形状记忆合金因具有形状记忆效应和超弹性等奇异的功能特性而受到广泛关注。但是，受限于一级马氏体相变的原理性制约，形状记忆合金的超弹性行为长期以来存在着能量耗散大的难题，并因此降低了材料的精密控制、疲劳性能和能量转化效率等，成为这类材料在高性能领域使用的瓶颈之一。从相变形核的角度综述了相关降低形状记忆合金超弹性能量耗散的研究工作，指出了通过降低材料相变能垒进而降低超弹性能量耗散的两个可行方案：(1)弱化自发晶格畸变量；(2)引入空间不均匀性。现有的分子动力学模拟发现纳米尺度的形状记忆合金由于其奇异的核-壳结构而同时满足以上两个解决方案，从而使得块体材料中强烈的一级马氏体相变转变为纳米尺度下的连续相变，导致材料出现奇异的零滞后的超弹性行为。这一理论也得到了近期实验的支持，从而为设计具有窄滞后超弹性行为的形状记忆合金提供了新思路与新方法。%Shape memory alloys ( SMAs) exhibit two closely related and unique properties:shape memory effect ( SME) and superelasticity ( SE) . Hysteresis in martensitic transformations ( MT) limits the usefulness of SMAs that require high sensitivity, high durability and high energy efficiency. Recent studies based on atomic simulations and experiments of nanosized SMAs have indicated promising solutions to slim the MT hysteresis that is associated with superelasiticity. It is summarized that SMAs at the nanoscale demonstrate a decreasing hysteretic superelasticity with reduced feature size. In particular, it exhibits nonhysteretic superelasticity below the critical size. Atomic level investigations show that the decrea-sing hysteresis is due to weaker spontaneous lattice distortion and spatial heterogeneity, leading to a more continuous phase transformation from the parent phase to martensite under external stress. The theoretical studies are also supported by the latest nanosized SMAs experiments. These findings suggest potential methods to achieve slim hysteresis in conventional bulk SMAs.
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