High-temperature Superelasticity Research Articles

Effect of ageing in austenite and martensite on superelasticity of the [001]-oriented FeMnAlNi single crystals

Effect of ageing conditions (ageing in the high-temperature phase (austenite) in free state and under stress and ageing in martensite under stress, ageing temperature and time) on the development of stress-induced BCC-FCC martensitic transformation (MT) and superelasticity (SE) was studied in the FeMnAlNi single crystals along the [001] direction under compression. It is shown that the precipitation of nanosized particles of the β-phase (ageing in austenite for 3 and 6 h at 473 K in a free state and under stress and ageing in martensite under stress for 3 h at 473 K) leads to an increase in the stress level for the onset of stress-induced BCC-FCC MT σcr and to the creation of crystals with high-temperature SE at temperatures above 373 K. SE is observed in a wide temperature range: from 273 to 473 K in quenched crystals; from 203 to 573 K after ageing in austenite at 473 K for 3 and 6 h in a free state and under stress and after ageing in martensite under stress at 473 K for 3 h. The maximum SE is 6.3–8.3% and 6.2% after ageing in austenite and in martensite under stress, respectively. It was shown for the first time that after ageing in martensite under stress (when transformation strain εtr=3%) for 3 h at 473 K, the SE curves are characterized by two stages, which are not observed after ageing in austenite under stress. The influence of particles on the σcr and the mechanical hysteresis Δσ is discussed.

Achieving superelasticity in additively manufactured Ni-lean NiTi by crystallographic design

Superelastic metallic materials possessing large recoverable strains are widely used in automotive, aerospace and energy conversion industries. Superelastic materials working at high temperatures and with a wide temperature range are increasingly required for demanding applications. Until recently, high-temperature superelasticity has only been achievable with multicomponent alloys fabricated by complex processes. In this study, a novel framework of multi-scale models enabling texture and microstructure design is proposed for high-performance NiTi fabrication via laser powder bed fusion. Based on the developed framework, a Ni-lean Ni(49.4 at.%)-Ti alloy is, for the first time, endowed with a 4% high-temperature compressive superelasticity. A 001 texture, unfavorable for plastic slip, is created to realize enhanced functionality. The unprecedented superelasticity can be maintained up to 453 K, which is comparable with but has a wider superelastic temperature range (∼110 K) than rare earth alloyed NiTi alloys, previously only realizable with grain refinement, and other complicated post-processing operations. At the same time, its shape memory stability is also improved due to existing textured 100 martensite and intergranular precipitation of Ti2NiOx. This discovery reframes the way that we design superior performance NiTi based alloys through directly tailoring crystallographic orientations during additive manufacturing.

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

• The B2-B19′ martensitic transformation was studied in (TiZrHf) 50 Ni 25 Cu 15 Co 10 high-entropy alloy crystals. • High-temperature superelasticity was found within the temperature range of T=M s =404K to 528K. • Maximum superelasticity value was 4.4% in [011] B2 -crystals under compression at 488K. • Shape memory effect was reached of 4.3-4.7% in [011] B2 -crystals under compression. Superelasticity (SE) and shape memory effect (SME) of [011] B2 -oriented single crystals in B2-phase of the (TiZrHf) 50 Ni 25 Cu 15 Co 10 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=M s =404K to 528K. The maximum SE value is 4.4%, and the SME reaches 4.3-4.7%.

High-temperature superelasticity in NiTiPt and NiTiPd shape memory alloys

Alloying NiTi shape memory alloys with sufficient Pt and Pd at the expense of Ni has been shown to increase transformation temperatures well above those possible with the binary composition, enabling consideration of a new class of high-temperature mechanical sensors and actuators. To achieve shape memory behavior at temperatures greater than 200 °C, previous studies of NiTiPt and NiTiPd compositions have focused primarily on alloys with greater than 16 at.% Pt and 25 at.% Pd. While generally not the focus, none of these previous studies demonstrated superelastic behavior at high temperatures. In an effort to identify alloys that transform to austenite at approximately 200 °C and exhibit superelastic behavior with recoverable strains greater than 2%, a series of Ti-rich NiTiPt ternary alloys with 15.5–16.5 at.% Pt, and Ti-rich NiTiPd ternary alloys with 25–26 at.% Pd have been targeted. The polycrystalline alloys were processed via arc melting followed by homogenization heat treatment. Thermomechanical properties were measured using electro-discharge machined tension test coupons and a miniature load frame equipped with a clamshell furnace. Ultimately, superelasticity in uniaxial tension with clear plateau regions was demonstrated and characterized in these alloys at temperatures between 219 °C and 270 °C.

