Friction and wear behaviors of polycrystalline diamond self-mated pairs in air and water lubrication conditions

Polycrystalline diamond (PCD) is one of the hardest man-made materials with excellent wear resistance, also a preferred friction pair material for sliding bearings on geological drilling and deep-sea energy development equipment which has demanding requirements for extreme load carrying and abrasive wear resistance. However, the friction and wear characteristics of PCD self-mated conformal contact sliding bearings are still not fully understood. PCD self-mated pairs may exhibit some special tribological characteristics, such as abnormal friction vibrations, even if the roughness of the friction surfaces is at the nanometer level, resulting in PCD damage and reliability problem of bearings. In order to reveal the cause of friction vibration and the wear mechanism of PCD self-mated pairs, the friction and wear behaviors of PCD self-mated pairs in air and water lubrication conditions were hereby studied using a ring-on-ring test apparatus. The friction torque at different rotational speeds and loads was measured, the wear surface features of the PCDs were examined, and the composition of the solid film formed during the test at the friction interface was identified. The results show that PCD self-matching pair tends to generate severe friction vibration due to the adhesion of diamond grains rather than the increase of friction interface roughness under the dry friction condition. Water matters considerably in reducing the adhesion. The wear forms of PCDs are adhesive and abrasive wear in dry friction, and abrasive wear in water. PCD with large diamond grains is provided with a better wear resistance.