Achieving well strength-ductility combination and anisotropy elimination in laser deposited titanium alloy by incorporating network substructures within equiaxed grains

Gradient titanium alloys can exhibit excellent performance over a wider range of temperatures and stresses, compared with single homogeneous titanium alloys that can only work effectively within specific temperature and stress ranges. An effective approach for the preparation of gradient titanium alloys involves combining additive manufacturing with forging, where metallic powders are deposited directly onto a forged plate. However, achieving a good strength-ductility combination while eliminating anisotropy in laser deposited titanium alloys remains a significant challenge. To mitigate the performance mismatch at the interface between dissimilar alloys in gradient components, premixed powders of near-α titanium alloy and Ti₂AlNb alloy at different proportions were deposited as a transition layer on the forged titanium alloy substrate by laser deposition in the present work. The microstructure and tensile behavior of the as-deposited mixed titanium alloy powders samples along the horizontal (scanning) and vertical (building) directions were systematically investigated. The results showed that abundant and continuous network substructures characterized by densely and parallelly arranged α₂ phase clusters were formed within equiaxed β/B2 grains of the laser deposited mixed titanium alloy powders containing 50 wt% near-α titanium alloy and 50 wt% Ti₂AlNb, which are conducive to achieving a favorable combination of strength (1007.63 MPa) and ductility (8.19 %), as well as the elimination of anisotropy. The strengthening contribution of the as-deposited sample with network substructures was primarily attributed to grain refinement and dislocation strengthening, rather than solid solution strengthening. Additionally, the achievement of isotropic strength and ductility was ascribed to the special network substructures with a similar volume fraction and distribution at both vertical and horizontal directions, which reduce the distribution difference in Schmid factor and promote more uniform deformation behavior.