Friction and wear behaviors of polycrystalline diamond under vacuum conditions

In this work, the friction and wear behaviors of the polycrystalline diamond (PCD) sliding against Si3N4 ball were evaluated under both ambient air and vacuum by a ball-on-disk tribometer. The microstructures of the PCD were characterized by scanning electron microscopy, X-ray diffractometry, and Raman spectroscopy. The results showed that the friction coefficients obtained under vacuum are much higher than those under ambient air, and it mainly attributed to serious adhesion under vacuum because of the absence of the absorbed layer formed under ambient air. The high friction heat and the catalyzing of Co resulted in the graphitization of PCD under vacuum. The diamond grains shedding off from the PCD surface can be easily found under vacuum, whereas no observable abrasion was formed under ambient air. Both the strong adhesion between counter surfaces and the weak bonding strength among diamond grains contributed to the serious wear under vacuum.