Microanalytical characterization of multi-rare-earth nanocrystalline magnets by transmission electron microscopy and atom probe tomography

Abstract

The partitioning behavior of various rare-earth (RE) elements during solidification and their segregation behavior at the grain boundaries were investigated in nanocrystalline (Y0.5Dy0.5)2.2Fe14B and (Nd0.5Y0.25Dy0.25)1.8Zr0.4Co1.5Fe12.5B alloys by transmission electron microscopy and atom probe tomography. The best hard magnetic properties obtained are Hcj=22kOe, Br=5.10kG, and (BH)max=5.97MGOe for the Y–Dy-based alloy and Hcj=10.6kOe, Br=6.64kG, and (BH)max=9.56MGOe for the Y–Nd–Dy based alloy. The grain size of the Y–Dy based alloy was ∼50nm. The Y–Nd–Dy based alloy had an overall finer, bimodal grain size. An intergranular (Y0.36Dy0.64)6Fe23 phase was detected in the Y–Dy based alloy. A uniform distribution of RE elements was found within the 2-14-1 grains in both alloys. The Y:(Dy+Nd) ratio in the Y–Nd–Dy alloy was lower than its nominal composition, indicating that the Y is segregating to grain boundaries or forming a second phase.