Behavior of Nb atoms in Nb substituted Nd/sub 2/Fe/sub 14/B nanocrystalline alloys investigated by atom probe tomography

The behavior of Nb atoms in Nd/sub 12/Fe/sub 82-x/B/sub 6/Nb/sub x/ (x=0 to 3) nanocrystalline alloys has been investigated by using atom probe tomography (APT) technique on near-atomic scale in the present paper. Three-dimensional atom probe (3DAP) analyses on the Nb substituted alloys clearly reveal that Nb atoms are enriched at grain boundaries with a peak concentration about 4 times higher than the average for Nd/sub 2/Fe/sub 14/B grains. A grain boundary region with a chemical composition near the Nb : Fe : B stoichiometry of 3 : 3 : 5 is also measured for the x=3 alloy. The results provide direct evidence of microstructural refinement due to solute drag of Nb atoms during solidification, resulting in Nb enrichment at grain boundaries and possibly the formation of a Nb-rich interfacial phase which give rise to enhanced magnetic properties.