Long term aging of Co5Sm-Pr and Co5Sm- Pr-Nd alloys

Cobalt rare earth (R) magnets were produced containing Sm-Pr and Sm-Pr-Nd for (R) in order to study their long term stabilities in air at temperatures of 125°C, 200°C and 300°C. The rare earth content was below 40 w/o, and most of the magnets had Hk/Hciratios greater than 0.65. All specimens were sintered in hydrogen to densities greater than 98% of theoretical. Periodic magnetic measurements were made on the magnets during the 10,000 hour aging test. Co-Sm-Pr alloys showed excellent stability at 125°C and 200°C storage, but at 300°C they came apart physically after 5000 hours. The Co-Sm-Pr-Nd magnets were stable at 200°C for 3000 hours and drastically deteriorated, thereafter, both magnetically and physically. Metallographic examination of the deteriorated specimens showed various degrees of oxidation along the cracked areas.