Corrosion Behavior of Conventional and Spark Plasma-Sintered Nd-Fe-B Permanent Magnets in Different Solutions

Spark plasma sintering (SPS) and conventional sintering techniques were used to fabricate sintered Nd-Fe-B permanent magnets. The corrosion behaviors of both magnets in sodium chloride (NaCl), sodium hydroxide (NaOH), and sulfuric acid (H₂SO₄) solutions were studied. The weight-loss curves indicate that both magnets exhibit passive behavior in alkaline solution and dissolve actively in acid solution. SEM observations show that the conventional sintered Nd-Fe-B magnets exhibit typical intergranular corrosion. In the SPS magnet, however, intergranular corrosion through the Nd-rich phase is suppressed effectively due to the unique microstructure of the magnets, i.e., the grain size of the Nd₂Fe₁₄B main phase is fine and uniform, and the fine Nd-richphase does notform along the grain boundaries of main phase as with conventional magnets, but agglomerates into the triple junctions. As a result, the SPS Nd-Fe-B magnets possess excellent corrosion resistance.