Elastocaloric Effect Research Articles

Elastocaloric, barocaloric and magnetocaloric effects in spin crossover polymer composite films

Giant barocaloric effects were recently reported for spin-crossover materials. The volume change in these materials suggests that the transition can be influenced by uniaxial stress, and give rise to giant elastocaloric properties. However, no measurements of the elastocaloric properties in these compounds have been reported so far. Here, we demonstrated the existence of elastocaloric effects associated with the spin-crossover transition. We dissolved particles of ([Fe(L)2](BF4)2, [L=2,6di(pyrazol-1-yl)pyridine]) into a polymeric matrix. We showed that the application of tensile uniaxial stress to a composite film resulted in a significant elastocaloric effect. The elastocaloric effect in this compound required lower applied stress than for other prototype elastocaloric materials. Additionally, this phenomenon occurred for low values of strain, leading to coefficient of performance of the material being one order of magnitude larger than that of other elastocaloric materials. We believe that spin-crossover materials are a good alternative to be implemented in eco-friendly refrigerators based on elastocaloric effects.

Accelerated learning and co-optimization of elastocaloric effect and stress hysteresis of elastocaloric alloys

Accelerated learning and co-optimization of elastocaloric effect and stress hysteresis of elastocaloric alloys

Unveiling the enhancing mechanism of cyclic stability in Tb doped Ni-Mn-Sn Heusler alloys

Rare-earth (RE) doping has been demonstrated as a feasible approach to improve the cyclic performance of Ni-Mn-based Heusler alloys, but the current demonstration of underlying mechanism is simply ascribed to strengthening of the grain boundary cohesion. In this work, the effects brought by RE doping on microstructure, stress induced martensitic transformation behavior and cyclic stability of Ni-Mn-based alloys were systematically investigated. By Tb doping, a stable adiabatic temperature change (|ΔTad|) of ∼ 5.5 K over 1000 cycles with no significant degradation was obtained in (Ni43Mn47Sn10)99.5Tb0.5. (1) Through the in-situ digital image correlation strain measurement and in-situ SEM observation upon loading process, it revealed a multipoint nucleation of the martensitic transformation across the specimen arising from the intergranular NiSnTb secondary phase as nucleate sites, which weakens the strain concentration and suppresses the crack tendency. (2) The multipoint nucleation promotes the transformation volume fraction, making the large |ΔTad| could be driven by a small transformation strain (Δεtr) and (Ni43Mn47Sn10)99.5Tb0.5 yields a |ΔTad/Δεtr| up to 8.7 K %−1. Such reduction in applied strain further alleviates the extension of the cracks. Both the two factors brought by Tb doping in (Ni43Mn47Sn10)99.5Tb0.5 give rise to the enhancement in cyclic stability of the large elastocaloric effect.

Data-driven high elastocaloric NiMn-based shape memory alloy optimization with machine learning

Shape memory alloys (SMAs) have the potential to improve the efficiency of solid-state refrigeration technology through coupled excitation of multiple thermal effects. Aiming to achieve high elastocaloric NiMn-based SMAs, this paper utilized machine learning to predict the adiabatic temperature change and first-principle calculations to elucidate the mechanism. Based on the optimal XGB Regressor model, the Ni50Mn33Ti17 SMA through directional solidification is predicted to have the highest adiabatic temperature change of 10 K (test temperature = 298 K, applied stress = 300 MPa). In addition, the volume change ratio after martensitic transformation reaches 2.375 % with first-principles calculations, which is expected to provide sufficient entropy and thus obtain an excellent elastocaloric effect. This study provides an available pathway to design and optimize the elastocaloric property of NiMn-based SMAs.

Cu- and Fe-Doped Ni-Mn-Sn Shape Memory Alloys with Enhanced Mechanical and Magnetocaloric Properties.

Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) are multifunctional materials that are promising for solid-state refrigeration applications based on the magnetocaloric effect (MCE) and elastocaloric effect (eCE). However, a combination of excellent multi-caloric properties, suitable operating temperatures, and mechanical properties cannot be well achieved in these materials, posing a challenge for their practical application. In this work, we systematically study the phase transformations and magnetic properties of Ni50-xMn38Sn12Cux (x = 0, 2, 3, 4, 5, and 6) and Ni50-yMn38Sn12Fey (y = 0, 1, 2, 3, 4, and 5) alloys, and the magnetic-structural phase diagrams of these alloy systems are reported. The influences of the fourth-element doping on the phase transitions and magnetic properties of the alloys are elucidated by first-principles calculations. This work demonstrates that the fourth-element doping of Ni-Mn-Sn-based FSMA is effective in developing multicaloric refrigerants for practical solid-state refrigeration.

Giant caloric effects in spin-chain materials

The giant electro- and elastocaloric effects in spin-chain materials are predicted. The theory is based on the exact quantum mechanical solution of the problem. It is shown that the giant jumps in the entropy and the temperature caused by the caloric effect are weakly affected by the initial temperature. The effect can be used for the cooling of new quantum devices (like systems of qubits in quantum computers). On the other hand, since large changes are predicted in the narrow neighborhood of the critical point, the predicted effect can be used in ultrasensitive electric and stress sensors for modern microelectronics. Published by the American Physical Society 2024

Enhancing elastocaloric performance: Ti-doped Co–V-Ga bulk polycrystalline alloys with minimal stress hysteresis

Currently, practical applications of shape memory alloy (SMA) solid elastocaloric refrigeration materials are limited by low elastocaloric effect (eCE), high applied stress, and large stress hysteresis (Δσhys). Here, we introduce a composition design strategy using Ti-doped Co–V-Ga SMAs to address these challenges. We combine first-principles calculations and experiments to verify this strategy. Our results show that the lattice distortion caused by the significant difference in atomic radius after Ti doping produces a solid solution strengthening effect inside the alloy, which significantly improves the superelasticity of the alloy, delays the plastic deformation of the austenite phase, and the volume fraction of martensitic transformation increases significantly. The newly developed Co51.7V31.3Ga16Ti1 bulk polycrystalline alloy exhibits a remarkable adiabatic temperature change (ΔTad) of −10 K at room temperature under a low stress of 400 MPa, a minimum Δσhys of 18 MPa, and a high coefficient of performance COPmat of 31.9. Importantly, the 100-cycle loading-unloading test at 350 MPa is done, and it reveals that the ΔTad for the Ti0 alloy was only 3.9 K, while it reached 6.2 K for the Ti1 alloy, marking a noteworthy 59 % performance enhancement. From the simplicity of the fabrication process to the comprehensive performance of the material, it exhibits a promising advantage for practical cooling applications This study presents a feasible design strategy for large-scale production of high-performance bulk polycrystalline alloys with high eCE, low stress, and Δσhys.

Low-fatigue large elastocaloric effect in NiTi shape memory alloy enabled by two-step transition

NiTi shape memory alloys are promising elastocaloric materials owing to their substantial adiabatic temperature change (ΔTad). However, the simultaneous attainment of large ΔTad and low fatigue poses challenges due to the significant hysteresis and severe functional fatigue associated with the autocatalytic avalanche-like martensitic transformation. This study demonstrates a continuous two-step transition in Ni50.8Ti49.2 (at.%), showcasing cyclic-stable superelasticity with large recoverable strain (5.9 %), substantial ΔTad (19.1 K) and high coefficient of performance. In-situ loading analysis indicates a stress-induced continuous transition from the B2 to R and subsequently to B19′. Nanoscale lattice analysis exposes heterogeneous strain network, harboring metastable R phase preceding the B19′ phase. By exploiting differences in critical stress and transformation potential between R and B19′ phases, this study demonstrates the possibilities to synergistically integrate functional performances of different martensitic phases in NiTi into a sequential and continuous two-step transition to provide controlled strain release with unprecedented properties.

