Elastocaloric Effect Research Articles

Giant Elastocaloric Effect in Ni-Mn-Ga-Based Alloys Boosted by a Large Lattice Volume Change upon the Martensitic Transformation.

High-performance elastocaloric materials are highly sought in developing energy-efficient and environmentally friendly solid-state elastocaloric refrigeration. Here, we present an effective strategy to achieve a giant elastocaloric response by enlarging the lattice volume change ΔV/V0 upon the martensitic transformation. Using the Ni50Mn50 binary alloy as the prototype, a large transformation entropy change ΔStr can be tailored in the vicinity of room temperature by simultaneously doping Cu and Ga. Especially, the |ΔStr| values in the ⟨001⟩A-textured Ni30Cu20Mn39.5Ga10.5 and Ni30Cu20Mn39Ga11 alloys prepared by directional solidification can be as large as 47.5 and 46.7 Jkg-1 K-1, respectively, due to the significant ΔV/V0 values, i.e., 1.81 and 1.82%, respectively. Such enhanced ΔStr values thus yield giant ΔTad values of up to -23.5 and -19.3 K on removing the compressive stress in these two alloys, being much higher than those in Heusler-type alloys reported previously. Moreover, owing to the relatively low driving stress endowed by the highly textured microstructure, the specific adiabatic temperature change (|ΔTad/Δσmax|) in the present work can be as large as 77.2 K/GPa. This work is expected to provide new routes in designing high-performance elastocaloric materials with the combination of a giant elastocaloric response and low driving stress.

Investigation of the Thermomechanical Response of Cyclically Loaded NiTi Alloys by Means of Temperature Frequency Domain Analyses.

Nickel–Titanium (NiTi) shape memory alloys subjected to cyclic loading exhibit reversible temperature changes whose modulation is correlated with the applied load. This reveals the presence of reversible thermomechanical heat sources activated by the applied stresses. One such source is the elastocaloric effect, accounting for the latent heat of Austenite–Martensite phase transformation. It is, however, observed that when the amplitude of cyclic loads is not sufficient to activate or further propagate this phase transformation, the material still exhibits a strong cyclic temperature modulation. The present work investigates the thermomechanical behaviour of NiTi under such low-amplitude cyclic loading. This is carried out by analysing the frequency domain content of temperature sampled over a time window. The amplitude and phase of the most significant harmonics are obtained and compared with the theoretical predictions from the first and second-order theories of the Thermoelastic Effect, this being the typical reversible thermomechanical coupling prevailing under elastic straining. A thin strip of NiTi, exhibiting a fully superelastic behaviour at room temperature, was investigated under low-stress amplitude tensile fatigue cycling. Full-field strain and temperature distributions were obtained by means of Digital Image Correlation and IR Thermography. The work shows that the full field maps of amplitude and phase of the first three significant temperature harmonics carry out many qualitative information about the stress and structural state of the material. It is, though, found that the second-order theory of the Thermoelastic Effect is not fully capable of justifying some of the features of the harmonic response, and further work on the specific nature of thermomechanical heat sources is required for a more quantitative interpretation.

Superelastic behavior and elastocaloric effect in a Ni51.5Fe21.5Ga27.0 ferromagnetic shape memory single crystal under compression

Ni51.5Fe21.5Ga27.0 single crystals have been subjected to different heat treatments resulting in a different degree of L21 ordering. Superelastic response has been measured at different temperatures in compression mode. The mechanical behavior strongly depends on axis orientation. In the [001] direction, perfect superelasticity over a wide range of temperatures is found. For the [110] orientation, the material fails by brittle fracture short above austenite transformation finish temperature, Af. A linear dependence of the critical stress with temperature has been found in agreement with Clausius-Clapeyron equation. The slope does not significantly change with the degree of order, but it is notably affected by the crystal orientation. The microstructure of the samples after mechanical tests has been studied by transmission electron microscopy. The superelastic cycling produces dislocations with a Burgers vector that suggests local microplastic deformation of the martensitic phase. Finally, the adiabatic temperature change has been used to chacterize the elastocaloric effect in this alloy. The adiabatic cooling is found to be larger in the [110] than in the [001] orientation at 240 K. However, the brittleness of [110] samples avoid testing the adiabatic temperature change at room temperature. The adiabatic cooling in [001] orientation decreases systematically with temperature, which is related to decrease of the strain and entropy change of transformation.

