Low Thermal Hysteresis Research Articles

Metal- and Alloy-Based Core–Shell Particles in Nitrate Senary Salt with Low Thermal Hysteresis for Solar Thermal Energy Storage

Metal- and Alloy-Based Core–Shell Particles in Nitrate Senary Salt with Low Thermal Hysteresis for Solar Thermal Energy Storage

Occurrence of the R-phase with increased stability induced by low temperature precipitate-free aging in a Ni50.9Ti49.1 alloy

The R-phase transformation presents low thermal hysteresis, high stability against thermal cycling and ultrahigh internal friction (IF). However, a clear explanation for the occurrence of the R-phase after low temperature aging and systematic characterization of the condition are still lacking. In this study, the evolution of the phase transformation behaviors and IF values after aging at 250 °C for different times are investigated in a Ni50.9Ti49.1 alloy. Direct experimental evidence for the microstructure evolution of the B2 phase and the corresponding R-phase is provided utilizing in-situ transmission electron microscopy (TEM) techniques, together with geometric phase analysis (GPA). The reason for the occurrence of a nanodomain-structured R-phase after low temperature precipitate-free aging and the mechanism of ultrahigh intrinsic IF are illustrated. The results show that Ni segregation indicated by the localized strain fields is responsible for the formation of the R-phase after low temperature aging. Longer aging time causes larger element heterogeneity in the matrix, as a result, a wider existing temperature window for the R-phase. The ultrahigh intrinsic IF plateaus (IFInt = 0.120 ∼ 0.183) found in NiTi shape memory alloys (SMAs) are predominantly determined by the volume fraction of nanodomain boundaries. These findings provide basic insights into the R-phase formation mechanism and provide a simple way to adjust ultrahigh IF performance suitable for different application scenarios.

Accelerated design for magnetocaloric performance in Mn-Fe-P-Si compounds using machine learning

• An effective method for predicting the magnetocaloric performance of Mn-Fe-P-Si alloys using machine learning is proposed. • Curie temperature, thermal hysteresis, and magnetic entropy change as a function of compositions are clearly displayed. • The composition window suitable for room temperature magnetic refrigeration is optimized to accelerate the alloy design. Magnetocaloric performance is of vital importance for Mn-Fe-P-Si alloys. However, when processes and compositions are considered, designing alloys with large magnetic entropy changes (Δ S m ), low thermal hysteresis (Δ T hys ), and Curie temperatures ( T C ) around room temperature become relatively complicated. In this study, we adopt machine learning methods to predict the magnetocaloric performance of Mn-Fe-P-Si compounds for the first time. To achieve this goal, 503, 465, and 660 data points for datasets with T C , Δ T hys , and Δ S m are collected, respectively. The collected datasets contain parameters of compositions, preparations, heat treatment, and magnetic field changes. We search for the optimal configuration using various methods and also compare their mean squared errors (MSE) and allowable errors. Evaluation results show that the performance of neural networks (NNs) is better than other methods. Therefore, we select NN to explore the T C , Δ T hys , and Δ S m values as a function of Mn, Si, metal/non-metal ratios, and B (Boron). We also propose to use the composition window with excellent magnetocaloric performance. These results not only help us gain deep insights into Mn-Fe-P-Si alloys but also accelerate the design process of alloys suitable for magnetocaloric materials. This work has the potential to solve the challenges and boost the research of Mn-Fe-P-Si alloys.

Martensite transformation behavior and magnetocaloric effect in annealed Ni-Co-Mn-Sn microwires

Effect of annealing on martensite transformation (MT) and magnetocaloric effect (MCE) in a Ni41.3Co6.3Mn42.4Sn10.0 microwire was investigated. After annealing at temperatures 723–1173 K, the MT temperatures and Curie points shifted to higher range; meanwhile, the thermal hysteresis (ΔThys) decreased. However, partial transition arrest appeared when annealed at temperatures > 1073 K, leading to decreased magnetization difference (ΔM) between martensite and austenite phases. The maxima ΔM and minima ΔThys were produced at an annealing temperature 1023 K. Consequently, a large magnetic entropy change (ΔSMmax) 20.1 J/kg·K, wide working temperature span (ΔTFWHM) 20 K and thus high effective refrigeration capacity (RCeff) 197 J/kg were obtained under a magnetic field 5.0 T after annealing at 1023 K for 1 h. These facts make Ni-Co-Mn-Sn microwires promising for miniature refrigeration devices due to their high specific surface area, low thermal hysteresis and markedly reduced annealing temperature and time.

