Nano-lamellar Ti₃Al/TiAl alloy prepared via dual-wire-fed electron beam-directed energy deposition: microstructure evolution and nanohardness enhancement

Nano-lamellar Ti₃Al/TiAl (α₂/γ) alloy with significantly improved nanohardness was prepared using dual-wire-fed electron beam-directed energy deposition (EB-DED) in this study. This investigation focused on the evolution of the colony shape and lamellar thickness of the Ti-43Al lamellar alloy at different heights. Nanoindentation tests were employed to evaluate deformation resistance, and numerical simulations provided deeper insights into the deposition process. The results indicate that the colonies are mostly columnar, except for a few equiaxed colonies at the top. Rapid cooling significantly refines the α₂ lamellae, resulting in an average spacing of 218 nm and thickness of 41 nm. Additionally, substantial microstrain and a nonequilibrium Al distribution lead to a significant generation of γ variants, refining the γ lamellae to 57 nm. Abundant γ/γ’ and α₂/γ interfaces, along with fine α₂ phases, contribute to improved deformation resistance. Consequently, the nano-lamellar TiAl alloy exhibited a notable 32% increase in nanohardness (8.3 GPa) while maintaining a similar modulus (197 GPa) to conventionally prepared alloys. This study holds significant promise for advancing high-performance TiAl alloys through the dual-wire-fed EB-DED process.