Synergistic effect of the multi-factors and deformation mechanisms on the low-temperature impact toughness in Ti-6Al-4V-0.55Fe alloy

The multi-factor effects impact property and deformation mechanisms with equiaxed microstructure (EM) and bimodal microstructure (BM) in Ti-6Al-4V-0.55Fe alloys were systematically investigated at −20 °C. The impact property of BM specimens was higher than that of EM specimens. The crack initiation zone of BM is larger than that of EM, indicating that BM has higher crack initiation energy. During crack propagation, the lamellar α_s and the spheroidization of α_p effectively deflect crack propagation and shorten the crack propagation length, forming a tortuous crack path. Tensile twinning, compressive twinning, and detwinning occur in BM, and these mechanisms effectively dissipate impact energy. As the solution temperature rises to 930 °C, a high density of geometrically necessary dislocations distributes uniformly near the crack region, combining with fractured α_p and highly kinked lamellar α_s, which dissipates more impact energy. Moreover, the coordination ability of deformation weakens due to the content of α_p decreases with rising solution temperature to 950 °C, leading to a reduction in impact energy. Spheroidization of α_p grains, lamellar α_s, crack path, twin kink deformation in α_p, the interaction between twins and α lamellar, and the α colony are the key factors influencing the impact toughness of BM.