Chemical Stability and Hydrogen Reaction Behavior of SmCo 2:17‐Type Permanent Magnets

Abstract

Herein, the reaction behavior and chemical stability of two commercially available SmCo 2:17‐type sintered magnets with nominal composition of Sm23.75Co48.67FebalCu4.91Zr2.37 and Sm24.95Co48.80FebalCu4.46Zr2.68 (wt%) are investigated. The magnets are placed in a hydrogen atmosphere with systematically varied pressure, exposure time, and temperature ranging from 1–11 bar, 2–10 d, and 25–500 °C, respectively. Hydrogen content, magnetic properties, microstructure, and lattice constants are characterized in detail. It is found that for short exposure times like 2 d an activation temperature of 120 °C is necessary to initiate the reaction and to increase the amount of hydrogen in the Sm–Co material. Hydrogen absorption starts at lower temperatures with longer exposure times. An increase in exposure time, temperature, or pressure leads to a higher hydrogen content and a decrease in remanence Br, energy product (BH)max, and coercivity HcB. Lattice expansion, estimated by X‐ray diffraction analysis, correlates with the increasing amount of hydrogen in the Sm–Co magnets. With respect to all varied parameters under investigation, the exposure temperature has the highest impact on the observed property changes followed by reaction time and H2 pressure.