Abstract: Titanium alloys usually use the method of adding beta-stabilizing elements to obtain a single beta phase to reduce the Young’s modulus, which simultaneously leads to the strength reduction. Metallic heterostructured materials achieve breakthroughs in mechanical properties by optimizing multiphase types and proportions. Here, we report the design strategy of a non-uniform dual-phase multiscale heterogeneous structure titanium alloy: a low-modulus and high-strength Ti-6Al-4V-5Cu (wt. %) alloy, which is achieved through in-situ alloying by additive manufacturing using mixed Cu and Ti-6Al-4 V powders. The resulting microstructure contains lamellar and equiaxed grain regions with heterogeneity, exhibiting a tensile strength of ∼1176 MPa and a low Young’s modulus of ∼47 GPa, which achieves a favorable strength-modulus-ductility balance. The outstanding mechanical performance observed in this study stems from the multiscale heterogeneous microstructure, which imparts multiple strengthening effects to the alloy, primarily through the soft-hard coupling of α/α″, hetero-deformation-induced back-stress, and sustained work hardening. Distinct from the traditional beta titanium alloys, the unique strategy of achieving excellent strength-modulus synergy by precipitating α″ phase in the spheroidized α phase without loss of strength in the Ti-6Al-4V-5Cu alloy, where the addition of Cu in the Ti-6Al-4 V alloy is appropriate to partition the solute elements, is by inhibiting the Ti₂Cu generation under a high cooling rate, creating conditions for the subsequent generation of a non-uniform multiscale heterogeneous microstructure.

Key words: In-situ alloying, High strength-low modulus combination, Non-uniform multiscale heterogeneous microstructure, Hetero-deformation-induced (HDI)