Giant high-temperature superelasticity in a Ni-Fe-Mn-Sn shape memory microwire

High-performance high-temperature shape memory alloys (HTSMAs) are greatly needed for applications as intelligent components in aerospace, automotive, manufacturing and energy exploration industries. Here we developed a high-performance Ni-Fe-Mn-Sn HTSMA microwire, which exhibits giant high-temperature superelasticity with a maximum recoverable strain as high as ∼20% in the broad temperature range from 503 K up to 793 K. Incorporating the advantages of low cost of constituent elements and easy fabrication, this microwire shows great potential for applications in miniature high-temperature intelligent devices. This work is instructive for the development of small-scale high-performance HTSMAs.

A Low-Cost Ni-Mn-Ti-B High-Temperature Shape Memory Alloy with Extraordinary Functional Properties.

The rapid development of aerospace, automotive, and energy exploration industries urgently requires high-temperature shape memory alloys (HTSMAs) which are utilized as compact solid-state actuators, sensors, and energy conversion devices at elevated temperatures. However, the currently prevailing Ni-Ti-X (X = Pd, Pt, and Hf) HTSMAs are very expensive owing to the high cost of Pd, Pt, and Hf elements, which greatly limits their widespread applications. Here, we have developed an inexpensive (Ni50Mn35.5Ti14.5)99.8B0.2 bulk polycrystalline HTSMA with extraordinary high-temperature superelasticity and a giant two-way shape memory effect (TWSME). This alloy exhibits perfect superelasticity with a fully recoverable strain of as high as 7.1% over a wide temperature range from 150 to 280 °C. Furthermore, it shows a giant TWSME with a remarkably high recoverable strain of 6.0%. Both the recoverable strain of superelasticity and the two-way shape memory strain of the present alloy are the highest among the bulk polycrystalline HTSMAs. The theoretical maximum transformation strain was calculated with energy-minimization theory using the crystal structure information of martensite and austenite obtained from in situ synchrotron high-energy X-ray diffraction experiments to help understand the superelastic behavior of the present alloy. Combining the advantages of low cost and easy fabrication, the present bulk polycrystalline (Ni50Mn35.5Ti14.5)99.8B0.2 alloy shows great potential for high-temperature shape memory applications. This work is instructive for developing cost-effective high-performance HTSMAs.

The superelasticity and shape memory effect in Ni-rich Ti-51.5Ni single crystals after one-step and two-step ageing

In this work the microstructure, superelasticity and shape memory effect in [001]-oriented Ti-51.5at.%Ni single crystals after one-step ageing (at 850 K, 1 h) and two-step ageing (at 850 K, 1 h + 673 K, 1 h) were investigated. Large Ti3Ni4 particles (d ~ 600 nm) were precipitated at first step of ageing (850 K, 1 h) and nanosized Ti3Ni4 particles (d < 30 nm) were formed between the large particles at second step of ageing (673 K, 1 h).It is experimentally shown that precipitation of Ti3Ni4 particles during ageing (both at one-step and two-step ageing) in nickel-rich B2-matrix (CNi = 51.5 at.%) made it possible to create ultrahigh-strength [001]-oriented single crystals in which the strength properties of the B2-phase exceeded 2 GPa and the high-temperature superelasticity with a completely reversible strain in temperature range from 200 K to 460 K were observed.The thermal- and stress-induced martensitic transformations in aged crystals were characterized by wide intervals of forward and reverse martensitic transformations within stress and temperature, which were determined by the microstructure: large Ti3Ni4 particles and its distribution and nanosized Ti3Ni4 particles. The effect of the nanosized Ti3Ni4 particles, precipitated during the second step of ageing, is concluded in an additional widening of martensitic transformation intervals, a significant increase in strength properties of the B2-phase (from 2.0 to 2.4 GPa), a modification of the mechanism of accumulation and dissipation of energy during martensitic transformation (increase in reversible elastic energy and reduce of energy dissipation). As a result a more stable microstructure with bimodal particle distribution for high-temperature and high stress cycling was obtained.

High temperature superelasticity realized in equiatomic Ti-Ni conventional shape memory alloy by severe cold rolling

Great interests on high temperature shape memory alloys (HTSMAs) are recently raised, driven primarily by the aerospace and automotive industries, for their potential to serve as solid state actuators at high temperatures over 373 K. Near equiatomic Ti-Ni conventional SMAs, as the most applied SMA system, were considered to possess appreciable shape memory effect and superelasticity only below 373 K, which owes to low martensitic transformation temperatures. Here we utilized the martensite stabilization effect and successfully expanded the viable zone of B19′ (monoclinic) martensite to 616 K in a 35% cold-rolled Ti-50Ni (CR35) SMA. After a training cycle, it exhibited quasi-linear superelasticity of narrow hysteresis, ~3% superelastic strain and high strength over 1.2 GPa in a wide temperature range up to 483 K. It is the first exploration of high temperature superelasticity associated with the stabilized martensite. Using transmission electron microscopy and in-situ heating/tensile synchrotron X-ray diffraction, we reveal the origin of martensite stabilization and the underlying mechanisms of unique superelasticity in the CR35. Our work provides an attractively facile approach to realize high temperature superelasticity in Ti-Ni conventional SMAs, as well as in other kinds of SMAs, for precise actuation within an expanded range of working temperature and stress.

