Spallation strength and microstructural damage evolution in TC4 titanium alloy subjected to high-velocity impact

TC4 titanium alloy is a vital structural material in aerospace applications, exhibiting dynamic failure behavior under high-velocity impact loads, which critically influence aircraft safety and reliability in extreme conditions. At the microscale, dislocation evolution and phase transformation drive macroscopic structural damage. This necessitates an in-depth investigation into the micro-failure mechanisms of TC4 titanium alloy under extreme impact conditions. This study utilizes molecular dynamics simulations to develop an α+ β dual-phase model. It simulates stress wave propagation, dislocation dynamics, and phase transformation processes across varying impact velocities, thereby analyzing the dynamic mechanical response of TC4 titanium alloy to uncover its microscopic spallation damage mechanisms. Results reveal that when impact velocity surpasses 0.7 km/s, rebound of free surface velocity and separation of elastic-plastic double waves are intimately linked to spallation damage. Furthermore, spallation strength σ_sp shows a dynamic interplay between strain rate hardening and thermal softening effects across different impact velocities. The study elucidates the synergistic roles of α and β phases in plastic deformation and their governance over void nucleation pathways. The impact process triggers HCP→BCC→FCC transformations and BCC→HCP reverse transformations. High-velocity impacts enhance amorphization of atomic structures while fostering dynamic recovery in the β phase. Emergence of the α' phase within the β phase creates a “strengthening-brittleness” dual effect through interface reinforcement and dislocation blockage, significantly influencing crack initiation and propagation. The study reveals synergistic failure mechanisms across stress wave propagation, dislocation dynamics, and phase transformation competition, enabling optimization of impact resistance of titanium alloys under extreme conditions.