Effect of twin-wire feeding methods on the in-situ synthesis of electron beam fabricated Ti-Al-Nb intermetallics

[Display omitted] •Three twin-wire feeding methods were adopted to fabricate Ti-Al-Nb intermetallics in-situ through electron beam freeform fabrication.•The twin droplet transition mechanism of the respective wire feeding methods was revealed.•The effect of different droplet transition modes on the morphology, composition, and mechanical properties of the deposited was studied.•Finite element model of twin-wire heating was proposed to assist explaining droplet transition. As a challenging but promising technology, wire-based in-situ additive manufacturing shows great advantages in material preparation and part manufacturing integration. However, compared with single-wire AM technology, it faces a more complex droplet transition pattern, which is closely related to the feeding modes of the elemental wires. In the current work, the effect of wire feeding methods on the droplet transition mode, the morphology, composition, and mechanical properties is for the first time systematically studied. Three wire feeding methods, including double-side-feeding, single-side-feeding, and parallel-feeding, were adopted to fabricate the Ti-Al-Nb intermetallics in-situ. The results show that the TiNb wire and pure-Al wire enter the molten pool separately and with a totally inconsistent droplet transition mode in the double-side-feeding and single-side-feeding methods. This droplet transition results in poor morphology, macro-segregation, and inconsistent mechanical properties. While in the parallel-feeding method, the TiNb and Al droplet transfer to the molten pool after forming a common droplet, which provides a better guarantee for the morphology and performance of the deposited parts. As a research oriented to the deposition process, the current work is of great significance for enriching the fundamental theory and promoting the development of the wire-based in-situ AM technology.