Abstract
Laser powder bed fusion (LPBF) enables the fabrication of β-titanium alloys with highly controlled microstructures and exceptional specific strength. Among them, Ti-5Al-5Mo-5V-3-Cr (Ti5553), a high-strength near-β alloy known for its excellent fatigue resistance and deep hardenability, exhibits significant improvements in mechanical performance when precipitation-hardening heat treatments promote α-phase formation within the β matrix. Despite these advantages, the alloy’s response under extreme loading conditions remains insufficiently understood. This study examines the high strain-rate deformation and failure mechanisms of as-built and heat-treated LPBF-Ti5553 using split Hopkinson pressure bar testing. The as-built alloy, characterized by columnar prior-β grains elongated along the building direction, exhibited pronounced strain-rate sensitivity. Localized shear instability led to the formation of adiabatic shear bands, ultimately promoting catastrophic fracture. In comparison with the as-built condition, heat-treated samples, solutionized at 800 °C for 3 h and aged at 600 °C for 4 h to promote α-phase precipitation, exhibited higher flow stress but reduced strain to failure, reflecting the strengthening effect and diminished ductility associated with fine α precipitates within the β matrix. The maximum ultimate compressive strength, reaching 1550 MPa, was achieved in heat-treated samples tested at a strain rate of 1000 s⁻¹. Post-impact OM, scanning electron microscopy, and electron backscatter diffraction analyses revealed a ductile–brittle mixed-mode failure in the as-built alloy, whereas the heat-treated condition failed predominantly by brittle fracture. These findings underscore the critical influence of microstructural state on dynamic strength, failure resistance, and energy absorption capacity of LPBF-Ti5553, offering valuable insights for the design of impact-critical aerospace and defense components.