Elastocaloric Effect Research Articles

Elastocaloric effect in amorphous polymer networks undergoing mechanotropic phase transitions

Deformations of amorphous polymer networks prepared with significant concentrations of liquid crystalline mesogens have been recently reported to undergo mechanotropic phase transitions. Here, we report that these mechanotropic phase transitions are accompanied by an elastocaloric response ($\Delta T = 2.9 \text{ K}$). Applied uniaxial strain to the elastomeric polymer network transitions the organization of the material from a disordered, amorphous state (order parameter $Q=0$) to the nematic phase ($Q=0.47$). Both the magnitude of the elastocaloric temperature change and mechanically induced order parameter are dependent on the concentration of liquid crystal mesogens in the material. While the observed temperature changes in these materials are smaller than those observed in shape memory alloys, the responsivity, defined as the temperature change divided by the input stress, is larger by an order of magnitude.

Enhanced working stability of elastocaloric effects in polycrystalline Ni-Fe-Ga dual phase alloy

Stable elastocaloric effect (eCE) over multiple stress cycles is an indispensable aspect for the commercialization of elastocaloric refrigeration. Here, we addressed the enhanced functional stability in polycrystalline Ni53.2±0.4Fe19.4±0.2Ga27.4±0.6 dual-phase alloy, where interstitial γ-phase was incorporated via aging precipitation. The intergranular γ-precipitates confirmed the reversible superelastic effects at room temperature (296 K), which is greatly conducive to multiple interphase movement. As a consequence, notable adiabatic temperature change (ΔTad) 6.2 K with a large coefficient of performance (COPmat) 14.5 was achieved under maximum stress 300 MPa. A stable eCE cooling performance (ΔTad~2.6 K) over 500 superelastic cycles with insignificant degradation was found under nominal stress 250 MPa. Consequently, the current work demonstrates that manipulating the microstructure by incorporating the interstitial secondary phase is a promising approach to enhance the mechanical and functional properties of ferromagnetic shape memory alloys (FMSMAs) for solid-state cooling technology.

Orientation dependence of elastocaloric effect in Ni50Mn30Ga20 single crystals

In this study, the orientation dependence of the elastocaloric effect and superelasticity in Ni50Mn30Ga20 single crystals undergoing L21–10M/14M–L10 martensitic transformations was investigated. The maximum value of the adiabatic temperature change ΔTad at reverse stress-induced martensitic transformations was shown to weakly depends on the orientation and equals 10.8 and 12.3 K in compression along the [001] and [011] directions, respectively. The superelasticity and elastocaloric effect temperature intervals were determined from the crystal orientation and were 80 K from 373 to 453 K for [001]-oriented crystals and 30 K from 373 to 403 K for [011]-oriented crystals. The strong orientation dependence of stress hysteresis Δσ (Δσ = 50–60 MPa for [001]-oriented crystals and Δσ = 110–142 MPa for [011]-oriented crystals) did not significantly affect the ΔTad, but determined the efficiency of the material for practical use as a solid state cooling device. The factors influencing the ΔTad(T) dependence were analyzed.

Elastocaloric effect in zinc oxide nanowire

In this work, zinc oxide (ZnO) nanowire is proposed for elastocaloric application which has been overlooked until now. The elastocaloric effect ([Formula: see text]CE) is calculated by Maxwell relation. The large elastocaloric temperature and entropy change evaluated as 17 K and 28 J/kgK, respectively, at 300 K correspond to the stress of 12 GPa or strain of 5.5% by the simulation data. The elastocaloric temperature can be increased to 22 K under the operating tempering of 600 K. However, [Formula: see text]CE estimated from the experimental data is found as 2.6 K at 300 K, which corresponds to stress of 6 GPa. These results are expected to significantly expand the knowledge of ZnO nanomaterials as a potential candidate for [Formula: see text]CE. The results are based on the indirect approximation; hence, a direct measurement is needed to verify the obtained results.

