Effect of Nb on microstructure and magnetic decay of sintered NdFeB magnets in NaCl solution

Herein, the influence of Nb on the microstructure and magnetic decay of sintered NdFeB magnets was investigated. The NbFeB and Fe ₂ Nb phases were determined through field emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and selected area electron diffraction. The effects of Nb on the crystal structure of the magnet were studied via electron backscatter diffraction analysis. Laser scanning confocal microscopy, a pulsed field magnetometer, and a fluxmeter were used to measure the changes in the surface roughness and magnetic properties of the magnet during corrosion. Based on the experimental result, Nb can optimize the distribution of the Nd-rich phase inside the magnet, reduce the generation of crystal defects, refine the grains, and promote the crystal orientation along the [001] direction. During magnet corrosion, the Nb compound captured hydrogen atoms, causing internal lattice distortion and stress concentration in the matrix phase thereby leading to crush. The broken matrix phase adhered to the magnet surface, isolating the magnet from contact with the corrosive solution and improving the corrosion resistance of the magnet. Moreover, Nb can reduce the impact of the surface structure damage on the demagnetization of the magnet during corrosion, thereby lowering magnetic decay.