Crystallization of cobalt amorphous alloys under field annealing

Crystallization of Co-rich amorphous ribbons annealed under a 10 Oe external magnetic field at the early 30 minutes from their glassy status to supercooled liquid status is investigated by high-resolution transmission microscope (HR-TEM), Selected Area Fourier Transform (SA-FT), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results indicate that the short-rang ordering feature can be refined very well in specimen annealed under temperatures about 87.4 degrees C below their glass transition (Tg), showing refined salt-pepper morphologies with a mean length changing from 1.2 +/- 0.8 nm to 0.8 +/- 0.2 nm and a mean width shifting from 0.5 +/- 0.2 nm to 0.3 +/- 0.1 nm. When the amorphous ribbons are field-annealed at temperature near to Tg (i.e., 450 degrees C), ultra-fine nanocrystalline structures can be formed on the top surface of ribbons with size of 3.5 +/- 0.5 nm and inter-grain spacing of about 0.4 +/- 0.2 nm even though the inner parts of the ribbons are still in amorphous phases. The nanocrystalline areas are featured by the formation of doped hcp cobalt phase orientated along the c-axis, with the inter-plane spacing ranging from 4 A to 6 A. When the annealing temperature is above Tg, the grain sizes are increased dramatically with multi-phased nanocrystals precipitating from the amorphous substrate, and finally reaching almost complete crystallization at 600 degrees C, causing greatly coarsening of the nanocrystal structures.     

Magnetic anneal anisotropy in amorphous alloys

The uniaxial magnetic anisotropy Kuinduced by a magnetic anneal has been determined, after stress relief, for a series of alloys given by (FeyNi1-y)80B20. For all of these alloys Kudepends on anneal temperature as predicted by directional order theory. The concentration dependence of Kuin these alloys is also consistent with directional order theory. The maximum Ku, corrected for its temperature dependence, occurs at the compositiony = 0.5. However, Kudoes not fall to zero aty = 1as predicted if directional order is assumed to arise only from Fe-Ni pair ordering. These results are interpreted as suggesting a role of the glass former, boron, in the directional ordering, perhaps as an "interstitial." The interaction energy derived from the results is negative as expected for interactions leading to precipitation. Its large value ofapprox -7.5 times 10^{-14}ergs corresponds to a critical temperature for precipitation of 3000 K.     

Formation of nanocomposites during annealing of amorphous Fe-P-V alloys

Annealing-induced nanocrystallization in amorphous Fe_79.3P_18.2V_2.5 and Fe_76.8P_18.2V₅ alloys has been studied using Mössbauer spectroscopy, X-ray diffraction, and elastic modulus and internal friction measurements. The annealing temperature has been optimized for producing nanocomposites. The alloy containing 2.5 at % V, free of paramagnetic phases, is shown to possess better magnetic properties in comparison with the alloy containing 5 at % V, in which a large percentage, up to 22 vol %, of paramagnetic phases was found.     

Formation of nanocomposites during annealing of amorphous Fe-P-Si alloys

Annealing-induced nanocrystallization in inhomogeneous, clusterized Fe-P-Si amorphous alloys has been studied using Mössbauer effect, elastic modulus, and internal friction measurements. The results demonstrate that flash lamp processing causes the clusters in the Fe₈₂P₁₆S alloy to dissolve, improving its magnetic properties, whereas the clusters in the Fe₇₈P₂₀Si₂ alloy persist, and its hardness rises significantly     

Magnetic anisotropy of electrodeposited Co--P amorphous alloys

The development of magnetic anisotropy with regard to thickness in amorphous electrolytic Co-P alloys (15 at % P) has been observed in the range of thicknesses between 0.06-7.00μm. The study has been undertaken starting from the ratio Mr/Msof the hysteresis loops. The results obtained indicate that for thicknesses below 4000 Å the samples show an axis of easy magnetization in the plane. In the case of greater thicknesses, the axis of easy magnetization develops gradually out of the plane, reaching a perpendicular position near 10 μm. Our results suggest that what we are dealing with here is a shape anisotropy such as that proposed by Cargill, III et al.     

Crystallization kinetics of mechanically alloyed amorphous Fe-Ti alloys during annealing

The crystallization behaviors of mechanically alloyed amorphous Fe-Ti alloys were studied. The α-Fe phase formed during annealing as a result of the devitrification of the amorphous phase. According to the Kissinger plot, the crystallization activation energy (E) was obtained as 171 kJ/mol, which is close to the activation energy for the diffusion of Fe in α-Ti. According to the non-isothermal Johnson–Mehl–Avrami (JMA) analysis and obtaining the volume fraction of the crystalline phase from the differential scanning calorimetry (DSC) plots, the average Avrami exponent (n) was determined as 1.61 and 5.67 for low and high heating rates, respectively. Moreover, a method for obtaining the value of E based on the non-isothermal JMA analysis was proposed. The value of E was determined as ~185 and 191 kJ/mol respectively for low and high heating rates, which are consistent with the value determined from the Kissinger plot for all heating rates.     