Giant elastocaloric effect at low temperatures in TmVO4 and implications for cryogenic cooling

Adiabatic decompression of paraquadrupolar materials has significant potential as a cryogenic cooling technology. We focus on TmVO[Formula: see text], an archetypal material that undergoes a continuous phase transition to a ferroquadrupole-ordered state at 2.15 K. Above the phase transition, each Tm ion contributes an entropy of [Formula: see text] due to the degeneracy of the crystal electric field groundstate. Owing to the large magnetoelastic coupling, which is a prerequisite for a material to undergo a phase transition via the cooperative Jahn-Teller effect, this level splitting, and hence the entropy, can be readily tuned by externally induced strain. Using a dynamic technique in which the strain is rapidly oscillated, we measure the adiabatic elastocaloric response of single-crystal TmVO[Formula: see text], and thus experimentally obtain the entropy landscape as a function of strain and temperature. The measurement confirms the suitability of this class of materials for cryogenic cooling applications and provides insight into the dynamic quadrupole strain susceptibility.

Advanced Design and Manufacturing Approaches for Structures with Enhanced Thermal Management Performance: A Review

AbstractAdvanced design methods and manufacturing techniques are crucial for developing thermal management structures, essential for the efficient operation of complex equipment. This study provides a thorough review of design methodologies and advanced manufacturing technologies for thermal management materials and structures. It identifies key challenges and critically evaluates the integration of innovative design principles, such as biomimicry and topology optimization, into thermal management solutions. The analysis delves into the evolution of design theories and preparation techniques, with a specific focus on modern needs and research directions, particularly highlighting components fabricated using additive manufacturing and their effectiveness in meeting advanced thermal management requirements. Current research focuses on designing structures tailored to various cooling methods, including air‐cooling, liquid‐cooling, heat exchanger cooling, and heat pipe cooling. These designs utilize phase change materials, electrocaloric cooling, and thermoelectric cooling materials to achieve optimal thermal management performance. Additionally, emerging innovations like solid‐liquid mixed heat transfer and the elastocaloric effect are garnering increased interest. Enhancing the design of thermal management structures through rigorous numerical simulations is critical for improving engineering applicability. However, overcoming challenges related to the commercialization and practical utilization of these advanced structures remains a pressing need.

Critical parameters governing elastocaloric effect in polyisoprene rubbers for solid-state cooling

The aim of this work is to study the critical parameters governing the eCe (elastocaloric effect) of poly-isoprene rubber (NR and IR) in use conditions of a cooling device, i.e. under partial cyclic loading. The effect of mechanical cyclic loading parameters (pre-extension ratio, waveform and frequency) on eCe was first studied. It shows that the eCe increases when the mimimum pre-extension ratio is increased and frequency is lowered from 1Hz to 0.001Hz, as it promotes strain-induced crystallization. However, it also leads to a decrease in potential cooling power, from 7 to 0.01 MW/m3 (i.e. 8 kW/kg to 0.01 kW/kg). At intermediate frequency (f ≈ 0.1 Hz), the comparison of square and triangular waveforms demonstrated that the former enables greater temperature variation. This is due to its holding step (at maximum extension ratio), which maximizes crystallization but also promotes stress relaxation, resulting in increased mechanical losses. Consequently, the square and triangular loadings have a COPmat of 12 and 25, with a temperature variation of 4.2K and 3.6K, respectively. Regarding the formulation, rubbers that do not have a great tendency to crystallize such as synthetic polyisoprene rubber seem to have the best COPmat, while to maximize ΔT, the best of our formulations are NR crosslinked with sulfur and having a crosslink density close to 1.5 × 10−4 mol/cm3, which combine large strain induced crystallization and entropic elasticity. This material has a COPmat of about 27 and allows a ΔT≈4K, i.e.performance comparable to that of the best Shape Memory Alloys (at equivalent COPmat).

