Abstract
The mechanical properties of nano-polycrystalline diamond (NPD) synthesized by the direct conversion of graphite under high pressure and high temperature have been investigated. Indentation hardness and bending strength tests revealed that NPD has considerably high hardness and high transverse rupture strength (TRS) at high temperature, far surpassing those of conventional polycrystalline diamond (PCD) and single-crystal diamond (SCD). The hardness remained higher than 100GPa even at 800°C, while the hardness of SCD sharply decreased to 60GPa above 300°C. The TRS remained at about 3GPa up to 1000°C, above which it showed a positive temperature dependence, while the TRS of PCD decreased rapidly at about 500°C. Wear tests using a diamond wheel indicated that the abrasive wear resistance of NPD is equivalent to those of the high wear-resistance directions on SCD, and from 10 to 50 times higher than those of PCD. These results suggest that NPD has outstanding potential for cutting tools.
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