Exceptional strength and ductility in heterogeneous multi-gradient TiAl alloys through additive manufacturing

Heterogeneous alloy designs have come to the forefront of material science due to their potential in achieving a superior combination of strength and ductility. To harness this potential, we proposed a structural strategy for the fabrication of a novel heterogeneous multi-gradient α-TiAl alloy through in-situ modulation of aluminium concentration during the additive manufacturing process. Compared with homogeneous Ti (with yield strength (σ_y) of 440 MPa and elongation to fracture (ε_f) of 37.6 %) and homogeneous Ti-10Al [at%] (σ_y ∼910 MPa, ε_f ∼6.1 %) fabricated using the same methodology, this heterogeneous multi-gradient α-TiAl alloy achieved a significant improvement in yield strength (σ_y ∼760 MPa) but with only a minor reduction in ductility (ε_f ∼33.4 %). Comprehensive experimental characterizations were carried out to probe the underlying mechanisms. The findings elucidate that the diffusion of aluminium in different printed layers promoted the formation of an innovative heterogeneous multi-gradient structure, engendering a synergy of multi-gradient strains that contribute to an exceptional combination of strength and ductility. These findings not only furnish an efficacious avenue for substantially augmenting the mechanical properties of α-Ti alloys but also applicable broadly in other alloy systems. The novel implementation of heterostructrure design could potentially overcome the enduring challenge of reconciling the trade-off between strength and ductility.