Abstract
A novel practice of surface nanocrystallization (SNC) to protect sintered Nd-Fe-B magnet from corrosion was achieved by a controlled hydrogenation-disproportionation-desorption-recombination (HDDR). The SNC magnet showed much better corrosion resistance compared with the originally unprocessed. The nanocrystallized surface of 50 μm thick layer with dispersed Nd-rich intergranular phases played crucial role in blocking intergranular corrosion. For SNC magnet, corrosion test showed a highly oxidized and chemically homogeneous film had formed preventing corrosion deep inwards. Hardness testing revealed the surface was strengthened showing a totally different cracking pattern. To verify its applicable ability, the influences of hydrogen reaction with bulk magnet on microstructures and magnetic properties in different depth were studied. For a large-sized magnet, the detrimental effects were almost negligible. This technique could be a possible new method of surface processing utilized in large bulk Nd-Fe-B magnet for good corrosion resistance and surface strength.
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