In the past decade, there has been an increased surge in the research on elastocaloric materials for solid-state refrigerators. The strong coupling between structure and magnetism inspires the discovery of new multi-field driven elastocaloric alloys. This work is devoted to magnetic shape memory alloys suitable for mechanical cooling applications. Some novel characteristics in magnetostructural transition materials other than conventional shape memory alloys are overviewed. From the physical and engineering points of view, we have put forward general strategies to maximize elastocaloric temperature change to increase performance reversibility and to improve mechanical properties. The barocaloric effect as a sister-cooling alternative is also discussed.

Elastocaloric effect for a Co50Ni20Ga30 single crystal has been investigated. A local adiabatic temperature change (ΔT) of − 6 K was observed on the removal of a uniaxial stress of 150 MPa at 291 K. Infrared thermography measurement reveal a correlated response of martensitic bands and temperature mapping. Both elastocaloric effect and superelasticity exhibit a good reversibility in the 100 times of cycling test. The experimentally obtained ΔT value agrees well with the theoretical one by analyzing the temperature dependence of critical stress based on the Clausius-Clapeyron equation.Download high-res image (140KB)Download full-size image

The influence of Cu substitution for Mn on martensitic transformation, superelasticity and associated elastocaloric effect in Ni44Mn45 − xSn11Cux (x = 0–4) magnetic shape memory alloys has been investigated. The transformation temperatures were tuned around room temperature by increasing the Cu content. Ni44Mn41Sn11Cu4 exhibits a giant adiabatic cooling of − 8 K at a small transformation strain of 1.3%, indicating it as a promising candidate material for elastocaloric refrigeration.(a) Steady stress-strain curves cycled for seven times in Ni44Mn41Sn11Cu4 at a low strain rate of 0.03% s− 1. (b) Near adiabatic stress-strain curve of Ni44Mn41Sn11Cu4 at a high strain rate of 3% s− 1. (c) Corresponding temperature evolutions of specimen surface in-situ measured by an infrared camera during adiabatic compression test in (b). (d) Local temperature-time profile of the central position of specimen (white circle), as well as the average temperature-time profile of the entire detected surface extracted from (c).Download high-res image (236KB)Download full-size image

•Martensitic transformation temperatures tuned by Tb addition in Ni-Mn-In-Tb alloys.•A large elastocaloric temperature change of 5.1 K in Ni50Mn34In15.6Tb0.4.•The enhanced compressive strength of 622 MPa in Ni50Mn34In15.6Tb0.4.The influence of partial substitution of Tb for In on the microstructure, martensitic transformation, mechanical properties, and elastocaloric effect of Ni50Mn34In16−xTbx (x = 0, 0.1, 0.3, 0.4, 0.5) alloys have been investigated. Single-phase alloys are obtained for x ≤ 0.3, and Tb-rich secondary phase precipitates distribute along the grain boundaries of the parent phase for x > 0.3. The phase transformation temperatures initially increase with increasing Tb addition, then decrease with more than 0.3 at.% Tb addition. The existence of secondary phase results in the grain refinement thus improves the mechanical properties of Ni-Mn-In-Tb alloys. A large adiabatic temperature change of 5.1 K induced by uniaxial stress application is observed in Ni50Mn34In15.6Tb0.4.

Solid-state caloric cooling is currently under extensive study owing to its great potential to replace the conventional vapor-compression technique. The search for refrigeration materials displaying a unique combination of pronounced caloric effect, low hysteresis and high reversibility on phase transformation, as well as multiferroic behavior is nowadays very active. Here we report a singular Ni50Mn31.5In16Cu2.5 metamagnetic shape memory alloy exhibiting giant adiabatic temperature changes of 13 K upon loading and −10 K upon unloading. This value significantly exceeds any previously reported data of ferroic materials. Simultaneously, a small thermal hysteresis of 3 K and an exceptional phase transformation stability over 105 magnetic field cycles have been achieved by ensuring the compatible kinematic conditions of specific lattice interface. Moreover, we propose a strategy to further reduce hysteretic losses and improve the reversibility of magnetocaloric effect by manipulating transformation paths evoked by magnetic field and stress, and therefore such a multicaloric approach is attractively beneficial for reaching high energetic utilization efficiency.Download high-res image (129KB)Download full-size image

