Investigations on the metallurgical features and magnetic properties of Nd/sub 16.8/Fe/sub 75.7-x/Al/sub x/B/sub 7.5/,O≤×≤6

Abstract

Alloys of nominal composition Nd/sub 16.8/Fe/sub 75.7-x/Al/sub x/B/sub 7.5/, with x=0.25, 0.5, 0.75, 1,5, 3 and 6 were selected and powder metallurgically processed into sintered magnets. Significant improvement in intrinsic coercivity (H/sub ci/) and marginal reduction in remanence (B/sub r/) and Curie temperature (T/sub c/) were observed in alloys with x=0.25 to 1.5. However, in alloys with x/spl ges/3 a fall in H/sub ci/, B/sub r/ and T/sub c/ was observed. All the alloys contain a multiphase microstructure with Nd/sub 2/Fe/sub 14/B (/spl phi/) as major phase and secondary phases including oxides. Al partly dissolves into the matrix phase and much of it goes for the formation of a separate phase (/spl mu/ or /spl delta/), which is distributed at the intergranular region with other secondary phases (Nd-rich and /spl eta/). The volume fraction of the intergranular phases increases with Al concentration in the alloy. The decrease in the coercivity value at x/spl ges/3 at.% is attributed to the distribution of these intergranular phases and the magnetic character of /spl mu/ and /spl delta/ phases.