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• Fe 84 Zr x B 16- x (x = 6, 8, and 10 at. %) alloys show pronounced β relaxation characteristic. • A positive correlation between the β relaxation and structural heterogeneity appears in Fe-based amorphous alloys. • With increased Zr/B ratio, β relaxation is easily activated and structure becomes more heterogeneous. • Alloys with easily activated β relaxation or more heterogeneous structure possess poor soft magnetic properties. Dynamic relaxation is an universal feature in amorphous alloys. However, few studies have been conducted on β relaxation of Fe-based amorphous alloys as most of them have insignificant β relaxation characteristics. In this work, the variation in β relaxation, structural heterogeneity, and soft magnetic properties are investigated in Fe-Zr-B amorphous alloys with pronounced β relaxation. β relaxation and structural heterogeneity are characterized by the ratio of β and α relaxation temperature (i.e., T β /T α) and correlation length, respectively. With the increase of Zr/B ratio, the value of T β /T α and the correlation length tend to decrease. Alloys with easily activated β relaxation or more heterogeneous structure possess poor soft magnetic properties, i.e., a significant reduction in saturation magnetic flux density and an increase in coercivity. [ABSTRACT FROM AUTHOR]

• The nanoscale structural heterogeneity and magnetic properties were analyzed by atomic force microscopy and Mössbauer spectroscopy. • The nanoscale structural heterogeneity of Fe 80 Si 9 B 11 amorphous alloy attenuates monotonically with a decrease in cooling rate. • The annihilation of flow units induces the enhancement in ferromagnetic exchange interaction and weakening of magnetic anisotropy. • The ameliorated magnetic properties with decreasing cooling rate can be attributed to the degeneration of nanoscale structural heterogeneity. Despite that the nanoscale structural heterogeneity of amorphous alloys has been confirmed by advanced experimental observations and theoretical simulations, the underlying link between the structural heterogeneity and magnetic properties remains poorly known. In this work, the effect of cooling rate on the nanoscale structural heterogeneity and magnetic properties of Fe 80 Si 9 B 11 amorphous ribbons (Fe-Si-BAR) was studied by atomic force microscopy and Mössbauer spectroscopy. The results show that the degeneration of nanoscale structural heterogeneity substantially induces an improvement in soft magnetic properties with decreasing cooling rate. Specifically, the volume fraction of flow units reduces significantly with the decrease of cooling rate, and some of the flow units annihilate and transform to the ideal elastic matrix. The structural densification and reduction of the number density of quasidislocation dipole result in an enhancement in ferromagnetic exchange interaction and weakening of magnetic anisotropy. Therefore, the saturation magnetic flux density increases and coercivity decreases with reducing cooling rate. Our results provide new insight into understanding the structural mechanism in the ameliorated magnetic properties of Fe-based amorphous alloys with decreasing cooling rate. [ABSTRACT FROM AUTHOR]

• Magnetic properties of a Fe-Si-B amorphous alloy with stress gradient were studied. • Magnetic anisotropy and coercivity evolve separately. • Compressive stress hinders the reversible magnetization vector rotation. • Coercivity is irrelevant to the coherent stress. The magnetic properties and domain structure of a Fe 78 Si 9 B 13 amorphous alloy with a stress gradient from upper to the lower surface were investigated. We found that the magnetic properties of the samples vary significantly upon stress variation. Specifically, the magnetic anisotropy increases linearly with the maximum stress, whereas the coercivity, although higher than the one without stress, remains reasonably small. The phase contrast in magnetic force microscopy image and the fingerprint-like domains in magneto-optical Kerr microscopy images for ribbon surface with compressive stress demonstrate the presence of perpendicular anisotropy due to the magneto-elastic coupling. As a result, the compressive stress hinders the reversible magnetization vector rotation and makes the magnetization hard to be saturated. However, the stress causes no irreversible effects, neither on the domain wall movement nor on the magnetization rotation. Thus it is irrelevant to the coercivity. These results are different from the situation of the inhomogeneously distributed quenched-in stress enlarging the coercivity in Fe-based amorphous alloys. [ABSTRACT FROM AUTHOR]

• Crystallization kinetics of FeNiPC(Nb) amorphous alloys was investigated. • Both thermal stability and activation energy increase after addition 1% Nb. • The magnitude of local Avrami exponent is altered with Nb addition. • The growth rate of primary crystallized phase is restrained with Nb addition. The effects of minor Nb addition on the crystallization mechanism for a FeNiPC(Nb) amorphous alloy were studied via investigating its non-isothermal crystallization kinetics. With minor Nb addition, the thermal stability of the alloy increases as evidenced by the enlargement of the supercooled liquid region. Meanwhile, the location activation energy of both Nb-added and without Nb-added alloys correlates positively with the crystallized volume fraction during the whole primary crystallization stages, as calculated by the isoconversional methods. However, the kinetics analysis using the modified Johnson-Mehl-Avrami-Kolmogorov equation indicates that the addition of Nb changes the crystallization mode of the alloys, that is, from the growth with a decrease nucleation rate to a constant nucleation rate in a diffusion-controlled manner. This can be further confirmed by the atomic force microscopy showing that Nb would restrain the atomic diffusivity and suppress the crystallization growth rate in this alloy. [ABSTRACT FROM AUTHOR]