•The formation of La(Fe,Co,Si)13 phase is promoted by the addition of excess La.•Microstructure and magnetic properties of the La1.5Fe12.2-xCo0.8Six (x = 1.0–1.4) alloys were studied in detail.•Effects of impurity phases on the microstructure and magnetic properties were studied.In this work, we have investigated the influence of annealing temperature and Si content on the microstructure and magnetocaloric properties of non-stoichiometric La1.5Fe12.2-xCo0.8Six (x = 1.0, 1.1, 1.2, 1.4) alloys. A high content of La(Fe,Co,Si)13 phase (∼80 vol.%) can be achieved after annealing at 1000 °C for 24 h. The morphology of the 1:13 phase evolves from facet to granule accompanying the aggregation of the α-Fe particles. The Curie temperature increases with increasing annealing temperature and decreases with the increase of nominal Si content. In addition, large entropy change values of 8.4 J/kg K and 8.0 J/kg K at 2 T are obtained for La1.5Fe11.1Co0.8Si1.1 and La1.5Fe11.1Co0.8Si1.2, respectively. The large entropy change, tunable transition temperature and short-time annealing make the currently studied non-stoichiometric La-Fe-Co-Si a promising magnetic cooling material.

•A large transformation strain was obtained in polycrystalline Ni–Mn–In–Co alloy.•Large and reproducible elastocaloric temperature changes at a moderate stress.•Excellent cyclic elastocaloric behavior is ascribed to reproducible transformation.As a generic feature in the application of shape memory alloys (SMAs), superelasticity is largely affected by microstructural variation and functional fatigues under cyclic loading, which limits the service life of shape memory components. In terms of elastocaloric cooling application originated from the superelasticity, it is essential to understand elastocaloric behavior under cyclic loading. Here we report elastocaloric effect of a Ni45Mn36.4In13.6Co5 metamagnetic SMA by cyclically deforming the sample using a compression testing instrument. The application and removal of a moderate stress of ~150 MPa are able to produce a large temperature change of about 3–4 K. No significant degradation of elastocaloric effect is observed after 15 cycles. This is quite different from the previous reported magnetocaloric behavior of Ni−Mn−In−Co alloy under a cycling magnetic field. The excellent cyclic elastocaloric behavior of this magnetic SMA should be attributed to the full reversibility of transformation as well as reproducible stress–strain response in transformation.

This article reviews the up-to-date progress in mechanocaloric effect and materials near ambient temperature. For elastocaloric materials, we focus on directly measured temperature change and its entropy origin in non-magnetic and magnetic shape memory alloys. In terms of barocaloric materials, change in magnetic state, volume and shift of transition temperature due to hydrostatic pressure are systematically compared. We propose advantages and challenges of elastocaloric materials for solid-state cooling. Strategies to enhance elastocaloric and mechanical stability under long-term mechanical cycles are presented. Finally, we conclude with an outlook on the prospect of elastocaloric cooling application.本文综述了室温附近变形诱发固态相变材料及其热效应的最新进展。对弹热材料而言,重点关注形状记忆合金的弹热效应及熵变来源。分别对不同特征(非磁性或磁性,一级相变或弱一级相变)的形状记忆合金体系的驱动应力、弹热温变和工作温度窗口进行了对比分析。对具有压热效应的巨磁热材料,系统对比了等静压力作用下磁状态、体积和相变温度的变化。基于等静压力和磁场驱动相变温度移动方向相反的特点,可以设计复合驱动场来精确调控材料的滞后。评述了弹热制冷的优势、挑战和应对策略。其优势为温变大、温区宽、变形方式多样和成本低;最主要的挑战在于大应变和高速率条件下的循环疲劳问题;基于成分设计的滞后控制、机械稳定性训练是提高材料抗疲劳性能的有效手段。最后,基于欧洲和美国在弹热制冷原型机和系统制冷效率优化设计的最新进展,对固态制冷技术的应用前景进行了展望。

