High-temperature tribological behaviors of polycrystalline diamond under water-based drilling fluid environments

For purposes of investigating the high-temperature tribological behaviors of polycrystalline diamond (PCD) thrust bearings under simulated deep drilling conditions, tribological experiments have been conducted under various drilling fluid environments, including pure water-based, potassium-based, calcium-based, sodium-based, and mud drilling fluids. The linear reciprocating mode of CSM-TRN model tribo-tester has been used to reveal the lubrication mechanisms of these fluids at a working temperature of 125 °C. Experimental results demonstrate the PCD compacts tested under pure water-based drilling fluid environment show a higher friction coefficient and wear rate, compared with that tested under potassium-based, calcium-based, sodium-based and mud drilling fluids. The high coverage of the graphitization tribo-chemical films can hinder the oxidization and exfoliation of the PCD, which finally leads to the wear rates under potassium-based, calcium-based, sodium-based and mud drilling fluids are lower than that under pure water-based drilling fluid. Compared with that calcium-based, sodium-based and mud drilling fluids, the PCD compacts tested under potassium-based drilling fluid environment exhibit a low friction coefficient of 0.073 and a low wear rate of 3.15×10⁻² mg/N·m resulting from the synergistic effect of low viscosity of drilling fluid, a smooth worn surface and the lubrication of graphitization tribo-chemical films.