Abstract
Mechanical properties of high-purity nano-polycrystalline diamonds synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures were investigated by microindentation testing with a Knoop indenter and observation of microstructures around the indentations. Results of indentation hardness tests using a superhard synthetic diamond Knoop indenter showed that the polycrystalline diamond synthesized from graphite at ⩾15 GPa and 2300–2500 °C (consisting of fine grains 10–30 nm in size and layered crystals) has very high Knoop hardness (Hk ⩾ 110 GPa), whereas the hardness of polycrystalline diamonds synthesized from non-graphitic carbons at ⩾15 GPa and below 2000 °C (consisting only of single-nano grains 5–10 nm in size) are significantly lower (Hk = 70 to 90 GPa). Microstructure observations beneath the indentations of these nano-polycrystalline diamonds suggest that the existence of a lamellar structure and the bonding strength of the grain boundary play important roles in controlling the hardness of the polycrystalline diamond.
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ACKNOWLEDGMENTS
The authors thank H. Yusa, T. Inoue, H. Ofuji, and K. Harano for their help with this study. This work was partially supported by a grant from the New Energy and Industrial Technology Development Organization, Japan (NEDO).
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Sumiya, H., Irifune, T. Hardness and deformation microstructures of nano-polycrystalline diamonds synthesized from various carbons under high pressure and high temperature. Journal of Materials Research 22, 2345–2351 (2007). https://doi.org/10.1557/jmr.2007.0295
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DOI: https://doi.org/10.1557/jmr.2007.0295