Study On Grinding Behavior Of Single Crystal Diamond And Anisotropic Mechanism Based On Phase Transformation And Plastic Deformation

Mechanical grinding technology is the key technology for fabricating highprecision diamond tools.The material removal method is that the surface diamond crystal undergoes phase transformation under mechanical stress,thereby achieving plastic removal.However,the formation of phase transformation layer not only affects the surface quality of diamond tools,but also restricts the subsequent performance of diamond tools.Therefore,how to improve the grinding process is the key problem to improve the surface quality and service life of diamond tools.In this paper,the removal mechanism of mechanical grinding is studied by molecular dynamics simulation and Transmission Electron Microscope(TEM)observation experiment.Combined with anisotropic analysis,the mechanical grinding process is improved,thereby improving the surface accuracy of the tool.The method of improving the subsurface phase transformation layer is studied by low temperature annealing simulation to improve the subsequent performance and service life of diamond tools after mechanical grinding.The main research contents are as follows:Firstly,the formation mechanism of plastic deformation in single crystal diamond nanoindentation is revealed from the atomic point of view by molecular dynamics simulation,and the simulation results are verified by TEM observation experiment.It is considered that the plastic deformation of single crystal diamond is the generation and growth of 1/2[110]{111} complete dislocation ring caused by the phase transformation from disordered sp3 carbon atom to ordered sp2 carbon atom.And the phase transformation is an important excitation source of plastic deformation at the atomic scale.The phase transformation process will make the adjacent carbon atoms break and recombine,tending to graphitization.This study provides a theoretical basis for controlling the plastic deformation induced by phase transformation in diamond mechanical grinding,thereby improving the surface accuracy of ultra-precision machining.Secondly,based on the experimental observation of anisotropic surface accuracy of diamond mechanical grinding,the intrinsic relationship between surface accuracy and removal rate of single crystal diamond mechanical grinding anisotropy is studied from the atomic point of view by molecular dynamics simulation.It is considered that the conversion of ordered sp3 carbon atoms to ordered sp2 carbon atoms in mechanical grinding will make the diamond surface softer and obtain higher removal rate.The increase of the proportion of 1/2[110]type complete dislocation will obtain better surface accuracy by diamond mechanical grinding.The intrinsic relationship between anisotropy and grinding accuracy and grinding efficiency revealed by this study provides better technical support for diamond mechanical grinding process.Finally,the evolution law of heat treatment on diamond surface material is revealed through the combination of the molecular dynamics simulation of low temperature annealing and the influence of anisotropy on low temperature annealing.It is considered that the internal factors of low-temperature annealing can improve the mechanical strength of diamond are the repair of defective carbon atoms and the generation of nano-graphite crystal structure.The proportion of amorphous carbon atoms in the damaged layer inside different substrates and the proportion of dislocation regions generated by mechanical stress determine the improvement of mechanical properties of low-temperature annealing.This study provides a theoretical basis for the repair of the surface damage layer of single crystal diamond tools and the improvement of mechanical properties and service life.