Study On Temperature Changes And The Formation Mechanism Of Silicon Carbide In Monocrystal Silicon Nanometric Cutting

In the process of nanometric cutting of single-crystal silicon using a single pointdiamond tool，the groove wear happening at the flank of the diamond tool seriously affectsthe tool’s used life-span and the workpiece surface quality. In nanometric cutting, the hardparticles may be an important factor which results in the groove wear. However theformation mechanism of the hard particles is not very clear. This thesis considers theinfluence of the energy of phase transformation of crystal silicon to the temperaturevariation and calculates the temperature of cutting region by means of molecular dynamics,and then investigates the formation mechanism of hard particles from the perspective ofchemical.Firstly, this thesis established the molecular dynamics model of crystal siliconuniaxial compression and simulated it considering the influence of phase transformation ofcrystal silicon to the temperature variation. It confirmed that the stress value of studyregion achieved the threshold of phase transformation of β-silicon, and also found thatcrystal silicon transformed from α-silicon to β-silicon by analyzing the coordinationnumber and radial distribution function of silicon atoms. And it observed the distributionof silicon atoms of phase transformation by visualization software. Then it analyzed therelationship between the free energy and enthalpy change and the temperature in thecutting progress and explored the energy of the single–crystal silicon phase transformationin theory to confirm the single-crystal silicon phase transformation is an exothermicprogress. In addition, it obtained the relations between the temperature and the energy ofsingle-crystal silicon phase transformation by calculating the energy which is released byphase transformation and temperature of phase transformation zone.Secondly, this thesis established the molecular dynamics model of monocrystaldiamod tool cutting monocrystal silicon considering the phase transformation ofsingle-crystal silicon at the cutting zone. It calculated the energy of monocrystal siliconphase transformation of cutting zone and applied the formula between temperature andenergy to obtain the temperature of cutting zone. Then it combined the common neighboranalysis of crystal structure of tool and workpiece to discusse the formation mechanism of hard particles from the temperature of cutting zone and lattice broken point view, so thisthesis hold that messy atom caused by lattice broken of tool and workpiece due to the hightemperature and high pressure within the cutting region was in favor of the generation ofhard particles.Finally, this thesis used the chemical reaction thermodynamics theory to calculate thegibbs free energy of the hard particles formation reaction in different temperature, thenfound that the temperature of cutting region achieved the threshold of formation reactionof hard particles and proved it could happen. On the basis of the least free-energy principle,this thesis conclude that the single-crystal can accelerate the formation of hard particleswhen it was oxidized by comparing the size of gibbs free energy of different chemicalreaction.