体心立方金属纳米线变形机制的原位透射电镜研究

Body-cantered cubic (BCC) nanomaterials hold great promises in the applications of nanodevices under harsh conditions, due to their excellent mechanical properties. However, the size-dependent deformation and fracture mechanisms of BCC metallic nanomaterials remain largely unknown. In this project, the BCC metals of Tungsten, Molybdenum and Niobium will be used as model systems for experiments. BCC metallic nanowires with different sizes and orientations will be fabricated directly inside a transmission electron microscopy (TEM), using a nanowelding method. In situ TEM nanomechanical testings, including tension, compression and bending etc., will be further conducted on the as-fabricated BCC metallic nanowires. The deformation mechanism of BCC metallic nanowires, such as dislocation, deformation twinning and phase transformation, will be systematically explored by combining the in situ observations with quantitative high resolution TEM analysis and atomistic modelling. The defect dynamics, deformation mechanism and twinning-antitwinning asymmetry in BCC metallic nanowires will be quantitatively studied and revealed by considering a variety of factors, including crystal size, orientation and loading mode. By conducting this project, we hope to establish a full deformation map of BCC metals deformed at small length scale, and to provide theoretical instructions for multiscale design of BCC metallic nanostructures.

由于其优异的力学性能，体心立方（BCC）金属纳米材料在极端环境下使用的微器件中有潜在应用价值，然而关于其变形和损伤机制的研究还比较欠缺。本项目拟选取W、Mo、Nb等BCC金属为研究对象，利用原位纳米焊接制备具有不同尺寸、取向的BCC金属纳米线，开展拉伸、压缩和弯曲等力学测试，结合高分辨定量分析和分子动力学模拟，系统研究BCC金属纳米线的变形机制（包括位错、孪晶、相变等），定量揭示BCC金属纳米线中的缺陷演化、变形机制和孪晶-反孪晶不对性随晶体尺度、取向、加载方式的变化规律。通过本项目的研究，希望能建立BCC金属在微尺度下变形、断裂的一般规律，从而为BCC金属微纳结构的多尺度设计提供理论依据。

体心立方（BCC）金属纳米材料具有优异的力学性能，因而在极端环境下使用的微器件中有潜在应用价值。然而，其塑性变形和损伤机制的研究还比较欠缺。本项目系统研究了BCC金属纳米材料的塑性变形行为，揭示了BCC金属纳米线缺陷动力学行为，阐明了位错-孪晶竞争、转变的物理机制及其影响因素，包括晶体学取向、加载方式、表面结构、孪晶-反孪晶不对称性、尺寸效应等；首次从实验上证实理论上不可能发生的反孪晶变形在极高应力下可通过 1/3<111>位错沿孪晶面滑移被激活，且其具有显著的晶体尺寸效应；发现了BCC金属纳米线可通过孪晶、相变、位错的相互协调发生多次重新取向，诱发超塑性；揭示了界面结构、界面偏聚对BCC/FCC层状金属材料塑性变形和断裂的显著影响，提出基于界面结构调控来改善金属纳米材料力学性能的手段。本项目研究成果系统构建了微纳尺度BCC金属的变形机制图，填补了传统位错理论中的若干认知漏洞，推动了BCC金属塑性变形理论的发展。项目执行期间，共发表了SCI 收录论文16篇，在TMS、MS&T、THERMEC等国内外知名学术会议上做报告18次，其中邀请报告13次，申请发明专利1项。培养博士生毕业研究生1名，硕士毕业研究生2名，在读博士生1名。