Elastocaloric cooling and heating using R-phase transformation in hot rolled Ni-Ti-Fe shape memory alloys with 2 and 4 at% Fe content

Iron-doped Ni-Ti shape memory alloys are known for their R-phase transformation. The stress-induced R-phase transformation and its reverse transformation can be utilized to create a temperature change based on elastocaloric heating and cooling. We studied the elastocaloric properties of hot rolled Ni-48 Ti50Fe2 and Ni46Ti50Fe4 alloys with three different approaches: 1) the calorimetry and specific heat measurements, 2) mechanical stress-strain behaviour and Maxwell relation based calculations and 3) direct measurement of adiabatic temperature change by stress application and removal. We compared the results related to different approaches and present the essential properties related to elastocaloric effect in these alloys. We show that the temperature change due to energy dissipation of the R-phase transformation is minor in comparison with the elastocaloric temperature change. The maximum adiabatic temperature change expected from the latent heat of R-B2 transformation is 12.4 K for the Ni48Ti50Fe2 alloy and 8.7 K for the Ni46Ti50Fe4 alloy. We also report an increasing tendency of the peak temperature for the elastocaloric effect when the applied stress increases. (C) 2018 Elsevier B.V. All rights reserved.