Effects of Co and Si co-doping on magnetostructural transformation and magnetocaloric effect in Ni-Mn-Sn based alloys

The remarkable magnetocaloric effect demonstrated in Ni-Mn-based multi-functional alloys benefits a lot from large magnetization difference ΔM and low thermal hysteresis ΔHhys upon the magnetostructural transformation. Here, we present the effective manipulation of the magnetostructural transformation as well as the related magnetocaloric effect through simultaneously introducing Co and Si to ternary Ni-Mn-Sn alloys. Such co-doping method allows not only large magnetization difference but also low thermal hysteresis, yielding giant inverse magnetocaloric effect in a Ni39Co9Mn42Sn9Si1 alloy. Under the magnetic field change of 5T, the field-induced entropy change ΔSM up to 23.5 Jkg−1 K−1 and the reversible ΔSM of 23.4 Jkg−1 K−1 are obtained. Moreover, giant refrigeration capacity up to 402 Jkg−1 is also achieved, being much higher than those reported previously. Furthermore, large field-induced adiabatic temperature change ΔTad up to −4.0 K and reversible ΔTad of −1.8 K are demonstrated through the direct measurements under a low magnetic field change of 1.5 T. Thus, multi-component alloying could be employed as an effective route towards the design of high-performance Heusler-type magnetocaloric materials.

Large Low-Field Reversible Magnetocaloric Effect in Itinerant-Electron Hf1-xTaxFe2 Alloys.

First-order isostructural magnetoelastic transition with large magnetization difference and controllable thermal hysteresis are highly desirable in the development of high-performance magnetocaloric materials used for energy-efficient and environmental-friendly magnetic refrigeration. Here, we demonstrate large magnetocaloric effect covering the temperature range from 325 K to 245 K in Laves phase Hf1−xTaxFe2 (x = 0.13, 0.14, 0.15, 0.16) alloys undergoing the magnetoelastic transition from antiferromagnetic (AFM) state to ferromagnetic (FM) state on decreasing the temperature. It is shown that with the increase of Ta content, the nature of AFM to FM transition is gradually changed from second-order to first-order. Based on the direct measurements, large reversible adiabatic temperature change (ΔTad) values of 2.7 K and 3.4 K have been achieved under a low magnetic field change of 1.5 T in the Hf0.85Ta0.15Fe2 and Hf0.84Ta0.16Fe2 alloys with the first-order magnetoelastic transition, respectively. Such remarkable magnetocaloric response is attributed to the rather low thermal hysteresis upon the transition as these two alloys are close to intermediate composition point of second-order transition converting to first-order transition.

Enhanced Refrigeration Capacity of Rare-Earth-Free Ni-Co-Mn-In-Si Heusler Alloys for Magnetic Refrigerants

NiMn-based Heusler alloy-based solid-state refrigeration technology has received great attention in the field of magnetic refrigeration due to their low energy consumption, environmental friendliness, high magnetization difference (ΔM), low thermal hysteresis (ΔThys) across the magneto-structural transformation, and giant magnetocaloric properties at the low magnetic field. We report the promising rare-earth-free magnetic refrigerant material of Ni45Co5Mn37In12Si1 prepared by arc melting followed by heat-treatment with an inverse magnetocaloric effect and notable inverse ΔSM of 8.6 J kg−1 K−1 around 241 K. Moreover, the large refrigeration capacity (RC) of 462 J kg−1 with a wide operating temperature of ∼53.8 K is obtained for sample thus annealed for 10 h, which is relatively comparable with rare-earth-based high-performance Gd5Si2Ge2 materials.

