Net-shape and crack-free production of Nd-Fe-B magnets by hot deformation

In order to reduce the amount of material waste and therefore to use the precious rare earth element Nd in a more efficient way, routes for the production of crack-free hot-deformed nanocrystalline Nd-Fe-B magnets (using melt-spun ribbons as a precursor) have been investigated. In contrast to the conventional route in which material flows into a cavity, pressing tool has been used in order to exert a back pressure during backward extrusion, leading to crack-free and net-shape production of radially oriented ring magnets, without detrimental influence on magnetic properties. Micrographs demonstrate overall good alignment of elongated platelet shaped grains with radially oriented c-axis in most parts of the ring. A mean remanence Jr = 1.27 T and coercivity μ0iHc = 1.5 T has been obtained. Degree of texture reaches around 0.7. Furthermore, die-upsetting has been performed for different degrees of deformation to obtain crack-free, mechanically and magnetically homogenous, axially oriented tablet magnets.