Study On Vacuum Tribological Behavior And Wear Mechanism Of Polycrystalline Cubic Boron Nitride

Polycrystalline cubic boron nitride（PcBN）is a superhard material sintered with cubic boron nitride（cBN）and a binder under certain conditions.Due to the regular tetrahedral structure of cBN,PcBN has excellent properties such as high hardness,high wear resistance,high thermal conductivity,high temperature chemical stability,and high temperature mechanical stability.Therefore,tools made of PcBN material have good red hardness,fracture toughness,and the advantage of maintaining chemical inertness with iron group metal materials.As a superhard material,PcBN has better high-temperature chemical stability and high-temperature mechanical stability than polycrystalline diamond,which is also a superhard material.Superhard materials usually face environmental conditions of high temperature,high humidity,high load,high speed and high vacuum in actual service conditions.Under different environmental conditions,superhard materials exhibit completely different friction and wear behaviors.The excellent properties of polycrystalline cubic boron nitride such as high-temperature chemical stability and high-temperature mechanical stability make it have important potential use value in the field of unconventional energy exploration and development and on-orbit manufacturing.This paper aims to study the tribological properties of PcBN and different materials by simulating different environmental conditions and changing loads under different working conditions.Through the friction coefficient,the wear rate is calculated,and the microscopic morphology and element content are analyzed.The wear mechanism of PcBN was determined to provide tribological basis for extending its application.Finally,the following experimental results are obtained:（1）The average friction coefficient of PcBN-Si3N4,PcBN-YG8 and PcBN-GCr15pairs under vacuum conditions and the average friction coefficient of PcBN-Si3N4 pairs under atmospheric conditions are negatively correlated with the load.The average friction coefficient of the PcBN-Al2O3 pair under different environmental conditions is the lowest when the load is10 N.PcBN-GCr15 has the lowest average friction coefficient when the load is 10 N under vacuum conditions.（2）Under vacuum conditions,PcBN and YG8 friction pairs have different unit strokes,and the wear rate ratios WY/WP of 2 N,5 N,10 N and 15 N are 7.0,6.4,6.0,5.3（ie YG8 wear rate/PcBN wear rate）,PcBN shows good tribological properties.Under vacuum conditions,the wear rate of GCr15 on the grinding balls is of the order of 10^-10,the wear rate of Al₂O₃ on the grinding balls in the atmosphere is 10^-10,and the abrasion rate of the vacuum environment can reach 10^-8,and the wear rate of Si3N4 in the vacuum environment.The order of magnitude of the Si3N4 wear rate is 10^-7,and the order of magnitude of the Si3N4 wear rate is 10^-9.（3）Under vacuum conditions,the wear forms of Al2O3,Si3N4,GCr15 and YG8friction pairs are mainly abrasive wear and adhesive wear;in addition,Al2O3 and Si3N4also cause serious furrow wear on the grinding balls;external load 15N,at this time,the Al2O3 surface wear scar appears to be cracked,forming a step surface;GCr15 has obvious irregular shapes on the grinding ball with the increase of external load.PcBN vacuum environment is mainly abrasive wear and adhesive wear.