Ballistic Response of a FCC-B2 Eutectic AlCoCrFeNi2.1 High Entropy Alloy

An AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA), comprising of FCC phase and a high volume fraction of plate and irregularly shaped BCC-ordered intermetallic B2 domains, was subjected to normal impact by spherical Tungsten-Carbide projectiles. Depending on projectile velocity, the impacted AlCoCrFeNi2.1 plates were partially penetrated (at the lowest velocity of 803 m/s), plugged (intermediate velocity of 1159 m/s), and fully penetrated (highest velocity of 1388 m/s). Electron microscopy was utilized to characterize the residual damage or deformation features in the recovered specimens. Failure in the partially penetrated conditions was dominated by interfacial decohesion at the plate-like B2 and FCC interfaces. At higher velocities where plugging occurred, failure was dominated by crack formation in regions containing adiabatic shear band. These results indicated a transition in failure modes as a function of projectile velocities, where the FCC-B2 microstructure dominate failure at lower velocities, while such microstructural features do not influence dynamic failure at higher velocities.