An investigation into Ti-22Al-25Nb in-situ fabricated by electron beam freeform fabrication with an innovative twin-wire parallel feeding method

Wire-based in-situ additive manufacturing technology realizes the integration of material preparation and part manufacturing with high deposition efficiency and material utilization. However, the complicated two-droplet transfer and fast cooling rate of the molten pool make this technology face the challenges of poor stability, repeatability, forming accuracy, and composition macro-segregation. In this work, an innovative wire feeding method, named twin-wire “parallel” feeding (TWPF), combined with the high-frequency of electron beam scanning for molten pool stirring was adopted to mitigate these issues. The multi-element Ti-22Al-25Nb (at%) intermetallic is taken as the target alloy, due to its huge application prospects in the aerospace field but great difficulties in traditional processing methods. Results show that the TWPF method can provide a stable and repeatable double-droplet transfer mode. Ti-22Al-25Nb parts with high forming accuracy and relatively good mechanical properties can be successfully fabricated. In addition, the two-droplet transfer, Al evaporation quantity, pore, and microstructure evolution mechanism are all systematically studied. This work is of great significance to solve the commonly existing challenges in wire-based in-situ AM technology, as well as to shorten the processing cycle and promote the wider application of the Ti-22Al-25Nb component.