Importance of surface defect removal and compressive residual stress introduction in improving fatigue strength of powder bed-fused Ti6Al4V and demonstration of fatigue strength beyond that of hot-rolled Ti6Al4V

• Key issue to improve fatigue strength (FS) of PBF-LS/Ti6Al4V is surface defect removal. • Fine particle bombarding (FPB) with garnet is effective for surface defect removal. • Cavitation peening (CP) introduces compressive residual stress into the surface. • FS of PBF-LS/Ti6Al4V treated by FPB + CP is larger than that of hot-rolled Ti6Al4V. • FS of PBF-LS/Ti6Al4V is estimated by surface residual stress and surface roughness. Additive manufacturing (AM) metals such as powder bed-fused and laser-sintered titanium alloys, i.e., PBF-LS/Ti6Al4V, have attracted considerable attention in recent times. However, their fatigue strength is almost half that of wrought materials, thereby limiting their practical applications. The primary reason for the weak fatigue strength is the presence of surface defects as deep as 0.15 mm due to incompletely melted particles during PBF-LS. In this study, to demonstrate the improvement of the fatigue strength of PBF-LS/Ti6Al4V by post-processing, as-built PBF-LS/Ti6Al4V was treated by fine particle bombarding (FPB) with garnet to remove the surface defects, followed by cavitation peening (CP), which introduced compressive residual stress. The fatigue properties of the treated specimen were evaluated through torsional fatigue tests and compared with those of hot-rolled Ti6Al4V and specimens treated using other post-processing methods such as submerged laser peening (SLP). According to the results, at N f = 10 7 , FPB + CP-treated PBF-LS/Ti6Al4V exhibited a fatigue strength of 446 ± 5 MPa, whereas as-built PBF-LS/Ti6Al4V and hot-rolled Ti6Al4V exhibited fatigue strengths of 210 ± 10 and 347 ± 26 MPa, respectively. The fatigue strength of as-built PBF-LS/Ti6Al4V was enhanced by the combination of FPB and CP, and the improved fatigue strength was greater than that of hot-rolling.