SM2FE17-NITRIDE-BASED PERMANENT-MAGNETS PRODUCED BY RAPID SOLIDIFICATION

The rapid solidification process in conjunction with nitrogenation has been employed to produce Sm2Fe17-nitride-based permanent magnets. In the as-quenched state, depending upon the alloy composition and process parameters, a mixture of the following phases was found: alpha-Fe, metastable SmFe7, SM2Fe17, SmFe3, SmFe2, Sm and an amorphous phase. In general, Sm-rich alloys solidified at high quenching rates (55 m s-1) consist of a mixture of metastable SmFe7 (TbCu7 type) and an amorphous matrix. Subsequent heat treatment at 650 -degrees-C for 10 min formS Sm2Fe17 (Th2Zn17 type) in metastable equilibrium with SmFe2 (MgCu2 type). SmFe, (PuNi3 type) also begins to precipitate and its amount increases for longer heat treatment times. The same mixture of phases (Sm2Fe17 + SmFe2 + SmFe3) could also be produced directly in the as-quenched state at lower quenching rates (25 m s-1). Nitrogenation of the SM2Fe17-based rapidly quenched alloys at about 450-degrees-C forms SM2Fe17 nitride exhibiting coercivities as high as 17.7 kOe with a (BH)max of 12 MG Oe and a Curie temperature of 470-degrees-C. The secondary phases present in the alloys (SmFe2 + SmFe3) decompose entirely into SmN + alpha-Fe.