Pressure-assisted zinc bonding of microcrystalline Sm2Fe17Nx powders

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Abstract
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 °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.