Rare earth based permanent magnets (RE PM) show the highest energy densities of all commercial magnetic materials, most importantly on Nd-Fe-B and Sm-Co basis. Nd-Fe-B exhibit higher energy densities around room temperature and the used elements are less critical than Sm-Co, but the latter is more temperature stable and has a higher corrosion resistance. The choice of the right material depends on the application environment of the magnet containing device. For applications with rough environmental conditions like low partial pressures of hydrogen, Sm-Co is the material of choice. To ensure a long lifetime under such conditions the knowledge of chemical stability of the magnet is important.
In this study, the reaction behavior of two commercially available Sm2Co17 magnets was investigated. For this, the magnets were placed in a hydrogen atmosphere with systematically varied partial pressure, exposure time and temperature ranging from 1 – 10 bar, 2 – 10 d and 25 – 500 °C, respectively. In dependence on the exposure parameters, material properties like hydrogen content, magnetic properties, microstructure and lattice constants were characterized in detail. It is shown that for short exposure times an activation temperature of 120 °C is necessary to start the reaction and increase the amount of hydrogen in the Sm-Co sample. In case of a longer exposure times, also lower temperatures lead to a reaction. An increase in exposure time, temperature or partial pressure leads to a higher hydrogen content and a decrease in remanence. Lattice expansion correlates with the increasing amount of hydrogen in the Sm-Co magnets. We find that the exposure temperature has the highest impact on the observed property changes followed by reaction time and H2 partial pressure. The influence of exposure temperature shows a maximum at 200 °C and decreases afterwards.