Caloric Effects Induced by Uniform and Non-uniform Stress in Shape-Memory Materials

Abstract

A Ginzburg–Landau model is developed that is adequate to describe a square-to-rectangle martensitic transition with associated shape-memory and superelastic properties. Using this model we study caloric effects in the vicinity of the martensitic transition induced by stress and we compare the case of a uniform uniaxial stress and the case of a non-uniform continuous distribution of stresses that produce bending of the material. The former case corresponds to an elastocaloric effect and the latter corresponds to a flexocaloric effect. The aim of the work is to quantitatively compare both cases, which we show must be accomplished in terms of equal amounts of exchanged mechanical work. It is then obtained that the flexocaloric effect is more efficient for low exchanged work but less efficient for large exchanged work.

Realization of Large Low-Stress Elastocaloric Effect in TiZrNbAl Alloy

“…Due to the large caloric effects and highly efficient heat transfer, shape memory alloys (SMAs) currently stand out as the most promising elastocaloric refrigerant [8][9][10], including Ni-Ti-based [11][12][13][14][15], Cu-based [16][17][18], Fe-based [19][20][21], and Heusler-type [22][23][24][25][26][27][28][29] alloys. Despite the enormous potential exhibited by these alloys, there is still considerable room for improvement.…”

“…The eCE of Ti-based SMAs originates from the stress-induced martensitic transformation from body-centered cubic austenite (β phase) to the orthorhombic martensite (α ′′ phase) [36][37][38]. TiZrNbAl, with compositions of Ti-18Zr- (12)(13)(14)(15)(16)Nb-(0-4)Al (at.%), is a kind of high-performance Ti-based SMA characterized by outstanding mechanical properties and superelasticity [39,40], but its elastocaloric performance has not been explored. In this context, the room temperature and temperaturedependent eCE of TiZrNbAl SMAs are studied systematically in this work.…”