Elastocaloric effect in Ni50Fe19Ga27Co4 single crystals

The elastocaloric effect of the [001](P), and [111](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 Delta 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 [001](P) specimen and 3 K at temperature near A(f) for[111](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 < 112 > 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 (vertical bar Delta T-adi/Delta sigma vertical bar approximate to 35 K/GPa), wide specific effective temperature window (vertical bar Delta T-win/Delta sigma vertical bar approximate to 320 K/GPa) and high coefficient of performance (COP approximate to 14) in a temperature range as wide as 50 K during the unloading process enable the [001](P) orientated Ni50Fe19Ga27Co4 single crystal as a potential elastocaloric material. (C) 2015 Acts Materialia Inc. Published by Elsevier Ltd. All rights reserved.