Elastocaloric effect in Ni50Fe19Ga27Co4 single crystals

Abstract The elastocaloric effect of the [0 0 1] P and [1 1 1] P orientated (subscript P represents the parent phase) Ni 50 Fe 19 Ga 27 Co 4 (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 Δ T adi 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 A f 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〉 L1 0 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 (|Δ T adi /Δ σ | ≈ 35 K/GPa), wide specific effective temperature window (|Δ T win /Δ σ | ≈ 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 Ni 50 Fe 19 Ga 27 Co 4 single crystal as a potential elastocaloric material.