Giant magnetoresistance, magnetostrain and magnetocaloric effects in a Cu-doped-textured Ni45Co5Mn36In13.2Cu0.8 polycrystalline alloy

Ni–Mn–Z (Z = In, Sn, and, Sb) metamagnetic shape memory alloys exhibit plenty of state-of-the-art magnetoresponsive effects owing to the magnetic-field-induced reversible martensitic transformation. For this compound, achieving high magnetization difference, large transformation entropy change, strong field dependence of transformation temperature, and low thermal hysteresis is essential to obtain significant magnetoresponsive functional properties. In this work, starting from the Ni45Co5Mn36In14 alloy, the substitution of Cu for In is introduced to optimize these properties simultaneously, giving rise to the substantial improvement in the magnetoresponsive effects. By composition design, a second-phase freed Ni45Co5Mn36In13.2Cu0.8 alloy with the phase temperature just below room temperature was selected. Using the directionally solidified technique, a strong<001>-textured sample is prepared to enhance magnetoresponsive behaviors. Measurements show that the reversible magnetoresistance and magnetic-field-induced strain of the prepared sample reach −79% and 0.24%, respectively. Moreover, a maximum isothermal magnetic entropy change of 16.0 J kg−1 K−1 and the maximum adiabatic temperature change of −3.4 K are measured under a field change of 1.5 T, showing excellent low-field magnetocaloric response. The work is expected to supply a prototype alloy of NiMn-based alloy to promote the development of magnetic shape memory alloy.

NiTiHf shape memory alloys as phase change thermal storage materials

Motivated by the recent advancements demonstrating the effectiveness of NiTi shape memory alloys (SMAs) as high figure of merit (FOM) phase change materials (PCMs) for thermal management and storage, NiTiHf SMAs were explored as candidate solid-solid PCMs with high temperature capability. Differential scanning calorimetry and Archimedes’ method were used to determine the transformation temperatures, thermal hysteresis, enthalpy of transformation, and density of several different NiTiHf SMAs with varying compositions. Ni50.3Ti29.7Hf20 (at. %) demonstrated a high transformation enthalpy of 32.5 J/g, a relatively low thermal hysteresis of 31°C and a thermal conductivity of 11.19 Wm−1K−1 in the austenite phase. In general, NiTiHf SMAs exhibited FOM values an order of magnitude higher than traditional PCMs and up to about 120 % higher than the FOM value measured in binary NiTi SMAs. The clear trends relating transformation temperatures, transformation enthalpy, and thermal hysteresis to composition presented here provide for tunability of NiTiHf SMAs to specific thermal energy storage applications through composition control. High FOM values combined with transformation temperatures surpassing 500°C allows NiTiHf alloys to populate previously empty regions of FOM vs. transformation temperature property space for high FOM PCMs.

Optical Forces on an Oscillating Dipole Near VO2 Phase Transition

We investigate optical forces on oscillating dipoles close to a phase change vanadium dioxide (VO2) film, which exhibits a metal-insulator transition around 340 K and low thermal hysteresis. This configuration emulates the interaction between an illuminated nanosphere and an interface and we employ a classical description to capture its important aspects. We consider both electric and magnetic dipoles for two different configurations, namely with the dipole moments parallel and perpendicular to the VO2 film. By using Bruggeman theory to describe the effective optical response of the material, we show that the thermal hysteresis present in the VO2 transition clearly shows up in the behavior of optical forces. In the near-field regime, the force on both dipoles can change from attractive to repulsive just by heating (or cooling) the film for a selected frequency range. We also verified that the optical forces are comparable to the Casimir-Polder force in a similar system, revealing the possibility of modulating or even changing the sign of the resultant force on an illuminated nano-object due to the presence of a thermochromic material. We hope that this work contributes to set the grounds for alternative approaches to control light-matter interactions using phase-change materials.

