AsianScientist (Jun 12, 2014) – A team of scientists from China and the US has found a way to grow diamonds that attained new levels of hardness, thermal stability and fracture toughness. The first of its kind, their discovery offers potential ways of producing new materials that yield more extraordinary properties than current alternatives.
Science and industry share the common quest of finding suitable materials for cutting tools.Currently, diamonds and diamond-based composites are preferred for their hardness and wear-resistant qualities, which means that they are highly resistant to pressure and deformation by long-term mechanical stress. However, they have poor thermal stability and oxidize at about 800˚C, which results in limitations to their industrial applications.
The team, which included scientists from Yanshan University and Jilin University, investigated ways that could improve the hardness and thermal stability of diamond simultaneously. In 2013, they discovered a process for making a nanotwinned form of boron nitride, called nt-cBN, which displayed high degrees of hardness and thermal stability, in addition to strong resistance against crack propagation. This last property is also known as fracture toughness.
Mirroring the methods applied in their previous research, the team attempted to synthesize a nanotwinned form of diamond (nt-diamond) by using an onion-like carbon precursor, a high-energy carbon consisting of concentric shells resembling graphite. When treated with high pressure and temperature, the onion carbon produced nt-diamond samples with similar microscale characteristics to those of nt-cBN.
Based on subsequent experimental measurements of the nt-diamond samples, their research published in Nature: Letters confirmed the superior characteristics expected of the nanotwinned diamond. The nt-diamonds displayed Vickers hardness, or resistance to pressure levels, up to 200 GPa; withstood oxidation at temperatures more than 200˚C higher than that of natural diamond; and yielded higher fracture toughness than other commercially available diamond composites.
“We showed that nanotwinning is not only an effective mechanism for acquiring a smaller characteristic size of microstructure to increase material hardness and toughness, but also that it may potentially increase a material’s thermal stability,” explained co-author Dr. Tian Yongjun from Yanshan University.
According to the researchers, the creation of nanotwinned microstructures offers a general pathway for manufacturing new advanced carbon-based materials with exceptional thermal stability and mechanical properties.
The article can be found at: Huang et al. (2014) Nanotwinned diamond with unprecedented hardness and stability.
Copyright: Asian Scientist Magazine; Photo: Bo Xu, Wentao Hu, and Quan Huang (Yanshan University, China).
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