Elastocaloric applications exploit the latent heat from a shape memory alloy (SMA) through its stress-induced phase transformation. The elastocaloric potential of a SMA depends on its latent heat, critical transformation stress, hysteresis, heat capacity and conductivity, and, most importantly, its cost-effectiveness. Increasing the latent heat and improving the transformation characteristics are critical to increasing the elastocaloric potential in copper-based SMAs, which depend heavily on their compositions and processing conditions. This paper reports on a comprehensive compositional optimization effort to maximize latent heat while maintaining the near room temperature transition window and minimizing hysteresis for copper-based SMAs. The effort uses a high throughput combinatorial approach to prepare and scan multiple samples with different compositions. The transformation characteristics of grouped samples were determined simultaneously using a novel differential thermal analysis (DTA) method via thermal imaging. Differential scanning calorimetry (DSC) was used to examine the down-selected compositions for verification.

Shape memory alloys such as NiTi can be used as recyclable, nontoxic, nonflammable, and environmentally friendly solid refrigerants in elastocaloric cooling/heat-pumping. Thin wires under tension and thin- walled tubes under compression that allow for fast and efficient heat transfer are excellent candidates to be applied in elastocaloric devices and were therefore selected for this study. Multiple thermodynamic cycles were studied with an emphasis on the parameters of the holding period of the cycle (essential for heat transfer between the elastocaloric material and the heat sink/source). The results reveal that the applied thermodynamic cycle significantly affects the thermomechanical response and thus the cooling/heating efficiency of the shape memory material.

Elastocaloric refrigeration using superelastic NiTi shape memory alloys (SMAs) has attracted much attention recently because it has a large energy saving potential, no environmental effects, and a low cost. Achieving the continuous operating of elastocaloric devices, i.e., separating the cold and hot areas on the NiTi alloys physically, helps the efficient release and absorption of heat and avoid the reciprocal parts and intervals of outputs in the system. In this paper, an analytical model and proof-of-concept experiments for continuous operating (elasto)caloric devices are presented. The experimental concept was developed based on a set of rotating NiTi sheets with which the copper heat sink and heat source contact cyclically.

Elastocaloric cooling, which exploits superelastic transitions of shape memory alloys to pump heat, has recently emerged as a frontrunner in alternative cooling technologies. Despite its intrinsic high efficiency, elastocaloric materials exhibit hysteresis associated with input work, a common attribute of caloric cooling materials. In this study, the authors created a Ni-Ti-based elastocaloric material by additive manufacturing nanocomposite materials using a laser directed-energy- deposition system. The material exhibited exceptional stability and unusual operational efficiency derived from the unique and intricate nanocomposite structures made by additive manufacturing. This demonstration shows the potential for using additive manufacturing to optimize caloric cooling by providing a highly desirable topology flexibility into materials components that serve as both refrigerants and heat exchangers.