Shock-induced dynamic response in single and nanocrystalline high-entropy alloy FeNiCrCoCu

The high-entropy alloys (HEAs) exhibit some unique atomic-scale plastic deformation mechanisms under extreme loading conditions (e.g., shock). Here, four samples are characterized and compared, including nanocrystalline and single-crystal samples in [001], [110], and [111] directions, in terms of their shock-induced dynamic plasticity and failure. Extensive molecular dynamics (MD) simulations show that the anisotropic crystal properties of FeNiCrCoCu HEA significantly affect the Hugoniot elastic limit and the corresponding two-zone elastic-plastic shock wave structures. Importantly, the plastic deformation mechanisms are also tuned by crystal anisotropy. The plastic deformation of the single-crystal sample along [001] direction is dominated by nanotwins and dislocation slip, while those of the other samples only exhibit dislocation slip. The nanotwins are formed by two adjacent stacking faults. In terms of the spallation, the critical shock intensities are different for the four samples. The shock speed threshold of spallation along the [001] and [111] directions is 0.7 km/s, while the [110] direction of 0.6 km/s. Nanocrystalline HEA shows a similar shock speed threshold with the single crystal along [110] direction. The simulation results of spall strength exhibit little discrepancy with the increase of shock velocity. In nanocrystalline HEA, the presence of grain boundaries leads to a low spall strength. During the spall evolution, the voids of single crystals nucleate in the amorphous region formed by the interaction of stacking faults. The spall defects of nanocrystalline samples display a heterogeneous nucleation mechanism at the grain boundaries.