Harsh synthesized pressure is required in constructing of excellent grain boundary (GB) connection for nano-polycrystalline cubic boron nitride (nPcBN) to yield high hardness and toughness. Therefore, it is urgent to fabricate robust nPcBN composite under relatively mild pressure by developing the hard nonmetal binders to form coherent/semi-coherent phase boundary (cPB, scPB) with cBN. Here, the slight content of nano‑boron was composited with nPcBN to achieve superhard property of 45.2 GPa and high fracture toughness 8.4 MPa‧m under a relatively mild condition of 5 GPa and 1800 °C. The hardness is comparable with single crystal cBN and the toughness is about three times higher than single crystal cBN. The nano boron connects the nano cBN grains by cPB and scPB, and nano boron filled the triangular space of cBN crystals, which eliminates the defects to prohibit the crack trigger sources and enhances the strength. This work provides a reference and a new strategy on composite engineering in superhard materials with high toughness by relatively mild synthesized pressure.

中文翻译：

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构建共格/半共格相界以增强超硬cBN-B复合材料的韧性


纳米多晶立方氮化硼（nPcBN）的优良晶界（GB）连接需要严酷的合成压力才能产生高硬度和韧性。因此，迫切需要通过开发硬质非金属粘结剂与cBN形成共格/半共格相界（cPB、scPB），在相对温和的压力下制造坚固的nPcBN复合材料。在此，微量纳米硼与nPcBN复合，在5 GPa和1800 °C的相对温和条件下实现了45.2 GPa的超硬性能和8.4 MPa·m的高断裂韧性。硬度与单晶cBN相当，韧性比单晶cBN高约3倍。纳米硼通过cPB和scPB将纳米cBN晶粒连接起来，纳米硼填充cBN晶体的三角形空间，消除了缺陷，抑制了裂纹触发源，提高了强度。该工作为相对温和的合成压力下高韧性超硬材料的复合工程提供了参考和新策略。