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 Sm₂Fe₁₇N_x powders. Starting from pure Fe and Sm powders, the formation process of the hard magnetic Sm₂Fe₁₇N_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 α-Fe phases in all compositions of Sm_xFe_100-x (x=11, 13, 15, 17). The effects of starting composition on the formation of Sm₂ Fe₁₇ 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 Sm₂Fe ₁₇. For preparation of hard magnetic Sm₂Fe₁₇ N_x powders, additional nitriding treatment was performed under N₂ 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