Direct observation of the interface reaction dynamics of the NdCeFeB phase <i>via in situ</i> annealing &amp; quenching STEM

Although the Rare Earth (RE)₂Fe₁₄B type magnets were invented in the 1980s and are widely used worldwide. Yet, the phase formation and dissolution mechanisms are still not crystal clear. The reaction dynamics between rare earth elements (REE) and the iron-enriched matrix are essential to understanding the formation of hard magnetic REE-Fe-B phase or, conversely, phase dissociation and performance degeneration. Developing a reaction mechanism is fundamentally important for process engineering and performance manipulation. This work investigates the interface reaction dynamics between REE and an iron enriched matrix <i>via in situ</i> scanning transmission electron microscopy (STEM). The focused ion beam (FIB) procedure and <i>in situ</i> STEM experiments are specifically designed to achieve both oxygen-involved and oxygen-free reaction mechanisms within one specimen. The high-temperature reaction dynamics are frozen to room temperature (RT) by rapid quenching, preserving the solid-liquid interface dynamics between Fe₂₃B₆ and liquid phases. Serial atomic resolution STEM images depict lattice evolution while REE atoms embed into the Fe₂₃B₆ lattice. The presented work also demonstrates that combining an advanced FIB procedure with <i>in situ</i> annealing & quenching STEM is a powerful tool for investigating the complex system's high-temperature reaction mechanisms and interface phenomena.