Influence of incorporated nanoparticles on superelastic behavior of shape memory alloys

The internal elastic strain resulting from an ensemble of nanoparticles in the crystal lattice of a shape memory alloy (SMA) is introduced as a key parameter into a quantitative theory of superelastic behaviour of SMA-nanoparticle composites. Experimental stress−strain loops obtained for a Co-Ni-Ga-nanoparticle system are analysed and a good agreement between the experimental and theoretical results is demonstrated. It is shown that even small (≈10−3) internal strains can lead to profound differences in stress−strain response between SMA-nanoparticle composites and “particle-free” SMA. The internal strains can enlarge the attainable value of superelastic strain, will strengthen the crystal lattice of the SMA and can give rise to high-temperature superelasticity of SMA-nanoparticle composites. The theory predicts that the larger the volume change is during the MT, the more pronounced is the influence of the nanoparticles on the superelastic behaviour of SMA.

Internal pressure as a key thermodynamic factor to obtain high-temperature superelasticity of shape memory alloys

Stress–strain loops illustrating the superelastic behaviour of shape memory alloys (SMAs) were computed based on the theory of ferroelastic phase transitions. The predictions of the theory demonstrate the possibility of drastic changes in the stress–strain dependences due to the expansion of the SMA upon heating. Specifically, the computations were carried out taking into account the characteristics of Co-Ni-Ga alloys, which exhibit a high-temperature superelasticity. It is shown that the expansion of crystal lattice, which can be caused by the appearance of small particles and crystal defects, or change of chemical order in SMA, can induce (i) an extension of the temperature range of superelastic behaviour of SMA to high temperatures; (ii) an increase of the superelastic strain at elevated temperatures; (iii) an increase of the stress needed to reach the superelastic strain plateau and (iv) a widening of the hysteresis of stress-induced martensitic transformation. Theoretical results are in a qualitative agreement with experimental data obtained for Co-Ni-Ga alloys.

Peculiarities of high-temperature superelasticity in Ni–Fe–Ga single crystals in compression

The high-temperature superelasticity and temperature dependence of the yield stress of 14M and L10 martensite in [001]-oriented single crystals of Ni54Fe19Ga27 (at %) in compression alloy have been studied. As the temperature increases, the sequence of stress-induced martensitic transformations (MTs) changes from L21–14M to L21–L10. The yield stress of L10 martensite weakly depends on the temperature and is 1.7 times lower than that of 14M martensite. The temperature interval of superelasticity in [001]-oriented single crystals of Ni54Fe19Ga27 under compression is determined by the growth of critical stresses with increasing temperature, the coefficient of strain-hardening, and the yield stress of L10 martensite.

Physics of Thermoelastic Martensitic Transformation in High-Strength Single Crystals

The thermoelastic martensitic transformations, shape memory effect and superelasticity in high-strength single crystals of ferromagnetic FeNiCoAlX (X = Ta, Nb, Ti), CoNiGa, NiFeGaCo alloys and TiNi alloy in monophase and heterophase states with nanoscale dispersed particles are investigated. The dependences of the thermal and stress hysteresis, superelasticity temperature range, reversible transformation strain on the size of the dispersed particles, crystal orientation, stress state, level of applied stress and test temperature are obtained. The criteria of high-temperature superelasticity and the conditions for narrow thermal and stress hysteresis, large value of reversible transformation strain, which exceeds the theoretical lattice strain, are established. The thermodynamic description of the effect of particles on the stress-induced martenstic transformation in single crystals of new high-ferromagnetic alloys are elaborated.

Effect of Thermomechanical Treatment on Superelasticity in Ni&lt;sub&gt;54&lt;/sub&gt;Fe&lt;sub&gt;19&lt;/sub&gt;Ga&lt;sub&gt;27&lt;/sub&gt; Single Crystals

In the present study the effects of thermomechanical treatment on the stress-induced martensitic transformation and superelasticity of [001]-oriented Ni54Fe19Ga27 (at.%) single crystals were investigated. It is shown that high-temperature superelasticity is observed up to 453 K in the as-grown Ni54Fe19Ga27 single crystals. Thermomechanical treatment result in increasing of the martensite yield stress, and so the SE interval, which is observed up to 523 K.

