Sintered neodymium-iron-boron (Nd-Fe-B) magnets with cube and flat geometries were exposed to pressurized heat-humidity corrosion tests for 96 and 240 h. Measurements of weight and flux losses were performed after the corrosion tests. The corroded specimens were further characterized using scanning electron microscopy and optical profilometry. The microcrystalline anisotropy of sintered magnets gave rise to heterogeneous corrosion, where the pole faces degraded preferentially to the side faces. The magnetic field from the magnet itself thus contributed to the amount and location of detached ferromagnetic grains. The magnets with cube geometry suffered greater losses than the flat magnets, even though the flat magnets had a higher relative pole-face area. The higher total flux (due to the larger volume) of the cube-shaped magnets led to the higher overall losses. In the flat magnets, the corrosion concentrated heavily on areas near the corners.
- hard magnetic materials
- Nd-Fe-B magnets