Research on laser solid forming of a functionally gradient Ti-Ti₂AlNb alloy

A functionally gradient Ti-Ti₂AlNb alloy, which has continuous compositional gradient and regular outline with a length about 17 mm, was fabricated by laser solid forming. Phase morphological evolution and microstructure evolution, and microhardness along the compositional gradient direction were analyzed. With the increase of aluminum and niobium contents, a series of phase evolutions along the compositional gradient occurred: α′→ α+β →α+α′ → α′→ α+β → α+β/B2+α₂ → β/B2+α₂ →β/B2 → B2+α+O →B2, and the compositionally gradient material accomplished a transition of α titanium alloy, α+β titanium alloy, β titanium alloy, finally Ti₂AlNb-based alloy. In the transition layers, the microhardness HV increased from 170 of Ti at the bottom to 470 of Ti₂AlNb at the top. Based on the non-equilibrium phase diagram of the Ti-rich corner, the phase morphological evolution during forming were explained with the analysis of the influences of the Al and Nb on the stabilities of α, β and α₂ phases in titanium alloys.