Research On Chipping Mechanism And Surface Integrity Of Aero-engine Single Crystal Components

Single crystal superalloys have excellent high temperature resistance and creep resistance,and have good development prospects in the fields of aerospace,optics,biomedicine and military.As a new type of material,compared to polycrystalline alloys,single crystal superalloys have only one grain,which eliminates the influence of grain boundaries,making the two parts have a large difference in the machining process.As an important machining method,milling has the advantages of high production efficiency,wide processing range and low production cost.The quality of the milled surface has an important influence on the service life of the components.A combination of experiments and theory was used to explore the milling chip formation mechanism and surface integrity of single crystal superalloys.In this thesis,an experimental study on the milling process of DD5 single crystal superalloy was carried out,and it was compared with GH4169 polycrystalline superalloy.The combination of simulation and experiment was used to explore the chip formation mechanism and surface integrity of single crystal components during milling.It was concluded that the milling force and surface integrity of single crystal superalloys depended on the milling process parameters(milling line speed,milling depth and feed rate)and anisotropy.The chip formation mechanism of single crystal superalloys,the change pattern of chip morphology,and subsurface microstructure were summarized.The main research contents are as follows:(1)The influence of microstructure and anisotropy on the properties of the single crystal superalloy was analyzed.Based on Abaqus simulation software,a two-dimensional orthogonal cutting model was established to complete the simulation of chip formation process.Research on the change law of temperature field,stress field and strain field of single crystal superalloy during milling.The law of influence of different process parameters on milling force was obtained(2)An experimental study of the milling process of single crystal superalloys was carried out.Based on the analysis results of orthogonal experiments,the primary and secondary order of the influence of milling process parameters on the milling force was obtained.At the same time,a single factor experimental scheme was designed to further explore the milling process parameters and anisotropy.The effect on the milling force was compared with the simulation results.(3)The chip formation mechanism research of single crystal superalloy milling process was carried out.Based on the theory of shear slip,the chip morphology of single crystal superalloy under different milling process parameters was analyzed,and the theoretical index of chip deformation was introduced to analyze chip formation.(4)The research on the surface quality of DD5 single crystal superalloy milling was carried out,the influence of milling process parameters on the surface roughness of DD5 single crystal superalloy workpieces was analyzed,and the processing parameters were optimized to obtain the optimal milling process parameter combination.At the same time,a single factor experiment was designed to analyze the specific influence of milling process parameters and anisotropy on the surface roughness of single crystal superalloys.(5)The research on the subsurface deformation of DD5 single crystal superalloy milling was carried out,and the variation of the depth of the milling subsurface deformed layer under different process parameters was analyzed.At the same time,the microhardness of the single crystal superalloy milling subsurface was studied.The hardening phenomenon of the milling subsurface was analyzed,the metallographic structure of the milling subsurface of DD5 is observed by scanning electron microscopy,the changes of the metallographic structure were analyzed,and the plastic deformation mechanism of single crystal superalloy milling was explained.