超硬B-C-N纳米结构材料界面结构和强化机理的基础性研究

Superhard B-C-N nanostructured materials have attracted much attention and interest in academic community due to their high hardness approaching or exceeding that of single crystal diamond. It has been known that the effect of nanostructure and interface on the plastic deformation mechanism plays an important role to understand the origin of the superior mechanical properties of these nanostructured materials. Although lots of studies have been done on the physical origin of strengthening and ductility enhancement based on the properties of relevant phases, it is however scarce for a detailed investigation on the relationship between the parameters of nanostructure and interface, and the mechanical properties such as strength and ductility because of the complexity and difficulty in modelling. By means of first principle calculations, interface electronic strengthening mechanism and dislocation theory, this proposal will focus on a systematic investigation on the interface structure, interface stability, and interface dominated mechanical properties of recently synthesized superhard B-C-N nanostructured materials such as superhard nanodiamond, nano-twinned BN and diamond, c-BN/w-BN nanocomposite and diamond/BN nanocomposite. The purpose of this proposal is to build up a correlation between microstructural parameters and superhardness based on a systematic analysis of the properties of various defects, the characteristics of interface and the nanosize effect, and consequently to get an in-depth understanding of the physics behind, providing a theoretical foundation for further improvement of mechanical performance of superhard nanostructured materials and an effective pathway in design of novel superhard materials.

超硬B-C-N纳米结构材料由于其接近甚至超越金刚石单晶的硬度，近年来引起了国际社会的高度关注。如何理解“纳米-界面”对于塑性变形机制的支配作用已成为揭示超硬纳米结构材料优异力学性能的关键。虽然近年来出现了针对超硬材料“本征晶格强韧化”的探索性研究，但是基于“纳米-界面”强韧化的理论研究由于建模计算的复杂性和难度，迄今为止国内外还很匮乏。本项目拟采用晶格稳定性微扰诊断和基于点阵变换的强度计算方法、界面电子强化机理和位错理论，系统研究超硬纳米金刚石材料、纳米氮化硼材料以及纳米氮化硼/金刚石复合材料等体系中观察到的各种缺陷结构、界面特征、纳米组成和分布等，阐明这些参量与强度和韧性的关联性。并在此基础上建立起显微结构特征与超硬性能的本征关系，揭示出“纳米-界面”强韧化的微观物理图像，为现有超硬B-C-N纳米结构材料的增强和增韧提供理论支撑，并为新型超硬纳米结构材料的设计探索出一条有效途径。

超硬B-C-N纳米结构材料由于其接近甚至超越金刚石单晶的硬度，近年来引起了国际社会的高度关注。如何理解“纳米-界面”对塑性变形机制的支配作用已成为揭示超硬纳米结构材料优异力学性能的关键。本项目以纳米结构金刚石和BN中发现的多种纳米级界面为基本研究对象，综合运用先进的第一性原理计算和分子动力学模拟技术，深入系统地研究了纳米结构金刚石和BN中纳米界面调制力学性能机理，并最终探讨超硬材料归一化设计理念。首先，开发了材料力学性能高通量第一性原理计算平台：AELAS高通量第一性原理弹性解析程序、ADAIS高通量第一性原理强度预测程序和PNADIS派纳位错塑性半离散变分求解程序，实现了多种力学参量的高通量计算。基于超硬纳米金刚石和BN材料中发现的堆垛次序相关面缺陷（包括纳米孪晶、堆垛层错、c-BN{111}/w-BN{0001}异构共格界面等）、五重孪晶、sp2键合界面和反相畴界等同质界面以及超硬金刚石/立方氮化硼材料中B-C键合异质界面等，构建了不同的纳米级界面模型并研究这些纳米界面的稳定性和电子结构特征。其次基于第一性原理计算、理想强度和位错派纳模型研究了这些纳米界面在不同力学载荷作用下的界面力学响应机理、畸变电子结构和电子失稳模式，以及这些纳米界面对界面附近键长、电子结构、位错结构和位错滑移阻力的影响，从而揭示出界面调制力学性能的内在强韧化机理。基于大尺寸分子动力学模拟研究了不同类型和界面间距的晶内纳米级界面以及不同厚度和密度的晶间非晶层对于纳米晶金刚石的力学性能和变形机理的影响，以及晶内纳米界面和晶间非晶层的耦合作用，并综合分析各种晶体缺陷对于力学强度的影响规律，结合纳米尺寸效应和界面电子结构在应力条件下的演变特征，获取纳米界面强化的物理起源。最后建立起显微结构特征与超硬性能的本征关系，揭示出“纳米-界面”强韧化的微观物理图像，为现有超硬B-C-N纳米结构材料的增强和增韧提供理论支撑，并为新型超硬纳米结构材料的设计探索出一条有效途径。