Hydrogen-induced degradation in sintered NdFeB magnets: A comprehensive study on microstructural evolution and multi-scale property deterioration

This study systematically investigates the hydrogenation behavior of N35-type sintered NdFeB magnets and its consequential effects on their mechanical and magnetic properties. The hydrogenation follows a distinct two-stage mechanism: hydrogen first preferentially reacts with the Nd-rich grain boundary phase to form brittle neodymium hydrides (NdH x ), before penetrating the main Nd 2 Fe 14 B phase to form Nd 2 Fe 14 BH x . This process, driven by alloy hydrogen trapping, induces severe microstructural damage through cracking and interfacial debonding. The hydrogen-induced degradation leads to a catastrophic decline in mechanical properties across scales. Macroscopically, the elastic modulus decreases by 10.6 GPa and compressive strength drops by 269 MPa. At the micro-scale, a dramatic collapse in nanohardness is observed: the average value plummets from initial levels of 13.37 GPa (main phase) and 2.84 GPa (Nd-rich phase) to merely 0.94 GPa after hydrogenation. In parallel, magnetic properties are severely impaired, with coercivity and maximum magnetic energy product decreasing by 1.60 kOe and 5.3 MGOe, respectively, due to the destruction of domain wall pinning sites and nucleation of reverse domains at hydrogen-generated microcracks. These findings provide a quantitative characterization and correlative analysis linking hydrogen-driven microstructural evolution to macroscopic performance decay. The insights are crucial for designing hydrogen-resistant magnets, predicting service life in hydrogen-containing environments, and optimizing recycling processes via hydrogen decrepitation.