Fractographic Analysis and Fatigue Crack Propagation Behavior of TC4-F Alloy with a Duplex Microstructure

The fatigue performance of titanium alloys is a critical determinant of the service life and structural integrity for aerospace and marine engineering components. But within the framework of damage tolerance design, resistance to fatigue crack propagation is regarded as a key indicator governing the fatigue performance of these engineering structures. In previous work, while the general fatigue performance of Ti-6Al-4V-0.55Fe alloy has received systematic study, targeted research focusing on its resistance to fatigue crack propagation remains limited. Therefore, in this work, compared with Ti-6Al-4V ELI alloy, the fatigue crack propagation behavior and fracture mechanism of Ti-6Al-4V-0.55Fe alloy with a duplex microstructure were systematically investigated. The results show that when ∆K < 12.75 MPa⋅m^1/2, Ti-6Al-4V-0.55Fe alloy demonstrates superior resistance to fatigue crack propagation. Fractographic analysis indicates that the primary difference between the two alloys lies in the stage of crack initiation and early propagation. This behavior is attributed to the addition of trace Fe, which enhances α/β boundary resistance and thereby retards crack growth. Moreover, crack propagation of TC4-F alloy is also slowed by the increased path length from bypassing the α_p phase.