Notch does not significantly reduce the load bearing capacity of high-entropy alloy at ultrahigh strain rates

Flaws usually play a critical role for the performance of structural materials under extreme service conditions. Particularly, under high strain rate loading, the effect of flaw exhibits significant differences compared to quasi-static loading conditions. In this work, the effect of notch (an example of external flaw) on tensile behavior of single-crystal CoCrFeMnNi high-entropy alloy at strain rates ranging from 10⁹ s⁻¹ to 10¹² s⁻¹ was studied using molecular dynamics simulation. We found that with the increase of strain rate, the plastic deformation mechanism shifts from being dislocation-dominated to amorphization-dominated, while the influence of notch on the load-bearing capacity gradually diminishes, exhibiting a nearly “flaw-independent” behavior at ultrahigh strain rate. This phenomenon originates from the unique fact that under the extreme condition: the enormous applied stress reduces the activation energy for dislocation motion to nearly zero, enabling dislocation velocities to approach the material's shear wave speed. Meanwhile, the limited range of atomic displacement restricts the timely formation of dislocations, leading to significant attenuation or even complete disappearance of the strain concentration effect at the notch root. This work provides new insights into the deformation behaviors of notched high-entropy alloy under high-speed loading, and suggests that crack-related models may require reconsideration at ultrahigh strain rates.