Novel composition of Nd-Fe-B gas atomized powder to produce compression bonded magnets.

[Display omitted] • A grain size of ∼ 1 µm was measured by EBSD for He atomized NdFeB powders. • Elongated grains grow from nucleation sites forming radial colonies. • Optimum annealing at 700 ˚C increased the BH max in > 25 %. • No significant grain growth observed after annealing up to 1050 ˚C. • Bonded magnets from novel composition NdFeB gas atomized powders could cover a market niche. New compositions of Nd-Fe-B powders were produced via gas atomization. Helium and argon were used as atomizing gases. For the same process parameters, helium resulted in a powder that is 6 times finer than the powder produced with argon. In both cases, the atomization conditions were set to achieve fine powders and, therefore, fine microstructures, since this is critical to obtain a suitable coercivity. The powders were sieved to separate the fraction below 20 μm (∼90 % of powder atomized with He). The microstructure is formed by a mix of elongated and equiaxial grains with random crystallographic orientation and an average grain size of ∼ 1 μm, which was measured by Electron Backscattered Diffraction. This kind of measurements and images were taken for the first time for fine helium atomized Nd-Fe-B powders. The embedding of the powder in copper was found to be useful, as the conventional mounting in metallographic conductive resin produced charging of the sample. Annealing up to 1000 °C did not cause any significant grain growth that could deteriorate the magnetic properties. Annealing at 700 °C for 15 min improved the magnetic properties due to the crystallization of residual amorphous phase. Warm compaction was used to produce magnets with a high volume fraction of magnetic powder (>70 %) and low real porosity (∼5 %). These magnets exhibit a high remanence (∼0.5 T) and maximum energy product (∼35 kJ/m3), combined with a suitable intrinsic coercivity (>500 kA/m). The new compositions and processing route could cover a market niche. The thoroughly analyzed powders could be also suitable for some additive manufacturing technologies that require spherical powders with very specific particle size distributions. [ABSTRACT FROM AUTHOR]