Study On Damage Characteristics Of Titanium Alloy Subsurface In High Speed Cutting

In the process of cutting,under the effect of thermal mechanical coupling between tool and workpiece,different types of defects will first appear in the subsurface area of materials,which will become the main cause of damage to the subsurface,and then affect the surface quality.Therefore,it is of great significance to analyze the defect information of material subsurface after cutting for optimizing cutting parameters and improving surface quality.In this paper,titanium alloy Ti-6Al-4V is taken as the research object to explore the influence of different cutting parameters on the type and concentration change of subsurface defects of materials.The main research methods and results are as follows:（1）The single factor turning test of titanium alloy Ti-6Al-4V was carried out.The phase changes of titanium alloy Ti-6Al-4V before and after cutting and under different cutting parameters were investigated by using X-ray diffraction（XRD）.The results show that titanium alloy Ti-6Al-4V is further oxidized after cutting,and the diffraction peaks ofα-Ti,β-Ti,Al₂O₃,Ti O₂（Anatase）and Ti O₂（Rutile）were detected.（2）In view of the changes in the surface and subsurface microstructures of titanium alloy Ti-6Al-4V,the machined surface and subsurface of titanium alloy samples were observed under different magnification using a metallographic microscope.The principle of surface coloration of titanium alloy Ti-6Al-4V was analyzed from the aspects of film interference and crystal structure.The results show that under the strong thermal mechanical coupling,the grain refinement of the surface microstructure of the material to be machined is enhanced,and the grain deformation is along the cutting direction.The different color of titanium alloy surface is caused by different optical path difference due to different film thickness at different positions of the machined surface.At the same time,the change of the content of anatase Ti O₂ and rutile Ti O₂ leads to the change of the refractive index of the oxide film,which is also the reason for the color of the surface.（3）The defect information of Ti alloy Ti-6Al-4V subsurface under different cutting parameters was analyzed by positron annihilation lifetime spectrum and Doppler broadening experiment.The results show that a large number of dislocation and vacancy complexes are produced in the subsurface layer of titanium alloy Ti-6Al-4V due to the combined effects of plastic deformation and thermal mechanical coupling during cutting.At the same time,under different cutting depth and cutting speed,the change of chemical environment phase transition is also detected,which is due to the increase of cutting temperature during the machining processα-βTransformation temperature and promote secondary hardening.（4）The depth distribution of Ti alloy Ti-6Al-4V subsurface defects under different cutting parameters was analyzed by coincidence Doppler broadening experiment.The results show that the surface of titanium alloy Ti-6Al-4V is machined to the interior of the substrate（～1.5μm）And atomic scale vacancy type defects are formed.Better sub surface quality can be obtained by changing feed rate and cutting speed.