铁基非晶合金退火脆化与防脆技术

综述了铁基非晶合金退火脆化的影响因素，分析了各种防止退火脆化的方法，认为在电脉冲快速加热的同时外加磁场退火，则是改善铁基非晶合金磁性能、防止其退火脆化的一种较好的方法。     

Enthalpy relaxation behaviour of Al-Si-Cr quasicrystalline and amorphous alloys upon annealing

Annealing-induced enthalpy relaxation behaviour was examined calorimetrically in quasicrystalline Al₆₂Si₁₉Cr₁₉ and amorphous Al₆₀Si₂₅Cr₁₅ alloys. When both alloys annealed at temperatures belowT _x are reheated, an excess endothermic reaction (enthalpy relaxation) occurs reversibly above the annealing temperature,T _a. The peak temperature of C _p,endo rises in a continuous manner with the logarithm of annealing time (t _a). The magnitudes of C _p,endo and H _endo of the amorphous alloy increase with increasingT _a while no appreciable change in C _p,endo and H _endo of the quasicrystal withT _a is seen. The activation energy,Q _m, for the enthalpy relaxation increases from 1.8 to 2.7 eV with the peak temperature of C _p T _m, for the amorphous alloy, whereas it remains constant (1.3 eV) for the quasicrystal. The endothermic reaction with smallO _m for the quasicrystal is thought to be attributable to the disappearance of short-range ordering of chromium and silicon atoms with stronger attractive interaction, which developed during annealing, i.e. the reversion phenomenon, in the unrelaxed localized regions with high free-energy isolately embedded in the more stable icosahedral structure. The similarity of the enthalpy relaxation behaviour between the quasicrystalline and amorphous phases allows us to infer that short-range atomic configuration is very similar between the quasicrystalline and amorphous phases.     

Magnetic anisotropy control in amorphous FeCoSiB films by stress annealing

It is important to control magnetic anisotropy of ferromagnetic materials. In this work, magnetic anisotropy of amorphous FeCoSiB films is controlled by stress annealing. FeCoSiB films are deposited on glass substrate and annealed with stress in vacuum. When the annealed films are released from clamp, permanent tensile or compressive strain can be introduced in the films. Influences of both tensile and compressive strain on the magnetic properties of FeCoSiB films have been studied. The results show that FeCoSiB films by stress annealing exhibit strong magnetic anisotropy while the samples by normal annealing exhibit magnetic isotropy. Easy axis along the stress is induced in the films with tensile stress, while easy axis perpendicular to the stress is induced in the samples with compressive stress. It has also been found that the magnetic anisotropy increases with the increase of the strain. The effects of strain on the magnetic properties of FeCoSiB films have been interpreted by stress induced anisotropy via magnetoelastic coupling.     

Enthalpy relaxation behaviour of metal-metal (Zr-Cu) amorphous alloys upon annealing

Anneal-induced enthalpy relaxation behaviour was examined calorimetrically for Zr_50-70Cu_50-30, Zr₇₀(Cu-Fe)₃₀ and Zr₇₀(Cu-Ni)₃₀ amorphous alloys. When the alloys annealed at temperatures belowT _g are heated, an excess endothermic reaction (enthalpy relaxation) occurs above the annealing temperatureT _a. The peak temperature of C _p,endo, evolves in a continuous manner with lnt _a. The magnitudes of C _p,endo and H _endo for Zr-Cu binary alloys increase gradually with risingT _a and then rapidly at temperatures just belowT _g, while their changes as a function ofT _a for the ternary alloys show a distinct two-stage splitting; a low-temperature one which peaks at aboutT _g — 150 K and a high-temperature peak just belowT _g. From the result that the addition of iron or nickel causes the two stage splitting of the C _p,endo (T _a), it was proposed that the low-temperature endothermic peak is attributed to local and medium range rearrangments of copper and iron or nickel atoms with weak bonding nature and the high-temperature reaction to the long-range co-operative regroupings of zirconium and copper, iron or nickel atoms which are composed of the skeleton structure in the metal-metal amorphous alloys. The mechanism for the appearance of the two-stage enthalpy relaxation was investigated by the concept of two-stage distributions of relaxation times proposed previously, and the distinct two-stage splitting was interpreted as arising from the distinctly distinguishable difference in the ease of atomic rearrangements between Cu-(Fe or Ni) and Zr-(Cu, Fe or Ni).     

Magnetic and magneto-optical properties of amorphous boron-cobalt and silicon-cobalt alloys

Amorphous alloys of the type B_1?xCo_x and Si_1?xCo_x were prepared by vapour deposition.Their magnetic properties were determined in the range 4.2 - 300 K. The polar Kerr rotation was measured at two wavelengths (λ = 633 nm and 830 nm) at room temperature. The magnetic properties of these alloys were compared with amorphous alloys in which Co is combined with Sn, P, Mg, Y, La or Zr. The magnetic properties were analysed in terms of a model in which proper account is taken of possible differences in chemical short-range ordering of the atoms.     

