Expanding the elastocaloric temperature range of ternary Ti–Ni–Fe alloys by laser-directed energy deposition additive manufacturing

Abstract

Elastocaloric cooling is an emerging solid-state refrigeration technology and offers a promising alternative to conventional vapor-compression systems. However, expanding its operational temperature range poses a critical challenge. In this work, we utilize laser-directed energy deposition (L-DED) additive manufacturing to precisely control microstructural features at the submicrometer scale, thereby extending the operational temperature range of elastocaloric Ti–Ni–Fe alloys. We fabricate Ti50Ni50-xFex (x = 2, 4, 6) alloys by feeding the elemental powders of Ni, Ti, and Fe in L-DED with the alloy composition controlled by adjusting the flow rate of each powder. Fe when used as the doping element induces lattice relaxation by substituting Ni sites, thereby reducing the geometric differences between the austenite and martensite phases. As the content of Fe increases from 2 at. % to 6 at. %, the martensitic transformation enthalpy decreases from 18.8 to 1.8 J/g, and the austenite finish temperature is lowered by 66 K. The Ti4Ni2O precipitates naturally introduced during the L-DED process are refined to the sub-micrometer scale and exert the effect of microstructural refinement on the martensitic transformation. As a result, the fabricated alloys exhibit a broad operational temperature window (253–318 K) with adiabatic temperature changes (ΔTad) of 1.5–2.8 K. Our work demonstrates the potential of L-DED additive manufacturing in fabricating elastocaloric materials.