PRESSURE-ASSISTED ZINC BONDING OF MICROCRYSTALLINE SM2FE17NX POWDERS

Highly coercive isotropic magnets were prepared by pressure-assisted Zn bonding of microcrystalline Sm2Fe17Nx powders. Mechanically alloyed and two-step heat treated powder was mixed with elemental Zn powder and compacted by uniaxial pressing at elevated temperatures. The maximum room-temperature coercivity of such magnets was 34.7 kA/cm (43.6 kOe), which represents an increase by about 50% relative to that of the starting powder. The density was about 80% of the theoretical value resulting in a relatively low remanence of 0.4 T. This was achieved after compaction using parameters optimized with respect to coercivity, i.e., a Zn content of 20 wt. % (referred to the 2:17:N weight), a temperature of 425-degrees-C and a pressure of 270 MPa. The coercivity increase induced by compaction with Zn presumably originates from improved magnetic decoupling of the 2:17:N grains which is caused by the paramagnetic Fe3Zn7 phase formed at the grain boundaries within the powder particles.