Research On Structural Relaxation, Crystallization Process And Magnetic Properties Of Fe-based Amorphous Alloys

The structural relaxation of Fe80Si9B11amorphous alloy has been investigated at atomic and clusterscale based on Synchrotron X-ray Diffraction, Extended X-ray Absorption Fine Structure Spectrum,Reverse Monte Carlo simulation and Voronoi Tessellation techniques. The average Fe and Sineighboring atom numbers in the first coordination shell of Fe atoms increase steadily during structuralrelaxation, while B neighboring atom numbers do not show any distinct variation. The bond lengths ofFe-Fe, Fe-Si and Fe-B pairs all reduce during structural relaxation, but those of Fe-Fe and Fe-Si pairsexhibit a more notable change in bond length than Fe-B pairs, which demonstrates that more atomicrearrangement happens in R2region (mainly occupied by Fe-Si clusters) than that in R1region (mainlyoccupied by Fe-B clusters). Besides, although the main types of Fe-centered clusters rarely changeduring structural relaxation, the fractions of clusters with high and low coordination numbers show aincreasing and decreasing tendency, respectively. Also, the mean volume of Fe-centered clusters growsassociated with structural relaxation. In addition, the main types of Si and B centered clusters do notshow any obvious variation. In spite of the fraction fluctuation of individual clusters, an evident changetendency can hardly be observed. In the meanwhile, the magnetic properties of Fe80Si9B11amorphousalloy during structural relaxation have been investigated. The minimum coercivity appears in the alloyannealed at523K for1h, and it deteriorates dramatically with incrasing annealing temperature. Thesaturation magnetic induction reaches its maximum at573K, and drops with increasing temperature.Based on the experimental results, the correlation between microstructural evolution and magneticproperties variations during structural relaxation has been proposed: the elimination of internal stressand the reduction of geometrical distortion have a significant effect on the magnetic properties in theinitial stage of structural relaxation; with the proceeding of structural relaxation, atomic interaction (e.g.coordination number, bond length) plays a dominant role in influencing magnetic properties.Besides, the correlation between the structural evolution and the variations of soft magneticproperties of Fe81Si4B12Cu1P2amorphous alloy during crystallization process has been investigated onthe basis of isothermal and non-isothermal kinetics. Pre-existent α-Fe clusters in melt-spun alloys witha size much smaller than critical nucleus size crystallize at a steadily-increasing nucleation rate owingto the “chain effect” of rising constituent fluctuation. The competition and “soft infringement” duringthe growth of nuclei leads to the formation of fine and uniform nanocrystallites and therefore superiorsoft magnetic properties. In contrast, pre-existent α-Fe clusters with a size approximate to the criticalnucleus size nucleate gradually at the initial stage of crystallization process driven by thermalactivation over the energy barrier of nucleation, and pre-existent α-Fe nanocrystallites with a size larger than critical nucleus size grow directly at the initial stage of crystallization process. Grains formed atthe initial stage enlarge further in the subsequent crystallization process, which gives rise to acontinuous decrease of the nucleation rate and the deterioration of soft magnetic properties.