Influence of Ni content on Fe–Nb–B alloy formation

In this work three alloys, Fe₇₄Nb₆B₂₀, Fe₆₄Ni₁₀Nb₆B₂₀ and Fe₅₄Ni₂₀Nb₆B₂₀, were obtained by mechanical alloying to analyze the influence of Ni content on Fe–Nb–B alloy formation. Structural analysis by X-ray diffraction (XRD) confirms that partial substitution of Fe by Ni favours the formation during milling of a more disordered structure. Furthermore, thermal stability study was performed by differential scanning calorimetry (DSC) because thermally induced structural changes can affect soft magnetic behaviour. After 40 h of milling time, all DSC curves show several exothermic effects on heating associated to structural relaxation and crystallization. All alloys present a crystallization process with associated activation energy values ranged between 238 and 265 kJ mol^–1 related to the crystalline growth of the bcc-Fe rich phase. In alloys with Ni, a second crystallization process appears at temperatures over 500°C with activation energies 397 (10% Ni alloy) and 385 kJ mol^–1 (20% Ni alloy) probably associated to the nucleation and crystalline growth of a new phase.     

SAXS study on the structure and crystallization of amorphous metallic alloys

The change in structure of several amorphous alloys as Fe-P-C, Fe-B and Pd-Au-Si alloys during isothermal ageing was examined using small angle X-ray scattering technique as well as transmission electron microscopy. The SAXS intensity was related to two different types of scattering sources depending on ageing period and temperature. As-splatted amorphous alloys and the specimens aged for short period at relatively low temperature, where specimens remained in amorphous state, showed a weak and spreaded SAXS intensity. This indicates an existence of electron density fluctuation in amorphous phase. The dimension of their scattering regions was estimated to be 1.8 to 2.4 nm for Fe-P-C alloys, and 1.2 to 0.8 rim. for Fe-B alloys, respectively, by analysing the electron density-density correlation function derived from observed SAXS intensity. The origin has been discussed based on one dimensional model. A compositional fluctuation was made clear to occur in fine scale of about 1 nm in amorphous Fe-B and Fe-P-C alloys. When the alloys were aged for longer period below their crystallization temperatures, fine crystalline particles precipitate; those are a two phase lamella structure of Fe₃P and-Fe for a Fe₈₃P₁₀C₇ alloy, an Ferich single phase for Fe₈₃B₁₇ alloy, and a Pd-rich single phase for Pd₇₆Au₆Si₁₈8 alloy, respectively. Their size and structure were determined from the analysis of SAXS data and TEM observation.     

The effect of Nb and Ni addition on crystallization behavior of amorphous–nanocrystalline Fe–Cr–B–Si alloys

The crystallization behavior of amorphous Fe–Cr–B–Si alloys in the presence of Ni and Nb elements was the goal of this study. In this regard, four different amorphous–nanocrystalline Fe₄₀Cr₂₀Si₁₅B₁₅M₁₀ (M=Fe, Nb, Ni, Ni_0.5Nb_0.5) alloys were prepared using mechanical alloying technique up to 20 h. Based on the achieved results, in contrast to Fe₅₀Cr₂₀Si₁₅B₁₅ alloy, the amorphous phase can be successfully prepared in the presence of Ni and Nb in composition. Although the crystallization mechanism of prepared amorphous phase in different alloys was the same, the Fe₄₀Cr₂₀Si₁₅B₁₅Nb₁₀ alloy showed higher thermal stability in comparison with other samples. The crystallization activation energy of this amorphous alloy was estimated about 410 kJ mol^?1 which was much higher than Fe₄₀Cr₂₀Si₁₅B₁₅Ni₁₀ (195.5 kJ mol^?1) and Fe₄₀Cr₂₀Si₁₅B₁₅Ni₅Nb₅ (360 kJ mol^?1) samples. The calculated values of Avrami exponent (1.5 < n < 2.2) indicated that the crystallization process in different alloying systems is the same and to be governed by a three-dimensional diffusion-controlled growth.     

Short range ordering and phase separation in rapidly quenched Ni80 57Fe1P19 amorphous alloys solution treated at different temperatures

Electrochemical measurements and Mössbauer spectroscopy were used to study a rapidly quenched Ni₈₀ ⁵⁷Fe₁P₁₉ amorphous alloy solution treated between 920 and 1500 °C. Different short range orderings were shown in amorphous alloys solution treated at different temperatures. This finding can be associated with phase separation occurring in the liquid state. This phase separation can be inherited in slightly relaxed amorphous state.     

