高纯纳米金刚石多晶材料的高温高压无助剂烧结与结构性能调控

High purity nano-polycrystalline diamond, which is usually synthesized through direct transformation of carbon sources under high pressure and high temperature conditions, has broad application prospect due to its high hardness, high fracture toughness, and good thermal stability. However, the direct transformation method has limitations. First, the carbon sources usually have low density, and large volume collapse occurs during the transformation, which is harmful to the synthesis process under extreme pressure and temperature conditions. Second, the process of the phase transformation and the resulted microstructures are complex, causing controversy in explaining the related mechanisms, such as hardness enhancement mechanism. In this project, nano-diamond powder will be used as the raw material, and the high purity nano-polycrystalline diamond will be prepared by sintering under high pressure without additives. Our method can avoid the interference caused by the complex phase transformations and the microstructure formation process in the direct transformation method, making the formation process of the samples more intuitive and controllable. By selecting proper raw materials and preprocessing methods, optimizing the pressure-temperature-time synthetic path, designing and developing the sample assembly, the applicant hope to get proper synthetic routines of high purity nano-polycrystalline diamond, which can practically be used in industry. In the mean time, by investigating the sintering behaviors of nano-diamond powders under different pressure-temperature-time conditions, combining with the comprehensive characterizations of the prepared samples, the applicant hope to adjust and control the microstructures, as well as the properties of the samples effectively. The applicant also intends to clarify the associations of preparation, microstructures, and properties, revealing the hardness enhancement mechanisms. This project will not only provide a reliable synthetic routine of nano-polycrystalline diamond, more importantly, it will provide a new idea for designing and preparing of new superhard materials.

高温高压直接转变碳源合成的高纯纳米金刚石多晶材料具有很高的硬度、断裂韧性和热稳定性，应用前景广阔。然而，直接转变法具有自身的局限性：碳源在超高压转变过程中体积塌缩较大；转变过程及产物显微结构复杂，导致硬度增强机制的解释等存在争议。本项目拟直接以纳米金刚石微粉为原料，高温高压无助剂烧结制备高纯纳米金刚石多晶材料，避免碳源大体积塌缩和复杂转变过程，使微结构形成更为直观、可控。申请人希望通过初始原料的选择和处理、烧结压力-温度-时间的优化、大尺寸样品腔的设计和改进等，发展可实用化的制备工艺；通过研究纳米金刚石高温高压烧结过程中物相与微结构的演变规律，结合样品理化性能的全面表征，实现对样品结构和性能的有效调控，阐明制备工艺-显微结构-理化性能的关联，揭示硬度增强机制。本项目不仅将为制备高纯纳米金刚石多晶材料提供可靠的技术工艺，更重要的是，将为新型超硬材料的设计与制备提供新的思路。

纳米多晶金刚石的硬度与单晶金刚石硬度相当甚至更高，其耐磨性、断裂韧性和热稳定性也优于常规金刚石材料，已在超精细切削和超高压技术等领域崭露头角，应用前景广阔。本项目直接以纳米金刚石微粉为原料，高温高压无助剂烧结制备了纳米多晶金刚石块体材料，避免了直接转变法中碳源的大体积塌缩和复杂转变过程，使材料的微结构形成更为直观、可控，开辟了一条制备新型纳米超硬材料的新路径。本项目通过初始原料的选择和处理、大尺寸样品腔的设计和改进、烧结压力-温度-时间的优化等，发展了可实用化的制备工艺。通过微结构分析、光谱分析、压痕测试等手段，对纳米多晶金刚石烧结样品进行了系统表征，揭示了纳米多晶金刚石材料制备工艺-微结构-理化性能的关联。通过分析测试数据并结合理论计算，揭示了纳米多晶金刚石的微结构特征，得到了纳米多晶金刚石高温高压无助剂烧结的微观机制和纳米多晶金刚石的硬度增强机制，研究了微观结构（如晶界、孪晶界等）对纳米多晶金刚石硬度的影响，对比实验研究了单晶金刚石和纳米多晶金刚石的压痕效应。项目这些成果的获得，不仅为制备纳米多晶金刚石材料提供了全新的技术工艺，也为设计和制备新型纳米超硬材料提供了新的思路和基础科学数据，具有重要的实际应用价值和科学价值。