Laser shock peening without coating induces deeper surface integrity changes in Ti60 than mechanical shot peening

Laser shock peening (LSP) is widely recognized for enhancing surface properties such as fatigue and wear resistance. LSP without coating (LSPwC) has emerged as an attractive alternative that eliminates the need for protective coatings, simplifies processing steps, and reduces costs. However, the comparative advantages of LSPwC and conventional mechanical shot peening (SP) for titanium alloy surface enhancement remain unclear. In this study, the effects of SP and LSPwC on the residual stress distribution and deformation characteristics of Ti60 alloy are systematically compared. The results reveal that although SP generates a higher maximum compressive residual stress (−549 MPa) than LSPwC (−392 MPa), it produces a shallower compressive layer (280 μm vs. 370 μm). Analysis of the full-width at half maximum (FWHM) indicates distinct stress profiles: SP induces the most severe elastoplastic deformation at ∼50 μm depth, accompanied by a non-monotonic stress distribution, whereas LSPwC primarily affects the outermost surface. Moreover, SP provides stronger surface strengthening within ∼150 μm depth, while LSPwC—due to its lower energy input—achieves a deeper compressive residual stress layer. These findings enhance the understanding of SP and LSPwC mechanisms, providing critical insights for optimizing surface processes in industrial applications.