Wire arc additive manufacturing of titanium aluminide alloys using two-wire TOP-TIG welding: Processing, microstructures, and mechanical properties

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Abstract Titanium aluminide (TiAl) alloys are promising high-temperature structural materials in the aerospace field. Additive manufacturing is a desirable process for fabricating TiAl alloys. In the process of wire arc additive manufacturing of TiAl alloys, Al-based and Ti-based wires were used as the feedstocks. However, it is hard to ensure the two different wires melt synchronously under the heat of one single arc, so the desired microstructures with γ (TiAl) phase and α2 (Ti3Al) phase are hard to obtain. A two-wire TOP-TIG-based additive manufacturing process for TiAl alloys is proposed in this paper. The Ti6Al4V wire and pure Al wire are used as the feedstocks. The Al wire is fed in TOP-TIG mode behind the molten pool, while the Ti6Al4V wire is fed in conventional TIG mode in front of the molten pool. The two wires melt synchronously in a broad range of parameters. The compositions of the component can be controlled by adjusting the two-wire feeding speeds. The main microstructures of the as-fabricated component contain α2/γ lamellae colonies, equiaxed γ grains, and α2 grains. In the top and middle regions, when the Al content is 45 at.%, the structures are full α2/γ lamellae; as the Al content increases to 50 at.%, some equiaxed γ grains distribute at the grain boundaries; the component with 55 at.% Al content exhibits the structures consists of equiaxed γ grains with snowflake-shaped α2/γ lamellae colonies. In the bottom region, all components exhibit the coarse equiaxed α2 grains with γ laths. As the Al content increases, the α2 phase decreases, but the γ phase increases, and from the top region to the bottom region, the volume fraction of the α2 increases by about 19.4 %. The hardness value of the top and bottom regions is higher, and the middle region exhibits the lowest hardness. As the Al content increases, the hardness decreases. The component with 50 at.% Al exhibits the highest compressive strength with 1762 MPa and the largest compressive ratio with 26.1%.