Thermal stability and the effectiveness of coatings for Sm-Co 2 : 17 high-temperature magnets at temperatures up to 550°C

Thermal stability and the effectiveness of coatings for high-temperature magnets are assessed. Based on several years of experiments and observations, these high-temperature magnets are determined to be metallurgically stable at temperatures up to 550°C. These uncoated high-temperature magnets, held at 300°C in air for more than three years, had only 0.8%-1.6% losses of their magnetic flux. At temperatures of 400°C-550°C, a number of different coatings were evaluated, including Al, Ni, Cr, Mo, W, and Cu. After 2630 h of exposure in air at 500°C, the degradation of magnetic flux was 0.54% for the magnets coated with Ni, compared to 18.63% for the uncoated magnets. Micrographs and Auger electron spectroscopy were used to study the diffusion of different atoms near the surface and the interface between the coating layer and magnet.