Tribological behavior of polycrystalline diamond compacts under alternating high and low temperature conditions in vacuum environment

The tribological behaviors of polycrystalline diamond compact (PDC) under alternating high and low temperature conditions in vacuum environment were evaluated by a ball-on-disk tribometer. The wear surface features and chemical composition were measured by FIB-SEM-Raman-TOF-SIMS microanalyzer (SEM, EDS, Raman), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the coefficient of friction (COF) was pretty low and stable at atmospheric room temperature condition, while it was much higher and fluctuated in vacuum environment with alternating high and low temperature condition. In atmospheric environment with room temperature, the continuous formation of adsorbed films on the contact surface kept the chemical composition of the friction pair virtually unchanged, and the wear mechanism was a combination of mild abrasive wear and oxidative wear. In vacuum environment with alternating high and low temperature condition, the adsorbed film on the contact surface desorbed and could not continue to form, and the adhesion of Si₃N₄ materials occurred on the wear area and the Si-C bonds were formed. In addition, a combination of high friction heat, localized flash temperature and Co binder led to the graphitization of diamond. The wear mechanism was a combination of abrasive wear and adhesive wear. The above results showed that the adhesion of Si₃N₄ and the Si-C bonds led to high friction force, while the graphitization phenomenon weakened the bonding force between diamond grains, and made them more likely to be detached during the sliding. These were the mainly reasons for the severe wear under vacuum environment with alternating high and low temperature condition.