Microscopic Mechanism Of The Chemical Wear Of Monocrystalline Diamond In Sliding Contact With Pure Metals

Monocrystalline diamond owns many outstanding mechanical,electrical,chemical and optical characteristics and therefore is widely applied in the fields of ultraprecision manufacturing,micro-nano measuring and micro-nano electrical mechanical system fabrication.However,diamond,the hardest natural material,suffers chemical wear under sliding contact with certain metals that are much softer than it,which influences the fabrication of diamond device and contracts the application of diamond.At present,researches on the chemical wear mechanism of monocrystalline diamond mainly concentrate on macroscopic wear phenomenon and qualitative analysis,providing no unified interpretation and prediction theory on the wear mechanism of diamond at the atomic scale or on the influence of the metal materials on the wear of diamond.Considering the above all,this study focuses on the microscopic mechanism of the chemical wear of monocrystalline diamond and performs the following researches:(1)Aiming at the atomistic removal mechanism of diamond,a series of molecular dynamics simulations is launched on the wear of monocrystalline diamond under friction with iron crystal.According to the simulation results,under high temperature and high load,the diamond atoms tend to get removed as carbon clusters after graphitization or amorphization,in a relatively high speed.And under low temperature and low load,the removal of single atom on the boundary is the dominant regime of the wear of diamond.(2)The transition state theory has been applied to describe the dissociation of single carbon atom from diamond surface under the wear regime of atomistic removal.Through the analytical analysis of the potential energy surface of the unit reaction,a function of the relationship between the energy barrier,which is a key parameter to decide reaction rate,and the reaction surface distance is built up.From the mathematical deduction and numerical simulations,it is concluded that there exists a minimal energy barrier of the unit reaction.After a contact model between diamond and metal bulks is built,an equation to predict the wear rate of diamond in macroscopic scale is given and the calculation requires the value of minimal energy barrier.(3)Based on the built barrier-distance equation,a search algorithm to work out the minimal energy barrier is developed.Via single point energy data obtained from quantum mechanical calculation methods,the minimal energy barrier values of Al(100)/diamond(100),Cu(100)/diamond(100)and Fe(100)/diamond(100)systems have been computed with the algorithm and predictions of the wear of diamond are made accordingly.The comparison between predictions and experimental results of references shows an accordance in the change trend of wear rate with metal specie.(4)Controllable friction experiments to study the wear of diamond under the contact with pure iron,manganese,tantalum and tungsten crystals are performed.The measured macroscopic wear rates,friction coefficients and the graphitization degrees are well explained by the built wear model.