Study of Rotating-Bending Fatigue Properties and Strengthening Mechanism of Laser Shock Peening on Ti17 Welded Joints

Although electron beam welding (EBW) can be performed on titanium alloys with a precise weld seam, certain process-inherent limitations, such as the accumulation of residual stresses, can lead to a loss in the fatigue life of EBWed joints. In this study, laser shock peening (LSP), as an innovative technique for generating compressive residual stress, was employed on EBWed Ti17 joints. The effects of LSP on microstructure, microhardness profiles, residual stress distributions, and rotating-bending fatigue life of EBWed Ti17 joints were systematically analyzed. Results indicated that LSP-induced high-density dislocations and mechanical twinning within α′ martensites, contributing to the grain refinement. Compared to the untreated joints, those subjected to LSP exhibited higher surface microhardness and compressive residual stress. Statistical analysis, conducted with a 95% confidence level, confirmed that LSP resulted in a minimum 2.2-fold enhancement in the rotating-bending fatigue life of the EBWed Ti17 joints. The microstructural refinement, compressive residual stress, and increased work hardening on the surface layer effectively inhibit fatigue crack initiation and decrease the crack growth rate. Therefore, the LSP-generated dominant mechanism for rotating-bending fatigue performance improvement in EBWed Ti17 joints was revealed.