Enhancing the elastocaloric effect in Ni–Mn–Ga alloys through the coupling of magnetic transition and two-step structural transformation

Elastocaloric effect driven by uniaxial stress in the Ni–Mn–Ga alloys can be greatly enhanced through introducing magnetic transition or inter-martensitic transformation to martensitic transformation. Here, we present large elastocaloric effect in a ⟨0 0 1⟩A textured Ni55Mn19Ga25Ti1 polycrystalline alloy prepared by directional solidification by exploiting the coupled multiple phase transformations, i.e., paramagnetic-ferromagnetic transition, martensitic transformation, and inter-martensitic transformation. Owing to such magneto-multistructural transformation, the transformation entropy change related to the inverse transformation is enhanced to 29.6 J kg−1 K−1. Consequently, on unloading from a compressive stress of 180 MPa, a large adiabatic temperature change of −12.9 K and specific adiabatic temperature change of −72 K GPa−1 are achieved, being much superior over those in the Ni–Mn–Ga based alloys obtained previously.

Combining magnetocaloric and elastocaloric effects in a Ni45Co5Mn37In13 alloy

• The polycrystalline button ingots of Ni 45 Co 5 Mn 37 In 13 was prepared by the directional solidification along with [001] orientation. • The Ni 45 Co 5 Mn 37 In 13 alloy exhibits excellent magnetocaloric and elastocaloric properties in adjacent temperature range. • By combining magnetocaloric and elastocaloric effect, a broad refrigeration temperature region including room temperature is obtained in a single alloy. • we propose a novel refrigeration system concept with rotary magnetocaloric refrigerator and elastocaloric system to fully utilize the combined caloric effect. Solid-state refrigeration technology has become a promising candidate to replace the traditional low-efficiency and environment-harmful vapor compression refrigeration. However, the narrow temperature region becomes a critical problem which hinders the practical applications of caloric materials to a refrigerator. Here, we report a potential way to solve this problem by combining different caloric effects in one refrigerant. A multiferroic ferromagnetic shape memory alloy Ni 45 Co 5 Mn 37 In 13 can exhibit large inverse magnetocaloric effect and elastocaloric effect in adjacent working temperature regions. Thus a broad refrigeration temperature span can be realized in Ni 45 Co 5 Mn 37 In 13 alloy by applying magnetic field or external stress at different temperature. Moreover, we propose a potential equipment schematic drawing to achieve it. The system can facilitate the multiferroic materials to produce useful cooling at a much larger temperature range. This combined caloric effect and the concept system proposed in this study would inspire researchers working in this field.

A study of physical effects in magnetic-phase-transition materials

<p indent=0mm>Magnetic-phase-transition materials possess abundant physical properties and exhibit magnetocaloric, magnetostrictive, elastocaloric, and negative thermal expansion effects under magnetic, stress or temperature fields. They show promising applications in many fields, including refrigeration, sensor, and energy conversion. As a new class of functional magnetic materials, research fields and contents based on the magnetic-phase-transition materials are becoming enriched. In this paper, we first introduce the phase transition types of magnetic materials and present some emphatic descriptions of the first-order magnetic-phase-transition materials. Thereafter, we review recent research progress on the related effects of the first-order magnetic-phase-transition materials driven by magnetic, stress, and temperature fields.

Characterization of caloric effects for magnetostructural transition materials: State-of-the-art and prospects

Due to its environmental friendliness and high theoretical energy conversion efficiency, solid-state refrigeration based on caloric effects of magnetostructural transition (MST) materials driven by external stimuli is deemed as the most promising technology to replace the current vapor compression refrigeration. To accurately and efficiently characterize caloric effects for a MST is one of the keys to solid-state refrigeration. The research of caloric effects for MSTs and associated solid-state refrigeration relies to a large extent on characterization techniques. Regular methods, for instance, thermocouple and calorimetry, are not capable of characterizing caloric effects of MSTs under external field(s) and of understanding the mechanism of magnetostructural coupling in these materials. Therefore, new methods are being introduced and new experimental setups are being built as the research deepens. In recent years, beyond single-index and macroscopic-parameter assessment, characterization of caloric effects is not only going deeply with multi-index measurement, in-situ methods, and microscopic techniques, but is being combined with new approaches including high-throughput methods and machine learning methods. Herein, we review the state-of-the-art and prospects of characterization of caloric effects for MSTs including basic principles, magnetocaloric effect, elastocaloric effect, barocaloric effect and multicaloric effect.

