Ultrahard nanotwinned cubic boron nitride
Ultrahard nanotwinned cubic boron nitride
复制标题
超硬纳米孪晶立方氮化硼
DOI：
10.1038/nature11728
复制
发表时间：
2013-01-17
期刊：
影响因子：
64.8
通讯作者：
Liu, Zhongyuan
中科院分区：
文献类型：
--
作者：
Tian, Yongjun;Xu, Bo;Liu, Zhongyuan
立方氮化硼（cBN）是一种众所周知的超硬材料，具有广泛的工业应用。cBN的纳米结构化是通过Hall-Petch效应提高其硬度的有效方法-硬度随着晶粒尺寸减小而增加的趋势（1，2）。多晶cBN材料通常通过使用类石墨BN前体的马氏体转变来合成，其中高压和高温导致BN层起皱（3）。此类方法已导致合成多晶cBN的粒度小至类似于14 nm（参考文献1、2、4、5）。在这里，我们报告的cBN的形成与纳米结构占主导地位的平均厚度类似于3.8 nm的细孪晶域。这种纳米孪晶cBN是由专门制备的BN前体纳米颗粒合成的，该BN前体纳米颗粒具有洋葱状嵌套结构，具有固有的褶皱BN层和许多堆垛层错。所得的纳米孪晶cBN块体样品是光学透明的，具有惊人的物理性质组合：极高的维氏硬度（超过100 GPa，人造金刚石的最佳硬度），高氧化温度（类似于1，294 ℃）和大的断裂韧性（> 1/2 MPa m（1/2），远超过商业烧结碳化钨的韧性，类似于10 MPa m（1/2））。我们发现，cBN的硬化是连续的，随着孪晶厚度降低到最小尺寸的研究，与预期的反向Hall-Petch效应低于临界晶粒尺寸或类似于金属和合金中发现的10-15 nm的孪晶厚度。
Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall-Petch effect-the tendency for hardness to increase with decreasing grain size(1,2). Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers(3). Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as similar to 14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness similar to 3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (similar to 1,294 degrees C) and a large fracture toughness (>12 MPa m(1/2), well beyond the toughness of commercial cemented tungsten carbide, similar to 10 MPa m(1/2)). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall-Petch effect below a critical grain size or the twin thickness of similar to 10-15 nm found in metals and alloys.