Ballistic Behavior of High-Strength Bimodal Ti-5553 Alloy Armor Against 7.62-mm Armor-Piercing Incendiary Projectile

This paper investigated the ballistic impact behavior of high-strength bimodal Ti-5553 alloy armor against a 7.62 mm armor-piercing incendiary projectile. The V₅₀ limit velocity of the armor is high as 415 m/s, which is much higher than that of titanium alloy armors that are fabricated by coarse-grain Beta titanium alloy or bimodal Ti-6Al-4V titanium alloy. The penetration mechanism of the armor is the pure plugging, and the plugging leads to the formation of the thin adiabatic shear band (ASB) on the penetration channel of the armor. Compared with the initial bimodal microstructure consisting of the rodlike primary Alpha phase and the equiaxial prior Beta grain, the microstructure within the ASB evolves drastically. First, the rodlike primary Alpha phase transforms into Alpha fiber with the diameter of 200 nm. Second, with the intragranular Alpha (Alpha_Intra) → Beta transformation and the dynamic recrystallization of the transformed Beta phase, the equiaxial prior Beta grain disappears. Here, we attribute to excellent ballistic performance of the bimodal Ti-5553 to the higher dynamic strength, high critical strain for ASB formation, and microstructural evolution during failure/plugging along the ASB. In addition, the ultra-high dynamic strength of the armor could result in the blunting of the steel core during the penetration, which is also beneficial to the ballistic performance of the armor.