Learning from Superelasticity Data to Search for Ti-Ni Alloys with Large Elastocaloric Effect

In the present study, the reversible adiabatic temperature change (ΔTad) of shape memory alloys was shown to be proportional to the mechanical work released by the reverse martensitic transformation during unloading (ΔWu). As there exists a considerable amount of data (ΔWu) on superelastic stress-strain measurements in shape memory alloys, the proposed relationship allows us to predict ΔTad without caloric measurements. The estimated ΔTad from the ΔWu of different Ti-Ni alloys shows good linear relationship with the directly measured values. Moreover, following such a design criterion and by tuning of composition and thermo-mechanical treatment, a group of Ti-Ni binary shape memory alloys with a directly measured ΔTad larger than 35 K under tension were achieved. The large ΔTad and ΔWu can be ascribed to the grain refinement and the heterogeneous internal stress fields after the thermo-mechanical treatment, which have enhanced the critical stress of superelasticity and recoverability of martensitic transformation during unloading.

Origin of the inverse elastocaloric effect in a Ni-rich Ti-Ni shape memory alloy induced by oriented nanoprecipitates

In the region of a martensitic transformation, conventional elastocaloric effect causes cooling when the forward parent to martensite transition is induced by loading under adiabatic conditions and by heating when the load is removed and the reverse transition occurs. An inverse elastocaloric effect might be expected if the reverse transition could be induced upon loading. However, this behavior is quite uncommon and inverse elastocaloric effect rarely occurs. Herein, we have successfully manufactured a Ti-50.8 at.% Ni crystal in a high proportion of favorable $R$ phase (martensite) variant containing single-variant ${\mathrm{Ti}}_{3}{\mathrm{Ni}}_{4}$ nanoprecipitates aligned along the ${\ensuremath{\langle}111\ensuremath{\rangle}}_{B2}$ direction of the $B2$ parent phase, by means of a compressive stress associated aging along the ${\ensuremath{\langle}111\ensuremath{\rangle}}_{B2}$ direction. The material displays inverse elastocaloric effect induced by compressive stress along the ${[111]}_{B2}$ direction in the temperature range of stability of the $R$ phase. This inverse elastocaloric effect is caused by the stress-induced reverse transformation of the high proportion of favorable $R$-phase variant that occurs when the external compressive stress is applied along the direction of the internal tensile stress induced by the aligned ${\mathrm{Ti}}_{3}{\mathrm{Ni}}_{4}$ nanoprecipitates. The mechanism giving rise to this inverse elastocaloric effect is explained by the transformation strain in the ${[111]}_{B2}$ and ${[1\overline{1}0]}_{B2}$ directions for different $R$-phase variants based on crystallography. Results indicate that the stress-associated aging process is an effective way of patterning materials to display inverse elastocaloric effect through controlling the alignment of the ${\mathrm{Ti}}_{3}{\mathrm{Ni}}_{4}$ nanoprecipitate in the Ni-rich Ti-Ni shape memory alloy.

Elastocaloric-effect-induced adiabatic magnetization in paramagnetic salts due to the mutual interactions

The temperature change under adiabatic stress, i.e., the elastocaloric effect, is a well-understood phenomenon and of particular interest due to its potential application in alternative ways for refrigeration. Here, we demonstrate that in the regime of low-temperatures (a few mK) real paramagnets can be magnetized when compressed adiabatically without applied magnetic field. Such adiabatic magnetization is a genuine many-body problem, stemming from the inherent dipolar mutual interactions between adjacent magnetic moments. We showcase experimental setups to carry out adiabatic magnetization and thus to access such a subtle effect. Perspectives of further investigations by controlling the mutual interactions in Bose–Einstein condensates in magnetic insulators and dipolar spin-ice systems via the adiabatic increase of temperature are also presented. Yet, we discuss the connection between the elastic Grüneisen parameter and the shift on the critical temperature of second-order phase transitions under adiabatic stress, as well as its connection with the Ehrenfest relation.

