Structure and energy of the (101) twin boundary in hot-deformed Nd-Fe-B magnets

Revealing the atomic structure and energy of twin boundaries in compounds has been a challenge, especially for compounds with complex crystal structure such as the tetragonal Nd₂Fe₁₄B phase in Nd-Fe-B magnets. In this paper, a large number of (101) twin boundaries were observed in grain-coarsening regions of hot-deformed Nd-Fe-B magnets. The atomic structure and twin boundary energy of the (101) twin boundaries were investigated based on the atomic-scale high-angle annular dark field scanning transmission electron microscopy observation and first-principles calculations. The (101) twin boundary has a considerably low energy of 0.008 J/m². The mechanism of twin-assisted grain coarsening was proposed.