Simultaneously achieving strength-ductility in additive-manufactured Ti6Al4V alloy via ultrasonic surface rolling process

Additively manufactured alloys have a great potential in engineering field, but there still have many issues to be addressed, i.e., the reliability, strength-ductility trade-off of manufactured parts. In this study, a treatment called ultrasonic surface rolling process (USRP) was utilized to achieve superior strength and ductility in the Ti6Al4V alloy prepared via electron beam melting (EBM). The treated additive-manufactured alloy obtained various gradient microstructures and excellent surface quality, as well as its mechanical properties were significantly improved. Especially, the USRP-3 specimen exhibited a high elongation of 17.1 ± 0.9 % and a good ultimate tensile strength of 1043 ± 5.0 MPa, which were both higher than those of untreated specimen; the fine laminated structure with a preferred orientation of ($10\bar{1}0$) direction and gradient structure promoted the hardening capacity and provided the rich dislocations sources, taking a better strength-ductility combination. In addition, the surface microhardness of the multi-pass processed specimen was markedly enhanced. However, excessive USRP treatment would induce micro-cracks in the nano-composite layer, resulting in a significant reduction in ductility. Therefore, appropriate USRP treatment is expected to expand the application range of additive-manufactured metallic materials.