A study on the congregation of Nd-rich phases on the surfaces of sintered Nd-Fe-B magnet

The congregation of Nd-rich phases on the surfaces of sintered Nd-Fe-B magnets is observed in this work. The thickness of the Nd-rich congregated layers is about 20-60 μm. The congregated phases in the base plane and hard plane are quite different. On the base plane, the gain boundary in the surface layer is obscure. On the hard plane, a strange structure like eutectic phase can be found between the matrix and the surface. This behavior of Nd-rich phases can be comprehended by referring to thermodynamics.