Microstructure of hot-pressed and die-upset NdFeB magnets

✍ Scribed by Mishra, Raja K.

• Book ID: 120406407
• Publisher: American Institute of Physics
• Year: 1987
• Tongue: English
• Weight: 981 KB
• Volume: 62
• Category: Article
• ISSN: 0021-8979
• DOI: 10.1063/1.339709

✦ Synopsis

Transmission electron microscopy was used to establish densification, alignment, and magnetization reversal mechanisms in hot-pressed and die-upset NdFeB magnets. Microstructures of these materials reveal two principal phases: Nd 2 Fe l4 B grains and a grain boundary phase of approximate composition Nd7Fe3' The grains in the hot-pressed material are polygonal and isotropic, while those in the die-upset material are flat platelets. The alignment of die-upset magnets arises exclusively from the fact that hot deformation produces platelets of Nd2Fe!4B grains with their c axes parallel to the stress axis. It is argued that yielding plays an important role in the densification of the hot-pressed samples, and diffusion slip is critical to the alignment. The grain boundary phase appears as a crystalline or noncrystalline phase in the hot-pressed samples but has an fcc structure in the die-upset samples. Magnetic domain walls are shown to be pinned at the grain boundary phase in both cases. A Nd-rich spongy phase is observed to form at the boundaries where two ribbons fuse, but has no significance for the magnetic properties.