Abstract Deformation processes derived from martensitic transformation in shape memory alloys are theoretically fully recoverable in a complete thermomechanical loading cycle across transformation range and do not leave any lattice defects in the microstructure. In reality, this is rarely the case in NiTi, since plastic deformation tends to accompany the martensitic transformation, particularly if it proceeds under large stress. Lattice defects observed in the microstructure of deformed NiTi wires (slip dislocations and deformation bands) attract the attention of researchers, since they are linked to unrecovered strains and play significant role in functional fatigue, shape setting or two-way shape memory effect. In this work, we present an experimental approach allowing for analysis of deformation bands in deformed NiTi consisting in: i) preparation of superelastic NiTi wires with recrystallized, small grained microstructure, ii) subjecting these wires to desired tensile test (e.g. superelastic or shape memory cycle) and iii) characterizing the deformation bands in TEM using selected area electron diffraction combined with dark field imaging following simple rules described in this work. If the deformed microstructure becomes too complex due to the high density and small size of deformation bands, ASTAR orientation mapping can be beneficially applied to reveal the refinement of the microstructure through the introduction of deformation bands.

中文翻译：

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超弹性镍钛丝拉伸变形产生的变形带的 TEM 分析

摘要 形状记忆合金中马氏体相变引起的变形过程理论上可以在整个转变范围内的完整热机械加载循环中完全恢复，并且不会在微观结构中留下任何晶格缺陷。实际上，NiTi 很少出现这种情况，因为塑性变形往往伴随着马氏体转变，特别是在大应力下进行时。在变形 NiTi 丝的微观结构中观察到的晶格缺陷（滑移位错和变形带）引起了研究人员的注意，因为它们与未恢复的应变有关，并且在功能疲劳、形状设定或双向形状记忆效应中发挥重要作用。在这项工作中，我们提出了一种实验方法，可以分析变形 NiTi 中的变形带，包括：i) 制备具有再结晶、小晶粒微观结构的超弹性 NiTi 线，ii) 对这些线进行所需的拉伸试验（例如超弹性或形状记忆循环）和 iii) 使用选区电子衍射结合暗场成像表征 TEM 中的变形带遵循这项工作中描述的简单规则。如果由于变形带的高密度和小尺寸而使变形微观结构变得过于复杂，则可以有利地应用 ASTAR 取向映射，通过引入变形带来揭示微观结构的细化。超弹性或形状记忆循环）和 iii) 使用选定区域电子衍射结合暗场成像，按照本工作中描述的简单规则来表征 TEM 中的变形带。如果由于变形带的高密度和小尺寸导致变形微观结构变得过于复杂，则可以有利地应用 ASTAR 取向映射，通过引入变形带来揭示微观结构的细化。超弹性或形状记忆循环）和 iii) 使用选定区域电子衍射结合暗场成像，按照本工作中描述的简单规则来表征 TEM 中的变形带。如果由于变形带的高密度和小尺寸而使变形微观结构变得过于复杂，则可以有利地应用 ASTAR 取向映射，通过引入变形带来揭示微观结构的细化。