Advancing Mechanocaloric Cooling Solutions through 3D Printing of Superelastic Lattice Structures

Solid-state refrigeration refers to a technology that uses reversible thermal changes in caloric materials. Caloric materials, in particular Shape Memory Alloys (SMAs), and solid-state refrigeration are attracting increasing interest as a more environmentally friendly, compact and efficient alternative to the traditional refrigeration technology based on gas-compression cycles. The variation of latent heat associated with the Thermoelastic Martensitic Phase Transformation (TMPT) enables caloric effects that can be exploited in cooling applications. The superelasticity of SMAs allows the operation of caloric cycles and therefore their application in solid-state refrigeration. Porous structures, from foams to lattices, offer a valid alternative to traditional bulk SMAs. The general advantages of porous structures are their tunable mechanical properties, lightweight and their broad surface area that allows a more efficient heat exchange. In particular, lattice structures offer an anisotropic strain localization and are suitable to introduce compositional or microstructural gradients. While such lattices are more studied for their mechanical and structural properties, despite their potential in solid-state cooling less is known about their caloric properties. In this work, we fabricated via laser powder bed fusion (LPBF), an additive manufacturing technique, NiTi and/or NiMnTi lattices. The aim is to assess their mechanocaloric property upon compression and torsional deformation and evaluate the relationships between forces-strain-caloric effects in such structures. Both material and lattice features affect their complex caloric response and a comprehensive characterization was carried out to identify the best solution for cooling applications.