Origins of Radial and Axial Inhomogeneity of Magnetic Performance in Cylindrical Nd-Fe-B Magnet Prepared by Hot Deformation

Cylindrical Nd-Fe-B magnets with different height reductions were prepared by hot deformation method. The inhomogeneity of the magnetic performance along the radial direction was revealed with a closed circuit B-H apparatus while that along the axial direction was shown with a vibrating sample magnetometer. The microstructure examined with scanning electron microscopy suggests that orientation variation and grain coarsening of Nd₂Fe₁₄B platelets cooperate to result in the deterioration of remanence along radial direction from center to edge. X-ray diffractometry was carried out over the end surfaces and axially across the middle cross-section of the cylindrical magnet, showing the important role of texture in determination of remanence along the axial direction. Further investigations on an intermediate hot-deformed magnets reveal the unevenness of deformation degree in the axial direction during hot deformation, which accounts for the axial variation of texture and consequent remanence.