Analysis Of Characteristics And Evolution Of Residual Stress Field Of Shot Peened Ti-6Al-4V Alloy

Due to the excellent comprehensive performance,Ti-6Al-4V alloy has important application value in the field of aerospace engineering et al.However,because of the poor antifatigue performance and the high probability of fatigue failure during service,the further development of Ti-6Al-4V titanium alloy was limited.Shot peening can effectively improve the fatigue resistance of Ti-6Al-4V alloy.The compressive residual stress(CRS)in the strengthened layer induced by shot peening is a key factor to improve the fatigue performance of materials.In this paper,the distribution of residual stress along the depth and the corresponding evolution of microstructure generated by wet peening and dry shot peening under different process parameters were thoroughly characterized by using X-ray diffraction method(XRD)and transmission electron microscopy(TEM),respectively.The formation mechanism of residual stress was analyzed on the basis of microstructure characteristics.In addition,dry shot peening process of Ti-6Al-4V alloy was simulated by the finite element simulation method,and the effect of process parameters on the residual stress field was explored.Combined results of experimental research and numerical simulation help us provide theoretical support and guidance for engineering applications.The results showed that:Compressive residual stress(CRS)was generated in the surface layer of peened Ti-6Al-4V alloy.And the characteristic parameter of the residual stress field,i.e.the residual stress on the surface,maximum compressive residual stress(MCRS)as well as its location and the depth of compressive stress,changed with peening parameters.With the increase of shot peening intensity,the depth of compressive stress as well as the MCRS increased,and the MCRS location moved inward.When the shot peening intensity increased to a certain extent,the residual stress field reached saturation.With the increase of shot peening coverage,the residual stress on the surface decreased,while the MCRS increased and its location moved inward and the depth of compressive stress increased.As the work hardening extent of the material surface was increased,the MCRS location shifted inward.In addition,in the dry shot peening process,the residual stress on the surface and MCRS by using the ceramic bead were larger than that of cast steel shot.Through the observation of the microstructure of the residual stress layer,the compressive residual stress field could be divided into four important regions: surface-stress region,near surface-stress region,maximum-stress region and near matrix-stress region.Long-term orderly dislocation pile-up groups were distinguished as the typical microstructure of the maximumstress region.This special configuration represented a high degree of stress concentration.Moreover,there was also some deformation twins or dislocation tangles present in this region under a certain shot peening parameters.Dynamic recovery took place in the surface-stress region,and interaction between dislocations took place in the near surface-stress region during shot peening,causing residual stress released as well as the MCRS located at the subsurface.A mechanical analysis of the residual stress curve showed that the location of the MCRS coincided with the location of maximum shear stress induced by Hertzian dynamic pressure.Therefore,the location of the MCRS is the result of a combination of microstructure and Hertzian dynamic pressure.The simulation results showed that characteristic parameters of the residual stress field were significantly improved with the increasing shot peening velocity.When the shot peening velocity increased to a certain extent,the residual stress field saturated.Further increasing the velocity might cause the residual stress on the surface and MCRS decreased.With the increase of shot peening coverage,the residual stress on the surface decreased,while the MCRS increased and its location moved inward and the depth of compressive stress increased.In addition,titanium alloy with higher strength could produce higher residual stress on the surface and MCRS.The simulation results were consistent with the experimental results,which proved the validity of the model.