In this work, a NiTi shape memory alloy (SMA) with excellent elastocaloric performance (with an ultrahigh coefficient of performance, i.e., COPmat of ∼46.5 and an adiabatic temperature change of ∼10.5 K) and good cyclic stability is prepared. A thermo-mechanically coupled and crystal-plasticity-based phase field model including both the descriptions of Ni4Ti3 precipitation and martensitic transformation (MT) is newly proposed to reveal the microscopic mechanism behind the cyclic stability of NiTi elastocaloric materials. The dependence of plasticity on the precipitate size is innovatively considered through a Hall-Petch-like relationship between the dislocation slip resistance and the distance between adjacent precipitates, and the pinning effect of dislocation on reverse MT is reflected by introducing an interaction energy. The elastocaloric effect (eCE) and its cyclic evolution of the single-crystal NiTi SMA systems containing Ni4Ti3 precipitates with different sizes are simulated. Combined with experimental observations and simulations, new insights are provided on the mechanism behind the enhanced cyclic stability of precipitation strengthened NiTi SMA elastocaloric materials. The results of this work can improve the valuable scheme and theoretical basis for the development of NiTi-based elastocaloric materials with outstanding eCE and good cyclic stability.

中文翻译：

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Ni4Ti3 纳米沉淀物增强 NiTi 形状记忆合金弹性热材料的循环稳定性：实验和相场建模


在本工作中，制备了一种具有优异弹性热性能（具有超高性能系数，即 COPmat 为 ∼46.5，绝热温度变化为 ∼10.5 K）和良好循环稳定性的 NiTi 形状记忆合金 （SMA）。新提出了一种热机械耦合和基于晶体塑性的相场模型，包括 Ni4Ti3 沉淀和马氏体相变 （MT） 的描述，以揭示 NiTi 弹热材料循环稳定性背后的微观机制。创新性地通过位错滑移阻力与相邻沉淀物之间距离之间的 Hall-Petch 关系来考虑塑性对析出物大小的依赖性，并通过引入相互作用能来体现位错对反向 MT 的固定效应。模拟了含有不同粒径 Ni4Ti3 沉淀物的单晶 NiTi SMA 体系的弹性热量效应 （eCE） 及其循环演变。结合实验观察和模拟，对沉淀强化 NiTi SMA 弹热材料增强循环稳定性背后的机制提供了新的见解。这项工作的结果可以提高开发具有出色 eCE 和良好循环稳定性的 NiTi 基弹热材料的有价值的方案和理论基础。