Microstructural characterization and functional performance of Ni54Mn25Ga21-xDyx high-temperature shape memory alloys

The present study investigated the influences of Dy-addition on the microstructural characterization, functional behaviour and deformation mechanisms in high-temperature Ni54Mn25Ga21 alloys. The results indicated that adequate Dy-addition contributed to a desirable trade-off among compressive strength, ductility and functional performance. Ni54Mn25Ga20.9Dy0.1 alloy showed the highest shape memory recoverable strain due to the improvement of mechanical properties and formation of small Dy-rich precipitates. Meanwhile, an obvious pseudoelasticity was observed over a wide temperature range with a maximum recoverable strain of 3.74% at 320°C in this alloy. All the Dy-containing alloys exhibited low thermal hysteresis. However, it was revealed that an abnormal relationship between thermal hysteresis and middle eigenvalue existed for the investigated alloys with a lattice transition from cubic to tetragonal.

Experimentally correlating thermal hysteresis and phase compatibility in multifunctional Heusler alloys

Thermal hysteresis is recognized as one of the main drawbacks for cyclical applications of magnetocaloric and ferromagnetic shape memory materials with first-order transformations. As such, the challenge is to develop strategies that improve the compatibility between the phases involved in the transitions and study its influence on thermal hysteresis. With this purpose, we explore the thermal, structural, and magnetic properties of the ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{\mathrm{Ga}}_{0.84}{\mathrm{Al}}_{0.16}$ Heusler alloys. The alloys present a thermal hysteresis reduction of \ensuremath{\sim}60% when the Cu content in the compound varies from $x=0.10$ to $x=0.25$, with a minimum hysteresis width of 6 K being achieved. We applied the geometric nonlinear theory of martensite to address the phase compatibility, quantified by the parameter ${\ensuremath{\lambda}}_{2}$, the middle eigenvalue of the transformation stretch tensor, and found that the minimum of hysteresis is associated with a better crystallographic compatibility (${\ensuremath{\lambda}}_{2}$ closer to 1) between the austenite and martensite phases. In addition, we show that the valleylike properties of hysteresis found in the ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{\mathrm{Ga}}_{0.84}{\mathrm{Al}}_{0.16}$ compounds is present in several other alloys in the literature. These results provide pathways to understand as well as to master the phase compatibility and ultimately achieve a low thermal hysteresis in multifunctional Heusler alloys.

Effect of Cu and B Co-doping on magnetocaloric effect, phase transition, and mechanical properties of Mn1.05Fe0.9P0.5-xSi0.5Cu0.10Bx alloys

With large entropy changes and flexible preparation processes, (Mn, Fe)2(P, Si) alloys have attracted wide interest from researchers for magnetic refrigeration. Cu doping can compensate for the mechanical properties, but will increase thermal hysteresis (ΔThys) and decrease the Curie temperature (TC) of (Mn, Fe)2(P, Si) alloys. To tune the TC to room temperature while maintaining low thermal hysteresis and good mechanical properties, Cu-B co-doping is applied to (Mn, Fe)2(P, Si) alloys. The results demonstrated that as the amount of B increases in Mn1.05Fe0.9P0.5-xSi0.5Cu0.10Bx alloys, the TC continuously increases from 261 K to 344 K, and the ΔThys decreases by 76%. Contour plots of XRD patterns show the shifts in Bragg angles near the Curie temperature, which are ascribed to the increase in the lattice parameters during phase transitions, leading to high internal stress. After long-term annealing, Cu tends to segregate at the grain boundaries to act as a buffer between the Fe2P-type main phase. Therefore, stress from lattice deformation during first-order phase transitions can be absorbed. This study presents a new technical route to obtain magnetic refrigeration materials with high magnetocaloric effects and good mechanical properties by co-doping Cu and B, which is instructive for engineering applications.

Combinatorial Exploration and Mapping of Phase Transformation in a Ni-Ti-Co Thin Film Library.

