Effect of Cr-doping on crystallization sequence and magnetic properties of Fe3B/Nd2Fe14B nanocomposite permanent magnets

Crystallization sequence starting from NdxFe82-xB18 and NdxFe79-xCr3B18(x=3.5-5.5 at%) amorphous alloys has been investigated using X-ray diffractometer. In the alloys with Nd concentration around 5 at%, the intermediate compound Nd2Fe23B3 first crystallizes along with Fe3B from the amorphous state. Then, the Nd2Fe23B3 phase decomposes to form a mixture of Nd2Fe14B, Fe3B and alpha Fe for the Cr-bearing systems, whereas it breaks up into another mixture of ape and NdFe4B4 for the Cr-free systems. Atom probe field ion microscopy analysis has revealed that Cr is preferentially partitioned into the Fe3B phase during the crystallization process, which may stabilize the Fe3B-containing mixture exhibited in the Cr-doped systems. We can conclude that a large fraction of Nd2Fe14B produced from the distinct decomposition scheme of the intermediate Nd2Fe23B3 phase exhibited in the Cr-doped systems brings about the high coercivity materials. (C) 1998 Acta Metallurgica Inc.