Relationship between Hydrogen Pressure and Temperature for Recombination Reactions in the HDDR Processing of Ce–Fe–B Alloys

Abstract

In recent years, to reduce manufacturing costs and alleviate the rare-earth supply/demand imbalance in the Nd–Fe–B magnet market, researchers have actively pursued the development of (Nd,Ce)–Fe–B magnets, in which Nd is replaced by Ce. In the present study, we focused on magnetic powders treated by the hydrogenation–disproportionation–desorption–recombination (HDDR) process and explored the relationship between the hydrogen pressure and temperature (P_H2–T curves) in the Ce–Fe–B system, which is essential for the development of (Nd,Ce)–Fe–B magnets. It was confirmed that the disproportionation and recombination reactions of both Ce₂Fe₁₄B and CeFe₂ take place in the Ce–Fe–B system. Furthermore, compared with Nd₂Fe₁₄B, the P_H2–T curve of Ce₂Fe₁₄B was found to be shifted to higher pressure and lower temperature, suggesting a corresponding shift in the HDDR conditions under which good magnetic properties can be obtained.

Fig. 8 Temperature dependence of the recombination pressure (P_H2–T curve) for the HDDR reactions of the (a) Ce–Fe–B and (b) Nd–Fe–B alloys.