Ballistic impact response of a heat-treated dual-phase Ti–5.2Mo–4.8Al–2.5Zr–1.7Cr alloy with hierarchical microstructure

In the present study, a dual-phase Ti-5.2Mo-4.8Al-2.5Zr-1.7Cr alloy was hot-rolled at 980 °C with a thickness reduction of 65% and then heat-treated with the strategy of 920 °C/1 h/water quenching +550 °C/6 h/air cooling, and a hierarchical microstructure was prepared, which contained micro-scale equiaxed primary α phase (αp), sub-micro scale rod-like α phase (αr), nano-scale acicular secondary α phase (αs) and β matrix segmented by αs and αr. In addition, the dislocation densities of α phase and β phase were determined as 0.3652 × 1015/m2 and 2.2502 × 1015/m2, respectively. Contributing to αr and αs, the hierarchical microstructure exhibited higher strength (yield strength: 1228 MPa, ultimate tensile strength: 1389 MPa, dynamic compressive strength: 1661 ± 27 MPa). Simultaneously, αp and αr were helpful to the strain transfer, and thus the plasticity was maintained at a considerable level (elongation: 13.4 ± 0.2%, critical fracture strain: 18.9 ± 0.2%). Such hierarchical microstructure overcame the limitation of the strength-ductility trade-off to a certain extent and exhibited a superior combination of strength and ductility. The ballistic impact behavior of the titanium alloy plates with the thickness of 20.3 mm (1#), 19.3 mm (2#) and 18.4 mm (3#) against 7.62 mm armour piercing projectiles illustrated that as the titanium alloy thicknesses decreased from 20.3 mm to 18.4 mm, more ASB-induced cracks were formed near the rear face and connected to form catastrophic cracks in the 2# and the 3# titanium alloy plates, even resulting in the failure for the 3# titanium alloy plate. Ultimately, the 1# and 2# titanium alloy plates exhibited preferable ballistic impact properties.