Reversible elastocaloric effect at ultra-low temperatures in nanocrystalline shape memory alloys

Ahadi, A.*; 川崎 卓郎; Harjo, S.; Ko, W.-S.*; Sun, Q. P.*; 土谷 浩一*

Acta Materialia, 165, p.109 - 117, 2019/02

https://doi.org/10.1016/j.actamat.2018.11.035

We report emergence of an unprecedented elastocaloric effect with a decrease of temperature, well below the temperature range of martensitic phase transformation, in a model nanocrystalline NiTi that preserves slim-hysteresis superelasticity at ultra-low temperatures. The new elastocaloric effect emerges at a temperature of about 90 K, exhibits an opposite sign than the conventional elastocaloric effect, and intensifies gradually with a decrease of temperature to 18 K. At 18 K, a large adiabatic temperature change of +3.4 K is measured upon rapid release of tensile stress. The measured adiabatic temperature change are larger and extend over a wider temperature span than the existing electrocaloric, piezocaloric, and barocaloric cryo-refrigeration materials.