Effect of annealing temperature on the notch impact toughness of a laser melting deposited titanium alloy Ti-4Al-1.5Mn

A laser deposited near-alpha titanium alloy Ti-4Al-1.5Mn was annealed in the α + β phase region at different temperatures in an attempt to obtain novel microstructure. Notch impact toughness of the annealed alloy was evaluated as a function of anneal temperature. Anneal microstructure and fracture surfaces of impact test specimens were characterized by OM and SEM. A unique bi-modal microstructure consisting of coarse crab-claw-like primary α and fine lamellar transformed β was generated by annealing the alloy in the α + β region. Area fraction of the crab-claw-like primary α decreased sharply with the increasing anneal temperature. The impact toughness of the as-deposited alloy was equivalent to that of wrought counterpart and was largely improved by annealing in α + β region. The unique bi-modal microstructure produced more interfaces which were obstacles for crack propagation, contributing to a higher impact toughness.