The well known trade-off between hardness and toughness (resistance to fracture) makes simultaneous improvement of both properties challenging, especially in diamond. The hardness of diamond can be increased through nanostructuring strategies 1 , 2 , among which the formation of high-density nanoscale twins — crystalline regions related by symmetry — also toughens diamond 2 . In materials other than diamond, there are several other promising approaches to enhancing toughness in addition to nanotwinning 3 , such as bio-inspired laminated composite toughening 4 – 7 , transformation toughening 8 and dual-phase toughening 9 , but there has been little research into such approaches in diamond. Here we report the structural characterization of a diamond composite hierarchically assembled with coherently interfaced diamond polytypes (different stacking sequences), interwoven nanotwins and interlocked nanograins. The architecture of the composite enhances toughness more than nanotwinning alone, without sacrificing hardness. Single-edge notched beam tests yield a toughness up to five times that of synthetic diamond 10 , even greater than that of magnesium alloys. When fracture occurs, a crack propagates through diamond nanotwins of the 3C (cubic) polytype along {111} planes, via a zigzag path. As the crack encounters regions of non-3C polytypes, its propagation is diffused into sinuous fractures, with local transformation into 3C diamond near the fracture surfaces. Both processes dissipate strain energy, thereby enhancing toughness. This work could prove useful in making superhard materials and engineering ceramics. By using structural architecture with synergetic effects of hardening and toughening, the trade-off between hardness and toughness may eventually be surmounted. A diamond composite with a hierarchical microstructure possesses a combination of hardness and toughness surpassing that of all known materials.

中文翻译：

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具有卓越韧性的分级结构金刚石复合材料

众所周知，硬度和韧性（抗断裂性）之间的权衡使得同时改善这两种特性具有挑战性，尤其是在金刚石中。金刚石的硬度可以通过纳米结构策略 1、2 增加，其中高密度纳米级孪晶的形成 - 与对称相关的结晶区域 - 也使金刚石 2 变韧。在金刚石以外的材料中，除了纳米孪晶 3 之外，还有其他几种有前景的增强韧性的方法，例如仿生层压复合材料增韧 4 – 7 、相变增韧 8 和双相增韧 9 ，但很少有研究钻石中的这种方法。在这里，我们报告了分级组装的金刚石复合材料的结构表征，该复合材料由相干界面的金刚石多型（不同的堆叠序列）、交织的纳米孪晶和互锁的纳米晶粒组成。复合材料的结构比单独的纳米孪晶增强了韧性，而不会牺牲硬度。单边缺口梁测试产生的韧性高达合成金刚石 10 的五倍，甚至大于镁合金的韧性。当断裂发生时，裂纹通过 3C（立方）多型体的金刚石纳米孪晶沿 {111} 面通过锯齿形路径传播。当裂纹遇到非 3C 多型区时，其传播扩散到弯曲的裂缝中，并在裂缝表面附近局部转变为 3C 金刚石。这两种工艺都会耗散应变能，从而增强韧性。这项工作可以证明在制造超硬材料和工程陶瓷方面很有用。通过使用具有硬化和增韧协同效应的结构结构，最终可以克服硬度和韧性之间的权衡。具有分级微观结构的金刚石复合材料具有超越所有已知材料的硬度和韧性的组合。