Highly Efficient Drive System for Elastocaloric Heat Pumps and Cooling Systems

The need for alternative cooling technologies aside from compressor based cooling is growing since more and more refrigerants get regulated. One promising technology is cooling with the elastocaloric effect by using a phase change of elastocaloric materials that induces a temperature change within the material. The crucial point in the commercialization of this technology is the efficiency of the elastocaloric system including elastocaloric material and the drivetrain. Literature often gives values for the efficiency without including the actuator that drives the system although this is necessary to determine the overall total efficiency. In this study, we introduce a highly efficient drive system based on energy recuperation and deduce the efficiency of this concept. The actuator drive consists of an oscillating armature and is driven by reluctance forces. For the characterization of the system, the elastocaloric material is exchanged with preloaded springs. This gives rise to the possibility of measuring the efficiency of the actuator system itself without considering the elastocaloric material. The efficiency of the drive system is determined to be ηA=95.7%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\eta }_{\ ext{A}}=95.7 \\%$$\\end{document}.

The nematic susceptibility of the ferroquadrupolar metal TmAg2 measured via the elastocaloric effect

Elastocaloric measurements of the ferroquadrupolar/nematic rare-earth intermetallic TmAg2 are presented. TmAg2 undergoes a cooperative Jahn-Teller-like ferroquadrupolar phase transition at 5K, in which the Tm3+ ion’s local 4f electronic ground state doublet spontaneously splits and develops an electric quadrupole moment which breaks the rotational symmetry of the tetragonal lattice. The elastocaloric effect, which is the temperature change in the sample induced by adiabatic strains the sample experiences, is sensitive to quadrupolar fluctuations in the paranematic phase which couple to the induced strain. We show that elastocaloric measurements of this material reveal a Curie-Weiss like nematic susceptibility with a Weiss temperature of T* ≈ 2.7K, in agreement with previous elastic constant measurements. Furthermore, we establish that a magnetic field along the c-axis acts as an effective transverse field for the quadrupole moments.

Effect of heat treatment on phase transformation behavior and properties of Ni-Co-Mn-Al-Y shape memory alloy by laser direct energy deposition

Laser direct energy deposition (LDED) of Ni-Co-Mn-Al-Y magnetic shape memory alloys (MSMAs) with high elastocaloric properties has important application prospects in solid-state refrigeration. However, because the microstructure of laser non-equilibrium metallurgy does not have reversible martensitic transformation, further regulating the microstructure of deposited samples through scientific post-heat treatment to obtain better properties is still a top priority. In this work, Ni-Co-Mn-Al-Y alloy samples were prepared by an optimized LDED process, and then the deposited samples were heat-treated with different temperatures. The results showed that the sample subjected to heat treatment with 550 °C × 3.5 h + 1100 °C × 20 h had maximum entropy change of the phase transformation, compressive properties, and elastocaloric effect. The compressive fracture strength was up to 1327 MPa, the maximum compressive strain was up to 26.2%, and an adiabatic temperature change was up to −4.3 K under the condition of rapid unloading. Characterization of the microstructure changes of the alloy under 11 cycles of compression revealed that the deformation mechanism was mainly planar sliding of dislocations in the martensite and dislocation cutting the γ(Y-rich) phase. The alloy prepared by the optimizing LDED and heat treatment process had better cycle stability and preliminary refrigeration capacity.

