Texture development and grain boundary phase formation in Ce- and Ce-La-substituted Nd-Fe-B magnets during hot-deformation process.

• The Ce- and Ce-La-substitution for Nd in Nd-Fe-B magnets hinder the texture development and grain boundary phase formation during the hot-deformation process. • The decrease in volume fraction of RE-rich liquid in the grain boundaries by Ce- and Ce-La substitution is a critical reason for the deterioration of magnetic and microstructural properties of Ce- and Ce-La-substituted Nd-Fe-B hot-deformed magnets. • Based on the results, a method to increase both the coercivity and remanence of the Ce- and Ce-La-substituted Nd-saving hot-deformed magnets was developed: intermediate infiltration (I-infiltration). In this study, the influence of Ce- and Ce-La-substitution for Nd in Nd-Fe-B magnets on their magnetic and microstructural changes in the course of the hot-deformation process was investigated to gain insight into further reducing the Nd content in fine-grained Nd-Fe-B hot-deformed magnets. We found that the [001] texture and microstructure of the RE-rich grain boundary phases, which are the factors that determine the remanence and coercivity of hot-deformed magnets, were deteriorated by the Ce- and Ce-La-substitution. This is because the volume fraction of the RE-rich liquid formed in the grain boundaries during the hot-press and hot-deformation decreased due to the Ce- and Ce-La-substitution, thereby increasing the friction between the 2:14:1 grains while the c -axes of grains were aligned by grain rotation and decreasing the RE concentration of grain boundary phases. In particular, the Ce-La-co-substitution further prevented the liquid formation within the grain boundaries of the magnets during hot-press and hot-deformation because the wettability of the RE-rich liquid on the 2:14:1 grains became poor when La was substituted for Nd in the 2:14:1 grains. These results indicate that there is room for further improvement in both the remanence and coercivity of the Ce- and Ce-La-substituted magnets by introducing additional liquid into the grain boundaries prior to hot-press and hot-deformation. By applying the Nd-Cu infiltration process to the melt-spun ribbons (intermediate infiltration, I-infiltration), both the remanence and coercivity of the Nd-saving (Nd 0.7 Ce 0.3)-Fe-B and (Nd 0.7 Ce 0.225 La 0.075)-Fe-B hot-deformed magnets were successfully improved. [ABSTRACT FROM AUTHOR]