Oxidation Behavior and Magnetic Property of Nd-Fe-B Permanent Magnets With Modified Microstructure

Anisotropic Nd-Fe -B magnet was prepared by Spark Plasma Sintering technique. Magnet with same composition was produced using conventional sintering method for comparison. The magnetic property before and after oxidation test of both magnets were studied. The oxidation kinetics and irreversible losses of both magnets under different temperature were also investigated at the same time. The microstructures before and after oxidation test were observed with scanning electron microscope. Compared with conventional sintered Nd -Fe -B magnets,the SPS magnets process less reduction of magnetic properties after high temperature oxidation test. Microstructure observation shows that SPS magnet has original microstructure,i. e. the grain size of the Nd₂Fe₁₄ B main phase is fine and uniform,and the fine Nd-rich phase does not form along the grain boundaries of main phase,but agglomerates into the triple junctions. Therefore,the pathways for oxidtion propagation are restricted and the inter-granular oxidation process though Nd-rich phase in the magnet is suppressed effectively. As a result,the SPS Nd -Fe -B magnet possesses excellent oxidation resistance.