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金属纳米线的弯曲力学性能直接决定了微纳器件的可靠性和使用寿命. 厘清纳米线在弯曲载荷作用下的力学响应特征和形变微观机制, 对设计和制造高性能微纳器件具有十分重要的理论意义和巨大的工程价值. 本文采用分子动力学模拟方法对不同取向B2结构FeAl合金纳米线的弯曲行为展开研究, 并同时考虑纳米线尺寸和横截面形状的影响. 结果表明, 在本文考虑的尺寸范围内, FeAl合金纳米线弯曲塑性变形的微观机制不随纳米线尺寸及横截面形状的变化而改变, 而只取决于纳米线轴向的晶体学取向. 其中, $\left\langle {111} \right\rangle $和$\left\langle {110} \right\rangle $取向纳米线的屈服均源于位错形核, 但$\left\langle {111} \right\rangle $取向纳米线在屈服后随即发生脆性断裂, 而$\left\langle {110} \right\rangle $取向纳米线则在位错连续形核与滑移过程中产生稳定的塑性流动, 从而表现出良好的塑性及延展性; 与上述两种取向纳米线不同, $\left\langle {001} \right\rangle $取向纳米线的弯曲形变机制以应力诱发B2→L10相变为主导, 同样表现出良好的弯曲塑性, 且具有较$\left\langle {110} \right\rangle $取向纳米线更高的断裂应变. FeAl合金纳米线弯曲行为的晶体学取向依赖性可借助Schmid因子得到解释. 此外, 塑性弯曲的$\left\langle {110} \right\rangle $和$\left\langle {001} \right\rangle $取向纳米线在卸载过程中可回复至初始形状, 特别地, $\left\langle {001} \right\rangle $取向纳米线的弯曲塑性变形可完全回复, 表现出超弹性特征. 本文从原子尺度阐明B2结构FeAl合金纳米线的弯曲形变行为及其关键影响因素, 对基于金属纳米线的柔性微纳器件设计和性能优化具有重要指导意义.
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关键词:
- B2结构FeAl合金纳米线 /
- 弯曲形变 /
- 位错密度 /
- 分子动力学模拟
In nanosystems, the metallic nanowires are subjected to significant and cyclic bending deformation upon being integrated into stretchable and flexible nanoelectronic devices. The reliability and service life of these nanodevices depend fundamentally on the bending mechanical properties of the metallic nanowires that serve as the critical components. An in-depth understanding of the deformation behavior of the metallic nanowires under bending is not only essential but also imperative for designing and manufacturing high-performance nanodevices. To explore the mechanism of the bending plasticity of the metallic nanowire, the bending deformations of B2-FeAl alloy nanowires with various crystallographic orientations, sizes and cross-sectional shapes are investigated by using molecular dynamics simulation. The results show that the bending behavior of the B2-FeAl alloy nanowires is dependent on neither their size nor cross-sectional shape of the nanowire, but it is highly sensitive to its axial orientation. Specifically, both $\left\langle {111} \right\rangle $- and $\left\langle {110} \right\rangle $-oriented nanowires are generated through dislocation nucleation during bending, with the $\left\langle {111} \right\rangle $-oriented nanowires failling shortly after yielding due to brittle fracture, while the $\left\langle {110} \right\rangle $-oriented nanowires exhibit good ductility due to uniform plastic flow caused by continuous nucleation and stable motion of dislocations. Unlike the aforementioned two nanowires, the bending plasticity of the $\left\langle {001} \right\rangle $-oriented nanowire is mediated by the stress-induced transition from B2 phase to L10 phase, which leads to excellent ductility and higher fracture strain. The orientation dependence of bending deformation can be understood by considering the Schmid factor. Moreover, the plastically bent nanowires with $\left\langle {110} \right\rangle $ and $\left\langle {001} \right\rangle $ orientation are able to recover to their original shape upon unloading, particularly, the plastic deformation in the $\left\langle {001} \right\rangle $-oriented nanowire is recoverable completely via reverse transformation from L10 to B2 structures, exhibiting superelasticity. This work elucidates the deformation mechanism of the B2-FeAl alloy nanowires subjected to bending loads, which provides a crucial insight for designing and optimizing flexible and stretchable nanodevices based on metallic nanowires.-
Keywords:
- B2-FeAl alloy nanowire /
- bending deformation /
- dislocation density /
- molecular dynamics simulation
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Orientation X Y Z $\left\langle {111} \right\rangle $ [111] $ [1\bar 1 0] $ $ [11\bar 2 ] $ $\left\langle {001} \right\rangle $ [001] $ [1\bar 1 0] $ [110] $\left\langle {110} \right\rangle $ [110] $ [1\bar 1 0] $ [001] 
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