Giant elastic response and ultra-stable elastocaloric effect in tweed textured Fe-Pd single crystals

The limit of elastic deformation in conventional metals and alloys is usually within 0.1%. When deformed further, these materials show plastic deformation effects, which are a consequence of dislocation movements. Here, we report that a much larger elastic-like strain of more than 4% can be achieved in a tweed textured Fe-Pd single crystal under a compressive stress of 300 MPa. We show that this giant elastic response gives rise to significant and homogenous elastocaloric effect (∼4.1 K) that can sustain 106 or even more mechanical cycles without degradation. The large and stable elastic-like strain in Fe-Pd originates from the continuous and reversible structural change associated with the tweed texture under stress as confirmed by the in-situ high energy X-ray diffraction tests. Phase field simulation also confirms this giant elastic response and ultra-stable elastocaloric effect under a compressive stress in the Fe-Pd alloy.

The role of texture on superelasticity and elastocaloric effect in severely rolled Ti-44Ni-5Cu-1Al (at%) shape memory alloy

The effects of crystallographic texture on the superelasticity and elastocaloric effect of nanograin Ti-44Ni-5Cu-1Al rolled sheet are investigated. Stress-strain curves with different orientation angles between tensile direction and rolling direction show that the tensile strain of the sheet is largest in rolling direction (RD) along <110> and smallest in transverse direction (TD) parallel to <100>. This texture dependence is further studied by analyzing the evolution of each strain component. With the increase of the orientation angle, intergranular constraint effect reaches the maximum in TD. As a result, transformation strain and adiabatic temperature change have a similar monotonic decreasing trend. The material coefficient of performance of the sheet reaches 11.2 in RD. This value makes it possible for severely rolled Ti-44Ni-5Cu-1Al sheet to be a potential candidate for solid-state refrigeration application at room temperature.

Elastocaloric effect in vulcanized natural rubber and natural/wastes rubber blends

Vulcanized natural/wastes rubber blends were prepared and their elastocaloric properties were analysed. A thermodynamic frame was used to discriminate the contributions of thermoelastic effects and strain induced crystallization/melting. The substitution of 20 wt% of the natural rubber matrix by waste rubber particles resulted in a maintain and even a slight improvement of heat exchanges (+10%), that we ascribed to a (i) high thermoelastic effect and a (ii) a high ability of the natural rubber matrix to crystallize due to a nucleation ability of the waste particles, both resulting from a strain amplification in the rubber phase due to undeformable carbon black aggregates in the waste particles. The materials coefficient of performance, COPmat, was estimated equal to 4.4 for the neat natural rubber and 3.8 for the blend containing 20 wt% of wastes due to larger mechanical energy originated from reinforcing effect of waste particles. Nonetheless, the elastocaloric (eC) abilities of these materials, especially their wide temperature spans (similar to those in films or polycrystals using rare earth elements) make these natural/waste rubber blends good candidates for application such as heating/cooling machines. Moreover, the partial replacement of natural rubber, a bio-source material showing risks of shortage, by industrial wastes rubber, place these blends as promising eco-friendly materials with high added value.

Elastocaloric effect induced by the strain glass behavior of Ti-18Zr-11Nb-3Sn alloy covering a wide temperature range

Here, an elastocaloric working temperature range of 200 K has been developed from Ti-18Zr-11Nb-3Sn alloy. The adiabatic temperature change of 6.5 K was obtained at 253 K. The strain glass transition regulated by the shuffling nanodomains was responsible for the elastocaloric effect. The moderate refrigeration capability together with unique phase transformation makes the Ti-based shape memory alloy a promising elastocaloric material.

