Intragranular glass/crystal conjugated particles in strip cast Nd-Fe-B flakes

•Intragranular rare earth (RE)-rich phase was characterized in strip-cast Nd-Fe-B flakes.•The intragranular RE-rich phase is made up of amorphous and crystalline regions.•Cu, Co, and Ga are enriched in the amorphous region.•The crystalline region is made up of hexagonal LRE-rich and cubic LRE/HRE/O-rich phases.•The formation of these intragranular glass/crystal phases was proposed. 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.