Investigation on microstructure, texture, and magnetic properties of hot deformed Nd-Fe-B ring magnets

Radially oriented Nd-Fe-B ring magnets have been prepared by backward extrusion of melt-spun powder. The position dependent of the microstructure, the magnetic properties, and the crystal alignment of the extruded rings have been investigated. The magnetic properties in radial direction increase slightly along the axis from the bottom to the middle then steeply decrease at the upper end of the ring. The magnetic properties and x-ray diffraction patterns of the upper end are very close to that of the isotropic pressed precursor. It suggests that the extruded ring approximately retains the initial structure at its upper end which is because the formation of texture is difficult at the initial stage of hot extrusion. Characteristic microstructure morphologies were found at different spatial positions: flake-shaped grains for the inner, elongated grains for the middle, and particle-shaped grains for the outer region in the cross section. Only particle-shaped grains were observed at the upper end of the ring. But the circumferential homogeneity of the surface magnetic flux densities is better in an extruded ring magnet than in a radially oriented ring prepared by sintering method. The deformation and texture formation processes were discussed. The deformation and texture formation in backward extruded magnets from melt-spun Nd-Fe-B precursors may possibly involve grain boundary sliding and grain rotation, solution-precipitation process, and preferred growth of Nd(2)Fe(14)B nanograins along the easy growth a-axis. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3339817]