Recently, the team led by Prof. Guo Lin and Prof. Yue Yonghai from Beihang University, together with the team led by Academician Tian Yongjun and Prof. Nie Anmin from Yanshan University (YSU), has achieved major breakthroughs in the room-temperature self-healing behavior of ultra-hard covalent bond materials. Their research findings were published in Nature Materials under the title of “Self-healing of fractured diamond” on September 21. Beihang Ph.D. candidates Qiu Keliang and Hou Jingpeng, and YSU Ph.D. candidate Chen Shuai are co-first authors. Prof. Yue Yonghai, Prof. Nie Anmin, Academician Tian Yongjun and Prof. Guo Lin are corresponding authors.
Being the hardest material in nature, diamond boasts prominent features such as high light-admitting quality, high thermal conductivity, and wide band gap and has promising application potentials. Yet its innate fragility may lead to catastrophic breakdowns, posing great threats to the reliability and durability of devices made of it. Therefore, how to enhance its toughness while maintaining its ultra-hardness has always been a great challenge. To this end, the team led by Prof. Guo Lin and Prof. Yue Yonghai cooperated with the YSU team, and created a new nanotwinned diamond composite by introducing multi-stage structures such as interlocked nanocrystalline grains, interwoven nanotwins and diamond polyforms coexisting with nanotwins. According to situ electron microscopy results, the synergistic effect of lamination toughening, twin toughening and phase change toughening has increased the fracture toughness to more than 5 times that of single crystal diamond. These findings were published in Nature (2020, 582, 370-374).
However, even though the fracture toughness of nanotwinned diamond composites (ntDCs) has reached nearly 27 MPam0.5, catastrophic accidents caused by micro-cracks were still inevitable. The researchers found that when the stress was removed in the unilateral notch beam test experiment, the cracks miraculously nearly disappeared. In this regard, if diamond can start to self-heal the moment micro-cracks appear, it will have revolutionary significance for improving the durability and reliability of diamond-based materials and devices.
To this end, the two teams conducted in-depth and systematic research on the self-healing phenomenon. The self-healing behavior of nano-twin diamond composite and single-crystal diamond was systematically studied from micro to nano and even atomic scale using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) instruments. The researchers found that the completely fractured ntDC showed remarkable fracture self-healing capability at room temperature without external intervention such as compressive stress. Quantitative study results showed that the healing efficiency of fractured ntDC after recovery is about 34%, which is significantly higher than that of single crystal diamond (DSC) of about 6.7% (see Figure 1). This self-healing behavior still exists even when the size reaches the micron level.
Figure 1 Quantitative study of self-healing behavior of fractured ntDC/DSC
To further reveal the intrinsic mechanism of ntDC's self-healing behavior, the researchers studied its healing mechanism in atomic scale with in-situ mechanical system under TEM. They named the amorphous tissues containing sp2- and sp3- hybrid carbon atoms generated at ntDC fracture Diamond Osteoblast (DO) after osteoblasts formed during bone healing (see Figure 2). As the DO interphase distance between the two fractures decreased, the interatomic force changed from repulsion to attraction and re-bonding, achieving self-healing (see Figure 3).
Figure 2 Microstructure of ntDC and in situ TEM observation of the formation of DO phases at the fractured surfaces
Figure 3 Dynamic healing process of two fractured surfaces with DO protrusions
This study opens up a new path for the design and development of brittle ceramic materials with high durability and fracture-resistance. At the same time, as a typical representative of covalent bonds, diamond’s self-healing behavior will provide guidance for the development and design of strong covalent bond self-healing materials, especially for the direct bonding of wafers at room temperature.
Link to the Article: https://www.nature.com/articles/s41563-023-01656-4
Written by: Liu Naipeng
Reviewed by: Liu Kesong
Edited by: Jia Aiping
Translated by: Zhang Anqi