The influence of laser annealing on the crystallization processes in amorphous Co-rich alloys

Crystallization of Co-rich amorphous alloys via thermal and laser annealing has been studied using X-ray diffraction and high resolution electron microscopy techniques. It has been found that microstructural properties of the resulting alloys can differ significantly for the two thermal treatments depending on their Co content. Co₇₈Fe₂Mn₂Si₉B₉, Co₇₂Fe₈B₂₀ and Co₅₀Fe₂₈Si₁₀B₁₂ amorphous alloys have been studied and only Co₇₂Fe₈B₂₀ has shown very different crystallization processes after thermal and laser annealing. The results of comparative analysis of the influence of laser and thermal annealing on optical and structural properties of the samples are discussed.     

Formation of nanocrystalline phases during thermal decomposition of amorphous Ni-P alloys by isothermal annealing

The microstructure and the average grain size were investigated by x-ray diffraction and transmission electron microscopy for nanocrystalline (n) Ni-P alloys with 18, 19, and 22 at.% P. A detailed study of the nanocrystalline states obtained along different heat treatment routes has been performed: (1) a-->ni by isothermal annealing of the melt-quenched amorphous (a) Ni-P alloys; (2) ni-->nii by isothermal annealing of the nanocrystalline ni state; (3) ni-->nii by linear heating of the ni state. The heats evolved during the structural transformations were determined by differential scanning calorimetry. From these studies, a scheme of the structural transformations and their energetics was constructed, which also includes previous results on phases obtained by linear heating of the as-quenched amorphous state of the same alloys. Grain boundary energies also have been estimated. In some cases it was necessary to assume a variation of the specific grain boundary energy during the phase transformation to understand the enthalpy and microstructure changes during the different heat treatments.     

Oxidation of amorphous alloys

Owing to their unique short- or medium-range ordered microstructures and excellent mechanical, physical, and chemical properties, amorphous alloys have attracted significant interest in recent years. For the application of amorphous alloys, clarifying their oxidation processes and mechanisms is necessary since many of the surface-related properties of amorphous alloys largely depend on the surface oxide layer. The aim of this paper is to review the recent research on the thermal oxidation behaviors of amorphous alloys under pure oxygen or air condition. The contents are divided into three categories according to the number of components the research considers, i.e., the oxidation of binary, ternary, and multi-component (>3) amorphous alloys. Each section discusses the thermal stability of the amorphous matrix, oxidation kinetics, and the oxide layer and amorphous substrate, which are strongly affected by internal factors (i.e., alloy elements and microstructure) and external factors (i.e., oxidation temperature, duration, and oxygen partial pressure, etc.). The general features of the oxidation of amorphous alloys – from simple binary to complex multi-component amorphous alloys – will be summarized. This overview of the current scientific understanding on the fundamentals of these materials may provide guidelines for the development of strongly corrosion-resistant amorphous alloys.     

The Fe--B--Ge amorphous alloys

The crystallization behavior, the saturation magnetization, and the Curie temperatures of Fe-B-Ge amorphous alloy ribbons are reported and compared to previously reported results for Fe-B, Fe-B-C, Fe-B-Si, Fe-B-Si-C, and Fe-B-Ga.     

Switching in amorphous alloys

In this paper we present a survey of recent developments in the field of memory switching and of recent insights into the mechanism of threshold switching, in “ovonic” multicomponent chalcogenide alloys.     

Nanostructured amorphous Si-Au alloys

Nanostructured amorphous Si_1-XAu_X-alloys (0.1 ≤x_Au ≤ 0.3) were produced by an inert-gas condensation and in-situ consolidation technique and investigated by Small Angle Neutron Scattering (SANS) and density measurements. The results are interpreted in terms of a microstructure which consists of nanometer-sized amorphous grains embedded in a matrix of lower density, formed by grain boundaries and free volumes. The relative densities were found to be dependent on the average particle sizes, but independent of the alloy composition.In all samples the SANS intensity decreases at low Q according to a power law ∼Q^−3.37, which is attributed to a surface fractal structure of dimension D_S=2.63. The surface fractal structure is traced back to the interface between the open porosity and the amorphous material. This is supported by a contrast variation experiment.     

Nanocrystallization of amorphous CoSiBFeNb alloys

The effect of Fe and Nb contents on the crystallization behavior of CoSiBFeNb alloys was studied using Mössbauer spectroscopy, transmission electron microscopy and X-ray diffraction. It was found that the structure formed by primary crystallization in the (Co₇₇Si_13.5B_9.5)₈₈Fe₇Nb₅ alloy is similar to that of the famous Fe_73.5Si_1.35B₉Cu₁Nb₃ nanocrystalline alloy. The data obtained are discussed regarding a random network of associates as a base structural element of amorphous metallic alloys.