Abstract We show in this paper how strain engineering alters the fundamental characteristic of a martensitic transformation (MT) and gives it a new set of properties including large quasi-linear elastic strain response with nearly vanishing hysteresis and low elastic modulus. The work is motivated and inspired by a recent experimental study on elastic and inelastic (transformation) strain matching in a pre-strained nano-composite with Nb nanowires embedded in a NiTi shape memory alloy matrix. In particular, we demonstrate by computer simulation that dislocations at Nb/NiTi interfaces produced by the pre-straining are responsible for the unprecedented properties. Microstructural evolution captured in the simulations reveals that local stress fields associated with the dislocations regulate the nucleation and growth of martensite, turning the otherwise sharp, strong first-order transition into a continuous, high-order like transition. The simulations predict that the stress-strain hysteresis and modulus of the composite decrease with increasing amount of pre-strain, which agrees well with the experimental measurement. This study suggests a design strategy by introducing non-uniform stress fields for enhanced properties of shape memory alloys.

中文翻译：

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预应变纳米复合形状记忆合金中马氏体转变的相场模拟

摘要 我们在本文中展示了应变工程如何改变马氏体相变 (MT) 的基本特征，并赋予其一组新特性，包括具有几乎消失的滞后和低弹性模量的大准线性弹性应变响应。这项工作的动机和灵感来自最近对预应变纳米复合材料中弹性和非弹性（转变）应变匹配的实验研究，其中 Nb 纳米线嵌入 NiTi 形状记忆合金基体中。特别是，我们通过计算机模拟证明，由预应变产生的 Nb/NiTi 界面处的位错是造成前所未有的性能的原因。模拟中捕获的微观结构演变表明，与位错相关的局部应力场调节马氏体的形核和生长，将原本尖锐、强烈的一阶过渡转变为连续的、高阶的过渡。模拟预测复合材料的应力-应变滞后和模量随着预应变量的增加而减小，这与实验测量结果非常吻合。这项研究提出了一种通过引入非均匀应力场来增强形状记忆合金性能的设计策略。