Atmosphere Dependence On The Tribological Properties And Mechanism Of Polycrystalline Diamond

The polycrystalline diamond compact(PDC)not only has the advantages of ultra-high hardness and excellent wear-resistance property,but also possesses the high strength and outstanding impact toughness.These excellent properties make the PDC extensively applied invarious engineering fields,such as aerospace field,geologic drilling and so on.The PDC tools also suffered terrible environment which influence the tribological performance.In aerospace field,the adhesion lead to drastic wear for PDC.Lubricating oil and solid lubricant are limited to use in precision cutting and dry cutting because of the dinky spatial scale and pollution,it can cause the premature failure for PDC tool.Atmosphere is intangible and environmental,therefore,this nature make atmosphere as a new style of lubricant for PDC in these special application.This article aimed to study the effect of different gases that make up atmosphere on tribological behaviors of PDC.In addition,the study also tried to control the change of gases pressure to decrease adhesion in vacuum environment,the experiment results showed that:(1)The friction coefficient of the PDC disc against Si3N4 ball in nitrogen and argon environment is 0.045 and 0.051,less than that in oxygen and air,because large friction reducing transfer films formed in nitrogen and argon.(2)The wear of the PDC disc against Si3N4 ball in nitrogen and argon environment is 15.3×10-9 mm3/Nmm and 15.8×10-9 mm3/Nmm,more terrible than that in oxygen and air.The wear mainly happened in the run in period.In this stage,plastic deformation and strong covalentreaction led to lots of materials spall from tribopairs.The long time and drastic run in period in argon and nitrogen environment cause the serious wear for PDC disc and Si3N4 ball(3)In vacuum environment,the adhesive in tribo-interface lead to serious tribological performance.Water and hydrogen can restrain the adhesive in low pressure of their environments,decrease the friction coefficient less than 0.1,however,the oxygen and nitrogen are not able to do that.(4)Oxygen is not able to restrain the adhesive in low pressure,but with the pressure rise,it can also decrease the adhesive.At the pressure of 103 pa,the friction coefficient is also decreased to low value.