Evolutions of superelasticity and elastocaloric effect of Ti50Ni48Fe2 and aged-hardened Ni-rich Ti49.2Ni49.3Fe1.5 shape memory alloys under cyclic compressive deformation

The transformation and superelasticity characteristics of solution-treated Ti50Ni48Fe2 and aged-hardened Ti49.2Ni49.3Fe1.5 shape memory alloys during cyclic compressive deformation were investigated. The Ti50Ni48Fe2 alloy could not be precipitation hardened, while the Ti49.2Ni49.3Fe1.5 alloy, aged at 400 °C, was hardened by Ti3Ni4 precipitates. During the cyclic deformation, the B2⇆R⇆B19′ transformation peaks broadened and spread to a large temperature span. At the same time, the superelasticity behavior became linear, and the associated elastocaloric cooling capacity decreased to a stable value. Among these samples, Ti49.2Ni49.3Fe1.5 alloy aged at 400 °C for 150 h exhibited the largest recoverable strain in superelasticity and retained the largest cooling effect after 1000 deformation cycles. Furthermore, it showed elastocaloric cooling of −4.1 °C to −7.0 °C at operating temperatures of −40–80 °C. Experimental results revealed that B19′ transformation was suppressed significantly by cyclic deformation, and thus the transformation occurred in a wide temperature range of −160 to −50 °C. Additionally, the linear superelasticity exhibited a low slope of the Clausius–Clapeyron relation of about 0.5 MPa/°C. These features allow the alloys to exhibit superelasticiy and the elastocaloric effect over a wider temperature range.

Microstructure engineering of metamagnetic Ni-Mn-based Heusler compounds by Fe-doping: A roadmap towards excellent cyclic stability combined with large elastocaloric and magnetocaloric effects

Ni-Mn-based metamagnetic shape-memory alloys exhibit a giant thermal response to magnetic fields and uniaxial stress which can be utilized in single caloric or multicaloric cooling concepts for energy-efficient and sustainable refrigeration. However, during cyclic operation these alloys suffer from structural and functional fatigue as a result of their high intrinsic brittleness. Here, we present based on Fe-doping of Ni-Mn-In a microstructure design strategy which simultaneously improves cyclic stability and maintains the excellent magnetocaloric and elastocaloric properties. Our results reveal that precipitation of a strongly Fe-enriched and In-depleted coherent secondary γ-phase at grain boundaries can ensure excellent mechanical stability by hindering intergranular fracture during cyclic loading. In this way, a large elastocaloric effect of -4.5 K was achieved for more than 16000 cycles without structural or functional degradation, which corresponds to an increase of the cyclic stability by more than three orders of magnitude as compared to single-phase Ni-Mn-In-(Fe). In addition, we demonstrate that the large magnetocaloric effect of single-phase Ni-Mn-In-(Fe) can be preserved in the dual-phase material when the secondary γ-phase is exclusively formed at grain boundaries as the martensitic transformation within the Heusler matrix is barely affected. This way, an adiabatic temperature change of -3 K and an isothermal entropy change of 15 Jkg−1K−1 was obtained in 2 T for dual-phase Ni-Mn-In-Fe. We expect that this concept can be applied to other single caloric and mutlicaloric materials, therewith paving the way for solid-state caloric cooling applications.

Highly sensitive elastocaloric response in a directionally solidified Ni50Mn33In15.5Cu1.5 alloy with strong A preferred orientation

Solid-state elastocaloric cooling based on elastocaloric effect resulting from superelastic martensitic transformation has been conceived as a very competitive alternative to the conventional vapor-compression refrigeration. Reducing the driving stress of elastocaloric effect is very beneficial to the miniaturization and compactness of refrigeration devices. Here, we demonstrate large elastocaloric effect driven by low stress in a directionally solidified Ni50Mn33In15.5Cu1.5 alloy. Owing to the coarse columnar shaped grains with strong <001>A preferred orientation, large adiabatic temperature change (ΔTad) values up to −9.5 K and −11.4 K can be achieved on removing the relatively low compressive stress of 113 MPa and 150 MPa, respectively, showing the high sensitivity of elastocaloric response with the specific adiabatic temperature change (|ΔTad/σmax|) up to 83.5 K/GPa. Such value is much higher than those in other Ni–Mn-X based alloys reported previously.

