Energy-efficient and environment-friendly elastocaloric refrigeration, which is a promising replacement of the conventional vapor-compression refrigeration, requires extraordinary elastocaloric properties. Hitherto the largest elastocaloric effect is obtained in small-size films and wires of the prototype NiTi system. Here, we report a colossal elastocaloric effect, well exceeding that of NiTi alloys, in a class of bulk polycrystalline NiMn-based materials designed with the criterion of simultaneously having large volume change across phase transition and good mechanical properties. The reversible adiabatic temperature change reaches a strikingly high value of 31.5 K and the isothermal entropy change is as large as 45 J kg −1 K −1 . The achievement of such a colossal elastocaloric effect in bulk polycrystalline materials should push a significant step forward towards large-scale elastocaloric refrigeration applications. Moreover, our design strategy may inspire the discovery of giant caloric effects in a broad range of ferroelastic materials.
We have studied the barocaloric properties associated with the martensitic transition of a shape memory Heulser alloy Ni50Mn31.5Ti18.5 which is composed of all-d-metal elements. The composition of the sample has been tailored to avoid long range ferromagnetic order in both ausenite and martensite. The lack of ferromagnetism results in a weak magnetic contribution to the total entropy change thereby leading to a large transition entropy change. The combination of such a large entropy change and a relatively large volume change at the martensitic transition gives rise to giant barocaloric properties in this alloy. When compared to other shape memory Heusler alloys, our material exhibits values for adiabatic temperature and isothermal entropy changes significantly larger than values reported so far for this class of materials. Furthermore, our Ni50Mn31.5Ti18.5 also compares favourably to the best state-of-the-art magnetic barocaloric materials.
The rapid development of aerospace, automotive, and energy exploration industries urgently requires hightemperature shape memory alloys (HTSMAs) which are utilized as compact solid-state actuators, sensors, and energy conversion devices at elevated temperatures. However, the currently prevailing Ni−Ti−X (X = Pd, Pt, and Hf) HTSMAs are very expensive owing to the high cost of Pd, Pt, and Hf elements, which greatly limits their widespread applications. Here, we have developed an inexpensive (Ni 50 Mn 35.5 Ti 14.5 ) 99.8 B 0.2 bulk polycrystalline HTSMA with extraordinary high-temperature superelasticity and a giant two-way shape memory effect (TWSME). This alloy exhibits perfect superelasticity with a fully recoverable strain of as high as 7.1% over a wide temperature range from 150 to 280 °C. Furthermore, it shows a giant TWSME with a remarkably high recoverable strain of 6.0%. Both the recoverable strain of superelasticity and the two-way shape memory strain of the present alloy are the highest among the bulk polycrystalline HTSMAs. The theoretical maximum transformation strain was calculated with energy-minimization theory using the crystal structure information of martensite and austenite obtained from in situ synchrotron high-energy X-ray diffraction experiments to help understand the superelastic behavior of the present alloy. Combining the advantages of low cost and easy fabrication, the present bulk polycrystalline (Ni 50 Mn 35.5 Ti 14.5 ) 99.8 B 0.2 alloy shows great potential for high-temperature shape memory applications. This work is instructive for developing cost-effective high-performance HTSMAs.
Fe-Mn-Ga magnetic shape memory alloys can undergo martensitic transformation (MT) from a paramagnetic cubic phase to a ferromagnetic tetragonal phase. The MT is accompanied by a large volume change; yet, these alloys have never been explored for technological applications as negative thermal expansion (NTE) materials. Here, by careful chemical modification, tunable NTE characteristics including wide operating temperature windows (ΔT) and large negative linear coefficients of thermal expansion (αl) have been achieved in Fe44−xMn28Ga28+x (x = 1, 2, and 2.5) alloys. Typically, a giant NTE ΔT of 81 K and αl = −50.2 × 10−6 K−1 were realized in the Fe43Mn28Ga29 alloy upon cooling from 290 K. The relationships between the NTE features, the MT, and the substitution of Ga for Fe were discussed. Furthermore, the Fe-Mn-Ga alloys possess excellent mechanical properties, high electrical conductivity and high thermal conductivity. With these advantages, the Fe-Mn-Ga magnetic shape memory alloys show promising prospects for use as advanced NTE materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.