Corrosion studies on highly textured Nd–Fe–B sintered magnets

The anisotropic corrosion behaviour of highly textured sintered Nd–Fe–B magnets in weakly acidic solutions has been evaluated by investigations of magnet surfaces, which are parallel or perpendicular to the crystallographic c-axis of the aligned ferromagnetic grains. The total corrosion process progresses more pronouncedly at the perpendicular magnets surfaces (the pole faces). Under free corrosion and anodic polarization conditions the parallel magnet surfaces exhibit a stronger active dissolution tendency due to an enhanced reactivity of grain surfaces parallel to the {1 0 0} planes of the Nd2Fe14B crystals. Single misoriented grains dissolve preferentially at both magnet sides. Under cathodic conditions, the hydrogenation process progresses more rapidly at the perpendicular sides, suggesting a local preferential penetration of atomic hydrogen into the material.