Gradient microstructure evolution and strength–ductility coordination in Ti-10V-2Fe-3Al alloy under laser shock peening

High-strength titanium alloys are promising for engineering applications, but simultaneously improving strength and ductility remains challenging. In this study, multi-pass laser shock peening (LSP) was applied to Ti-10V-2Fe-3Al alloy to reveal the LSP-induced gradient microstructure, two-phase evolution, and the strength-ductility simultaneous enhancement mechanism. Results show that LSP does not change the phase composition of the alloy, but produces a pronounced gradient microstructure near the surface. During LSP-induced severe plastic deformation, the β matrix preferentially deforms and accumulates high-density geometrically necessary dislocations (GNDs), whereas the α phase gradually participates in coordinated deformation with increasing deformation intensity. Meanwhile, LSP increases the content of the secondary α phase (α_s) and modifies its size. In the LSP-2 specimen, the increased content and refined distribution of α_s enlarge the α_s/β interfacial area, hindering dislocation motion and promoting GND accumulation. Differences in plastic response across the gradient layers and between the α phase and β matrix may induce strain partitioning and plastic strain gradients, thereby contributing to HDI-related strengthening, sustained work hardening, and delayed strain localization. As a result, the LSP-2 specimen exhibits the best mechanical properties, with elongation, tensile strength, and fracture energy increased by 45.37%, 9.29%, and 60.23%, respectively, compared with the untreated specimen. However, four LSP passes cause excessive pre-deformation and α_s coarsening, reducing the subsequent dislocation-storage capacity and sustained work-hardening capability. These findings provide theoretical support and processing guidance for the engineering application of LSP in the surface modification of near-β titanium alloys.