Fe-Cr-Co permanent magnet alloys heat-treated in the ridge region of the miscibility gap

By heat-treating in the ridge region of the miscibility gap, the magnetic properties of the Fe-Cr-Co permanent magnet alloys have been remarkably enhanced. The optimum procedure of the heat treatments, such as thermomagnetic treatment and step-aging sequence for the "ridge" alloys, is examined. Such heat treatments are discussed in conjunction with their microstructures. It is found that thermomagnetic treatment in the ridge region is effective in aligning and elongating the FeCo-rich particles parallel to the applied magnetic field direction. An Fe-22Cr-15Co alloy achieves the magnetic properties as Br = 1.56 T (15.6 kG), bHc = 51.6 kA/m (645 Oe) and (BH)max = 66.4 kJ/m³(8.3 MGOe), which are almost comparable to those of the columnar Alnico family.