Effect of soaking time on the friction properties of polycrystalline diamonds

• The friction behavior of PCDs soaked for different periods were evaluated.
• The relationship between chemical transformations and soaking time was studied.
• The two-dimensional and three-dimensional surface morphologies were examined.

The friction behaviors of polycrystalline diamonds (PCD) soaked for different periods at temperatures of 700 °C, 800 °C and 900 °C were evaluated using a ball-on disk tribometer in air. X-ray diffraction experiments were performed to study the chemical transformation of the surface of PCD. The two-dimensional and three-dimensional surface morphologies of PCDs were examined by scanning electron microscopy and atomic force microscopy, respectively. Results show that the friction coefficient and average surface roughness (Ra) are not sensitive to the soaking time at 700 °C. Meanwhile, no special chemical transformations were detected on the surface of PCD, except for the oxidation of Co when the soaking time exceeded 20 min. The value of Ra was observed to decrease slightly (from 79.5 nm to 91.0 nm) with the increase in soaking time at 800 °C while an outstanding decrease in the average friction coefficient of PCD was observed when the soaking time exceeded 60 min due to the transformation of diamond into graphite. The average value of the friction coefficient decreased greatly with the increase in soaking time at 900 °C due to the enhancement in the graphitization of diamond.