Role of thermal expansion anisotropy on the elastocaloric effect of shape memory alloys with slim-hysteresis superelasticity

We reveal the mixed-mode mechanism of elastocaloric effect in the course of slim-hysteresis superelasticity in a severely deformed NiTi shape memory alloy with tailored (negative/zero/positive) thermal expansion anisotropy. It is shown that in addition to the latent heat of phase transformation, the reversible heat from elastic deformation (known as the thermoelastic effect) plays a significant role in the overall elastocaloric response. The magnitude of the adiabatic temperature change associated with the thermoelastic effect |Delta T-ad(TeE) | can reach 3.1 K, which is comparable to that from the phase transformation latent heat (|Delta(TPT)(ad)| = 2.9 K). The sign and magnitude of the Delta T-ad(TeE) scales with the sign and magnitude of the coefficient of thermal expansion (CTE) along the stressing direction. For the directions with negative CTEs, the Delta(TeE)(ad) < 0 while for those with positive CTEs the Delta(TeE)(ad) > 0 upon rapid release of tensile stresses. As such, the cooling performance is strongest when the material is tensioned along the direction of the strongest negative CTE (-14.3 x 10(-6)K(-1)) owing to the synergistic interplay of ATadPTand AT TeE ad . The results reveal the importance of thermal expansion property on the elastocaloric effect.