A bimodal microstructure to improve the strength-ductility properties of Ti-Cu alloys by using eutectoid reactive laser depositing

A novel bimodal structure was achieved in Ti-6wt%Cu by laser metal deposition. The microstructures and tensile behaviors of this heterostructure, comparing with typical colony structure, were examined to understand the mechanisms of strengthening and deformation. The bimodal structure consisting of nano-scale eutectoid lamellae and fine Widmanstätten-α exhibits the strength-ductility combination and excellent strain hardening ability. The shear deformation mechanism in ultrafine lamellae and hetero-deformation induced hardening in bimodal structure contribute to the high strain hardening. In contrast, the colony structure with coarse laths and Ti2Cu precipitates show inferior dislocation strengthening leading to a lower tensile strength, while the formation of deformation twins ensures a higher ductility.