa and an inverse elastocaloric effect (heat absorption) under load- ing. Superelasticity is observed in the second stage with σcr2 ≥100 MPa. In this temperature range, the martensite variant reorientation occurs through reverse and then forward martensitic transformation