Analysis Of TC4-DT Titanium Alloy By Shot Peening

Being a damage tolerance and medium strength titanium alloy,TC4-DT alloy is developed aiming at the application in structural parts of aerocraft.In this study,shot peening can enhance the fatigue property greatly by means of surface microstructure and residual compressive stress.So it plays an instructive role to study the shot peening techniques of medium strength and high toughness titanium alloy.Double-sided shot peening was treated by using CNC peening machine.The main shot peening parameters selected four Allmen intensities of 0.1mm A,0.15mm A, 0.2mm A and 0.3mm A.The surface microstructures of shot peening were analyzed by means of optical microscope,scanning electronic microscope(SEM),transmission electronic microscope(TEM).The results show that the plastic deformation of material increases with the shot peening intensity.High density dislocation and deformation band produced by shot peening treatment in material surface.The dislocation movement plays a main role in TC4-DT alloy.The shot peening can cause a certain depth residual compressive stress field on the material surface.The residual stress distributions of original and shot peened specimens were measured by an X-ray diffraction method.The residual compressive stress profiles accord with the characteristic curve of residual stress field.The maximum residual compressive stress is located at subsurface layer.The depths of maximum residual compressive stress and strengthening layer increase with the shot peening intensities. The intensity of 0.2mm A is the optimal effect.The shot peening intensity of 0.3mm A is too large,which makes defects and cracks in material surface,and then leads to the maximum residual compressive stress release. The surface microhardness and roughness increase largely with the shot peening intensities.So it is important to decrease the surface roughness.The residual compressive stress relaxes partically under temperature.The higher test temperature induced a greater stress relaxation.The maximum stress relaxation rate occurs mainly in the initial stage of ageing process.Temperature and time effects on the residual stress relaxstion during ageing are controlled by thermally activated processes. The result of trials indicates that the dynamic process of stress thermal relaxation corresponds to the Zener-Wert-Avrami function.The low cycle fatigue properties of shot-peened specimens are higher than the unpeened specimens.However,all in all,the degree of improvement is little.The residual compressive stress induced by shot peening relaxed greatly under high strain and low cycle fatigue.Results show lower surface roughness can improve the fatigue properties.