非晶/纳米晶复合材料原子尺度塑性机制

Metallic glasses are a new category of materials with superior mechanical, physical, and chemical properties. However, they usually suffer from very limited tensile ductility at ambient temperature, which hinders their applications as engineering structural materials. According to recent experiments, nanoscale amorphous-crystalline composite exhibits both superhigh strength and obvious tensile ductility, which provides a new pathway to the utility of metallic glasses. However, the mechanism underlying the observed excellent ductility is not well understood. Due to the difficulty of experimental techniques at nanoscale, here, we use multi-time-scale molecular dynamics to investigate the possible microstructural origin of its excellent tensile ductility. We propose nanoscale metallic glasses as ‘strain diffuser’ of amorphous-crystalline nanocomposite and built the corresponding diffusion equation, which is suggested as a mechanism of accommodating plastic strain generated by the mobility of crystalline dislocations. This is a possible atomic mechanism of the homogenous deformation of nanocomposite. Based on the experimental time scale atomistic simulations, we will also study how the nanocrystal could block the formation and propagation of shear banding in metallic glasses, the atomic structure and dynamics of unit plasticity of metallic glasses, the interaction of crystalline dislocation and amorphous-crystalline heterogenous interface, size effect etc.. In one words, we recognize the deformation mechanisms of nanocomposite according to fundamental physics. This study aims at unveiling the correlation of microstructures and macroscopic mechanical performance of amorphous-crystalline nanocomposite. We hope it will benefit the design of more advanced amorphous composite materials, and further promote their applications as engineering structural materials.

金属玻璃是一类具有优异力学、物理、化学性质的新型材料。但该材料缺乏明显室温拉伸塑性，阻碍其作为工程结构材料的应用。实验发现，纳米尺寸的非晶/晶体复合材料兼具超高强度和良好的拉伸塑性，为金属玻璃的应用提供了一条新途径。但是，其良好塑性的微观机制并不清楚。由于实验技术在纳米尺度的困难，本项目将基于跨时间尺度分子动力学探索非晶/纳米晶复合材料的塑性原子根源。提出纳米非晶在复合材料中的‘形变扩散器’作用并建立相应扩散方程，建议该机制作为调解晶体位错塑性，导致纳米复合材料均匀形变的根源。基于实验室时间尺度的原子模拟，认识纳米晶体对非晶剪切带的抑制，非晶流变单元结构和动力学，位错与非晶-晶体异质相界面相互作用，尺寸效应等。从基本的物理规律出发认识纳米复合材料形变。该项目拟揭示非晶/纳米晶复合材料微观结构-宏观力学性能的内在联系，指导设计具有更优异性能组合的非晶复合材料，推动其作为工程结构材料的应用。

非晶合金与纳米金属作为一类典型的高强度新型金属结构材料，具有巨大的应用潜力，但是这两种材料都存在拉伸塑性及其有限的缺陷，从而阻碍了其进一步的工程应用。提高塑性对应的核心科学问题为非晶、纳米晶材料的原子级变形机理及其调控。本项目围绕两类材料的塑性变形机理，开展大规模的分子动力学模拟，以及蠕变、应力松弛、内耗实验，结合弹塑性理论模型构建，解析该类材料的原子级塑性机理。项目在非晶变形的热力学熵焓补偿、剪胀效应、滞弹性变形理论、剪切带形核机理；纳米晶体的蠕变和应力松弛、断裂、晶界位错形核的原子机理和跨时间尺度计算机模拟等研究方向取得了重要进展，从而在原子尺度明晰了纳米晶和非晶材料的变形行为，为理解和调控该类材料的拉伸塑性提供了有益参考。在项目支持下，团队共发表SCI论文12篇，包括JMPS (1)/Acta, Scr. Mater. (3)/PRB (5)等力学、材料、物理领域的经典期刊，在国内外微纳米力学领域产生了一定的影响。