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Ti 2 AlNb alloys are expected to have applications in the aerospace field because of their excellent high-temperature performance and moderate density. Multi-wire arc-directed energy deposition (MWA-DED) technology enables the in-situ formation of Ti 2 AlNb alloys. However, Ti 2 AlNb alloys fabricated by MWA-DED face challenges such as compositional segregation and poor mechanical properties. In this study, high-performance Ti 2 AlNb alloys were efficiently prepared using MWA-DED technology, and their microstructure evolution was systematically analyzed. Hot-wire technology was proposed to assist in melting the TiNb wire to minimize the difference in the physical properties of the two wires. A pre-alloy droplet transfer mode with a large arc length was developed to eliminate composition segregation. The results showed that the Ti 2 AlNb alloys exhibited a homogeneous composition that matched the target Ti-22Al-23 Nb. Lots of strengthening phases (O phases higher than 90%) were precipitated throughout the sample. Temperature fields calculated from finite element simulation revealed that the precipitated phases were attributed to the "in-situ" heat treatment during deposition. The ultimate tensile strength and elongation reached 1002 MPa and 8% at room temperature, and 756 MPa and 8.3% at high temperature (650 ℃), respectively. The outstanding mechanical properties of Ti 2 AlNb alloys fabricated by MWA-DED are superior to those of cast and previously reported additively manufactured alloys. This study proposes novel ideas for additive manufacturing of high-performance Ti 2 AlNb alloys. [Display omitted] • Ti 2 AlNb alloys were efficiently in-situ manufactured by the multi-wire arc-directed energy deposition technique. • Hot-wire technology was proposed to eliminate the difference in physical properties of the two wires. • A pre-alloy droplet transfer model with high arc-length was explored to overcome compositional segregation. • Numerical simulations of heat transfer were developed to reveal the microstructure evolution mechanism. • High-performance Ti 2 AlNb alloys were obtained and the strengthening mechanisms were revealed. [ABSTRACT FROM AUTHOR]

The twin-wire arc additive manufacturing (TWAAM) technology is an effective method for the in-situ fabrication of Ti 2 AlNb-based alloys relative to conventional cast and wrought routes. However, composition segregation is still challenging in the field of in-situ TWAAM. To homogenize the chemical composition, here we proposed a novel single droplet pre-alloying transfer mode of TWAAM based on the original droplet transfer mode of double wires directly fed into the molten pool. The designed nominal composition of Ti-25Al-23Nb was set as the target alloy. The as-printed parts were investigated systematically. The results showed that this unique droplet transfer mode could not only improve the forming accuracy but also effectively mitigate the composition segregation. In addition, the inconsistency of microstructure caused by the composition segregation was successfully solved by this mode and appears a fully lamellar microstructure. The improvement of composition uniformity played a positive role in enhancing the mechanical properties of the alloy, in which the tensile strength of room and high temperature were improved by 76.8% and 74.1% respectively compared with our previous research. This work is of great significance to alleviate the composition segregation of intermetallics and further promote the in-situ TWAAM fabrication of Ti 2 AlNb-based alloys. • The composition segregation that challenges the Ti 2 AlNb-based alloy in-situ fabricated by twin-wire arc additive manufacturing (TWAAM) was successfully mitigated by a novel single droplet pre-alloying transfer mode. • This single droplet pre-alloying transfer mode also promotes the forming stability and accuracy during the TWAAM process. • The improvement of composition uniformity played a positive role in solving the inconsistency of microstructure and enhancing the mechanical properties. [ABSTRACT FROM AUTHOR]

• Ti 2 AlNb-based alloys are in-situ manufactured by DWAAM technology. • Hot-wire technology is introduced to overcome the problem of the obvious difference in physical properties between two wires. • Composition distribution and macrosegregation mechanism of the in-situ prepared alloy are revealed. • Microstructure and mechanical properties of the in-situ prepared alloy are studied. • The integration of material-preparation and parts-processing is attractive for industrial production. For the reason of high temperature strength, high oxidation resistance and low density, Ti 2 AlNb-based alloy is expected to replace nickel-based alloy in the range of working temperature 600–800 °C and become a new generation of high-temperature structural alloys in the aerospace industry. However, Ti 2 AlNb-based alloys have great high-temperature deformation resistance and high brittleness, which greatly restricts its preparation and processing using traditional technology. In this research, an innovation method named double-wire arc additive manufacturing technology was adopted to in-situ manufacture Ti-22Al-24Nb (at%) alloy, and the TiNb and pure Al wire with designed feeding speed were taken as raw materials. The deposited component was investigated systematically. Results show that the composition error between the average testing value and designed value are under 1.1%, but there are also existing local segregation of composition and microstructure. The segregation phenomenon further deteriorates its mechanical properties, which means the ultimate tensile properties and elongation under room temperature and high temperature (650 °C) are 504 ± 38.59 MPa, 0.41 ± 0.03% and 375 ± 32.60 MPa, 0.76 ± 0.05% respectively on average. At the same time, the prepared alloy exhibits fully lamellar structure and XRD results show that the basic composition phases B2, O and α 2 of the Ti 2 AlNb-based alloy successfully appeared. The in-situ manufacturing method demonstrated in this work is expected to significantly promote the wider application of AM due to its low cost advantage and high flexibility. [ABSTRACT FROM AUTHOR]