Manipulating molten pool in in-situ additive manufacturing of Ti-22Al-25 Nb through alternating dual-electron beams

Wired-based in-situ additive manufacturing (AM) technology couples in-situ metallurgy for material-synthesis and near net-shaping for part-fabrication. However, the manipulation and control of the in-situ metallurgy quality is one of the most critical challenges it faced now, as insufficient metallurgy not only causes inherent defects but also leads to fatal damages to the deposited component. Till now, there is almost no effective way to manipulate it. In this study, we proposed to use the alternating dual-electron beam to flexibly control the molten pool, thereby, achieving the purpose of manipulating the in-situ metallurgical process. Ti-22Al-25 Nb (at%) alloy was taken as the target alloy and fabricated in-situ with the raw materials of pre-alloyed TiNb wire and pure-Al wire. Results show that this technology not only exhibits powerful control ability to the molten pool characteristics but also brings additional in-situ co-frequency forced vibration behavior to the molten pool. The regulated elongated molten pool, as well as its vibration behavior further promotes composition homogenization, porosity reduction(densification as high as 99.999%), and grain refinement(about 32%). As a result, the tensile strength of the in-situ deposited components is as high as 993.6 ± 32.4 MPa on average. In addition, employing an alternating heat source model, numerical simulation was also carried out for revealing the unique temperature evolution and molten pool flow mechanism of the alternating dual-beam AM technology. This work not only provides valuable guidance for the regulation of the in-situ metallurgy quality in the wired-based in-situ AM field but also supplies an unprecedented processing method for the Ti-22Al-25 Nb alloy.