Multicaloric Effects and Additively Manufactured Elastocaloric Materials with Tailored Transformations

The field of caloric cooling has undergone a series of transformations in the past decade bolstered by the advent of new materials and devices, and yet there remain challenges that need to be overcome before they can enjoy widespread commercialization. An exciting new direction in the field is multicaloric materials systems, which inherently display several first-order transitions and thus can be cooled using multiple fields. In this talk, we survey the emerging field of multicaloric cooling and explore state-of-the-art caloric materials systems responsive to multiple fields. We show that all caloric cooling processes fall into one of the four schemes of multicaloric cooling modes depending on whether a material is a single-phase or a composite and whether a single field or multiple fields are required for pumping heat. We examine the physics of multicaloric cooling concerning intrinsically coupled ferroic order parameters in multiferroic materials. We will also discuss the key factors governing the overall system efficiency of multicaloric cooling devices.<br/><br/>Because the mechanocaloric effect plays an important role in multicaloric cooling configurations, we revisit the definition of the mechanocaloric effect and expand its scope beyond the limited two members of elastocaloric and barocaloric effects. Further, we employ additive manufacturing to design highly-reversible superelastic transition pathways at a microscopic level in elastocaloric Ni–Ti-based alloys. Through rapid cooling and high-precision compositional tuning, we have fabricated Ni–Ti binary nanocomposites with unique curved nano-interfaces, which give rise to quasi-linear stress-strain behaviors with unusually narrow hysteresis, resulting in an enhancement in the materials coefficient of performance by a factor of four to seven. Our nanocomposite NiTi is stable over 1 million cycles of superelastic transitions. In addition, we have fabricated Ni–Ti-based ternary alloys whose transformation temperature and latent heat can be tailored in a large range.<br/><br/><b>REFERENCES</b><br/><b><i><u>Nature Reviews Materials</u></i></b> 2022, 7: 633–652.<br/><b><i><u>Science</u></i></b> 2019, 366 (6469): 1116.<br/><b><i><u>Nature Communications</u></i></b> 2018, 9: 4075.