Orientation dependence of the shape memory effect and superelasticity in ferromagnetic Co49Ni21Ga30 single crystals with γ'-phase particles

This paper reports on the orientation dependence of the shape memory effect and superelasticity in [001] and [overline 123] single-phase and aged at 623K, 1 hour single crystals of ferromagnetic Co49Ni21Ga30 (at.%) alloy with B2-L10 martensitic transformation. It was demonstrated that in single-phase crystals the values of reversible strain and the values of thermal and stress hysteresis depend on the crystal orientation. Precipitation of γ'-phase particles reduces the value of the shape memory effect and superelasticity and reduces their orientation dependence, increases the thermal and stress hysteresis in comparison with singlephase crystals

High-temperature superelasticity and shape memory effect in [0 1 1]B2-oriented single crystals of the (TiZrHf)50Ni25Cu15Co10 high-entropy alloy

Superelasticity (SE) and shape memory effect (SME) of [0 1 1]B2-oriented single crystals in B2-phase of the (TiZrHf)50Ni25Cu15Co10 high-entropy alloy (at.%), with B2-B19′ martensitic transformation, have been studied in the post-growth state under compression. It is shown that SE is observed within a wide temperature range of T = Ms = 404 K to 528 K. The maximum SE value is 4.4 %, and the SME reaches 4.3–4.7 %

The influence of hydrogen on the mechanical and functional properties of TiNi and TiNiFe single crystals

The effect of hydrogen on temperature dependence of critical stress σcr(T), the shape memory effect and superelasticity for [11]-oriented single crystals of Ti-50.7Ni (at.%) and [23]-oriented single crystals of Ti-49%Ni-1%Fe (at.%) alloys at tensile deformation has been studied. It was shown that the change of temperatures of the martensitic transformation, symmetry of thermal hysteresis and level of σcr(Ms) and σcr(B2) stresses are determined by the phase state of the material (martensite or austenite) in the process of hydrogenation

The effect of hydrogen on shape memory effect and superelasticity in single-phase nickel titanium single crystals

The effect of hydrogen on temperature dependences of axial stresses σcr(T), shape memory effect, and superelasticity of [1¯11]-oriented Ti-50.7% Ni (at %) alloy single crystals has been studied under tensile strain in a single-phase state. It is established that the level of σcr(Ms) and σcr(B2) stresses is determined by the state of hydrogen (in solid solution or titanium hydride particles) in the initial B2 phase. Superelasticity up to 2.0–2.5% occurs when hydrogen is present in the solid solution

Shape memory effect and superelasticity in single crystals of iron-based alloys

It was demonstrated that in single crystals of disordered iron-based (Fe-28%Ni-17%Co-11.5%Al-2.5%Х (at. %) (X = Ti, Ta, Ti + Ta) alloys, which undergoing γ-α' thermoelastic martensitic transformation (γ – fcc – face-centered cubic lattice, α' – bct – body-centered tetragonal lattice), the precipitation of ordered γ'-phase particles at aged at 973 K for 0.5 h and 7 h results in the shape memory effect and superelasticity. It was experimentally discovered, that the both mechanical and functional properties – the shape memory effect and superelasticity – can be controlled by changing the chemical composition, the size and the volume fraction of dispersed particles of γ'-phase

Critical resolved shear stress for twinning and twinning-induced plasticity in single crystals of the CoCrFeNiMo0.2 high-entropy alloy

