Vacancy dependent shock response of high-entropy alloy FeNiCrCoCu

Abstract

Large-scale molecular dynamics simulations are employed to investigate the effect of vacancies on the dynamic response of single-crystal high-entropy alloy FeNiCrCoCu to shock loading, including plasticity and spallation. The shock direction is along four typical crystallographic orientations, [001], [011], [111] and [122], and initial vacancy concentration for each orientation varies from 0% to 2%. Our simulation results indicate that vacancies exhibit a pronounced effect on free surface velocity histories, stress evolution, plastic deformation, and spall damage when vacancy concentration exceeds a critical threshold. Below this threshold, the influence of vacancies is negligible. The critical vacancy concentrations are found to be 1% for [001], 1.5% for [111] and [122], and beyond the explored range (2%) for [011]. Further analysis indicates that this threshold corresponds to the onset of plasticity during compression stage, as increasing vacancy concentration reduces critical shear stress for dislocation activation. The trigger of compression plasticity reduces the strain rate and indirectly promotes the plasticity by altering the stress evolution, during tension stage. In contrast, the direct impact of vacancies on tension plasticity and damage evolution is found to be minimal. The observed reduction in spall strength is attributed to either a lower strain rate, increased tension plasticity, or a combination of both mechanisms.