Effect Of High Energy Shot Peening On The Microstructure And Properties Of GH4169 Alloy

GH4169 alloy has been widely used in the aerospace field due to its excellent properties,such as good high temperature mechanical properties,strong thermal corrosion resistance and excellent high temperature oxidation resistance.However,the low hardness and fatigue strength limit its further application in aviation structure.In this paper,the effect of shot peening time and projectile size on the surface state,surface roughness,microhardness,residual stress and microstructure evolution was studied.Besides,the difference of surface microstructure and properties between dry shot peening and wet shot peening was researched,the mechanism of shot peening strengthening of GH4169 alloy was explored.The main research contents and results are as follows:After dry shot peening treatment,the surface defects of GH4169 alloy increased.When projectile sizes are 1mm and 2mm,mainly surface defects are warp,peeling,collapse,while for 4mm projectile,they are long strip and multilateral shape defects.The surface roughness,microhardness and residual stress of GH4169 alloy are significantly improved after dry shot peening treatment.The smallest surface roughness(2.857?m)is obtained with 1mm shot peening for 3min.The microhardness raises up to 401 HV with 4mm shot peening for 10 min.Compared with the original specimen hardness(289HV),it is increased by 39%.With the shot peening time prolonging,the surface residual stress field intensity increases,the maximum residual stress of the surface layer is(-684MPa)obtained with 1mm shot peening for 10 min.XRD analysis shows that no phase transition occurs during dry shot peening.With the increase in projectile size and duration,the X diffraction peak intensity reduces and the FWHM gradually increases,indicating that microstructure is refined.In addition,the thickness of shot peening layer increases,and the biggest layer thickness(450?m)is obtained with 4mm shot for 10 min.Compared with dry shot peening,the surface defects of wet treated samples obviously decrease,which is mainly skin peeling.Furthmore,the surface roughness of the sample treated by wet shot peening is significantly lower than that of dry shot peening.The largest reduction of surface roughness reaches 53%,with 2mm wet shot peening for 10 min.In addition,the residual stress of the sample treated by wet shot peening is much larger than that of dry peening,and the residual stress of the surfaceis increased by about 9% with 2mm wet shot peening for 10 min.After shot peening,the strong residual stress field forms in the surface layer of GH4169 alloy,large number of deformation twins appeared in the surface grains,and the microstructure is refined.These are three reasons for the surface hardening of GH4169 alloy.