Die-upset Pr-Fe-B-type magnets from melt-spun ribbons

In order to optimize the magnetic properties of die-upset Pr-Fe-B magnets, we have systematically altered alloy compositions, including partial substitution of cobalt and neodymium, and low-level additions of gallium. In general, the remanences of Pr-Fe-B die-upset magnets were lower by ∼1 kG, and coercivities were higher by ∼4 kOe, than analogous Nd-Fe-B magnets. The microstructure of the Pr-Fe-B die-upset magnets was similar to Nd-Fe-B magnets. Both systems are two phase, consisting of oriented flat platelet-shaped grains of 2-14-1 separated by a rare earth-rich intergranular phase. The intergranular phase is thicker for the Pr-Fe-B magnets, resulting in enhanced magnetic domain wall pinning and increased coercivity. Even higher coercivities were obtained with small amounts of cobalt substitution (≤5 at. % of the transition metal) and by very low-level additions of gallium (≤0.5 at. %). The largest remanence (Br=13.7 kG) for a Pr-based 75% die-upset magnet was obtained with the alloy (R13TM81B6)0.9975Ga0.25, where R=(Pr0.8Nd0.2) and TM=(Fe0.95Co0.05).