Shape memory effect and high-temperature superelasticity in high-strength single crystals

Abstract In the present study the temperature interval of superelasticity in Ti49.4Ni50.6, Co49Ni21Ga30, Ni54Fe19Ga27 and Fe41Ni28Co17Al11.5Ta2.5 (at%) single crystals are investigated. It is shown that it is necessary to produce materials with (i) a high yield stress level of the high-temperature phase of |σcrA| ∼ G/300−G/100 (G is shear modulus), and (ii) a low value of α = d|σcrM|/dT (|σcrM| is the critical stress required for stress-induced martensitic transformation) to achieve high-temperature superelasticity at Т > 373 K. A high stress level of austenite |σcrA| can be obtained through selection of the crystal axis orientation, the stress state (tension vs. compression), variation of the chemical composition of the intermetallic compounds, and precipitation of dispersed particles. Low values of α are realized for crystal orientations providing maximum values for the transformation strain |ɛ0|.

Tension/compression asymmetry of functional properties in [001]-oriented ferromagnetic NiFeGaCo single crystals

In the present study the effects of stress state (tension/compression) and test temperature on the critical stress level for the stress-induced martensitic transformation, the shape memory effect and superelasticity of [001]-oriented Ni 49Fe 18Ga 27Co 6 (at.%) single crystals were investigated. It is shown that the strong tension/compression asymmetry of the critical stress levels for the stress-induced martensitic transformation can be described by a modified Clausius–Clapreyron relationship, which takes the difference between the elastic moduli of austenite and martensite into account. The temperature interval in which superelasticity occurs and the reversible strain values associated with superelasticity and the shape memory effect are both strongly dependent on the stress state (tension/compression). Moreover, the conditions necessary for the development of high-temperature superelasticity in Ni 49Fe 18Ga 27Co 6 single crystals have been determined. For the Ni 49Fe 18Ga 27Co 6 single crystals a large interval of superelasticity (315 K < T < 723 K) was obtained when the single crystals were loaded in tension along the [001]-orientation.

High-temperature superelasticity and competing microstructural mechanisms in Co49Ni21Ga30 shape memory alloy single crystals under tension

A large temperature range of stress-induced martensitic transformation with >8% superelastic strain is demonstrated in [1 0 0]-oriented Co49Ni21Ga30 single crystals. The nature of the superelastic response is greatly affected by temperature and test history due to the temperature-dependent dominant microstructural mechanisms. We provide an insight into these mechanisms and divide the response into three temperature stages. Interestingly, a small stress hysteresis of only 2 MPa was achieved after the superelastic experiments at 300 °C compared to 20 MPa of the virgin sample.

Effect of orientation on the high-temperature superelasticity in Co49Ni21Ga30 single crystals

The temperature interval ΔTSE of superelasticity in [001]-, [\( \bar 1 \)23]-, and [\( \bar 1 \)24]-oriented Co40Ni21Ga30 (at. %) single crystals strained at compression has been studied. It is established that ΔTSE in the [001]-oriented single crystal amounts to 441 K and the reversible B2-L10 martensite transformations in loaded samples take place at T2 = 698 K. In [\( \bar 1 \)23]- and [\( \bar 1 \)24]-oriented samples, ΔTSE decreases to 233 K and the superelasticity is observed up to T2 = 523 K.

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.

High-temperature superelasticity in CoNiGa, CoNiAl, NiFeGa, and TiNi monocrystals

The influence of the crystal orientation on the thermoelastic martensitic transformations developing under load was investigated for Co49Ni21Ga30, Co40Ni33Al27, Co35Ni35Al30, Ni54Fe19Ga27, and Ti49.4Ni50.6 (аt. %) monocrystals. It has been shown that the superelastic temperature range depends on the crystal orientation and reaches a maximum for [001]-oriented crystals. In monophase crystals of Co49Ni21Ga30, Co40Ni33Al27, Co35Ni35Al30, and Ni54Fe19Ga27 (at. %), segregation of dispersion particles takes place at test temperatures T > 623 K. A criterion for high-temperature superelasticity has been proposed which implies the attainment of high strength of the high-temperature phase due to a proper choice of the crystal orientation, deviation from stoichiometry, and segregation of dispersion particles.

High-temperature superelasticity during B2-L10 martensite transformations in Co40Ni33Al27 crystals

The temperature interval ΔT SE of superelasticity in [001]-oriented Co40Ni33Al27 (at. %) single crystals strained by tension and compression has been studied. It is established that ΔT SE in tension amounts to 220 K, and the reversible B2-L10 martensite transformations in loaded samples take place at 590 K. In the samples strained by compression, ΔT SE decreases to 105 K, and the superelasticity is observed up to 420 K.