Study On Friction Characteristics In Mechanical Scratching

With the development of micro-electromechanical technology,the processing technology of the micro-nano scale structure put forward higher requirements.Mechanical scratching processing technology is flexible and convenient to achieve the processing of micro-structure,so it becomes a hot spot in recent years.In this paper,the friction characteristics between the probe and the material in mechanical scratching process are studied,which reveals the mechanism of material removal and microstructure formation,which is of great significance to the optimization of mechanical scratching process.In this paper,the law of adhesion at nanometer scale is studied by means of experiment and simulation.The calculation model of friction coefficient of micro-nano process is established.Based on the analysis of experimental results,the friction in mechanical scratching process is divided into interface-driven friction and plow-dominated friction.The molecular dynamics simulation was used to simulate the scratching mechanism from the atomic angle.The influence of the interface friction and plowing friction on the surface characteristic was analyzed.The adhesion phenomenon is confirmed based on AFM.And MD(molecular dynamics)simulation results show that the adhesion phenomenon of single crystal silicon is affected by the normal load,and the adhesion force increases with the depth of indentation,the tip radius,and the detachment velocity.And the greater the plastic deformation,the greater the adhesion force.In this paper,the mathematical model of the friction coefficient is established.The model is used to discuss the interfacial friction coefficient,the plowing friction coefficient.Thus to reveal the friction mechanism of scratching on the single crystal silicon.With the scratch speed,scratch distance,the number of scratching increases,the interface friction coefficient decreases,when the scratch speed is 6?ms-1,the scoring distance is 15?m,the number of scratching times is 5,the interface friction coefficient starts less than the plowing friction coefficient,the friction mechanism begins to be dominated by plowing friction.With the scratch load,the scratch distance increases and the friction coefficient of the plow increases,and when the scratch load reaches 10mN,the friction coefficient of the plow is larger than the interfacial friction coefficient,and the friction mechanism between the tip and the sample begins to lead to the plow The friction change.The influence of the number of scratching on the friction coefficient has obvious difference with the other experimental parameters.Under low load(1mN),the interface friction is always dominant.However,under the high load(10mN),with the increase of the number of scratching,the friction mechanism begins to change the friction between the interface and the plow.The MD simulation of the nano scratching process of single crystal silicon are carried out.The results show that atoms beneath the tip are subjected to a large compressive stress(>200 GPa),and tensile stress appear in the scratched surface.With the depth of scratching,scratching distance,the of the tip radius increase,the number of atoms in tensile and compressive stress increases,and the contact area of the tip-sample increases.The impact of velocity on friction is not obvious.Under the condition of interfacial friction,with the number of scratching increased,the radius of the groove is reduced,which is closer to the actual probe shape.When the scratching distance<40?m,with the cumulative scratching distance and the number of scratching increases,the groove is more likely to crack.As the indent depth increases(<32nm),more material is removed by material buildup or debris,and the uplift on both sides of the trench is weakened.When the scratching speed is less than 6?ms-1,the discontinuous accumulation of the material in the trench decreases as the scratching speed increases.Under the scratching conditions dominated by plowing friction:the unevenness of the trenches is related to the interface and plowing friction.With the coefficient of friction decreases,the unevenness of both sides of the groove decrease.The disappearance of the material uplift is related to the change in the mechanism of friction.When the load is less than 10mN,the height of the uplift is increased and the number of uplift decreases with the increase of the load.When the load(<18mN)is large than 10mN,The uplift is weakened until it disappears.With the increase in the number of scratching,the role of plowing is strengthened,and the characterization of the accumulation of material intensified.