Martensitic transformation and elastocaloric effect of Co51.5+xV31.5-xGa17 (x = 0.1, 0.2, 0.3) alloys

Co-V-Ga alloy, a newly discovered multifunctional material based on martensitic transformation (MT), has promising application prospects in spintronics and solid-state refrigeration fields. In this work, we investigated the MT behaviors and the elastocaloric effect (eCE) of Co51.5+xV31.5-xGa17 (x = 0.1, 0.2, 0.3) alloys. The alloys undergo a MT from paramagnetic austenite to paramagnetic martensite, accompanying by a large latent heat (about 6–9 J g−1). The MT temperature increases with the increase of the ratio of Co to V. The digital image correlation (DIC) combined with infrared thermography (IR) techniques were utilized to in situ characterize the stress-induced MT and temperature change of the sample. For the sample of x = 0.2, at a testing temperature of 301 K, it heats with a giant adiabatic temperature change up to 13.4 K upon loading, while cools only 2.4 K when stress releasing, showing an irreversible eCE. Raising the test temperature (319, 327 and 333 K) can greatly improve the reversibility of the eCE. Such an asymmetric elastocaloric temperature change at 301 K is closely related to the irreversibility of stress-induced MT, which can be attributed to several factors including the self-cooling effect, heat dissipative mechanism and the valence bond structure of Co-V-Ga alloys.

Elastocaloric signature of nematic fluctuations

The elastocaloric effect (ECE) relates changes in entropy to changes in strain experienced by a material. As such, ECE measurements can provide valuable information about the entropy landscape proximate to strain-tuned phase transitions. For ordered states that break only point symmetries, bilinear coupling of the order parameter with strain implies that the ECE can also provide a window on fluctuations above the critical temperature and hence, in principle, can also provide a thermodynamic measure of the associated susceptibility. To demonstrate this, we use the ECE to sensitively reveal the presence of nematic fluctuations in the archetypal Fe-based superconductor Ba([Formula: see text])2[Formula: see text] By performing these measurements simultaneously with elastoresistivity in a multimodal fashion, we are able to make a direct and unambiguous comparison of these closely related thermodynamic and transport properties, both of which are sensitive to nematic fluctuations. As a result, we have uncovered an unanticipated doping dependence of the nemato-elastic coupling and of the magnitude of the scattering of low-energy quasi-particles by nematic fluctuations-while the former weakens, the latter increases dramatically with increasing doping.

Direct measurement of temperature change due to elastocaloric effect in poled piezoelectric ceramics attached to metal

We directly measured the temperature changes accompanying deformation of poled piezoelectric ceramics attached to metal for applications to new solid-state cooling devices. Due to the use of supporting metal, the fracture of the piezoelectric ceramics was suppressed, and the elastocaloric effect could be measured. A temperature increase of 0.02 K was observed due to dent deformation of the piezoelectric body with 0.07% distortion of the supporting metal, and a temperature drop of 0.03 K due to spread deformation of the piezoelectric body with 0.15% distortion of the supporting metal. The measurement results of the change in electrical properties during deformation suggested that entropy increased and temperature decreased by applying stress in the direction that disturbed the polarization alignment.

