Elastocaloric switching effect induced by reentrant martensitic transformation

Takumi Odaira,Xiao Xu,Toshihiro Omori,Sheng Xu,Ryosuke Kainuma

doi:10.1063/5.0007753

Abstract

Vapor compression technologies widely used for refrigeration, heating, and air-conditioning have consumed a large fraction of global energy. Efforts have been made to improve the efficiency to save the energy, and to search for new refrigerants to take the place of the ones with high global warming potentials. The solid-state refrigeration using caloric materials are regarded as high-efficiency and environmentally friendly technologies. Among them, the elastocaloric refrigeration using shape memory alloys has been evaluated as the most promising one due to its low device cost and less of a demand for an ambient environment. General caloric materials heat up and cool down when external fields are applied and removed adiabatically (conventional caloric effect), while a few materials show opposite temperature changes (inverse caloric effect). Previously reported shape memory alloys have been found to show either a conventional or an inverse elastocaloric effect by the latent heat during uniaxial-stress-induced martensitic transformation. In this paper, we report a self-regulating functional material whose behavior exhibits an elastocaloric switching effect in Co-Cr-Al-Si Heusler-type shape memory alloys. For a fixed alloy composition, these alloys can change from conventional to inverse elastocaloric effects because of the change in ambient temperature. This unique behavior is caused by the sign reversal of latent heat from conventional to the re-entrant martensitic transformation. The realization of the elastocaloric switching effect can open new possibilities of system design for solid-state refrigeration and temperature sensors.

Highlights

Among all the alternative non-vapor-compression technologies for refrigeration, the elastocaloric refrigeration technique using shape memory alloys (SMAs) has been evaluated as the most promising one owing to its low device cost and flexibility in ambient environment, which is expected to be useful in various applications in different climates
We show the superelastic behavior at RT related to the martensitic transformation on a single-crystal Co55Cr23.5Al11.5Si10 alloy (Sample 1) in Fig. 3(a), where the superelastic strains of eSE 1⁄4 2.5%, 3.8%, and 4.6% beyond the elastic regime were applied
The superelastic and elastocaloric properties were investigated on the Co-Cr-Al-Si alloys showing the unique re-entrant martensitic transformation behavior

Summary

Introduction

Various caloric effects in solid-state materials—the barocaloric, electrocaloric, magnetocaloric, and elastocaloric effects (eCE)4—have been expected to be used in highefficiency and environmentally friendly refrigeration systems as a substitute for the conventional vapor compression refrigeration system. Among all the alternative non-vapor-compression technologies for refrigeration, the elastocaloric refrigeration technique using shape memory alloys (SMAs) has been evaluated as the most promising one owing to its low device cost and flexibility in ambient environment, which is expected to be useful in various applications in different climates. By the martensitic transformation, the temperature of an SMA sample can change when uniaxial stress is applied or removed, even in the absence of heat flow from or to outside. The temperature of an SMA sample can change when uniaxial stress is applied or removed, even in the absence of heat flow from or to outside. As shown, under an adiabatic condition, applying uniaxial stress causes the caloric material to heat up (DTad > 0), whereas it cools down (DTad < 0) when the uniaxial stress is removed. The eCE has been reported in many kinds of SMAs, including Ti-Ni-,11,12 Cu-,4,13,14 Ni-,15–17 Fe-Pd-,18 and Co-Ni-based alloys.

Results

Discussion

Conclusion