Effects of different mechanical surface treatments on surface integrity of TC17 alloys

The effects of shot peening (SP), ultrasonic surface rolling (USR), and laser shock peening (LSP) processes on the surface integrity of TC17 alloys, including the surface topography, in-depth residual stress and microhardness distributions, and microstructure, are investigated and compared. The results show that the lowest surface roughness values of 0.04–0.12 μm and a smooth surface topography are achieved from the USR process, while those after the SP and LSP processes are 0.50–1.07 μm and 0.36–0.73 μm, respectively. The depth of the compressive residual stress layer induced from the USR and LSP processes is mostly in the range of 0.7–2.0 mm, which is larger than that induced from the SP process. The surface compressive residual stresses generated from the SP, USR, and LSP processes are in the range of −570 to −870 MPa, depending on the applied parameters. The induced work hardening is observed and the increased surface microhardness is approximately 6.4% after all treatments compared with the initial states. Gradient changes in the plastic deformation and grain refinement are observed in the subsurface microstructure. Moreover, the USR and LSP processes demonstrate a deeper plastic deformation layer compared with the SP process. The impact intensity of the mechanical surface treatments has a notable effect on the surface integrity characteristics compared with the impact coverage. The USR process is more effective at improving the surface integrity characteristics of TC17 alloys compared with the SP and LSP processes due to its relatively smooth surface, high-amplitude and deep layer of compressive residual stress, deep work-hardened layer, and large gradient microstructural changes.