Tribological Properties And Mechanism Of Sintered Polycrystalline Diamond Under Vacuum

With super hardness and excellent tribological properties, polycrystalline diamond is widely used for tools and petroleum drilling bits. The excellent performances make it possible to be applied in the space equipment manufacturing. It is significant meaningful to study the tribological properties of polycrystalline diamond in vacuum. In this work, the friction and wear behaviors of the polycrystalline diamond(PCD) were evaluated under vacuum by RM-1 ball-on-disk tribometer. The research includes the following contents. The friction coefficients and wear morphology of PCD in ambient air and vacuum were compared. The effect of applied load, degree of vacuum and counter materials on the tribological properties of PCD in vacuum were researched. The microstructures of the PCD were characterized by scanning electron microscopy, X-ray diffractometry, and Raman spectroscopy. The results showed that,(1) The friction coefficients obtained under vacuum are much higher than those under ambient air, and it increases with applied load increasing. The diamond grains shedding off from the PCD surface can be easily found under vacuum, whereas no observable abrasion was formed under ambient air.(2) The tribological properties of PCD varied when sliding against different materials in vacuum. Obvious adhesion was detected when sliding against Si C and Si3N4, and diamond grains shedding off from the PCD surface can be easily found. In addition, the degree of wear was much higher when sliding against Si C. When sliding against GCr15, the diamond grains shedding off from the PCD was inlaid to the counter ball, which caused the abrasive wear on the PCD surface.(3) The degree of vacuum has an obvious effect on the tribological properties of PCD. The friction coefficients and degree of wear increases with the degree of vacuum increasing.(4) 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 could 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.