仿生层状CNTs/Ti复合材料设计制备与强韧化机理研究

Inspired by the optimal combination of strength and toughness of shell nacre which is caused by the elaborate hierarchical micro/nano structure, in this project it is innovatively proposed that carbon nanotubes (CNTs) reinforced layers are built by means of electrophoretic deposition technique. And low temperature spark plasma sintering (SPS) and rolling deformation are subsequently employed to fabricate and regulate the biomimetic laminated structure of CNTs/Ti composites. Based on their perfect structure effect, the inverse relationship between strength and toughness (plasticity) of titanium matrix composites (TMCs) is likely to be solved. Firstly, the key problems of TMCs including the nonuniform dispersion of CNTs in titanium matrix and the interfacial reaction between CNTs and Ti will be solved by optimizing the fabrication parameters and thus a feasible fabrication method for biomimetic laminated CNTs/Ti composites is successfully exploited. In addition, the formation mechanism of biomimetic laminated structure will be clarified. Secondly, the relationship among fabrication parameters, laminated structure and mechanical properties will be established and the regulation mechanism of laminated structure and mechanical properties will be revealed. Thirdly, in situ scan electron microscope tensile experiment and digital image correlation (DIC) technique are combined to investigate the effect of laminated structure parameters on macroscopic deformation reductions, local strain distribution and deformed microstructure in order to illuminate the plastic deformation mechanism of biomimetic laminated CNTs/Ti composites. Hence, the unique structure effect will be revealed. Moreover, the fracture characteristic will be characterized by X-ray tomography technique. Finally, strengthening-toughening mechanism of the novel biomimetic laminated CNTs/Ti composites will be proposed. The finding of this project will provide a theoretic guide and experimental basis for realizing the optimal combination of strength and toughness (plasticity) of TMCs.

受贝壳微纳米层状结构具有强度与韧性最佳匹配启发，本项目创新性地采用电泳沉积方法构建碳纳米管（CNTs）强化层，结合放电等离子烧结与轧制变形实现CNTs/Ti复合材料仿生层状结构的构建与调控，利用其优异的结构效应，解决钛基复合材料强度-韧性（塑性）倒置问题。优化制备参数，开发出CNTs/Ti复合材料的新型制备方法，突破CNTs均匀分散与CNTs/Ti界面控制等关键问题，揭示仿生层状结构形成机理。建立“制备参数-层状结构-宏观力学性能”的关系，揭示层状结构与力学性能调控规律。结合原位加载与数字图像关联技术研究层状结构参数对宏观变形特性、局域应变分布和微观组织演化的影响规律，阐明仿生层状CNTs/Ti复合材料塑性变形的微观机制，揭示其结构效应。利用X射线断层扫描技术原位研究其断裂特性。基于以上分析，揭示仿生层状CNTs/Ti复合材料的断裂与强韧化机制，为实现钛基复合材料强韧化提供理论与试验依据。

钛基复合材料（TMCs）具有比强度高、比刚度高、高温性能好等优点，能够满足航空航天等领域对结构减重与性能提升的双重要求，然而传统TMCs存在强度-韧性（塑性）倒置问题，极大限制了其实际应用。针对此难题，受贝壳精细纳米叠层结构具有最佳强韧化匹配的启发，本文首先采用电泳沉积法在纯Ti箔上构建碳纳米管（CNTs）强化层，即获得CNTs/Ti单层材料，随后将若干CNTs/Ti单层材料堆叠，利用放电等离子烧结（SPS）结合控温轧制技术制备出仿生层状CNTs/Ti复合材料。优化制备参数，制备出CNTs与Ti基体界面反应可控并形成了良好的冶金结合界面，绝大多数CNTs形态完整且在Ti基体中呈明显的层状分布特征，其中CNTs层间距为5-8μm且CNTs基本呈现理想的单根分散状态。即通过调控制备参数同时解决了CNTs在钛基体中难以均匀分散以及CNTs与钛基体界面反应等共性问题。此外，系统探讨了CNTs含量对仿生层状CNTs/Ti复合材料微观组织与力学性能的影响规律。研究表明：当CNTs含量仅为0.02wt.%时，仿生层状CNTs/Ti复合材料抗拉强度达到637MPa，相比于纯Ti板（573MPa）提高11.2%，且复合材料延伸率仍保持在高水平，约31%。同时阐明了仿生层状结构与力学性能的调控规律。最后，利用原位扫描电镜结合数字图像相关DIC技术探明了仿生层状CNTs/Ti复合材料的局域应变分布演变规律，并利用原位拉伸技术结合计算机X射线断层扫描技术系统研究了复合材料的断裂行为，最终揭示了仿生层状CNTs/Ti复合材料的强化机制与断裂特性。结果表明：仿生层状CNTs/Ti复合材料优异的强度和塑性匹配应归因于其独特的仿生微纳层状组织的优异结构效应和CNTs超高强化作用。本项目开发出一种新型制备方法构建了仿生微纳层状CNTs/Ti复合材料，并利用此独特组织的优异结构效应，获得了优异强塑性匹配的新型钛基复合材料，这为解决金属基复合材料强度-韧性（塑性）倒置问题提供了理论与试验依据。同时发表学术论文12篇，获2019年黑龙江省自然科学一等奖1项，参编国家级规划教材1部。申请国家发明专利9项，已授权5项。培养博士生2名、硕士生5名。