Crack propagation and energy dissipation mechanism of AlCoCrFeNi high entropy films under high-strain-rate micro-ballistic impact

With the rapid development of experimental technology, high-entropy alloy materials have attracted increasing attention for applications in high-speed impact and extreme environments, owing to their outstanding mechanical properties. At the microscale, the impact resistance of high-entropy alloy (HEA) films has garnered significant attention due to the pronounced size effect, but experimental investigations at this scale remain limited to comprehensive insights. Here, we explore the mechanical response of AlCoCrFeNi films subjected to laser-induced microparticle impacts at velocities ranging from 254 m/s to 400 m/s. The results show that impact induces crater formation on the film surface, followed by radial cracks, with crack lengths increasing as the impact velocity increases. Molecular dynamics (MD) show that the diameter of the crater is equal to that of the sphere, and stack faults and dislocations occur around the crater. Post-impact analysis indicated brittle damage behavior under high-strain-rates. The dynamic strength of the crater indentation depth (V) region measured by three-dimensional (3D) confocal microscopy was 1647 ± 266 MPa, with a hardness of approximately 6 GPa. The AlCoCrFeNi films exhibit significant strain rate effects in the high-strain-rates regime (10⁷-10⁸s^-1). Increasing the film thickness enhanced energy dissipation capacity, with the specific inelastic energy reaching 1.25 to 1.31 times that of Kevlar under identical impact velocity. These findings offer insights for the design of protective films and electronic components.