Revealing the Epitaxial Interface between Al₁₃Fe₄ and Al₅Fe₂ Enabling Atomic Al Interdiffusion

Steel is the most commonly manufactured material in the world. Its performances can be improved by hot-dip coating with the low weight aluminum metal. The structure of the Al∥Fe interface, which is known to contain a buffer layer made of complex intermetallic compounds such as Al₅Fe₂ and Al₁₃Fe₄, is crucial for the properties. On the basis of surface X-ray diffraction, combined with theoretical calculations, we derive in this work a consistent model at the atomic scale for the complex Al₁₃Fe₄(010)∥Al₅Fe₂(001) interface. The epitaxial relationships are found to be [130]Al₅Fe₂∥[010]Al₁₃Fe₄ and [1 1̅0]Al₅Fe₂ ∥[100]Al₁₃Fe₄. Interfacial and constrained energies, as well as works of adhesion, calculated for several structural models based on density functional theory, identify the lattice mismatch and the interfacial chemical composition as main factors for the stability of the interface. Molecular dynamics simulations suggest a mechanism of Al diffusion to explain the formation of the complex Al₁₃Fe₄ and Al₅Fe₂ phases at the Al∥Fe interface.