Thermal evolution of ferromagnetic metallic glasses

A traditional TG apparatus was modified by placing two permanent magnets producing a controlled magnetic field (TG(M): Magneto Thermogravimetry). This technique proved to be useful to study both structural relaxation and crystallisation of ferromagnetic metallic glasses. Results obtained for the amorphous alloys Fe₄₀Ni₄₀P₁₄B₆ and Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅, are reported in this paper. Structural relaxation can be evaluated by measuring changes in Curie temperature induced by thermal treatments. Crystallisation in TG(M) is detected through a change in the measured apparent mass (difference between the sample mass and magnetic force driving it upward). These results were confirmed by DSC analysis. Whether the obtained crystalline phase is ferromagnetic, it can be identified through its Curie temperature, measured by TG(M). In fact the value of 770°C measured as Curie temperature of crystallised Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅led to conclude that the only ferromagnetic crystalline phase is a-Fe. These hypothesis was confirmed by XRD analysis, showing that the first crystallisation yields to a-Fe nanocrystals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and characterization of Co80Nb20-xBx amorphous metallic ribbons

Co₈₀Nb₁₄B₆, Co₈₀Nb₁₂B₈ and Co₈₀Nb₁₀B₁₀ amorphous alloys were obtained through the melt-spinning process. The ribbons structure was investigated by X-ray diffractometry and the crystallization process and the thermal stability were studied by means of differential thermal analysis and thermomechanical technique. It was observed that the crystallization temperature depends on the alloy composition and occurs in a temperature range between 420 and 730°C. The coercive field of all alloys was determined by magnetic susceptibility measurements, the values of which range from 2.78 to 5.95 A m^-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Oxidation of carbon monoxide and hydrogen on the surface of crystalline and amorphous Cu60Zr40 alloys

The activity of amorphous and crystalline Cu₆₀Zr₄₀ alloys has been studied. Preoxidation of the alloys results in enhanced activity. The amorphous samples reveal a lower catalytic activity. An active catalyst for the oxidation of CO is obtained from the crystalline copper-zirconium alloy.     

Hard magnetic properties of rapidly quenched Nd4−xDyxFe77.5B18.5 alloys

Effects of the substitution of dysprosium for neodymium on the magnetic properties of rapidly quenched Nd₄Fe_77.5B_18.5 alloy were studied. The Curie and crystallization temperatures of amorphous Nd_4−xDy_xFe_77.5B_18.5 alloys were found to have a small dependence on the dysprosium concentration x. The as-quenched samples were magnetically soft but developed a coercive field of 0.1–3.6 kOe after crystallization by annealing at 600–810°C. The highest energy product in the samples studied was found to be 13 MG Oe. X-ray diffraction and thermomagnetic measurements on the optimal annealed samples showed a multi-phase structure mainly consisting of Fe₃B in addition to (Nd, Dy)₂Fe₁₄B and small amounts of α-Fe. The hard magnetic properties in crystallized Nd_4−xDy_xFe_77.5B_18.5 alloys originate from the presence of the hard magnetic 2: 14: 1 phase.     

Investigation of core-excited BK quantum yield spectra of amorphous and crystalline Fe40Ni40P14B6 alloys

X-ray quantum yield spectra from the BK edge in amorphous and crystalline Fe₄₀Ni₄₀P₁₄B₆ alloys are presented. ESCA core level binding energies were also measured. The quantum yield spectra are discussed together with calculated densities of states. A good coincidence between band structure calculations and experimental results is obtained. A small structure at absorption onset is interpreted as due to oxidation products at the sample surface. Crystallization effects after heating of the compound are discussed.     

原子簇Ni2Fe2P结构稳定性的理论研究

利用DFT(密度泛函理论)方法在B3LYP/Lan12dz水平下对原子簇模型Ni2Fe2P的二十余种可能构型分别在二、四重态下进行优化计算,分析比较了优化结果的能量、结合能、吉布斯自由能变化和过渡态.结果表明原子簇Ni2Fe2P十种异构体没有虚频,有可能稳定存在于非晶态合金中;其中以具有二重态的构型1的能量最低,结合能、吉布斯自由能变化及过渡态能垒最大,最为稳定;四重态中异构体1',2',3'和4'共存的可能性比较大.     

Effect of thermomechanical processing on the thermal stability of amorphous Fe-B alloys

Results from investigating the effect of thermomechanical processing on the thermal stability of amorphous Fe-B alloys are presented. It is shown that the combined thermomechanical processing of amorphous alloys raises the temperature of intense crystallization onset by 80 K for binary alloys; by 20–50 K, for multicomponent alloys. The greater expansion of the thermal stability interval of binary alloys relative to multicomponent alloys is explained by the presence of alloying dopants such as molybdenum, nickel, and silicon that inhibit the diffusion of boron and thus hinders nucleation and the growth of the crystalline phase. The enhanced thermal stability of amorphous alloys induced by thermomechanical processing is explained by the reduction in size of amorphous-phase frozen crystallization centers and by the formation of a nanostructured state.     

