Layer–Island Mixed Growth and Non-Equilibrium Structural Evolution of Fe-Co-Ni-Mn-Al High-Entropy Alloy Thin Films: Insights from Molecular Dynamics Simulation

Molecular dynamics (MD) simulations were used to study the deposition and growth of Fe-Co-Ni-M-Al multi-component alloy films on a Si(100) substrate. By comparing the surface topography at incident energies of 0.1~0.5 eV, it was observed that an increase in incident energy enhances local impact perturbations and induces surface roughening, with the film’s root-mean-square (RMS) roughness increasing from 0.3393 nm to 0.4870 nm. The selection of input data was consistent with the preparation conditions of the electron beam evaporation deposition process. The 0.1 eV condition, which yielded the best surface quality, was selected to study the deposition and growth process. The results indicate that deposited atoms first form a continuous covering layer on the substrate surface, followed by localized accumulation and island-like thickening, exhibiting characteristics of a mixed layer–island growth pattern. The radial distribution function (RDF) exhibits a stable first-neighbor peak at approximately 2.5 Å, with higher-order peaks and shoulders gradually appearing during the deposition process, indicating that short-range order formed within the film and gradually evolved into medium-range order. Polyhedral template matching (PTM) results show that the film exhibits a non-equilibrium structure characterized by a predominance of FCC structure, accompanied by the coexistence of HCP, BCC, and amorphous structures. Based on the solute formation rules derived from the atomic size difference δ and Ω parameter, as well as the empirical criteria of VEC, this composition exhibits the potential to form a solid solution and a structure with a tendency toward FCC. Meanwhile, both Debye-simulated XRD results and experimental data show a broadened main peak near 44°, cross-sectional SEM characterization confirms that the film surface is not completely flat but exhibits some local topographical variations, and TEM characterization reveals the presence of nanocrystalline/polycrystalline structures within the film; together, these findings demonstrate the ability of the MD model to predict the average atomic spacing and primary local order characteristics of the experimental film.