Improvement surface integrity and high cycle fatigue performance of the additively repaired titanium alloy by shot peening

The non-uniform structure and residual stresses significantly limit the fatigue performance of titanium alloy additively repaired components. In this study, shot peening (SP) surface treatment was applied to arc additive repair titanium alloy components to enhance their service life, and improvement mechanisms of surface integrity and fatigue performance were investigated. Results revealed that SP induced a high density of dislocations throughout the repaired component, and the continuous dislocation evolution led to a significant microstructure refinement. These refined structures, including nanoscale twins and stacking faults, exhibited a gradient in a specific depth direction. The hardness and compressive residual stress (CRS) of this gradient structure were significantly enhanced, with its depth exceeding 200 μm. Due to the synergistic effect of the gradient microstructure and CRS enhancement, the instant fracture zone decreased from 2.726 mm² to 2.094 mm², and the crack initiation site shifted from the free surface to a subsurface location about 103.46 μm beneath the surface, resulting in a significant increase in the fatigue limit of the repaired component to 602.16 MPa.