Wear Properties Of Ultrahard Polycrystalline Diamond And Its Application Exploration

Ultrahard polycrystalline diamond(UHPCD) material is a kind of novel composite material which is synthesized from diamond powders and chemical vapor deposition(CVD) diamond column under high temperature and high pressure. To investigate the tribological properties of UHPCD under different working condition can be the theoretical basis for its application in practical production. In this thesis, the wear characteristics of the UHPCD were verified comparing with polycrystalline diamond(PCD) through a lathe used here by grinding against granite. The tribology characteristics of UHPCD under micro-nano scale were surveyed by a CSM friction test rig against GCr15 balls. Specific UHPCD bits were designed in order to evaluate the advancement of ultrahard polycrystalline diamond materials in the drilling performance of practical bits. The results are shown as followed:(1) Both UHPCD and PCD materials show good performance in grinding against granite. The wear resistance of UHPCD is about two times than that of PCD in four different test conditions. The wear surface of PCD gradually jointed the column surface of granite during grinding, while a convex structure as the cutting edge is formed in UHPCD. The UHPCD possesses a better self-sharpening ability related to PCD.The higher wear resistance and the convex structure of UHPCD can be attributed to the high hardness of CVD diamond. The breakage of CVD diamond in UHPCD is mainly caused by bed separation resulted from fatigue, and the breakage of PCD material is mainly caused by the drop of diamond particles.(2) The tribology performances of CVD diamond and PCD on the polished end of UHPCD sample are quite close. In the range of 1 × 101 ~ 1 × 102 μN, the friction coefficient is relatively high and fluctuating severely and with the increasing of normal load the friction coefficient descends rapidly. The main reason is the interlock of the asperities. In the range of 1 × 102 ~ 1 × 104 μN, the friction coefficient is much lower and its fluctuation is relatively weak. The main factor is the surface roughness which affects the friction. In the range of 1 × 104 ~ 1 × 107 μN, the friction coefficient is stable and with the rising of the normal load the friction coefficient drops gradually. This may because that the increasing load enhanced the ability to overcome the adhesion force. The sliding velocities had little influence on the friction coefficient of both CVD diamond and PCD in the range of 10- 1000 μm/s.(3) The UHPCD bits were designed and prepared successfully and the bits ran well in Qianchen mining area where the drillability of the rocks are 9-12. The drilling lifespan of the bits with ultrahard polycrystalline diamond materials was prolonged 10% at least compared to the bits with PCD. The superior service life of UHPCD bits relative to PCD bits can be attributed to the better wear resistance of UHPCD. In addition, the cutting efficiency of UHPCD precedes that of PCD so it can be recognized that the drilling efficiency of UHPCD bits overmatches the PCD bits.