2D thermo-fluidynamic rotary model of an elastocaloric cooling device: The energy performances

Elastocaloric cooling has been considered a promising solid-state technology for cooling and heat pumping among the alternatives to vapor compression, at room temperature range. The technology is based on elastocaloric effect that is a thermophysical phenomenon occurring in materials like Shape Memory Alloys (SMA). The effect is detectable as a temperature change in the material if adiabatically subjected to a forcing field of mechanical nature. The latter provokes to the materials a stress that can derive from tension, compression, bending, torsion solicitations. As a result, the SMA experiments a structural phase change from austenite to martensite (coupled with heat addition) and temperature rise. Dually when the stress is removed, the SMA releases heat with a temperature decrease. In this paper the SUSSTAIN-EL rotary elastocaloric heat pump has been deeply investigated to test the energy performances while it works on open loop and closed loop, through a 2D numerical model based on the finite element method, for cooling and heating operation modes. The device employs a binary NiTi SMA as elastocaloric refrigerant and air as heat transfer medium. A wide set of working conditions has been considered like variable inlet mass flow rate, rotation frequency and thermal loads. The acquired results demonstrate that, both in open and closed loop, the prototype’s energy performances are promising and highly favourable for the intended macroscale collocation of the device.

Large elastocaloric effect covering a broad temperature window in a composition-graded Ni50Mn31.5Ti18.5 alloy prepared by magnetic field-assisted directional solidification

Elastocaloric effect in shape memory alloys relies on the latent heat associated with stress-induced martensitic transformation, which can be exploited for solid-state cooling applications. However, large stress hysteresis inherent to the first-order transformation greatly restricts the energy conversion efficiency and working temperature window. Here, by utilizing compositional gradient engineering to tailor mechanical hysteresis and microstructure texturing to promote elastocaloric response, a composition-graded Ni50Mn31.5Ti18.5 alloy with <001>A preferred orientation has been fabricated through magnetic field-assisted directional solidification. Owing to the composition segregation induced by a transverse magnetic field applied during solidification, considerable amounts of preexisting martensite domains are embedded in the austenite matrix, which contributes to the reduced critical driving stress and stress hysteresis of martensitic transformation. In combination with large cooling capacity favored by highly preferred orientation, the material's coefficient of performance has been greatly improved. Moreover, a broad refrigeration temperature span of 200 K covering 263 K to 463 K is also realized, with a maximum adiabatic temperature variation of –18.4 K. We attribute the enhanced elastocaloric properties to the synergy of preferred orientation and compositional gradient, which can be developed as an effective route towards performance improvement of elastocaloric materials.

Tension-compression asymmetry in superelasticity of SrNi2P2 single crystals and the influence of low temperatures

ThCr2Si2-type intermetallic compounds are known to exhibit superelasticity associated with structural transitions through lattice collapse and expansion. These transitions occur via the formation and breaking of Si-type bonds, respectively, under uniaxial loading along the [0 0 1] direction. Unlike most ThCr2Si2-type intermetallic compounds, which have either an uncollapsed tetragonal structure or a collapsed tetragonal structure, SrNi2P2 possesses a third type of collapsed structured: a one-third orthorhombic structure, for which one expects the occurrence of unique structural transitions and superelastic behavior. In this study, uniaxial compression and tension tests were conducted on micron-sized SrNi2P2 single crystalline columns at room temperature, 200 K, and 100 K, to investigate the influence of loading direction and temperature on the superelasticity of SrNi2P2. Experimental data and density functional theory calculations revealed the presence of tension-compression asymmetry in the structural transitions and superelasticity, as well as an asymmetry in their temperature dependence, due to the opposite superelastic process associated with compression (forming P-P bonds) and tension (breaking P-P bonds). Additionally, following thermodynamics, the observations suggest that this asymmetric superelasticity could lead to an opposite elastocaloric effect between compression and tension, which could be beneficial potentially in obtaining large temperature changes compared to conventional superelastic solids that show the same elastocaloric effect regardless of loading direction. These results provide an important fundamental insight into the structural transitions, superelasticity processes, and potential elastocaloric effects in SrNi2P2.

