典型高性能纳米孪晶硬质陶瓷的微结构设计与性能优化

Nanocrystalline hard ceramics have attracted increasing attentions due to their excellent mechanical properties, but the bottleneck of grain size and poor toughness limit their applications. It has been proven that the nanotwinned structure can improve the strength and toughness of the materials significantly. The doping and vacancy in ceramics are found to induce the formation of twin formation by experiment, but the regulative twinning methods and its influence on mechanical properties are still in the initial stage. In this project, combining numerical simulation, theoretical analysis and experimental verification, high performance TiC (of B1 structure) and SiC (of B3 structure) are selected as typical representatives to perform a comparative study: based on first principles calculation and molecular dynamics (MD) simulation, the physical twinning mechanisms induced by doping/vacancy will be investigated, and theoretical preparation approaches will be proposed to guide the experimental preparation of twinning ceramics. Then effects of doping/vacancy and twin boundary and their coupling effects on plastic deformation behavior are to be studied clearly to uncover the microplastic deformation behavior of nanotwinned TiC and SiC by MD simulation and experiment. The strengthening and weakening mechanisms of twin boundaries and their dependence on microstructure will be further investigated. The mechanical models to describe the intrinsic and extrinsic properties are to be developed based on the dominant strengthening and weakening mechanisms, which would establish the relationships among the induction parameters, microstructure and mechanical properties, and eventually suggest corresponding induction parameters and microstructure conditions to obtain optimum mechanical properties, providing theoretical support for the design and development of high performance nanotwined hard ceramics.

纳米晶硬质陶瓷以优异的力学性能备受关注，但晶粒尺寸瓶颈和韧性差限制了其应用。已证明纳米孪晶结构可克服这两大局限，实验发现陶瓷中掺杂和空位可诱导孪晶形成，但其孪生可控方法和对力学性能影响研究还在起步阶段。本项目以高性能陶瓷TiC（B1结构）和SiC（B3结构）为研究对象，结合数值模拟、理论分析和实验验证进行研究：基于第一性原理计算和分子动力学（MD）模拟研究掺杂/空位诱导孪生的物理力学机理，提出其理论制备方案，指导孪晶陶瓷的实验制备；MD模拟和实验结合进行力学测试，明确掺杂/空位和孪晶界对塑性变形行为的影响及其耦合，揭示孪晶TiC和SiC的塑性变形行为和孪晶的强弱化机理及其微结构依赖；由主导的强弱化机理构建诱导参数和微结构与计及本征和非本征性能的力学模型，建立诱导参数、微结构和力学特性间的联系，并给出性能最优的诱导参数和微结构条件，为设计和研发高性能孪晶硬质陶瓷提供理论支持。

引入孪晶结构可改善纳米晶硬质陶瓷的力学性能，但孪晶结构的形成机理及其对硬质陶瓷力学性能的影响机制和规律仍不清楚，限制了高性能纳米孪晶陶瓷的设计与研发。本项目采用第一性原理计算和分子动力学模拟研究了B1结构（TiC、NbC、ZrC、HfC、TaC）和B3结构（SiC、金刚石、氮化硼）等陶瓷的本征物理力学性能；获得了两类陶瓷在不同热力载荷下的变形与失效模式，并与B2结构金属间化合物（CuZr和NiTi）的变形与失效进行对比，分析了离子键与金属键对变形模式影响的异同点。在此基础上，对比研究了孪晶、共格和半共格界面对硬质陶瓷和金属多层膜力学性能的影响差异，研究了不同孪晶厚度、孪晶厚度比对B1和B3结构孪晶陶瓷力学响应和微结构演化的影响，明确了强弱化机理；基于微结构演化和强弱化机理，建立了用以描述孪晶多晶硬质材料流动应力与晶粒尺寸及孪晶界含量间关系的理论模型。最后基于此理论关系，设计了力学性能更加优异的共格孪晶修饰晶界的新型纳米孪晶结构材料。本项目研究成果可为设计和研发高性能孪晶硬质陶瓷提供理论支持。