Introduction
Ternary rare earth permanent magnet alloys (RPMAs) have attracted significant attention due to their excellent magnetic and mechanical properties, such as high coercivity, high saturation magnetization, and good temperature stability. With the development of electrical equipment and permanent magnet motors, double-phase nanocrystalline rare earth permanent magnet alloys (DPMAs) have become a kind of ideal magnetic materials.
The double-phase nanocrystalline rare earth permanent magnet alloys (DPMAs) have recently attracted considerable attention due to their outstanding properties, such as high coercivity and high saturation magnetization, as well as their ability to work effectively at high temperatures. The DPMAs are composed of two main phases: rare earth nanocrystals embedded in a soft permanent magnet matrix, connected by a thin glassy phase. This composition significantly enhances the magnetic properties of the alloy due to the high magnetostriction of the nanocrystalline phase, which has better magnetic domain control compared to the single-phase alloy.
Structure and Properties of DPMAs
The structure of double-phase nanocrystalline rare earth permanent magnet alloys consists of grains of rare earth (RE) nanocrystals embedded in a soft permanent magnet (PM) matrix, connected by a thin glassy phase. The grain size of RE nanocrystals is typically between 20 and 40 nm.
The microstructure of DPMAs is typically composed of a thin adhesive layer between the RE nanocrystals and the PM matrix and a thin glassy phase. The glassy phase allows RE nanocrystals to be connected to each other and prevents grain boundaries from further reducing the coercivity.
The good property of DPMAs relies on the formation of an appropriate microstructure through a proper combination of the glassy phase and the nano grain size of the RE. With a proper microstructure, the coercivity of DPMAs can be significantly improved. The saturation magnetization of DPMAs is also improved due to their larger domain wall pins.
Processing of DPMAs
The important processes in the processing of DPMAs are the preparation of the RE powder and the sintering. For the preparation of RE powder, the rare earth powder is typically pre-alloyed with a small amount of Dy and Sm, and then atomized via water or inert gas.
After RE powder preparation, the powder is compacted into a green compact and sintered under an appropriate sintering condition. In order to obtain a good sintering density and a fine grain size of RE nanocrystals, a two-step sintering process usually needs to be employed. The sintering temperature should be high enough to coalesce the chains of nanocrystals into the desired structure, but the temperature should not exceed the Curie temperature of rare earth.
Application of DPMAs
Due to their excellent magnetic properties and temperature stability, DPMAs have been widely used in various applications such as electric motors, generators, sensors, and transducers. Additionally, DPMAs can be used as hard drive recording heads and as a recording medium for information storage.
Conclusion
In summary, double-phase nanocrystalline rare earth permanent magnet alloys (DPMAs) have recently attracted considerable attention due to their outstanding properties, such as high coercivity and high saturation magnetization, as well as their ability to work effectively at high temperatures. The RE nanocrystals and glassy phase give the DPMAs their unique magnetic and mechanical properties. The processing of DPMAs includes the preparation of RE powder, compaction of the powder, and sintering. DPMAs are widely used in various applications such as electric motors, generators, transducers, and sensors due to their excellent magnetic properties and temperature stability.
