Structure of Cast Nd–R–Fe–B (R = Pr, Ce, La) Alloys for Sintered Permanent Magnets

X-ray diffraction and differential thermal analyses are used to study multicomponent Nd–R–Fe–B (R = Pr, Ce, La) alloys prepared by induction melting in an inert gas atmosphere and subsequent forced cooling upon casting in a massive cast iron mold. The effect of substitution of light rare-earth metals for neodymium on the phase composition and morphology of the cast alloys with 0–6.9 wt % Pr, 0–10.0 wt % Ce, and 0–9.0 wt % La, which are used as precursors in manufacturing sintered permanent magnets with high hysteretic characteristics, is studied. The main structural constituents of the alloys are shown to be a magnetic phase with the Nd2Fe14B-type structure and Nd-rich, R1.1Fe4B4, and R2Fe17 phases. The phase transformation temperatures of the alloys are determined, which allow us to correct the sintering temperatures of permanent magnet powder blanks prepared from the cerium- and lanthanum-containing alloys.