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. 2022 Oct 13;15(20):7123.
doi: 10.3390/ma15207123.

Elastocaloric Properties of Polycrystalline Samples of NiMnGaCu Ferromagnetic Shape Memory Alloy under Compression: Effect of Improvement of Thermoelastic Martensitic Transformation

Francesca Villa  1   2 , Emanuele Bestetti  3 , Roberto Frigerio  3 , Michele Caimi  3 , Corrado Tomasi  4 , Francesca Passaretti  1 , Elena Villa  1
Affiliations

Elastocaloric Properties of Polycrystalline Samples of NiMnGaCu Ferromagnetic Shape Memory Alloy under Compression: Effect of Improvement of Thermoelastic Martensitic Transformation

Francesca Villa et al. Materials (Basel). .

Abstract

Shape memory alloys (SMAs) and ferromagnetic shape memory alloys (FeSMAs) have recently attracted interest for solid state refrigeration applications. Among NiMnGa-based quaternary systems, NiMnGaCu exhibits an interesting giant magnetocaloric effect thanks to the overlapping of the temperatures related to the magnetic transition and the thermoelastic martensitic transformation (TMT); in particular, for compositions with Cu content of approximately 6 at%. In the present work, we investigated the improvement effect of TMT on the total entropy change (ΔS) in the elastocaloric performances of polycrystalline Ni50Mn18.5Cu6.5Ga25 at% alloy samples, just above room temperature. We report an extensive calorimetric and thermomechanical characterization to explore correlations between microstructural properties induced by the selected thermal treatment and elastocaloric response, aiming at providing the basis to develop more efficient materials based on this quaternary system. Both ΔT and ΔS values obtained from mechanical curves at different temperatures and strain recovery tests under fixed load vs. T were considered. Maximum values of ΔS = 55.9 J/KgK and ΔT = 4.5 K were attained with, respectively, a stress of 65 MPa and strain of 4%. The evaluation of the coefficient of performance (COP) was carried out from a cyclic test.

Keywords: NiMnGaCu; elastocaloric effect; ferromagnetic shape memory alloys; mechanical properties; microstructure; thermal analysis.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
Optical microscopy observations for samples A (A) and B (B).
Figure 2
Figure 2
Strain recovery test vs. T under fixed stress and recovery strain vs. stress for samples A (A) and B (B).
Figure 3
Figure 3
Value for ΔS vs. T obtained by discrete integration from strain recovery curves in the heating (top) and cooling (bottom) parts for samples A (A) and B (B).
Figure 4
Figure 4
Value for ΔS vs. strain obtained using discrete integration from stress–strain curves at different temperatures in the loading and unloading stages for samples A and B.
Figure 5
Figure 5
Stress–strain curves at 353 K for COP evaluation.
Figure 6
Figure 6
ΔT range for samples A (A) and B (B) measured by ad hoc prepared thermocouples system.
See this image and copyright information in PMC

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