The influence of β heat treatment and quasi-β heat treatment on strength, plasticity, fracture toughness and fatigue crack propagation rate of damage-tolerant titanium alloy Ti-6Al-4V ELI thick section forgings have been studied. The results show that, the increasing of the first annealing temperature from T<sub>b</sub>+15℃ to T<sub>b</sub>+30℃, T<sub>b</sub>+60℃ will lead to lower plasticity observably.
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