TOWARDS AN EASY PRODUCTION ROUTE FOR ISOTROPIC RARE-EARTH BASED PERMANENT-MAGNETS

The fact that the tetragonal Nd2Fe14C phase is formed in a solid state transformation reaction at comparatively low temperatures is used for the generation of microstructures in annealed ingot samples which give rise to substantial coercivities. This type of formation of the tetragonal phase by a solid state transformation is restricted to R-Fe-C systems and does not occur in the corresponding R-Fe-B systems. In the systems R2Fe14C1-xBx (R = Pr, Nd) the upper limit of the temperature stability range of the tetragonal phase was found to increase very steeply with boron content in the range 0 less-than-or-equal-to x less-than-or-equal-to 0.05, offering better possibilities to optimize the annealing treatment with respect to the attainment of high coercivities. Substantial shifts in this stability range to higher temperatures by boron substitution were also observed in the corresponding systems with R = Ce, Sm and Gd, while for the heavier rare earth elements the effect of boron substitution remains small.