Abstract Fe-based amorphous alloys with excellent soft magnetic properties always suffer catastrophic annealing embrittlement. The soft magnetic and mechanical properties of a series of Fe 84.3- x Co x Si 2 B 13 Cu 0.7 (x = 0, 2, 4, 6, 8) amorphous alloy ribbons were investigated. With appropriate substitution of Co for Fe, the B S of the alloys shows a slight increase and the H C remains at a low level. From two-point bending tests, a sharp transition from ductility to brittleness can be observed upon annealing. The embrittlement can be attributed to localized shear bands due to shear bands branching during deformation. It is found that the ductile-brittle transition temperature increases slightly by applying cryogenic thermal cycling treatment to annealed ribbons, indicating that the annealing embrittlement can be improved to some extent by cryogenic thermal cycling treatment. According to nanoindentation results, the increased shear transformation zone volume is responsible for the bending ductility increment. Ultimately, a ductile Fe 80.3 Co 4 Si 2 B 13 Cu 0.7 amorphous alloy ribbons with a B S of 1.68 T and a H C of 4.8 A/m were obtained by cryogenic thermal cycling treatment after annealing. Highlights • With appropriate substitution of Co for Fe, the B S shows a slight increase, and the H C remains at a low level. • The bending ductility of the annealed ribbons is recovered to some extent by cryogenic thermal cycling. • The increased shear transformation zone volume is responsible for the bending ductility increment. [ABSTRACT FROM AUTHOR]

Abstract Crystallization is a uniform behavior for amorphous alloys while it can be fairly complex. For Fe-B-C alloys with high Fe content, the precipitation of α-Fe is ahead of the Fe-metalloid compounds with temperature increasing. It is found that the crystallization products of Fe-B-C amorphous alloys with Fe content lower than 82% can be modulated by appropriate annealing. The Fe 82 B 12 C 6 alloy is eutectoidally crystallized with the simultaneous precipitation of α-Fe and Fe-metalloid compounds under conventional annealing. It is a diffusion controlled three-dimensionally growth with a constant nucleation rate. However, only α-Fe nanocrystals with a low volume fraction form under rapid annealing, which is evidenced by the results of X-ray and electron diffractions along with the magnetometry. The transmission electron microscopy bright-field images show that the α-Fe nanocrystals obtained by rapid annealing have two different morphologies. One is dendritic with a large characteristic length and the other is equiaxed-like. Highlights • Single α-Fe phase is obtained under suitable rapid annealing for Fe 82 B 12 C 6 alloy. • The α-Fe nanocrystals obtained by rapid annealing have two different morphologies. • The coercivity is drastically reduced due to the absence of hard magnetic phase. [ABSTRACT FROM AUTHOR]

• The nanoscale structural heterogeneity was analyzed by small-angle X-ray scattering and atomic force microscopy. • The microalloying of Co and Ni exhibits an opposite effect on the nanoscale structural heterogeneity. • The variation of mechanical behavior further proves the evolution of the nanoscale structural heterogeneity with Co and Ni substitution. • The evolution of magnetic properties induced by microalloying can be attributed to the variation of nanoscale structural heterogeneity. Nanoscale structural heterogeneity is a critical parameter for understanding the structure-property relationships in amorphous alloys. Herein, the small-angle X-ray scattering and atomic force microscopy were utilized to quantitatively investigate the nanoscale structural heterogeneity of the Fe 80- x M x Si 9 B 11 (M = Co and Ni; x = 0, 2, 4) amorphous alloys. The results show that the nanoscale structural heterogeneity of the amorphous alloys increases prominently with Ni substitution, but gradually decreases with the increase of Co content. Such evolution of structural heterogeneity was further verified by the changes in mechanical behavior. The microalloying of Ni can increase the plastic deformation ability and reduce the microhardness, whereas an opposite effect is found in the Co-doped alloys. Finally, Mössbauer spectroscopy reveals an enhancement in ferromagnetic exchange interaction and magnetic anisotropy with Co substitution, while the microalloying of Ni leads to a deteriorative result. Such variations in magnetic properties can be attributed to the evolution of nanoscale structural heterogeneity with Co and Ni additions. Our observation serves as a link between the nanoscale structural heterogeneity and magnetic properties, providing a new sight into understanding the structural origin of the changes in magnetic properties of Fe-based amorphous alloys. [ABSTRACT FROM AUTHOR]

The structure-property relationships in amorphous alloys are far from being fully understood. Here we show an unusual structural rearrangement occurring over medium-range length scale prior to crystallization for a (Fe 0.5 Co 0.5) 72 Si 4 B 20 Nb 4 amorphous alloy ribbon upon heating by in-situ synchrotron diffraction, whereas the short-range structure shows no anomaly. During the above process, local stress field generates and results in the enlargement of coercivity. This can be further supported by the magnetic force microscopy images showing an enhancement of magnetic phase contrast after annealing the sample at a temperature where the unusual structural change occurs. Moreover, the average grain size derived from the transmission electron microscopy images of the crystallized (Fe 0.5 Co 0.5) 72 Si 4 B 20 Nb 4 ribbon is much smaller than that of (Fe 0.5 Co 0.5) 76 Si 4 B 16 Nb 4 , suggesting the slow crystallization kinetics caused by the local stress field. This work highlights the role of medium-range order in determining the properties of amorphous alloys. • Unusual structural change at medium-range occurs in a Fe-based amorphous alloy. • Coercivity increases drastically due to the enhanced stress-induced anisotropy. • The structural rearrangement results in slow crystallization kinetics. [ABSTRACT FROM AUTHOR]