Microstructure modification of additive manufactured Ti-6Al-4V plates for improved ballistic performance properties

Titanium alloys such as Ti-6Al-4V offer a potential lightweight alternative to traditional armour steels for ballistic protection due to their reduced density of approximately 60 % that of steel and tensile properties better than rolled homogenous armour steel. The manufacture of metallic armour often requires substantial thermomechanical processing to meet necessary ballistic performance specifications and thus restricts the complexity of armour designs. Additive manufacturing of Ti-6Al-4V has matured significantly in recent years, achieving outstanding mechanical properties in the as-built condition. In this study, Ti-6Al-4V plates were additively manufactured using both laser powder bed fusion and direct laser metal deposition for ballistic testing. The plates were built in different orientations and subjected to pre-heating or post heat-treatment to investigate the microstructural effect on the ballistic velocity limit (V50). The results show that plates with lamellar microstructure formed through martensite decomposition had higher V50 compared to lamellar microstructure formed via slow cooling through the β-transus. The post heat-treatment increased the V50 due to coarsening of the α-lath and stress relief. It is also apparent that anisotropy of the microstructure, specifically the columnar prior-β grains, affects the ballistic performance. A higher V50 was achieved when the columnar grains were aligned perpendicular to the projectile impact direction.