YSU makes major progress in diamond polytypes and its toughness
June 19, 2020
[News from the News Center] Funded by National Key Research and Development Project and Natural Science Foundation of China, Prof. Tian Yongjun and his group of YSU Metastable Materials Science and Technology State Key Laboratory and Prof. Guo Lin and his group of the School of Chemistry, Beihang University produced hierarchically structured diamond composite with exceptional toughness. On June 18, 2020, their achievement was published in the article “Hierarchically structured diamond composite with exceptional toughness” on Nature at https://doi.org/10.1038/s41586-020-2361-2.
HAADF-STEM image of nanotwinning diamond composite
In the Figures above, 3C represents cubic diamond; 2H, 4H, 9R and 15R respectively represent 4 different polytypes of cubic diamond.
Hardness and fracture toughness between nanotwinning diamond composite and typical engineering materials
(Photos above from Metastable Materials Science and Technology State Key Laboratory)
Diamond is the most brittle among known inorganic crystal materials. How to improve its hardness and toughness simultaneously has always been one of the challenging tasks in materials science research. YSU’s early research has confirmed that those two properties can be increased through nanostructuring strategies: with Vickers hardness increasing to 200GPa, the fracture toughness can be improved to a level comparable to cemented carbide.
YSU, Beihang University and other institutes proposed a new idea to toughen diamond. The team reported the structural characterization of a diamond composite hierarchically assembled with diamond polytypes, interwoven nanotwins and interlocked nanograins. Through nanotwinning, laminated composite toughening and transformation toughening, the architecture of the composite enhances the toughness of diamond to 26.6 MPam0.5, a toughness up to five times that of synthetic diamond10, even greater than that of magnesium alloys, and equivalent to that of aluminum alloys, while maintaining the Vickers hardness of 200GPa.
This work confirms the four 4 diamond polytypes in sp3 hybridization: 2H, 4H, 9R and 15R. Furthermore, it could prove useful in making superhard materials and engineering ceramics.
Yue Yonghai, Gao Yufei, Hu Wentao, Xu Bo, serve as the co-first authors of the work, and Zhou Xiangfeng, Guo Lin, Tian Yongjun serve as the corresponding authors.
[Translated by Xing Tong]