Ni-Mn-Ti shape memory alloys show great potential in solid-state elastocaloric cooling owing to very prominent elastocaloric effect along with first-order stress-induced martensitic transformation. However, large stress hysteresis inherent to martensitic transformation greatly restricts the energy efficiency and cyclic stability of elastocaloric response. Here, we demonstrate the effective manipulation of stress hysteresis as well as the resulting elastocaloric effect through doping boron to Ni-Mn-Ti alloys. With the incremental boron content in (Ni₅₀Mn₃₁Ti₁₉)_100–xB_x (x = 0, 0.2, 0.5, 1, 1.5) alloys, a plateau-type superelastic behavior with large stress hysteresis gradually evolves into a quasi-linear one with slim hysteresis, giving rise to significant improvement in the energy conversion efficiency of elastocaloric response. In a (Ni₅₀Mn₃₁Ti₁₉)₉₉B₁ alloy, the coefficient of performance of material (COP_mat) can be as high as 24 ∼ 33. Moreover, under a compressive strain of 4%, large cooling |ΔT_ad| values higher than 6.5 K in the (Ni₅₀Mn₃₁Ti₁₉)₉₉B₁ alloy are maintained for over 8000 superelastic cycles, showing an enhancement of one order of magnitude in the cyclability with respect to that of boron-free Ni₅₀Mn₃₁Ti₁₉ alloy. We attribute the enhanced elasocaloric response to the significantly improved mechanical properties but reduced stress hysteresis endowed by relatively high content of boron doping.

中文翻译：

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硼掺杂多晶 Ni-Mn-Ti 合金中的准线性超弹性和相关的弹性热量效应


Ni-Mn-Ti 形状记忆合金由于非常突出的弹性热量效应以及一级应力诱导的马氏体转变，在固态弹性热量冷却中显示出巨大的潜力。然而，马氏体转变固有的大应力滞后极大地限制了弹性热量响应的能源效率和循环稳定性。在这里，我们展示了应力磁滞的有效操纵，以及通过将硼掺杂到 Ni-Mn-Ti 合金中产生的弹性热量效应。随着 （Ni₅₀Mn₃₁Ti₁₉）_100–xB_x （x = 0， 0.2， 0.5， 1， 1.5） 合金中硼含量的增加，具有大应力磁滞的平台型超弹性行为逐渐演变为具有细磁滞的准线性超弹性行为，从而显著提高了弹性热量响应的能量转换效率。在 （Ni₅₀Mn₃₁Ti₁₉）₉₉B₁ 合金中，材料的性能系数 （COP_垫） 可高达 24 ∼ 33。此外，在 4% 的压缩应变下，大冷却 |ΔT_ad|（Ni₅₀Mn₃₁Ti₁₉）₉₉B₁ 合金中高于 6.5 K 的值保持超过 8000 次超弹性循环，表明与无硼 Ni₅₀Mn₃₁Ti₁₉ 合金相比，循环性提高了一个数量级。我们将增强的 elasocaloric 响应归因于相对较高的硼掺杂所赋予的显着改善的机械性能但降低的应力滞后。