A periodic-layered structure was observed in solid-(Cr, Fe)2B/liquid-Al diffusion couple at 750 °C. The interface morphology, the reaction products, and the potential formation mechanism of this periodic-layered structure were investigated using an electron probe microanalyzer (EPMA), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). The results indicate that the reaction between (Cr, Fe)2B and liquid Al is a diffusion-controlled process. The formation of intermetallics involves both the superficial dissolution of Fe and Cr atoms and the inward diffusion of Al at the interface. The layered structure, as characterized by various experimental techniques, is alternated by a single FeAl3 layer and a (FeAl3 + Cr3AlB4) dual-phase layer. A potential mechanism describing the formation process of this periodic-layered structure was proposed based on the diffusion kinetics based on the experimental results.
Keywords: focused ion beam; interface diffusion; periodic-layered structure; phase transformations; self-assembly.