Elastocaloric effect of all-d-metal Heusler NiMnTi(Co) magnetic shape memory alloys by digital image correlation and infrared thermography

Abstract

We have studied the stress-induced martensitic transformation behaviors and the associated elastocaloric effect (eCE) for non-textured polycrystalline all-d-metal Heusler alloys of Ni50Mn32Ti18 and Ni35Co15Mn35Ti15 by a combination of Digital Image Correlation (DIC) and Infrared (IR) thermography techniques. A large but irreversible adiabatic temperature change (ΔTad) of 10.7 K at a strain level of 3.9% is observed for Ni50Mn32Ti18, whereas Ni35Co15Mn35Ti15 exhibits a reversible eCE with ΔTad = 9.0 K at a strain level of 4.6%. At lower strain levels (<2.4%), both specimens exhibit full superelasticity without residual strain. While in a higher strain range (>3.2%), Ni50Mn32Ti18 is plastically deformed with small strain variation in space from the DIC map. In contrast, Ni35Co15Mn35Ti15 can be deformed superelastically accompanied by large strain variation in space, which can be ascribed predominately to the crystalline orientation dependence of both the transformation strain and the Young's modulus from different orientated grains under mechanical loading. The improved reversibility of eCE for Ni35Co15Mn35Ti15 is supposed to be associated with the enhancement of d-d hybridization by the introduction of the element Co.