APFIM studies of nanocrystalline microstructural evolution in Fe-Zr-B(-Cu) amorphous alloys

Primary crystallization of Fe-Zr-B(-Cu) alloys has been studied by atom probe field ion microscopy and the results were compared with the case of Fe-Si-B-Nb-Cu alloy. In the case of Fe-Zr-B, nanocrystalline microstructure is formed by primary crystallization of the initial amorphous phase even without Cu. By analyzing concentration depth profiles during the nucleation and growth stage, it was shown that growth of the primary crystal was controlled by diffusion of Zr. The nucleation sites seem to be provided by the quenched-in nuclei which was observed by transmission electron microscopy as medium range ordered domains. Addition of Cu to the ternary Fe-Zr-B caused formation of Cu clusters prior to the onset of the crystallization reaction. This observation is very similar to a previous report in Fe-Si-B-Nb-Cu. Cu induced significant fluctuations in Fe concentration without affecting concentrations of Zr and B.