Chinese scientists have developed a new material for hardness super diamond single crystal
July 27 12:21:35, 2025
**Summary**
A groundbreaking study led by Professor Tian Yongjun from the State Key Laboratory of Metastable Materials Science and Technology at Yanshan University, in collaboration with scientists from China and abroad, successfully synthesized a nano-twinned cubic boron nitride material with a hardness exceeding that of diamond single crystals. The research was published on January 17, 2013, in the prestigious journal *Nature*. The paper was highlighted on the cover and in the editorial section of the issue, with detailed illustrations showcasing the synthetic samples and their remarkable properties. The article vividly depicted the material’s extreme hardness, comparing it to both diamond and cubic boron nitride.
In the mid-1950s, scientists first created diamond and cubic boron nitride single crystals, which became essential superhard materials in industrial applications. Superhard materials have a Vickers hardness above 40 GPa, while extremely hard ones exceed 80 GPa. Diamond, known as the hardest natural material, has a hardness range of 60–100 GPa, whereas cubic boron nitride has a lower hardness (30–43 GPa). However, diamond is limited by its low oxidation temperature (~600°C) and reactivity with iron-based materials, restricting its use to non-ferrous materials. Cubic boron nitride, on the other hand, is more stable at high temperatures and does not react with iron, making it widely used in steel processing. But despite this, its hardness and toughness are still significantly lower than those of diamond.
Over the past decade, Professor Tian Yongjun has focused on understanding and enhancing material hardness through theoretical and experimental research, supported by multiple national science projects. In 2003, he proposed a microscopic theory of covalent crystal hardness, enabling the quantitative prediction of single crystal hardness. By 2012, he extended this theory to polycrystalline materials, developing a model that predicted ultra-fine nanostructures could make existing hard materials superhard or even extremely hard.
Guided by this theory, Tian and his team successfully synthesized a transparent nano-twinned cubic boron nitride with an onion-like structure, achieving a hardness of 108 GPa—higher than that of diamond. The twin thickness was only 3.8 nm, far below the traditionally accepted limit for hardening. Surprisingly, the material not only remained hard but continued to increase in hardness as the structure became finer. Additionally, its toughness and oxidation resistance were significantly improved.
Based on the 2012 theoretical model, the researchers found that the hardening mechanism of polycrystalline covalent materials includes an additional quantum confinement effect beyond the well-known Hall-Petch effect. This quantum effect can counteract softening caused by the anti-Hall-Petch effect, allowing continuous hardening without degradation. Experimental results confirmed this, challenging traditional views on material strengthening and paving the way for advanced superhard materials.
The discovery has attracted global attention. *Nature* featured the work in a press release titled “Excellent Super-Hard Materials,†noting that the new material could open up wide industrial applications. Media outlets such as German National Radio, *Scientific American*, and *American Connection* covered the breakthrough. Nathan Hurst of *American Connection* remarked, “Diamond is the hardest material in the world—this is just a misinformation.†The Materials360 website highlighted the potential of the new cubic boron nitride, stating that it could challenge diamond’s status as the hardest material. With its superior hardness, toughness, and stability, the material may even surpass diamond in practical applications.
This achievement marks a significant step forward in materials science, offering new possibilities for the future of machining and industrial technologies worldwide.