Elastocaloric effect in Ni50Fe19Ga27Co4 single crystals

The elastocaloric effect of the [0 0 1]P and [1 1 1]P orientated (subscript P represents the parent phase) Ni50Fe19Ga27Co4 (at.%) single crystals exhibiting first-order martensitic transformations have been studied at temperatures of 298-448 K under different compressive stresses. The adiabatic temperature change ΔTadi shows a significant dependence on the crystal orientation. The temperature decrease caused by adiabatic removal of stress 300 MPa reaches to about 9-10 K in a temperature range 328-398 K for [0 0 1]P specimen and 3 K at temperature near Af for [1 1 1]P one. The large elastocaloric effect is essentially attributed to the entropy change during the stress-induced martensitic transformation. The accumulated defect such as the a/2〈1 1 2〉 L10 type dislocation is the main reason for the attenuation of the elastocaloric effect in a fatigue test up to 3000 cycles. Large specific adiabatic temperature (|ΔTadi/Δσ| ≈ 35 K/GPa), wide specific effective temperature window (|ΔTwin/Δσ| ≈ 320 K/GPa) and high coefficient of performance (COP ≈ 14) in a temperature range as wide as 50 K during the unloading process enable the [0 0 1]P orientated Ni50Fe19Ga27Co4 single crystal as a potential elastocaloric material.