Structural change of amorphous Fe90Zr7B3 alloy in the primary crystallization process studied by modern electron microscope techniques

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 SROs 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.