  Elastocaloric cooling, which exploits the latent heat released and absorbed
as stress-induced phase transformations are reversibly cycled in shape memory
alloys, has recently emerged as a frontrunner in non-vapor-compression cooling
technologies. The intrinsically high thermodynamic efficiency of elastocaloric
materials is limited only by work hysteresis. Here, we report on creating
high-performance low-hysteresis elastocaloric cooling materials via additive
manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established
knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are
found to be beneficial to elastocaloric performances when they are combined
with the binary Ti-Ni compound in nanocomposite configurations. The resulting
microstructure gives rise to quasi-linear stress-strain behaviors with
extremely small hysteresis, leading to enhancement in the materials efficiency
by a factor of five. Furthermore, despite being composed of more than 50%
intermetallic phases, the reversible, repeatable elastocaloric performance of
this material is shown to be stable over one million cycles. This result opens
the door for direct implementation of additive manufacturing to elastocaloric
cooling systems where versatile design strategy enables both topology
optimization of heat exchangers as well as unique microstructural control of
metallic refrigerants.
