Study On Strengthening Mechanism And Process Optimization Of Ti-10V-2Fe-3Al Alloy Surface By Wet Shot Peening

Ti-10V-2Fe-3Al alloy is the most widely used new type of near metastable btitanium alloy due to its excellent properties,such as high strength,good toughness,excellent hot working performance,good hardenability and low anisotropy.However,Ti-10V-2Fe-3Al alloy has low hardness and fatigue strength,which limits its further application in aerospace industry.In this paper,the impact of Ti-10V-2Fe-3Al alloy on the thickness,surface structure,surface morphology,microhardness,surface roughness were studied through high-energy wet shot peening intensification treatment in different parameters of action time and shot peening sizes.Finally,the optimum technological parameters of Ti-10V-2Fe-3Al alloy were investigated by orthogonal test method of dry-wet shot peening combination.The conclusions are exhibited as following :After wet shot peening,the surface morphology of Ti-10V-2Fe-3Al alloy samples have different defects,and the surface integrity is reduced.The surface morphology of the sample mainly shows peeling and collapse performance under 1 mm diameter balls,while under 2 mm and 4 mm diameter balls the surface morphology mainly shows strip and polygon defects.With the increase of shot peening time,the depth of the alloy action layer increases first and then keeps approximately stable trend.When the sizes of steel ball are equal to 1 mm,2 mm and 4 mm,the maximum depth of the action layer reaches 626mm,785mm and 1421mm respectively.The results of surface microhardness show that the surface microhardness increases with shot peening time,wherein the maximum microhardness reaches 362 HV,390HV and 367 HV when the sizes of steel ball are equal to 1mm,2mm and 4mm,which is increased by 29%,39% and31%compared with the original sample respectively.Roughness analysis shows that when the size of steel ball is equal to 1mm,2mm and 4mm,the maximum surface roughness of wet shot peening is 43.6%,47.6% and 53.6% lower than that of dry shot peening,respectively.When the size of 2mm is wet peening,the surface roughness has the smallest value as only 0.513mm.Microstructure analysis shows that the Ti-10V-2Fe-3Al alloy action layer performs the route of nanocrystalline,multi-system twin,single-system twin and transition zone to matrix zone from surface to inside,meaning its microstructure is refined.XRD results show that the diffraction peaks of the b phase in surface layer are weakened,and the diffraction peaks of a" phase are heightened and their peak widths are enlarged,indicating that the grain size and micro-distortion have changed greatly.At the sametime,the phase transformation also occurs in Ti-10V-2Fe-3Al alloy samples after shot peening,and the content of a" phase increases with the increase of shot peening time.Meanwhile,the smaller the shot size is,the easier the phase transformation of b?a".The results of orthogonal test show that the influence of shot peening parameters on the microstructure and properties of Ti-10V-2Fe-3Al alloy is different.The optimum parameters of dry-wet shot peening to Ti-10V-2Fe-3Al alloy are obtained by comprehensive analysis on the effects of various factors to the microstructure and properties of the alloy as the ball size of dry shot peening is equal to 4mm,the time of dry shot peening is in 25 min,accompany with the size of wet shot peening is equal to2 mm and the time of wet shot peening is in 25 min.Compared with matrix and the sample treated by wet shot peening for 25 minutes and then by 2 mm projectile for 25 minutes was increased by 44% and 36% respectively,and the depth of action layer was also increased by 5%.Compared with the first 4mm projectile 25 min dry shot peening,and then the 2mm projectile dry shot peening for 25 min,the roughness was reduced by 63%.