Synthesis and characterization of hard magnetic Sm-Fe-N powders produced by mechanical alloying technique

The mechanical alloying technique was applied to prepare hard magnetic Sm/sub 2/Fe/sub 17/N/sub x/ powders. Starting from pure Fe and Sm powders, the formation process of the hard magnetic Sm/sub 2/Fe/sub 17/N/sub x/ phase by mechanical alloying and subsequent solid-gas reaction was studied. As milled condition powders were found to consist of Sm-Fe amorphous and /spl alpha/-Fe phases in all compositions of Sm/sub x/Fe/sub 100-x/ (x=11, 13, 15, 17). The effects of starting composition on the formation of Sm/sub 2/Fe/sub 17/ intermetallic compounds was investigated by heat treatment of mechanically-alloyed powders. When Sm content was 15 at.%, heat-treated powders consisted of nearly single phase Sm/sub 2/Fe/sub 17/. For preparation of hard magnetic Sm/sub 2/Fe/sub 17/N/sub x/ powders, additional nitriding treatment was performed under N/sub 2/ gas flow at 450 C. The increase in coercivity was proportional to the nitrogen content, which increased drastically at first and then increased gradually as the nitriding time was extended to 3 hours.