Grain size dependent tribological behaviors of 700 °C annealed polycrystalline diamond

The role of original diamond grain size in the tribological behaviors of the 700 °C annealed polycrystalline diamond (PCD) is discussed in view of experimental studies using complementary analytical techniques (SEM&EDS, TGA-DSC, XRD and Raman). The original diamond grain size has a strong effect on the tribological behaviors of the annealed PCD, which can be accounted for by the various cobalt content and distribution shape. The annealed PCD with the original diamond grain size of 2 μm possesses the lowest cobalt content and presents severe abrasive wear, which is due to the plowing action of exfoliated diamond grains. During the annealing treatment of PCD with large original diamond grain, the large amount of leaf-like distributed cobalt facilitates the diamond graphitization by the catalytic action, which accelerates the formation of friction reducing carbonaceous transfer film, thus yields to a low friction coefficient. The fully oxidation filling into the spalling inhibits the serious grain exfoliation, thus further prevents the annealed PCD wearing substantially. Overall, the cobalt-catalytic diamond graphitization without an excessive wear resistance sacrifice can be exploited to achieve excellent tribological properties of PCD after 700 °C annealing treatment.