高韧性金刚石/SiC异质多层膜的结构设计与界面微结构的原子尺度研究

Diamond materials have attracted much attention, due to its excellent properties such as the highest hardness, high thermal conductivity and high chemical inertness. However, the low fracture toughness of diamond limits its application for cutting tools. Inspired from the “brick/motar” structure of biomaterials with high toughness, diamond/SiC multilayer films are believed to be a promising solution for diamond based cutting tool with high toughness. However, the influence of the different interfacial microstructures between diamond and SiC on the fracture toughness in the multilayer films at the atomic level has not yet been understood. .. In this project, diamond/SiC multilayer fims with different modulation rations and different growth sequences are prepared by microwave plasma enhanced CVD technique. The fracture toughness and structure characterization of the films are investigated by means of nano-indentation, X-ray diffraction, Raman spectroscopy, SEM and TEM. At the atomic level, we will systematically analyse the influence of the different microstructure between diamond and SiC on the strain distribution, including the growth orientation, grain size and crystal defects in the film and the misfit dislocations, by using high resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA). And the interface feature preventing crack propagation will be discussed by measuring the strain at the tip of crack after deformation. The interplay between the interface microstructure and high fracture toughness in diamond/SiC multilayer will be established through the study of the interface strain... Our finding will be of significance in understanding the microstructure property relationship in the multilayer film system, and also in designing diamond based materials with high toughness by means of controlling the layered microstructure in the fabrication processing.

金刚石低的断裂韧性严重限制其作为刀具涂层材料的使用。本项目受高韧性生物质材料层状结构启发，拟通过精确控制制备工艺生长不同结构的金刚石/SiC多层膜，采用纳米压痕测试其断裂韧性，利用高分辨透射电子显微术(HRTEM)以及几何相位分析方法(GPA)从原子尺度研究具有不同调制比的薄膜生长取向，薄膜层内缺陷和界面失配位错对应变分布的影响，以及同一调制比下基体取向与薄膜掺杂元素对界面应变的贡献；分析变形后裂纹尖端的应变分布，揭示影响裂纹扩展的界面结构特征，阐明金刚石/SiC多层膜断裂韧性与界面微结构的内在联系，提出高韧性金刚石/SiC多层膜的结构设计原则。本项目研究成果将为研究脆性材料的显微结构与韧性关系这一重要科学问题提供可靠的实验证据，更为构建高韧性的金刚石刀具涂层材料提供设计思路和理论基础。

金刚石(diamond)，碳化硅(SiC)等材料具有非常低的断裂韧性，提高这类材料的断裂韧性具有非常重要的基础研究和实际应用价值。本项目利用微波等离子CVD方法(MPCVD)围绕金刚石和SiC薄膜设计并生长了多种复合薄膜，利用高分辨电子显微术(HRTEM)和几何相位分析方法(GPA)在原子尺度对薄膜的微结构演化进行了深入系统的研究，利用纳米压痕对薄膜的结合力及断裂韧性进行测试，获得了薄膜微结构与断裂韧性的关系。.首先利用MPCVD在(001)Si衬底上制备了外延SiC薄膜，在原子尺度对薄膜中缺陷诱导的应变演化进行了研究，发现SiC内存在界面失配位错，层错和孪晶等缺陷，而沿SiC/Si界面分布的90°刃型Lomer位错对薄膜的应力释放的影响最大。.利用MPCVD在外延SiC过渡层上制备了管状石墨烯锥阵列，对其微观结构进行研究发现SiC (111)面可外延生长多层石墨烯，而这些具有粗糙起伏结构的(111)面最终诱导石墨烯弯曲形成管状石墨烯阵列结构。.利用MPCVD通过一步法在(001)Si衬底上制备了高韧性的SiC/石墨烯纳米多层复合薄膜，HRTEM研究发现SiC内沿(111)面的缺陷能诱导石墨烯形核导致SiC被插层薄化，然后SiC生长和被石墨烯插层薄化依次重复形成多层复合薄膜。SiC和石墨烯的厚度均在纳米尺度，且两者具有外延关系，最终导致该纳米层状薄膜具有非常高的断裂韧性。.对Si掺杂的金刚石薄膜的微结构演化进行研究发现，TMS的添加导致金刚石的晶粒尺寸细化到纳米尺度，在低温下TMS流量的增加则形成金刚石/SiC复合薄膜。利用金刚石/15%SiC复合结构提高了Ti基体上纳米金刚石薄膜的结合力，此时薄膜内残余应力最小。.总之，在本基金资助下，发现了一种缺陷诱导第二相形核的复合材料生长方法，制备出SiC/石墨烯纳米多层复合薄膜，该薄膜具有非常高的断裂韧性，为开发高韧性材料提供了实验数据和理论依据。.在Carbon, ACS Appl. Mater. Interfaces, Nanoscale, CrystEngComm等国际学术期刊发表SCI论文8篇。