Effect of Strain Rate and Measuring Temperature on Elastocaloric Effect and Multi-caloric Properties of Co37.5 Ni34.5 Al28 Paramagnetic Shape Memory Alloy

Effect of Strain Rate and Measuring Temperature on Elastocaloric Effect and Multi-caloric Properties of Co37.5 Ni34.5 Al28 Paramagnetic Shape Memory Alloy

Thermoelastic Properties and Elastocaloric Effect in Rapidly Quenched Ribbons of Ti2NiCu Alloy in the Amorphous and Crystalline State

The thermoelastic properties and the elastocaloric effect (ECE) were studied in rapidly quenched ribbons of the Ti2NiCu alloy samples in amorphous and crystalline states under periodic mechanical tension with a frequency of up to 50 Hz. In the amorphous samples, elastic behavior is observed, described by Hooke’s law, with a high coefficient of thermal expansion α = 1.7 × 10−4 K−1. Polycrystalline ribbons of the Ti2NiCu alloy have the classical shape memory effect (SME), the temperatures of the forward and reverse thermoelastic martensitic transitions being Ms = 345 K, Mf = 325 K, As = 332 K, and Af = 347 K and the coefficient of the dependence of the transition temperature on mechanical stress being β = 0.12 K/MPa. The experimentally measured value of the adiabatic temperature change under the action of mechanical stress (ECE) in the amorphous state of the alloy at room temperature (Tr = 300 K) was ΔT = −2 K, with a relative elongation of ε = 1.5% and a mechanical stress of σ = 243 MPa. For crystalline samples of Ti2NiCu alloy ribbons, the ECE is maximum near the completion temperature of the reverse thermoelastic martensitic transformation Af, and its value was 21 K and 7 K under cyclic mechanical loads of 300 and 100 MPa, respectively. It is shown that the ECE value does not depend on the frequency of external action in the range from 0 to 50 Hz. The specific power of the rapidly quenched ribbon was evaluated as a converter of thermal energy at an external mechanical stress of 100 MPa; its value was 175 W/g at a frequency of 50 Hz. The thermodynamic model based on the Landau theory of phase transitions well explains the properties of both amorphous ribbons (reverse ECE) and alloy ribbons with EPF (direct ECE).

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 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.

Toward efficient elastocaloric systems: Predicting material thermal properties with high fidelity

A critical need to accurately model thermal behaviors of materials that exhibit strong elastocaloric effects, including predicting the effects themselves at varying stresses and temperatures, has been addressed using a simple and versatile physics-based approach. The key factor leading to the high precision is approximating the underlying elastic phase transition as a smooth modification of lattice entropy between coexisting phases. Once the phase transformation entropy is modeled to match experimentally measured strain as a function of temperature and applied stress, estimating the heat capacity, entropy, and isothermal entropy and adiabatic temperature changes in temperature-stress coordinates becomes straightforward. This approach provides insight into how thermal properties of elastocaloric materials vary through the transition based on strain measurements that are simple to perform and interpret. In addition to aiding in the rapid evaluation of new and existing elastocaloric materials, this advance is expected to prove invaluable for accurate heat transfer modeling aimed at designing efficient regenerative elastocaloric cooling devices.

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.

Large elastocaloric effect around room temperature in directionally solidified Co49Fe3V33Ga15 superelastic alloy

Elastocaloric refrigeration based on the elastocaloric effect (eCE) is a promising solid-state replacement to the conventional vapor-compression one due to the environment-friendly and energy-efficient advantages. Here, a Heusler-type 〈111〉-oriented Co49Fe3V33Ga15 superelastic alloy fabricated by the directional solidification method is designed showing large eCE around room temperature. Large adiabatic temperature change of 11.0 K upon fast loading is obtained at 290 K when the uniaxial pressure is perpendicular to the solidification direction. Moreover, the cycle stability of textured alloy is remarkably improved with respect to untextured counterpart. This work may inspire the discovery of newly promising elastocaloric materials for solid-state refrigeration.

Alloying-assisted precipitation strengthening of Ti50Ni15Pd25Cu10 shape memory alloy

The precipitation strengthening effect of Ti50Ni15Pd25Cu10 shape memory alloy is effectively promoted by adding a small amount of vanadium. Cu-rich TiPdCu precipitates formed when Ti50-xNi15Pd25Cu10Vx alloys were aged at 573 K for 1 h. The shape memory effect, the pseudoelasticity, and the elastocaloric effect were effectively improved after precipitation strengthening.