Synthesis of nanostructured materials has received lot of attention during the past twenty years or so. The two major drivers for this enhanced activity were to produce materials that are much stronger than are available presently and also to explore new phenomena at these small scales. 

Since it is known that high strength materials are usually brittle at room temperature, it was also thought possible to increase the ductility of these hard and strong materials to improve their fabricability, especially of the intermetallics. The expected increased strength has been achieved in metals, alloys, and ceramic materials, reaching a strength level, which is about 4-5 times higher than the corresponding coarse-grained materials. But increased ductility has not been achieved to any significant effect, even though (super)plastic deformation has been achieved at temperatures significantly lower than those needed for their coarser-grained counterparts. Another serious difficulty with these nanostructured materials has been their thermal stability; they degrade at higher temperatures. Consequently, when these materials are exposed to high temperatures, grain coarsening occurs and they lose their strength and other benefits, negating the effects of nanostructure processing.1,2 Hence, efforts are being made all over the world to synthesize materials in the nanostructured condition that exhibit high strength, good ductility, and high-temperature stability. It is, therefore, interesting to see the recent report by Huang et al. of the synthesis, for the first time, of nanotwinned diamond with extremely high hardness and increased thermal stability.3

Scientists have previously produced copper and copper-based alloys that are much stronger than nanostructured copper by increasing their twin density through modification of the electrodeposition processing method.4 But such a phenomenon is mainly confined to materials with a face-centered cubic (fcc) structure. Thus, the synthesis of nanotwinned diamond starting from onion carbon nanoparticles is very significant.3 This has followed from the group’s earlier successes in synthesizing nanotwinned cubic boron nitride starting from onion-like cubic boron nitride precursors. A high density of puckered layers and stacking faults has been suggested to increase the nucleation of nanotwinned diamond. Fine twinning on the scale of 5 nm in width in diamond results in a hardness of about 200 GPa, which is almost twice that of nanodiamond produced by other methods. This nanotwinned diamond also appears to be thermally stable up to about 980oC, about 200oC higher than the thermal stability of natural diamond. Such materials could be very useful for industrial applications such as drilling bits. Since materials with an fcc structure and low stacking fault energy are likely to produce heavy twinning, this approach could be applied to other fcc materials to see whether these could also be strengthened. Further, the combination of strength, ductility, and thermal stability also need be explored.

Huang et al.’s report of the synthesis of nanotwinned diamond using onion carbon nanoparticles at high pressures of 12-25 GPa and high temperatures of 2,300 – 2,500oC, only produces small quantities. Industrial applications, however, will require materials that are well characterized and can be reproduced reliably and in large quantities. Above all, industry would like to have these materials as inexpensive as possible. But these latest nanotwinned diamonds may be quite expensive the way they are currently produced. Some revolutionary ideas may have to be explored to achieve nanotwinned diamond in an economically viable way.


  1. Gleiter, H. (1989) Nanocrystalline materials. Prog. Mater. Sci., 33 (4) 223-315.
  2. Suryanarayana, C. (1995) Nanocrystalline materials. Internat. Mater. Rev., 40 (2) 41-64.
  3. Huang, Q., Yu, D.L., Xu, B., et al. (2014) Nanotwinned diamond with unprecedented hardness and stability. Nature, 510 (7504), 250-253.
  4. Lu, L., Shen, Y.F., Chen, X.H., and Lu, K. (2004) Ultrahigh strength and high electrical conductivity in copper. Science, 304 (5669), 422-426.

Author affiliation

Professor and Interim Chair, Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816-2450, USA