The effect of alloying with Mo atoms 4 at.% on the twinning deformation, critical resolved shear stresses (CRSS) for slip τslcr and twinning τtwcr and plasticity was studied in [111]-, [144]- and [001]- oriented crystals of the Co24Cr24Fe24Ni24Mo4 (at.%) high-entropy alloy (HEA) under tension at 296 and 77 K. The stacking fault energy of the Co24Cr24Fe24Ni24Mo4 HEA, measured in the resent paper on the triple dislocation nodes, is equal to 0.027 J/m2. It is shown that initial yield behavior along studied orientations is governed by dislocation slip and the CRSS for slip are independent of crystal orientation. Under tensile strain, twinning develops in the [111]- and [144]- oriented crystals only at 77 K and is not detected in the [001]-oriented crystals. Two types of twins are found in the [111]- and [144]-oriented crystals (thin nanotwins and macrotwins). Nanotwins develop after a low slip deformation of 5–10% and are observed only by transmission electron microscopy. Macrotwins are detected after a significant slip deformation of 20 and 60% and are determined metallographically and X-ray by the precession of the crystal axis, respectively, in the [111]- and [144]-oriented crystals. In the [111]- oriented crystals, there is no precession of the crystal axis due to the development of slip simultaneously in several systems. It is shown that CRSS for nano- and macrotwins are dependent on the crystal orientation. In the [144]-oriented crystals, τtw cr = 212 MPa for nanotwinning and τtw cr = 400 MPa for macrotwinning. In the [111]-oriented crystals, τtw cr = 250 MPa for nanotwinning and τtw cr = 335 MPa for macrotwinning. For the transition to deformation by macrotwinning, it is necessary that the effective stacking fault energy γef is approaching to zero and the condition τtwcr <τslcr is satisfied. Deformation by macrotwinning suppresses slip multiplicity and shifts the formation of the neck formation according to the Consid`ere condition to higher stress levels. This increases plasticity from 72% at 296 K to 108% at 77 K in [144]-oriented crystals and from 48% at 296 K to 57% at 77 K in [111]-oriented crystals

Mechanisms of plastic deformation of CoCrFeNi high-entropy alloy single crystals during solid solution hardening by Mo atoms

The effect of alloying with Mo atoms 4 at % on the temperature dependence of critical resolved shear stresses (CRSS) τcr(T), strain hardening coefficient, plasticity and deformation mechanism was studied on [1¯11]-oriented crystals of the fcc CoCrFeNi (at %) high-entropy alloy (HEA) within the temperature range T = 77-973 K under tension. It was shown that during solid solution hardening by Mo atoms, the CRSS τcr increased by 45 and 23 MPa, respectively, at 77 and 296 K compared to crystals of this orientation of the equiatomic CoCrFeNiMn HEA. The onset of plastic deformation is associated with slip, and a planar structure with dislocation pile-ups was found at T = 77-296 K. At 77 K, with the development of twinning in one system simultaneously with slip, high values of Θ = dσ/dϵ = 1750 MPa and maximum stresses before failure σmax = 1650 MPa were found, and the plasticity was 57%. With an increase in the test temperature, deformation developed only by slip; Θ = dσ/dϵ, and σmax decreased, but the plasticity remained at the level of 50-57%

Shape memory effect of [111]-oriented Cr20Mn20Fe20Co35Ni5 high-entropy alloy single crystals

Shape memory effect (SME) governed by the γ–ε martensitic transformation (MT) was studied in the [111]-oriented Cr20Mn20Fe20Co35Ni5 high-entropy alloy crystals under tension. The dependence of SME on the conditions of isothermal and isobaric deformation was established. It was shown that the maximum reversible strain of 7.4% and SME of 6.8% were observed under conditions of isothermal deformation

Investigation of the orientation dependence of marforming on superelasticity and shape memory effect in equiatomic TiNi single crystals under compression

The shape memory effect (SME) and superelasticity (SE) after marforming (deformation in the martensitic phase at 203 K, followed by annealing at 713 K, 0.5 h) were studied in the equiatomic TiNi crystals under compression. Marforming was carried out along [0 0 1]B2 and [0 1 1]B2 directions of B2-phase after strain of ε = 1.5ε0 (ε0 is the lattice deformation, which depends on the crystal orientation). SME and SE after marforming were studied along [0 0 1]B2 direction. It was shown that the maximum stress level of B2-phase σcr(B2) = 750 MPa, the lowest values of mechanical Δσ = 100 MPa and thermal ΔTh = 32 K hysteresis and the maximum temperature range of SE ΔTSE = 77 K were observed when marforming under compression was realized along the [0 0 1]B2 direction

Shape memory effect and superelasticity in [001] single crystals of FeNiCoAlNb(B) alloys

In given paper presents data research of influence of boron on the functional properties - the shape memory effect and superelasticity in the [001] single crystals FeNiCoAlNb(B) alloys aged at 973 K for 5 hours. On the [001] single crystals FeNiCoAlNbB at aging at T = 973 K for 5 hour, it is shown, that boron leads to decrease the start Ms temperature of γ-α' martensitic transformation on cooling, to the development of γ-α' stress induced martensitic transformation at higher stress at one test temperature and to increase of thermal ΔT and stress Δσ hysteresis is compared to [001] crystals without boron