Effect of Cu On Microstructural Evolution of Nanocrystalline Soft and Hard Magnetic Materials

The nanocrystallization processes in Fe-Si-B-Nb-Cu and Fe-Nd-B(-Cu-Nb) amorphous alloys have been studied by transmission electron microscopy (TEM) and a three dimensional atom probe (3DAP). Cu additions are effective in refining the nanocrystalline microstructures of both alloys, because Cu atom clusters formed prior to the crystallization reaction serve as heterogeneous nucleation sites for the primary crystals. However, the clustering behaviors of Cu atoms in these two alloy systems are different, i.e. , Cu completely dissolves in the Nd 2 Fe 1 4B phase in the final microstructure of the Nd 4.5 Fe 75.8 B 18.5 Cu 0.2 Nb 1 alloy, whereas Cu clusters grow to fcc-Cu particles in the Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 alloy. The nanocrystallization processes in these two alloys clarified by the 3DAP results are compared.