Passivity characteristics on Ni(Cr)(Fe)SiB glassy alloys in phosphate solution

Passivity characteristics of three nickel-metalloids glassy alloys (Ni_92.3Si_4.5B₃₂, Ni_82.3Cr₇Fe₃Si_4.5B_3.2 and Ni_75.5Cr₁₃Fe_4.2Si_4.5B_2.8) and the immersion time effect on the corrosion resistance were carried out by AC and DC electrochemical methods and SEM and XPS analyses. The study also focused on the effect of H₃PO₄ concentration and its role on the corrosion rate, passivation ability of nickel base glassy alloys surface. The present investigation revealed (i) corrosion resistance of Cr-free alloy shows pseudo passivity at all examined H₃PO₄ concentrations, (ii) high corrosion resistance of Cr contains alloys due to the formation of protective layer of chromium oxyhydroxide on the surface which acts as a diffusion barrier against alloy dissolution, (iii) the negative resistance observed in the case Ni_75.5Cr₁₃Fe_4.2Si_4.5B_2.8 alloy revealed the sudden transition of metal/solution interface from a state of active dissolution to the passive state.     

Vibrational dynamics of Fe-based glassy alloys

The well recognized model potential is used to investigate the vibrational properties of four Fe-based binary glassy alloys viz. Fe₉₀Zr₁₀, Fe₈₀B₂₀, Fe₈₃B₁₇ and Fe₈₀P₂₀. The thermodynamic and elastic properties are also computed from the elastic limits of the phonon dispersion curves (PDC). Three theoretical approaches given by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS) are used in the present study to compute the PDC. Six local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) and Sarkar et al.’s local field factor (SLFF) based excgange and correlation function are employed to see the effect of exchange and correlation in the aforesaid properties.     

Study of the crystallization kinetics in amorphous Fe83P17 alloy

The crystallization kinetics of Fe₈₃P₁₇ amorphous alloy has been studied by Mössbauer spectroscopy and X-ray diffractometry. The samples were annealed isothermally at two different temperatures (315 °C and 325 °C). During isothermal annealing of the samples three phases were observed: crystalline Fe₃P phase, crystalline -Fe phase and the amorphous phase. The value of the Avrami exponent was found to be about 2.0 at each annealing temperature. This suggests that the growth rate of the crystals is controlled by volume diffusion and the nucleation rate decreases during crystallization. The activation energy obtained for the overall crystallization process was 193±43 kJ mol^–1.     

Thermal induced structural and magnetic transformations in Fe73.5−xCex=0,3,5,7Si13.5B9Nb3Cu1 amorphous alloy

Structural and magnetic properties of amorphous and partly crystallized Fe_73.5?xCe_x=0,3,5,7Si_13.5B₉Nb₃Cu₁ alloys, were analysed in the temperature ranging from RT to 800 °C with scanning calorimetry and magnetometry. The Fe(Si) and Fe(B) structures were identified and characterised with set of crystallization temperatures and activation energies. Also, Curie temperatures for amorphous and for crystalline structures were determined and analysed as functions of Ce content.     

Electrocatalytic evolution of hydrogen on amorphous Fe-Nb-B-Rare-Earth-Metal electrodes from alkaline solutions

Cathodic processes for electrochemical generation of hydrogen in aqueous KOH solutions in the presence of active electrodes made of Fe-Nb-B-based amorphous metallic alloys alloyed with rare-earth metals (Y, Gd, Dy) were studied. All the amorphous alloys exhibit a catalytic effect in the electrochemical evolution of hydrogen from 5 M aqueous KOH solutions. The electrocatalytic system with Fe₈₂Nb₂B₁₄Gd₂ and Fe₈₂Nb₂B₁₄Dy₂ electrodes exhibiting a prolonged autocatalytic effect can be recommended for practical application.     

