Abstract
Intragranular rare earth-rich phases play a vital role in affecting the intrinsic coercivity of sintered Nd-Fe-B permanent magnets. To explore the origin of these intragranular rare-earth-rich phases, the starting material-strip cast Nd-Fe-B flakes were characterized by a variety of high-end microscopy techniques. It was surprisingly found that the intragranular rare-earth-rich phase is spherical in a diameter of ~150–300 nm and consists of amorphous regions rich in additive elements (e.g., Cu, Co, and Ga) and crystalline regions which are a combination of hexagonal light-rare-earth-rich phases and body centered cubic phases rich in light and heavy rare earth, and oxygen. Amorphous interfacial layers between the glass/crystal particles and the crystalline matrix were observed, probably due to insufficient time to reach a crystalline equilibrium state. Based on the microstructural observation, we proposed a formation mechanism of these intragranular glass/crystal conjugated particles in strip cast Nd-Fe-B flakes, which may facilitate to minimize the volume of these detrimental intragranular phases during the strip casting process.
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