Bulk anisotropic composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets with (BH)max=45–50MGOe have been synthesized by blending a Nd–Fe–Ga–B powder with an α-Fe or Fe–Co powder followed by hot compaction at 600–700 °C and hot deformation (die upsetting) at 850–950 °C with a height reduction of 71%. The composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets show microstructures consisting of a very large soft phase up to ∼50μm, which is more than 1000 times larger than the upper size limit of the soft phase expected from the existing models of interface exchange coupling.
An effort to increase the impact toughness of Nd–Fe–B sintered magnets by adding small amounts of Al, Nd, Ga, Cu, and Nb was successful. No significant compromise to magnetic properties occurred. Based on this work, a series of sintered Nd–Fe–B magnets with improved toughness was developed, which we call ToughNEO™. Small precipitates, which may contribute to the improvement of toughness, were observed using scanning electron microscope for all samples with improved toughness. Tumbling and drilling tests further verified the improved toughness of these developed ToughNEO™ magnets.
Advanced power systems require soft magnetic materials with a combination of high saturation magnetization and high creep resistance. When the Fe–Co–V alloy laminate is used in a rotor at high temperatures (500–600 °C) coupled with very high rpm, significant creep occurs, which destroys the device integrity. Since grain boundary slide is predominantly responsible for creep deformation in the Fe–Co–V alloy at temperature higher than ∼430 °C, the approach in this study was to reduce the volume fraction of the grain boundaries by making a Fe–Co–V alloy with very large grains. Very large grains, up to mm range, were readily obtained after small cold deformation of ∼3% followed by a normal recrystallization anneal. Fe–Co–V alloy with large grains displays lower coercivity and higher permeability than the commercial Fe–Co–V alloy. Even though its yield strength at 600 °C is lower than the commercial Fe–Co–V, the creep strains of the Fe–Co–V alloy with large grains are only 1/10–1/2 of that for the commercial alloy in the initial and middle periods of the creep test performed at 600 °C under 150 MPa. At the end of the test before the specimens were broken, the Fe–Co–V alloy with large grains showed an accelerated creep strain rate. Better balancing the high-temperature yield strength and creep resistance by creating the optimum grain size would further improve the high-temperature creep resistance of the Fe–Co–V alloy.
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