Nanotwinned diamond with unprecedented hardness and stability
Nanotwinned diamond with unprecedented hardness and stability
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纳米孪晶金刚石具有前所未有的硬度和稳定性
DOI：
10.1038/nature13381
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发表时间：
2014-06-12
期刊：
影响因子：
64.8
通讯作者：
Tian, Yongjun
中科院分区：
文献类型：
--
作者：
Huang, Quan;Yu, Dongli;Tian, Yongjun
虽然金刚石是最硬的切削工具材料，但较差的热稳定性限制了其应用，特别是在高温下。同时提高金刚石的硬度和热稳定性一直是人们所期望的。根据Hall-Petch效应（1，2），金刚石的硬度可以通过纳米结构（通过纳米晶粒和纳米孪晶显微结构）来增强，如先前的研究（3-7）所示。然而，对于烧结良好的纳米金刚石，粒度在技术上限制在10-30 nm（参考文献3），与天然金刚石相比，热稳定性降低（4）。最近成功合成纳米孪晶立方氮化硼（nt-cBN），孪晶厚度降至约3.8 nm，这使得同时实现更小的纳米尺寸、超硬度和上级热稳定性成为可能（5）。目前，通过各种碳前驱体（如石墨、无定形碳、玻璃碳和C-60）的直接转化制备纳米孪晶金刚石（nt-diamond）（3，6，7）尚未成功。在这里，我们报告了直接合成的纳米金刚石的平均孪晶厚度接近5纳米，在高压和高温下使用洋葱碳纳米粒子的前体，并观察到一种新的单斜晶体形式的金刚石共存的纳米金刚石。这种纯合成块状纳米金刚石材料显示出前所未有的硬度和热稳定性，维氏硬度高达200 GPa，空气中的氧化温度比天然金刚石高出200摄氏度以上。纳米孪晶微结构的产生为制造具有优异热稳定性和机械性能的新型先进碳基材料提供了一条通用途径。
Although diamond is the hardest material for cutting tools, poor thermal stability has limited its applications, especially at high temperatures. Simultaneous improvement of the hardness and thermal stability of diamond has long been desirable. According to the Hall-Petch effect(1,2), the hardness of diamond can be enhanced by nanostructuring (by means of nanograined and nanotwinned microstructures), as shown in previous studies(3-7). However, for well-sintered nanograined diamonds, the grain sizes are technically limited to 10-30 nm (ref. 3), with degraded thermal stability(4) compared with that of natural diamond. Recent success in synthesizing nanotwinned cubic boron nitride (nt-cBN) with a twin thickness down to similar to 3.8 nm makes it feasible to simultaneously achieve smaller nanosize, ultrahardness and superior thermal stability(5). At present, nanotwinned diamond (nt-diamond) has not been fabricated successfully through direct conversions of various carbon precursors(3,6,7) (such as graphite, amorphous carbon, glassy carbon and C-60). Here we report the direct synthesis of nt-diamond with an average twin thickness of similar to 5 nm, using a precursor of onion carbon nanoparticles at high pressure and high temperature, and the observation of a new monoclinic crystalline form of diamond coexisting with nt-diamond. The pure synthetic bulk nt-diamond material shows unprecedented hardness and thermal stability, with Vickers hardness up to similar to 200 GPa and an in-air oxidization temperature more than 200 degrees C higher than that of natural diamond. The creation of nanotwinned microstructures offers a general pathway for manufacturing new advanced carbon-based materials with exceptional thermal stability and mechanical properties.