The Surface Material Removal Mechanisms Of Nanotwinned Diamond And Its Tool Wear By Simulation

Nanotwinned diamond is a promising candidate material for cutting tools,highpressure physics,and other fields due to its excellent properties of much higher hardness and fracture toughness as compared to single-crystal diamond.Remarkable achievements have been achieved in understanding the mechanical properties and deformation mechanism when nanotwinned diamonds are subject to compression,fracture,or indentation.However,the mechanism of surface material removal in nanotwinned diamond tool manufacturing and its wear resistance characteristics have not been investigated intensely.For the purpose of analyse the microscopic change mechanism for the unique crystal structure of nanotwinned diamond under various loading forms at the atomic scale,this paper investigates the surface material removal of nanotwinned diamond under conditions and the wear process of nanotwinned diamond tools in cutting using molecular dynamics simulation by comparison with single-crystal diamond.Firstly,computational models for scratching nanotwinned diamond with diamond abrasive grain and cutting single-crystal silicon carbide with nanotwinned diamond tools are established based on the computational principles of molecular dynamics,and parameters such as suitable integration algorithms,potential functions and boundary conditions are selected.For the anisotropy of nanotwinned diamond,nanotwinned diamond workpieces and tools with typical crystal orientations have been established.Secondly,the morphology of chips and subsurface damage,the distribution of temperature and stress,the formation process of subsurface damage,and the plastic deformation mechanism were systematically investigated.Compared with single-crystal diamonds,more obvious plastic deformation was found in nanotwinned diamonds.The main dislocations in single crystal diamonds are perfect dislocations and the plane of dislocation slip is the {111} plane which is inclined to the scratching direction,whereas the main type of dislocation in nanotwinned diamonds is partial dislocations and the dislocations only slipp on the {111} planes parallel to the twin boundaries.Furthermore,detwinning was also observed during subsurface damage formation besides amorphism.Finally,in cutting with nanotwinned diamond tools,the evolution of tool wear morphology,wear rate,amorphization process and tool stress and temperature during cutting were analysed,as well as the effect of different crystal orientations and different twin boundaries distribution positions on tool wear rate were investigated.Twin boundaries have no influence on the amorphization process in tools,i.e.the transition from a perfect crystal structure to an amorphous sp3 hybrid atomic structure and subsequently to an amorphous sp2 hybrid atomic structure.A part of the atoms of the amorphous sp2 hybrid structure transforms into an sp1 hybrid structure and leaves the tool,while another part of the atoms leaves the tool directly in an sp2 hybrid structure.The amorphization process of diamond tool atoms in cutting is mainly induced by stress rather than temperature.The above findings can provide theoretical support to study the application of nanotwinned diamond materials in cutting tool manufacturing and tool cutting performance.