Combinatorial synthesis and high-throughput characterization of a Ni-Ti-Co thin film materials library are reported for exploration of reversible martensitic transformation. The library was prepared by magnetron co-sputtering, annealed in vacuum at 500 °C without atmospheric exposure, and evaluated for shape memory behavior as an indicator of transformation. Composition, structure, and transformation behavior of the 177 pads in the library were characterized using high-throughput wavelength dispersive spectroscopy (WDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and four-point probe temperature-dependent resistance (R(T)) measurements. A new, expanded composition space having phase transformation with low thermal hysteresis and Co > 10 at. % is found. Unsupervised machine learning methods of hierarchical clustering were employed to streamline data processing of the large XRD and XPS data sets. Through cluster analysis of XRD data, we identified and mapped the constituent structural phases. Composition-structure-property maps for the ternary system are made to correlate the functional properties to the local microstructure and composition of the Ni-Ti-Co thin film library.

Large refrigeration capacity in a Ni48Co1Mn37In14 polycrystalline alloy with low thermal hysteresis

For Ni–Mn–In based alloys, simultaneously achieving large magnetic field-induced transformation temperature shift and low thermal hysteresis is of vital significance to obtain significant magnetocaloric properties. In this work, we employ low content Co doping to tune the magnetostructural transformation parameters and demonstrate large inverse magnetocaloric effect in a Ni48Co1Mn37In14 alloy. It is shown that 1% Co doping confers a strong magnetic field dependence of transformation temperature, i.e., 7.2 KT−1, giving rise to a wide refrigeration temperature window of 34 K under the magnetic field change of 5 T. Together with relatively low thermal hysteresis, i.e., ~8 K, giant effective refrigeration capacity up to 284 Jkg−1 is achieved under the magnetic field change of 5T. The present work is expected to offer some instructions for the design of Ni–Mn-based alloys with excellent magnetocaloric properties.

Effect of Hf solute addition on the phase transformation behavior and hardness of a Ni-rich NiTi alloy

Hf substituted NiTi alloys are crucial for high temperature shape memory applications owing to their martensitic phase transformation temperatures around 100°C. For further high temperature applications above this limit, a balanced combination of high phase transformation temperatures, high strength and low thermal hysteresis is the foremost criterion. Here, we show that substitution of an array of Hf concentrations (5–25 at.%) to Ni50.3Ti49.7 alloy leads to a wide range of phase transformation temperatures from sub-zero to 280°C. Our studies establish complete solid solution solubility of Hf in the Ni50.3Ti49.7 alloy up to 25 at.% Hf. As a result, the hardness Ni50.3Ti49.7 alloy increases linearly with Hf concentration on account of solid solution strengthening effect. We further show that the Ni50.3Ti29.7Hf20 alloy exhibits least thermal hysteresis combined with high phase transformation temperatures and hardness amongst the compositions investigated. Our study paves the way for designing Ni-rich NiTiHf high temperature shape memory alloys, with operating temperatures up to 250°C and thermal hysteresis as low as 30°C.

Effect of Al substitution on the magnetocaloric properties of Ni-Co-Mn-Sn multifunctional alloys

Ni-Mn-based metamagnetic shape memory alloys have been extensively studied due to their multifunctional properties including magnetocaloric effect (MCE), magnetoresistance effect, and magnetic-field-induced strain. However, the large intrinsic thermal hysteresis of these alloys sets a limit on further development for practical applications. Here, with a few atomic percent Al substitution, we greatly reduced the thermal hysteresis and transformation temperature interval while maintaining the large magnetization difference (ΔM) between austenite and martensite. The simultaneous achievement of a large ΔM and low thermal hysteresis leads to a remarkable enhancement in MCE upon Al substitution, and a maximum magnetic entropy change of 31.6 J/kg K is achieved under a field of 5 T in Ni39Co11Mn40Sn8Al2. Furthermore, our in situ high-energy X-ray diffraction experiments show that the Ni39Co11Mn40Sn8Al2 has good geometric compatibility between austenite and martensite, which accounts for the reduced thermal hysteresis in this alloy. This study is instructive for the development of high-performance magnetocaloric materials in the metamagnetic shape memory alloys.

Optimizing the Caloric Properties of Cu-Doped Ni-Mn-Ga Alloys.

