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論文

Neutron diffraction study of temperature-dependent elasticity of B19' NiTi; Elinvar effect and elastic softening

Ahadi, A.*; Khaledialidusti, R.*; 川崎 卓郎; Harjo, S.; Barnoush, A.*; 土谷 浩一*

Acta Materialia, 173, p.281 - 291, 2019/07

 被引用回数:10 パーセンタイル:70.55(Materials Science, Multidisciplinary)

The temperature-dependent elasticity of the B19' NiTi is unknown today. To gain insights into the lattice-level temperature-dependent elasticity of the B19' crystal, we present results of ${it in situ}$ neutron diffraction experiments performed on polycrystalline martensitic specimens in the temperature range of 300 down to 50 K. The experimental results are compared with the density functional theory molecular dynamics (DFT-MD) and Quasi Harmonic Approximation (QHA) calculations. The results confirm that the temperature-dependent Young's modulus (TDYM) of the B19' crystal is strongly anisotropic. The experimental results along with the first-principles calculations confirm that the Elinvar and Invar are two confluent properties in NiTi SMAs and can be tailored by texturing B19' crystallographic orientations.

論文

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

 被引用回数:19 パーセンタイル:91.93(Materials Science, Multidisciplinary)

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.

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