Thermal Stability and the Effectiveness of Coatings for Sm–Co 2 : 17 High-Temperature Magnets at Temperatures up to 550 ᶜirchboxC

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/spl deg/C. These uncoated high-temperature magnets, held at 300/spl deg/C in air for more than three years, had only 0.8%-1.6% losses of their magnetic flux. At temperatures of 400/spl deg/C-550/spl deg/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/spl deg/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.