Fabrication of heterostructured Ti alloys with exceptional strength and ductility by direct laser deposition

Most metallic structural materials possess an intrinsic inverse relationship between strength and ductility. Heterostructured materials are expected to address this issue. Through composition regulation, TC4/TC4+2.5Ni layered heterostructures with exceptional strength and ductility were fabricated by direct laser deposition (DLD), exhibiting a significant increase in strength compared to that of TC4 while retaining excellent ductility. The mechanism of strength–ductility synergy was investigated under different alternating interlayer design conditions. The addition of nickel refined the microstructure of TC4, promoting the transformation of coarse columnar grains into nearly equiaxed grains. The DLD-fabricated TC4/TC4+2.5Ni layered heterostructure comprised alternating regions of columnar and near-equiaxed grains. By appropriately adjusting the thickness of alternating components (three to four DLD-deposited layers), a significant compositional and microstructural heterogeneity was achieved, resulting in a synergistic effect on strength and ductility in TC4-TC42.5Ni layered heterostructures. Moreover, strength–ductility synergy was achieved under the combined effect of hetero-deformation-induced stress, crack deflection near the component interface, and inhibition of strain localization by alternating soft and hard regions. This study provides a theoretical foundation and key evidence for designing DLD-deposited heterostructured titanium alloys with improved strength–ductility synergy, offering novel insights and contributions to improving the performance of titanium alloys.