Ballistic impact of metastable dual-phase Fe50Mn30Co10Cr10 high-entropy alloy

Abstract

Ballistic impact experiments are conducted on ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{30}{\mathrm{Co}}_{10}{\mathrm{Cr}}_{10}$ high-entropy alloy (HEA) plates over a wide impact velocity range of 376–1981 m s⁻¹. The deformation and damage mechanisms under high-velocity penetration are analyzed via high-speed photography, finite element simulation, and multi-scale characterization techniques. The HEA targets exhibit ductile failure characteristics. Shear plugging failure dominates near the ballistic limit velocity. During high-velocity perforation, the perforation surface develops a gradient morphology comprising a molten zone, a shear dimple zone, and an intact dimple zone. The crater/perforation diameter is governed by projectile deformation at low velocities, shifting to a cavity expansion mechanism at high velocities, with the transition threshold occurring near 1270 m s⁻¹. Microstructural analysis reveals that plastic deformation is driven by dislocation slip, deformation twinning, and transformation-induced plasticity (TRIP). Pronounced deformation gradients and adiabatic heating are observed in the vicinity of the bullet hole. The adiabatic heating ($\sim$750 K) on the bullet hole surface leads to a significant increase in the stacking fault energy (exceeding 20 mJ m⁻²). As the distance from the bullet hole surface decreases, the plastic deformation mechanism transitions from the TRIP effect to deformation twinning and dislocation slip. Finite element simulations based on the Lagrangian algorithm successfully reproduce the experimental results, validating the reliability of the Johnson–Cook constitutive model. The simulations further indicate that the stress state governs crack propagation: straight cracks form due to high shear stress, while V-shaped cracks form due to the combined effect of shear and tensile stresses. This study elucidates the high-velocity penetration failure behavior and underlying micromechanisms of this HEA, providing valuable insights for its safety assessment under extreme loading conditions and microstructural design optimization.