Study On The Effect Of High Energy Shot Peening On Surface Strengthening Treatment Of TC4

Titanium and titanium alloys are widely used in military,chemical,aviation,daily life,biomedicine and other industries because of their good biocompatibility,low density,corrosion resistance and wear resistance.However,due to the low hardness of the surface layer,the poor resistance to plastic deformation and the poor protective effect of oxide generated on the surface,the lower friction and wear properties of the surface of titanium alloys limit the further application of titanium alloys.Therefore,it is necessary to strengthen the surface and optimize the surface properties.Hard coatings were formed on the surface of titanium alloy by surface modification technology,which can improve the surface properties without changing the excellent properties of the matrix and meet the application requirements.The effect of pre-treatment high energy shot peening(HESP)technology on hydrogen-free carburizing and micro-arc oxidation of TC4 titanium alloy was studied in this paper.Firstly,the surface of TC4 matrix was pretreated by high energy shot peening,and the mechanism of microstructure refinement was analyzed.Then,the surface of TC4 was treated by hydrogen-free carburizing and micro-arc oxidation respectively.The effects of high energy shot peening on the structure and properties of the carburized layer and the oxide layer formed by micro-arc oxidation after hydrogen-free carburizing were studied.Microstructure,surface morphology and composition of the surface,carburized hard layer and oxide layer of TC4 were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),metallographic microscope(OM)and energy dispersive spectrometry(EDS).Hardness,wear resistance and corrosion properties were tested by hardness tester,friction and wear tester and electrochemical workstation.The structure and mechanical properties of carburized layer and oxide layer after shot peening for different time were compared and analyzed,and the wear mechanism was discussed.The results show that high energy shot peening can cause severe plastic deformation on the surface layer of TC4 matrix,and increase the dislocation and grain boundary defects in the deformation layer structure,which provides a large number of diffusion channels for atoms to enter the matrix smoothly.Therefore,the thickness of carburized layer of TC4 titanium alloy after high energy shot peening pretreatment without hydrogen carburizing is higher than that of TC4 direct carburizing sample.After high-energy shot peening treatment,Ti C structure can be refined,the thickness of carburized layer can be increased,and the hardness of carburized layer can be increased.The microhardness of surface layer of direct carburized sample is 928.1HV.After High-energy Shot peening,the hardness of carburized sample's hard layer rises to 1061 HV.With the increase of High-energy Shot Peening time,the hardness also increases,and the wear resistance is improved.The oxide film of TC4 titanium alloy produced by micro-arc oxidation after high-energy shot peening is refined.With the prolongation of shot peening time,the structure is uniform,the surface is smoother,and the bonding strength between the film and the substrate is improved.At the same time,the thickness of the film is also increased.After 40 minutes of High-energy Shot peening,the film obtained by micro-arc oxidation is the thickest,reaching 40 micron,and the hardness is also increasing.Friction wear Damage has been greatly improved.