Achieve an excellent strength-ductility balance by introducing heterogeneous structure in wire arc additively manufactured Ti-Cu alloys

The low hardness difference between martensite alpha (alpha') and eutectoid structure (ES) in additively manufactured Ti-Cu alloys led to the insignificant heterogeneous deformation behavior and the resultant severe strengthductility trade-off. In the current work, the Ti-xCu (x = 1, 4, 7, 10 wt%) was fabricated by the gas metal arcbased wire arc additive manufacturing (GMA-WAAM), and the microstructure evolution, deformation behaviors, and tensile properties were investigated. The results showed that, in the Ti-4Cu, a unique heterogeneous structure was introduced, as manifested by a balanced phase ratio of 1:1 and a large hardness difference of 3.4 GPa between alpha' and ES. A significant heterogeneous deformation behavior was triggered, as manifested by a large multiplication of geometrically necessary dislocations (Delta rho GNDs) of 3.45 x 1015 m- 2 and a tortuous main crack propagation path. An excellent strength-ductility balance was achieved, as manifested by a yield strength (YS) of 971 MPa and an elongation to fracture (EF) of 11.6 %. The large hardness difference was attributed to the in-situ Cu-solute diffusion from alpha' into ES resulting from the intrinsic heat treatment (IHT) effect. The strengthening mechanism was attributed to the 330 MPa resulting from the hetero-deformation-induced (HDI) strengthening. The toughening mechanism was attributed to the strain hardening resulting from the multiplication of GNDs and the mitigation of strain concentration. The current work provided a new insight into the design of heterogeneous structure.