Effect of Ni4Ti3 precipitates on the functional properties of NiTi shape memory alloys: A phase field study

Ni4Ti3 precipitates, which generally exist in aged Ni-rich NiTi shape memory alloys (SMAs), can have a profound effect on material properties. However, the fundamental insights into the effects of Ni4Ti3 precipitates on the functional properties, including the superelasticity (SE), elastocaloric effect (eCE), and shape memory effects (SMEs), are not well understood yet, especially those originating from the B2-B19′ martensite transformation (MT). In this work, a phase field model coupling the precipitation of Ni4Ti3 and the B2-B19′ MT is proposed, where the thermo-mechanical coupling effect and grain size effect are considered. The precipitate-dependent SE, eCE, one-way SME (OWSME), and stress-assisted two-way SME (SATWSME) of single-crystal, polycrystalline, and gradient-nanograined NiTi SMAs are simulated. The effects of the precipitate density, grain orientation range (texture), and gradient-distributed precipitate are examined, and the underlying microscopic mechanisms are revealed. The simulation results and new findings not only contribute to a more comprehensive insight into the effect of Ni4Ti3 precipitates on the MT, martensite reorientation, and functional properties of NiTi SMAs but also provide a reference for the development of excellent SMA-based solid refrigerants or SMA smart materials with designable functional properties.

Enhanced Elastocaloric Effects in γ-Graphyne.

The global emphasis on sustainable technologies has become a paramount concern for nations worldwide. Specifically, numerous sustainable methods are being explored as promising alternatives to the well-established vapor-compression technologies in cooling and heating devices. One such avenue gaining traction within the scientific community is the elastocaloric (eC) effect. This phenomenon holds promise for efficient cooling and heating processes without causing environmental harm. Studies carried out at the nanoscale have demonstrated the efficiency of the eC effect, proving to be comparable to that of state-of-the-art macroscopic systems. In this study, we used classical molecular dynamics simulations to investigate the elastocaloric effect for the recently synthesized γ-graphyne. Our analysis goes beyond obtaining changes in eC temperature and the coefficient of performance (COP) for two species of γ-graphyne nanoribbons (armchair and zigzag). We also explore their dependence on various conditions, including whether they are deposited on a substrate or prestrained. Our findings reveal a substantial enhancement in the elastocaloric effect for γ-graphyne nanoribbons when subjected to prestrain, amplifying it by at least 1 order of magnitude. Under certain conditions, the changes in the eC temperature and the COP of the structures reach expressive values as high as 224 K and 14, respectively. We discuss the implications of these results by examining the shape and behavior of the carbon-carbon bond lengths within the structures.

Characterization of the temperature-dependent superelastic and elastocaloric effects of a NiTi tube under compression at 293–330 K

Comprehensive characterizations of the superelastic and elastocaloric effects of NiTi and NiTi-based shape memory alloys (SMA) in the operation temperature region are highly desirable for using them in elastocaloric coolers with a large temperature lift. In this article, we report the superelastic and elastocaloric effects of a commercially available superelastic polycrystalline NiTi SMA tube with an outer diameter of 5 mm and a wall thickness of 1 mm between 293 and 330 K. The NiTi tube sample was subjected to a training of 250 cycles to stabilize its superelastic and elastocaloric effects. We observed that temperature dependencies existed for both superelastic and elastocaloric effects of the NiTi tube, and stress–strain curves differed much between isothermal and adiabatic loading conditions. The largest temperature rise and temperature drop measured at 293 K under an applied strain of 3.66% and a strain rate of 0.1 s−1 during loading and unloading were 21 and 11 K, respectively. The loading conditions (loading function and holding time) also impacted the superelastic effect of the NiTi tube. We identified two major reasons for the irreversibility of the adiabatic temperature change: the hysteresis heat dissipation and the temporary residual strain after unloading, and they affected the cooling performance of the elastocaloric cooler in different ways. We investigated the dependencies of the superelastic and elastocaloric effects on the maximum applied strain and the temperature distribution on the NiTi tube during loading and unloading. The results are beneficial to the modeling of elastocaloric coolers with large temperature lifts.