Giant low-field actuated caloric effects in a textured Ni43Mn47Sn10 alloy

In this work, based on composition adjusting and texture control, we demonstrate giant elastocaloric and magnetocaloric effects in a directionally solidified Ni43Mn47Sn10 polycrystalline with strong <001>A texture. On removing a low compressive stress of 210 MPa, giant adiabatic temperature change up to −17.3 K is achieved. Such value is much higher than those in some elastocaloric materials reported previously. Besides, giant magnetic field induced entropy changes of 23.5 Jkg−1K−1 and 37.1 Jkg−1K−1 are also obtained under the magnetic field changes of 2 T and 5 T, respectively. Simultaneously achieving giant elastocaloric and magnetocaloric effects actuated by relatively low external field is of great importance to explore multi-caloric or coupled caloric effects in developing efficient and eco-friendly solid-state refrigeration technology.

Phase field simulation on the super-elasticity, elastocaloric and shape memory effect of geometrically graded nano-polycrystalline NiTi shape memory alloys

• A 2D non-isothermal phase field model considering multiple variants which can describe the thermo-mechanical deformation of NiTi SMAs is newly proposed. • The SE, ECE, OWSME and SATWSME of the geometrically graded nano-polycrystalline NiTi SMAs are simulated and predicted by phase field method for the first time. • The controllability of SE and SATWSME can be effectively improved by designing geometrically graded structures. • The design of geometrically graded structures has the potential to regulate ECE. A two-dimensional non-isothermal phase field model considering multiple martensite variants which can describe the thermo-mechanical deformation of polycrystalline NiTi shape memory alloys (SMAs) was newly proposed. The super-elasticity (SE), elastocaloric effect (ECE), one-way shape memory effect (OWSME) and stress-assisted two-way one (SATWSME) of the geometrically graded nano-polycrystalline NiTi SMA systems (for instances, the trapezoid, concave and convex ones) were simulated and predicted by phase field method for the first time. The simulated results show that: Due to the stress gradient caused by the heterogeneous geometry under an external applied load, the martensite transformation (MT) and its reverse in the geometrically graded systems propagate progressively along the direction with stress variation, resulting in an obviously wider transformation stress window or transformation temperature one (with the assistance of external applied load) there than that in the rectangular system (where no heterogeneous geometry is involved), thus, the controllability of the SE and SATWSME can be effectively improved; however, since the sensitivity of martensite reorientation to the external load is much higher than that of stress-induced MT, the stress gradient along the tensile direction of the geometrically graded systems cannot strictly control the gradual propagation of martensite reorientation, so the improvement of the controllability of OWSME is not considerable; moreover, the temperature field evolution is consistent with the progressively propagating MT within the geometrically graded systems in the SE process, and the variation rate of the average temperature is lower than that of the rectangular system, which means that designing the geometrically graded structure components of NiTi SMA systems has the potential to control their ECE. Phase-field simulated microstructure evolution in the processes reflecting super-elasticity (SE) and one-way shape memory effect (OWSME) of rectangular and geometrically graded nano-polycrystalline NiTi SMA systems.

Achieving Excellent Superelasticity and Extraordinary Elastocaloric Effect in a Directionally Solidified Co-V-Ga Alloy

We demonstrate excellent superelasticity and giant elastocaloric effect in a directionally solidified Co50.7V33.3Ga16 alloy. Owing to the formation of [001]A preferentially oriented columnar grains, the as-grown alloy displays nearly perfect superelastic behaviors with fully reversible compressive strain of up to 5.4%, narrow stress hysteresis of about 40 MPa and a wide operating temperature window from 258 to 373 K. Simultaneously, a giant adiabatic temperature change ΔTad of -18.7 K is obtained on removing a uniaxial stress of 400 MPa at room temperature, which is in good agreement with the theoretical values based on Maxwell relation (-19.0 K) and calorimetric measurements (-19.9 K). A large |ΔTad| of greater than 12.5 K is obtained over a wide temperature span of at least 115 K. Moreover, both superelasticity and elastocaloric effect remain good functional stability without any evident degradation for 100 cycles.

