Structural change of amorphous Fe 90Zr 7B 3 alloy in the primary crystallization process studied by modern electron microscope techniques

Abstract

Structural changes in the primary crystallization process of amorphous Fe 90Zr 7B 3 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, Fe 2Zr and Fe 3Zr-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 Fe 2Zr or Fe 3Zr phases. The PDF and HREM results strongly suggest a polymorphic reaction from the Zr-enriched matrix regions to the Fe 2Zr or Fe 3Zr nanoprecipitates in the crystallization stage. The formation of the Fe 2Zr or Fe 3Zr-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.