Microstructure evolution and mechanical properties of wrought/wire arc additive manufactured Ti-6Al-4V joints by electron beam welding

Wrought-additive hybrid manufacturing technology effectively combines the advantages of high efficiency of traditional manufacturing and high flexibility of additive manufacturing technology. Mechanical Properties of welded joints is the key to evaluate the performance of parts. In this study, the wire and arc additive manufacturing (WAAM) Ti-6Al-4V alloy was successfully connected with the wrought Ti-6Al-4V plate by electron beam welding (EBW). The effect of welding direction on microstructure and tensile properties of welded joints was studied. The results show that a large amount of needle martensite α’ phases exists in the joint due to the rapid cooling rate. The mechanical properties tests show that compared with the Wrought + SD (Scanning direction) sample, the Wrought + BD (Building direction) sample has higher tensile strength, but lower elongation. All samples fractured at the WAAMed Ti-6Al-4V side, which was related to the initial state of the WAAMed Ti-6Al-4V sample. The experiment also explored the fracture mechanism by TEM, which involved the nucleation, growth of cracks caused by vertical dislocation accumulation at the α/α’ phase interface, and occurrence of the displacement of the α (or α’)/β phase interface caused by the parallel dislocations.