Mechanical and elastocaloric effect of Fe and Co co-doped Ni–Mn–Al ferromagnetic shape memory alloys

The martensitic transformation (MT), microstructure, mechanical properties and elastocaloric properties of Ni40FexCo10-xMn32Al18 (x = 2, 4, 6 at.%) polycrystalline alloys were comprehensively investigated. The MT temperature of these alloys shifts to lower temperatures as Fe/Co ratio increases. The fracture strength is significantly enhanced from 905 MPa of Ni40Fe2Co8Mn32Al18 to 1275 MPa of Ni40Fe6Co4Mn32Al18. Among these alloys, Ni40Fe4Co6Mn32Al18 exhibits the best elastocaloric properties. A large temperature change of 6.1 K was obtained by applying a uniaxial stress of 400 MPa, and the temperature change about −5.2 K maintains almost constant after 100 stress cycles in the Ni40Fe4Co6Mn32Al18 alloy. The research results demonstrate an effective method to optimize elastocaloric materials used in solid-state refrigeration field.

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 Ni49Fe18Ga27Co6 single crystals was investigated 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 L10-martensite variant reorientation. At higher temperatures between the forward and reverse transformation 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 loading. Super-elasticity 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.

Reversible elastocaloric effect related to B2–R transformation in Ni50.5Ti49.5 alloy

In Ti–Ni alloys, the low hysteresis emanating from the B2 ↔ R transition enables a fine control of reversibility in elastocaloric effects when there are lower values of applied stress. In this paper, we reported a Ni50.5Ti49.5 alloy synthesized by arc melting promoting the R phase. Using energy dispersive x-ray analysis, differential scanning calorimetry, x-ray diffraction, and elongation measures as a function of temperature, we have studied properties in an isolated R phase. We observe that there are similarities between the isothermal entropy change curves and the reversible adiabatic temperature changes, where a maximum value of reversible isothermal entropy of 14.6 J kg−1 K−1 at 310 K is obtained when a stress of 222 MPa is applied. We show that precipitates formed on the R phase play a role in the elastic behavior affecting the values of adiabatic temperature change.

Unlocking large compressive strains in thin active elastocaloric layers

• • Durable composites enabling compression of elastocaloric layers are demonstrated. • • Elastocaloric materials can be in any thin-layer geometry, e.g., strip, plate, foil. • • Composites achieve 8.1 K temperature change at 2.5% strain. • • Mechanical and thermal properties are stable after 104 loading cycles at 2% strain. Elastocaloric cooling attracts broad interest and rapidly growing attention due to its potential for high efficiency and low environmental impact. While it is common knowledge that triggering reversible entropy and temperature changes with stress applied in compression prevents rapid failures of materials, realizing this regime in elastocaloric systems is highly challenging because nearly all geometries suited for efficient heat transfer are prone to buckling even under modest loads. This work describes a concept of a novel composite, where an active NiTi layer is embedded into a polymer support structure such that the elastocaloric material is entirely in compression when the assembly is subjected to bending. The active layer achieves 8.1 K temperature change at 2.5% compressive strain without buckling. After 10,000 cycles at 2% compressive strain, the composite maintains mechanical integrity without degradation of the elastocaloric effect. The results show that NiTi and, potentially, other elastocalorically active materials in geometries previously thought impossible can be successfully implemented in regenerative cooling systems operating in compression.

Elastocaloric material shows promise for environmentally friendly refrigeration applications

A cobalt-vanadium–gallium-based alloy achieves a large elastocaloric effect and excellent cyclability.

Large elastocaloric effect in a Heusler-type Co50V35Ga14Ni1 polycrystalline alloy

Solid state refrigeration technology relies on the high-performance materials with remarkable caloric properties. Here, we demonstrate a large elastocaloric effect through stress-induced martensitic transformation in a Heusler-type Co50V35Ga14Ni1 polycrystalline alloy. By rapidly removing a moderate compressive stress of 400 MPa, a large adiabatic temperature change up to −12.1 K is achieved. Moreover, high cyclability of the elastocaloric effect with more than 4000 loading/unloading cycles is also obtained. With the combination of a large elastocaloric effect and good cyclability, Co-V-Ga based alloys hold great potential for environment-friendly solid-state refrigeration applications.