Study On Element Diffusion Characteristics Of Carbide Tool Cutting Cylindrical Shell Material In Tool-chip Contact Zone

The cemented carbide tool will appear adhesion in the process of machining cylindrical shell material(the phenomenon of "sticking knife"),and along with the continuation of cutting process,the tool will be damaged,which will further affect the tool processing and performance.Aiming at this phenomenon,in the support of the National Natural Science Foundation "heavy cutting hard alloy face welding layer damage mechanism research"(project number: 51575146),this paper carried out the research by cutting shell material,2.25Cr-1Mo-0.25 V,as the machined material,and the forming process of adhesion is analyzed.The diffusion equation of cutting contact area in the cutting process is established to predict the concentration distribution between the contact area,and the fracture mode on the rake face is analyzed combined with the micromorphology of the damaged tool which provides the basis for improving the performance of anti-bond and breakage.In the first place,in order to obtain samples that are sticky welded under different cutting conditions,the cutting experimental platform is set up,and the cutting conditions of tool-chip adhesion appearance are obtained by combining the micro-hardness analysis,the observation of the Super-depth of field and the scanning electron microscope.Through the analysis of the force and heat data and the micro surface topography of the rake face,the formation process of the adhesion is analyzed,and the force-heat conditions when the adhesion occurs are obtained,which provides a basis for the parameter setting of the subsequent diffusion model.Secondly,according to the analysis of the forming process of tool-chip adhesion,the diffusion micro-mechanism of tool-chip contact zone is obtained.Combined with Fick's second law,the element diffusion concentration equation containing unknown parameters is established,and diffusion coefficients of different elements are received with five-frequency method,to determine the final form of element diffusion theory model.By scanning the energy spectrum of the welded tools produced in the cutting process,the concentration distribution of different elements is obtained,which is compared with the curves calculated by the equation theory,and the correctness of the model is verified.Again,by using molecular dynamics software,combined with tungsten carbide(WC)microstructure,two simplified models of cemented carbide(WC-Co structure)and shell material(steel structure based on Fe)are established,respectively,and the change of temperature and energy and the model after diffusion are obtained in the process of dynamic analysis to analyze the diffusion characteristics of the contact area.By analyzing the partial enlarged detail of the microstructure at the tool side after diffusion,the formation of holes in the matrix is observed,and with the continued diffusion process,holes are more likely to cause the crack nucleation and propagation by absorbing holes around the vacancy.Finally,by analyzing the stress field and displacement field at the crack tip,the existence of the plastic zone at the crack tip is determined.Combined with the microstructure of the tool,the two ways of crack nucleation are analyzed: nucleation at the initial crack and nucleation on the heterogeneous interface.Combined with the microscopic fracture surface of the material,the microstructure of the bonded rake face is analyzed,and the main way of its destruction is determined,which provides a basis for improving the properties of cemented carbide and preparing new cemented carbide characterized by concentration gradient.