Underlying toughening mechanisms of TB9/TC4 laminated composite suffering impact load

In this study, a heterogeneous titanium alloy laminated composite, consisting of high-strength TB9 and high-toughness TC4 layers, was successfully prepared by hot rolling. Following a heat treatment at 950 ℃ for 0.5 h and 480 ℃ for 14 h (air cooling), the TB9/TC4 composite demonstrated a high shear bonding strength of 821 MPa. Furthermore, Charpy impact tests indicated that the impact energy (A_KU2) of the composites with TB9 thickness ratios of 25 %, 35 % and 45 % (A_{KU2–25 %} = 58.5 J, A_{KU2–35 %} = 59.5 J, A_{KU2–45 %} = 60.1 J) was significantly higher than that of the individual materials (A_KU2-TB9 = 10.9 J, A_KU2-TC4 = 46.8 J). This enhancement in A_KU2 is attributed to the formation of a Burgers coherent orientation relationship, [1̅11]β∥[21̅1̅0]α and (011̅)β∥(011̅0)α, at the interface, so that the strong metallurgical bonding interface facilitates coordinated deformation between the layers. Additionally, by decoupling the integral area of the impact load-displacement curves, the crack initiation energy (W_i) and propagation energy ₍W_p) were calculated. Notably, W_i exhibited unexpectedly increase with higher proportions of low-toughness TB9, reaching 45.7 J at 45 % TB9 compared to 25.8 J at 25 %. LS-DYNA finite element simulation revealed that this improvement in W_i was due to the diminished fluctuation of stress triaxiality (η) across the interface region during the impact, indicating a lower degree of stress concentration in this area. The uniform distribution of stress effectively delays the onset of interface cracking, thereby enabling the sample to withstand impact load for an extended period before failure.