With the purpose to optimize the functional properties of Heusler alloys for their use in solid-state refrigeration, the characteristics of the martensitic and magnetic transitions undergone by Ni50Mn25−xGa25Cux (x = 3–11) alloys have been studied. The results reveal that, for a Cu content of x = 5.5–7.5, a magnetostructural transition between paramagnetic austenite and ferromagnetic martensite takes place. In such a case, magnetic field and stress act in the same sense, lowering the critical combined fields to induce the transformation; moreover, magnetocaloric and elastocaloric effects are both direct, suggesting the use of combined fields to improve the overall refrigeration capacity of the alloy. Within this range of compositions, the measured transformation entropy is increased owing to the magnetic contribution to entropy, showing a maximum at composition x = 6, in which the magnetization jump at the transformation is the largest of the set. At the same time, the temperature hysteresis of the transformation displays a minimum at x = 6, attributed to the optimal lattice compatibility between austenite and martensite. We show that, among this system, the optimal caloric performance is found for the x = 6 composition, which displays high isothermal entropy changes (−36 J·kg−1·K−1 under 5 T and −8.5 J·kg−1·K−1 under 50 MPa), suitable working temperature (300 K), and low thermal hysteresis (3 K).

Highly Durable and Thermally Conductive Shell-Coated Phase-Change Capsule as a Thermal Energy Battery.

Robust and thermally conductive phase-change capsules (PCCs) can be effectively used as dispersoids for heat transfer fluids (HTFs) to utilize waste heat. Here, we demonstrate PCCs encapsulated with a cross-linked poly(2-hydroxyethyl methacrylate) shell that showed high durability and low thermal hysteresis for effective heat uptake and release. The circulation system was manufactured by mimicking the 4th Generation District Heating (4GDH) system to confirm the heat delivery efficiencies of PCC-dispersed slurries (PCSs) as the HTFs. The enthalpy change of water after it received heat from the PCS improved by up to 41.1% on increasing the amount of PCCs in the PCS. Furthermore, a high PCC recovery of 92 wt % was achieved after 1500 cycles, which accompanied a phase transition. The PCC developed by us can thus enable effective storage/delivery of waste heat-driven energy for zero-energy buildings and a 4GDH system, as well as thermal management of electronics.

Microstructural Characterization, Functional Behavior and Deformation Mechanism of Ni&amp;gt;sub&amp;gt;54Mn &lt;sub&gt;25&lt;/sub&gt;Ga &lt;sub&gt;21-x&lt;/sub&gt;Dy &lt;sub&gt;x&lt;/sub&gt; High Temperature Shape Memory Alloys with Low Thermal Hysteresis

Potential applications at elevated temperatures require shape memory alloys (SMAs) to possess high transformation temperature, excellent shape recovery ability and thermal/functional stability. The present study investigated the influences of Dy addition on the microstructural characterization, functional behavior and possible deformation mechanisms in high temperature Ni54Mn25Ga21 SMAs. The results indicated that adequate Dy addition contributed to a desirable tradeoff among compressive strength, ductility and functional performance. Ni54Mn25Ga20.9Dy0.1 alloy showed the highest shape memory recoverable strain due to the improvement of mechanical properties and formation of small Dy-rich precipitates. Simultaneously, an obvious pseudoelasticity was observed over a wide temperature range with a maximum recoverable strain of 3.74% at 320°C in this alloy. All the Dy-containing alloys exhibited high thermal cyclic stability and quite low thermal hysteresis. However, it was revealed that a complicated and abnormal relationship between thermal hysteresis and the middle eigenvalue λ2 existed for the investigated alloys with a lattice transition from cubic to tetragonal. Calculated results based on energy minimization theory revealed that both the transformation strain and critical stress for inducing martensitic transformation varied with crystallographic orientations. The detwinning of pre-existing (112) compound twins and formation of (112) deformation twins were the dominant deformation mechanisms of martensite, which were highly compatible with the macroscopical recoverable strain. The present study provided valuable insights for developing high-performance multifunctional shape memory alloys for high temperature applications.