EFFECT OF MILLING ATMOSPHERE ON THE PREPARATION OF SM2FE17NX POWDER BY MECHANICAL GRINDING (REPRINTED FROM J JAPAN INST METALS, VOL 60, PG 427, 1996)

The preparation of Sm2Fe17Nx permanent magnet powders has been tried b y mechanical grinding (MG) for a short time without crystallization he at treatment which was usually needed to obtain a Th2Zn17 structure in the conventional method by MG or MA. MG was carried out in three kind s of atmospheres; i.e., Ar, N-2 and NH3 gas. Untreated and hydrogenate d Sm2.5Fe17 alloy powders were used as the starting materials. The (Y- Fe precipitation was detected in the powder after MG for over 14.4 ks. The grain size of powder obtained by MG for 10.8 ks was around 10 nm which was much finer than the single magnetic domain size of about 300 nm. The existence of hydrogen promoted not only the nitriding of powd ers but the oxidation. The hydrogenated powder after MG in NH3 and nit riding had a high oxygen content of about 13000 ppm. This oxidation pr evented the absorption of nitrogen during the nitriding process. The u ntreated powders after MG in NH3, however, were nitrided efficiently u p to 38000 ppm at a low temperature of 623 K, and the oxygen content w as about 7000 ppm. The maximum coercivity of 0.93 MA . m(-1) (11.7 kOe ) was obtained with the untreated powder after MG in NH3 and nitriding at 623 K for 10.8 ks in N-2.