Precipitation response and hardening behaviors of Fe-modified Ti5553 alloy

Ti5553−xFe (x=0.4, 1.2, 2.0, wt.%) alloys have been designed and fabricated through BE (blended element) sintering to investigate the effect of Fe-addition on athermal ω-phase transformation, α-phase evolution and age hardening behavior. The results show that the formation of athermal ω-phase is fully suppressed in water-quenched specimens when Fe-addition is up to 2 wt.%. The relevant timescales of α formation during initial stages of aging indicate that incubation time increases with Fe-addition. Further aging results in continuous nucleation and growth of α-phase but finer intragranular α lamellae exhibit in Ti5553−2Fe alloy. In addition, the width and extent of grain boundary α-film increase slightly with incremental Fe-addition, especially in furnace cooling condition. Result of Vickers hardness manifests that Fe-addition leads to a strong hardening effect in both solution and aging treatment. The solid solution strengthening is quantitatively estimated by ab initio calculation based on the Labusch−Nabarro model. The evolution of α-precipitate is rationalized by Gibbs free energy. The prominent hardening effect of Ti5553−2Fe alloy is attributed to both large lattice misfit of β-matrix and fine α-precipitate distribution.