First principle MD study on the structural and electronic properties of liquid and amorphous NI81B19 and NI80P20 alloy

Atomic and electronic structures of liquid and amorphous Ni₈₁B₁₉ and Ni₈₀P₂₀ alloys were simulated by ab initio molecular dynamics. Pair correlation function, bond pair analysis, electronic population analysis, and density of states were calculated. It was found that amorphous Ni₈₁B₁₉ and Ni₈₀P₂₀ alloys can be prepared by rapid quenching, and their structures are similar to those of liquid alloys. Bond pair analysis indicated that the environment of each atom in Ni₈₁B₁₉ system is dominated by icosahedral and distorted icosahedral inherent structures; however, in Ni₈₀P₂₀ system, the tetrahedral order is preponderant. Strong interactions occur between the d‐electrons of Ni and the p‐electrons of B (or P), which leads to the covalent interactions between Ni and B (or P) atoms. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Crystallization kinetic studies: A means to evaluate time-temperature-transformation curves. Application to metallic glasses

It is shown that the study of the kinetics of crystallization of an amorphous alloy may be used to obtain the correct form of the low temperature part of the time-temperature-transformation (T-T-T) curves. A unified review of the current kinetics of crystallization studies is presented and the general kinetic equation which gives the reaction rate as a function of temperature and crystalline fraction is shown to contain information related to theT-T-T-curves. Finally examples of application to two metallic glasses, Nd₃Fe₇₇B₂₀ and Fe_67.5Co₁₅Nb_1.5B₁₆, obtained by rapid solidification techniques are presented. The comparison between theory and experiment is satisfactory.

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Zusammenfassung Es wird gezeigt, daß die Untersuchung der Kristallisationskinetik von amorphen Legierungen genutzt werden kann, die korrekte Form des Niedertemperaturbereiches der Zeit-Temperatur-Transformation (T-T-T) Kurven zu erhalten. Es wird ein einheitlicher Überblick über die jüngsten Untersuchungen von Kristallisationskinetiken gegeben und an der allgemeinen Gleichung der Reaktionsgeschwindigkeit als eine Funktion von Temperatur und Kristallanteil wird gezeigt, daß sie Informationen bezüglich der T-T-T-Kurven beinhaltet. Letztlich wird eine Anwendung an zwei, durch schnelles Erstarren gewonnenen metallischen Gläsern Nd₃Fe₇₇B₂₀ und Fe_67.5Co₁₅Nb_1.5B₁₆ dargelegt. Zwischen Theorie und Praxis konnte eine ausreichende Übereinstimmung festgestellt werden.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday

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This work was supported by the Comision Interdepartamental de Cienca y Tecnologia, CICYT (project No. MAT88-0439) which are acknowledged.     

Nanocrystallization of hydrogen-charged Mg<Subscript>76</Subscript>Ni<Subscript>19</Subscript>Y<Subscript>5</Subscript> amorphous alloy

The crystallization of a hydrogen-charged melt-spun Mg₇₆Ni₁₉Y₅ amorphous alloy was studied in order to understand the influence of hydrogen absorbed on the crystallization kinetics and mechanism. Hydrogenation does not affect the thermal stability, but decreases significantly the enthalpy of crystallization. The glass transition, which is well manifested in the hydrogen-free alloy, is not observed after hydrogen charging. The main crystalline phases in the H-free and H-charged alloys are the same after complete transformation, but with finer microstructure for the hydrogenated samples.Analysis of the crystallization kinetics reveals that during annealing of hydrogen charged Mg₇₆Ni₁₉Y₅ growth of nanocrystals surrounded by amorphous phase takes place just in the beginning of the transformation, followed by grain growth in fully crystallized material, which is the main process.This revised version was published online in November 2005 with corrections to the Cover Date.     

Influence of variation in the silicon content on the silicon precipitation in the Al–Si binary system

Ti-based amorphous alloys produced by ultra-rapid melt cooling represent an excellent option as biomaterials because of their mechanical properties and corrosion resistance. However, complete elimination of toxic elements is affecting the glass-forming ability and amorphous structure could be obtained only for thin ribbons or powders that are subsequently processed by powder metallurgy. Amorphous ribbons of special Ti₄₂Zr₄₀Ta₃Si₁₅ alloy, which is completely free of any toxic element, were produced by melt spinning, and the thermostability of resulting material was investigated in order to estimate its ability for further heat processing. Isochronal differential scanning calorimetry (DSC) was used to determine transformation points such as glass transition temperature T _g or crystallization temperature T _x. The activation energy for crystallization of amorphous phase was calculated based on Kissinger method, using heating rates ranging between 5 and 20 °C min^?1. Amorphous structure of resulting ribbon was evidenced by means of X-rays diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). It was determined that amorphous Ti₄₂Zr₄₀Ta₃Si₁₅ alloy has a high activation energy for crystallization, similar to other Ti-based amorphous alloys, which provides good thermal stability for subsequent processing, especially by means of powder metallurgy techniques.