Structural changes in the primary crystallization process of amorphous Fe90Zr7B3 alloy have been investigated using modern electron microscope techniques. In the as-quenched specimen, bcc-Fe clusters as small as 1 nm were observed by high resolution electron microscopy (HREM). Nanoprobe energy dispersive X-ray spectroscopy revealed a development of Zr-enriched zones beside the α-Fe nanocrystals in the initial crystallization stage at 733 K. Besides the α-Fe nanocrystals, Fe2Zr and Fe3Zr-type nanoprecipitates were identified by nanodiffraction and HREM after annealing at 923 K. Electron diffraction pair distribution function (PDF) analysis were performed for the as-quenched and annealed specimens. The PDF analysis of the amorphous matrix combined with the reverse-Monte-Carlo simulation revealed that bcc-like Fe clusters are formed already in the as-quenched state. The coordination number and Zr-Fe distance of the short-range order (SRO) structures around Zr atoms in the amorphous matrix both decreased on annealing towards a formation of local structures resembling structure units in the Fe2Zr or Fe3Zr phases. The PDF and HREM results strongly suggest a polymorphic reaction from the Zr-enriched matrix regions to the Fe2Zr or Fe3Zr nanoprecipitates in the crystallization stage. The formation of the Fe2Zr or Fe3Zr-like S-2Os in the amorphous matrix is thought to stabilize the matrix structure, and contributes to suppress the growth of α-Fe nanocrystals towards the optimized structure of the good soft-magnetic property.
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