纳尺度多层金属薄膜是将两种或多种金属交替溅射或淀积在基体上形成的具有层状结构的复合材料。界面对位错运动的强烈约束使其具有超高的强度和显著下降的塑性。针对三种具有典型界面结构（共格、半共格、非共格）的纳尺度多层金属薄膜，本项目围绕"位错-界面相互作用"这一核心科学问题，通过宏细微观实测、多尺度模拟和理论分析，研究多层薄膜变形与断裂的尺度效应及其界面约束机理。首先，通过微细观观测，获取多层膜中位错-界面作用、界面约束与强度增强、微裂纹启裂与塑性降低之间的关联信息；其次，通过对"位错-界面"、"位错-微裂纹"等相互作用过程的原子模拟，提炼出升尺度的"界面-位错相互作用"和"位错-裂纹粘聚力扩展"等模型，融入并发展三维离散位错多尺度模拟框架；最后，通过三维离散位错模拟，多尺度地揭示多层薄膜变形、断裂的尺度与界面效应。成果将为高强-高韧多层金属薄膜层状结构的优化设计、强度分析提供理论和技术支撑。

By alterlating vapor deposition or sputtering of different kinds of metals onto a substrate, a new composite named as nanoscale metallic multilayer (NMM) can be produced. Due to the strong constraint effect on gliding dislocations by phase interfaces and grain boundaries, NMM usually has ultrahigh strength but with remarkably reduced ductility. In this project, NMMs with three different kinds of layer interfaces (the coherent, semi-coherent and incoherent interfaces) are to be considered. Based on macro-meso-microscopic experiments, multiscale modeling and theoretical analysis, the length scale effect on the plastic deformation and fracture behavior of NMMs (induced by layer thickness and grain size) and the intrinsic dislocation-interface interaction mechanism will be investigated systematically. First, by micro-meso-scopic experimental observations, it can be established that the dislocation-interface interaction mechanism, the relationship between interface constraint and length-scale-dependent deformation strengthening, and the relationship between microcrack initiation/propagation and remarkable reduction in the ductility. Then, by performing molecular dynamics simulations focusing on dislocation-interface interaction and dislocation-microcrack interaction, "up-scale" constitutive rules can be obtained, which can be embedded into the multiscale modeling framework for three-dimensional discrete dislocation dynamics (MMF-3D DDD). Finally, employing the so-developed MMF-3D DDD, the effect of length scale and interface constraint on NMMs deformation strengthening and fracture can be revealed. Such research can provide strong theoretical and technological supports to the optimum design of the microstructure of NMMs with both high strength and high ductility, as well as to the strength analysis and safety assessment of NMMs.