纳米复合晶界韧化高强金属铜及其机理研究

There is a conflict between strength and ductility in metals. The existed strength/ductility trade-off becomes an intrinsic “Achilles’ heel” of nano/ultrafine grained metals, hindering the scalable applications of this new material family. The past decade has witnessed significant progress in toughening of high strength metals. One major consideration is to reduce the grain boundary/interface energies, by forming low-energy interfaces, such as twin boundaries and low-angle grain boundaries. In this project, a new and more universal way will be provided to realize the same goal: we try improve the ductility of high strength metals by tailoring the grain boundary stability through nanofiller modification, and expected that the presence of a reduced dynamic recovery rate of defects and increased dislocation storage abilities in nanostructured metals, which will finally enhance its work hardening abilities during plastic deformation. Here, we will take graphene nanosheets reinforced Cu matrix as a representative and will investigate its interface design, bulk composites fabrication, mechanical behavior and the strengthening /toughening mechanisms in great detail, by virtue of molecular dynamic simulations and multiple characterization methods, including successive stress-relaxation cycles, multi-scale microstructure characterizations and in-situ mechanical testing. The aim of this project is provide a new route for toughening high-strength metals, as well as a practical method to fabricate the bulk nanostructured metals possessing both high strength and ductility/toughness.

金属强度的提升通常以塑/韧性的减小为代价，即存在强度-塑/韧性倒置关系。如何改善这种倒置关系矛盾，进而获得高强高韧力学性能，一直是金属力学行为基础研究的核心与目标。本项目旨在从改善引起“强度-塑韧性”矛盾关系的本征原因出发，探索利用晶界纳米相引入调控金属晶界能，进而实现高强金属韧化的可行性。采用石墨烯增强纳米晶/超细晶金属铜复合材料作为技术原型，依托于分子动力学理论与界面能实验测定，预先设计石墨烯/铜复合界面，通过优化前期研究掌握的“片状粉末冶金”工艺实现纳米晶/超细晶石墨烯/铜块体制备，并综合运用跨尺度组织表征、连续应力弛豫实验、原位力学表征等方法等研究形变过程组织演变规律、位错动力学行为以及复合界面-基体形变机制影响等关键问题。以期揭示金属界面能量调控的强韧化机制，阐明界面能调控强韧机制的基本原理，为高强高韧金属体系的整体发展与实际应用提供理论依据与技术途径。

项目围绕基于界面能量调控的复合界面设计原则以及强韧化机制两大关键科学问题，开展了石墨烯/铜复合界面计算与设计、石墨烯/超细晶铜可控复合、复合材料形变机理表征与分析的系统化研究。首先，构建复合界面分子动力学模型，确定了复合界面能以及复合界面键合状态与石墨烯中缺陷种类的依赖关系，开发微观力学表征平台，研究了不同类型石墨烯/铜复合界面强度与界面形变行为，实现了石墨烯/铜复合材料的界面能量与界面结合的优化设计；依托“片状粉末冶金”制备出具有近纳米尺度、完全致密化的超细晶铜基复合材料，复合材料拉伸强度与塑性相较于超细晶铜基体实现了同步、大幅提升；利用多种、跨尺度微观组织分析，并结合宏观多应力弛豫实验，研究了低能复合界面对基体形变方式以及位错存储能力的影响，揭示出低能复合界面对高强超细晶金属形变机制的调控机制，构建界面调控强韧化的理论基础。