Critically Percolated States in High-Entropy Alloys with Exact Equi-Atomicity

Abstract

The formation of site-percolated states of exact equiatomic high-entropy alloys (HEAs) with body-centered-cubic (bcc) and face-centered-cubic (fcc) structures was investigated where their critical concentrations (p_c^site) are given as 0.245 and 0.198, respectively, from conventional percolation theory. Molecular dynamics simulations were performed for WNbMoTa and WNbMoTaV HEAs with a bcc structure and AuCuNiPt and AuCuNiPdPt HEAs with an fcc structure. The simulation conditions included a generalized embedded atom method potential under NTp ensemble where the number of elements (N), absolute temperature (T), and pressure (p) were maintained constant. N-element alloys (N = 4 and 5) with a fraction of constituent elements (x = 1/N) were initially prepared in 10 × 10 × 10 supercells randomly in terms of chemical species and were simulated under atmospheric pressure at T = 1000 K. The total pair-distribution functions of the alloys revealed that the nearest neighbor distance (d_n) for fcc ranged from 0.20 to 0.33 nm, whereas d_n and the second neighbor distance (d_nn) for bcc ranged from 0.235 to 0.305 nm and 0.305 to 0.370 nm, respectively. A 3-dimensional topological analysis for atomic correlations revealed that the alloys were in percolated and isolated states, respectively, when x ≥ p_c^site and x < p_c^site and that the values of 1/p_c^site correspond to the ideal values of N for exact equi-atomic HEAs. Furthermore, it was observed that exact equi-atomic quaternary alloys (N = 4) with a bcc structure and quinary alloys (N = 5) with an fcc structure are in the critically percolated states.