•Glass-forming ability and magnetocaloric properties were studied in FeCrNbYB alloys.•Bulk metallic glasses with diameters up to 5 mm were obtained in the alloy system.•These metallic glasses exhibit TC of 271–367 K and |ΔSMpk| of 0.76–1.05 J/kg K in 1.5 T.The influences of Cr addition on the Curie temperature (TC), glass-forming ability (GFA), and magnetocaloric effect were investigated in FeCrNbYB metallic glasses. It was found that the addition of Cr element slightly decreases the GFA and saturation magnetization, whereas effectively modulates TC. By the method of copper mold casting, bulk metallic glasses (BMGs) with critical diameters up to 5 mm can be obtained in Fe68−xCrxNb4Y6B22 (x = 2–6) alloys. The resulting metallic glasses exhibit TC of 271–367 K and excellent magnetocaloric properties, including magnetic entropy change of 0.76–1.05 J/kg K, and refrigerant capacity of 83–93 J/kg under a low field change of 1.5 T. In addition, they exhibit a wide supercooled liquid region of 116–135 K. The successful synthesis of the FeCrNbYB BMGs with near room-temperature magnetocaloric properties is encouraging for the future development of Fe-based BMGs as a new magnetic refrigerant in magnetic cooling system.

•Microstructure and phases were studied in La2Fe11Si2 alloy annealed for a short time.•A morphology of La(Fe,Si)13 grains surrounded by La5Si3 phase was observed.•Large entropy change and zero magnetic hysteresis were achieved in the bulk sample.A study of the microstructure and magnetocaloric effect in bulk La2Fe11Si2, as an off-stoichiometric NaZn13-type La(Fe,Si)13 composition, was carried out. The microstructure and phase constitution strongly rely upon heat treatment processing, especially on annealing temperature. Upon annealing at 1423 K, a unique morphology containing granular-like La(Fe,Si)13 grains with a high fraction of ~80 vol.%, surrounded by Cr5B3-type La5Si3 phase was observed. A large entropy change of 14.5 J/kg K in 2 T was achieved in this bulk sample after annealing for a relatively short time (e.g. 24 h). In addition, the bulk sample also exhibits pronounced first-order magnetic transition behavior with zero thermal and magnetic hysteresis. The syntheses of bulk La2Fe11Si2 alloy with good magnetocaloric performance by simplified preparation process are encouraging for future development of LaFe-based magnetocaloric alloys as a magnetic refrigerant for magnetic cooling system applications.

La(Fe,Si)13H-based materials are considered to be one of the most promising room-temperature magnetic refrigerants. The intrinsic brittleness and relatively low thermal conductivity in La-Fe-Si-H alloys, however, have severely hindered its preparation, shaping and application. To solve this long-standing problem, in this work we propose a novel approach to fabricate stable La-Fe-Si-H blocks and plates by adding extra α-Fe as a reinforcing phase to enhance mechanical integrity. Much better bending strength compared to that in the stoichiometric composition has been observed in our dual phase La-Fe-Si-H magnetic refrigerants. Such novel Fe-rich plates can be exposed to 105 magnetic field cycles without losing mechanical integrity. In addition, a large and reproducible ΔTad of 5.4 K in 1.93 T and a thermal conductivity of 6 W/mK at room temperature have been obtained.In the dual phase La-Fe-Si-H alloys, materials can be fabricated to the block shape, where the toughening α-Fe guarantees the mechanical integrity and offers significantly enhanced thermal conductivity.

•La(Fe,Si)13 phase directly forms on slow cooling by directional solidification technique.•Large magnetic entropy change of 13.5 J/kg K in 2 T.•Small hysteresis in directionally solidified La-Fe-Si.We have demonstrated that the La(Fe,Si)13 magnetocaloric phase can be directly formed from molten on extremely slow cooling by the employment of directional solidification technique. A large amount of this magnetocaloric phase of about 85% was achieved in the as-solidified state with a cooling rate of 0.005 K/s. A large magnetic entropy change of 13.5 J/kg K under an applied field of 2 T was obtained at 202 K for the LaFe11.6Si1.4 composition without post-annealing processing.