Formation and mechanical behavior of (Fe0.5Ni0.5)80−xMoxB20 (x = 0–8) amorphous alloys

Glass forming ability, thermal stability and mechanical behavior of (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ (x = 0, 2, 4, 6, 8) amorphous alloys were studied by XRD, TEM, SEM, DSC, tensile test, microhardness test and tearing test. The effects of Mo addition on glass formation, strength and ductility of (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ amorphous alloys were discussed. The substitution of Mo for Fe and Ni simultaneously causes improvement in glass forming ability and thermal stability, and changes the crystallization process. The tensile fracture strength of amorphous alloy depends on both hardness and ductility; the alloy with high hardness and good ductility simultaneously also has a high tensile fracture strength. The (Fe_0.5Ni_0.5)₇₈Mo₂B₂₀ amorphous alloy exhibits good glass forming ability and the highest tensile fracture strength among (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ alloys. Micro-plastic deformation occurred in ductile and brittle amorphous alloys that both show viscous flow characteristics. The mechanical behavior of (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ amorphous alloys is related to the average outer shell electron concentration of metal atoms.     

Thermal embrittlement of Fe-based amorphous ribbons

Thermal embrittlement of amorphous Fe_78?xNi_xSi₁₀B₁₂ and Co₇₈Si₁₀B₁₂ alloys has been studied. The majority of Fe-based amorphous alloys became brittle after annealing to temperatures significantly lower than their crystallization temperatures, whereas the non-Fe-based amorphous alloys remained ductile after annealing up to their crystallization temperatures. The present results emphasize on the key difference between the embrittlement behavior of Fe-based and non-Fe-based amorphous alloys. We point out a possible correlation between different phenomena like Invar effect, compositional inhomogenity, and residual stress playing a critical role in the thermal embrittlement of Fe-based amorphous alloys.     

Mössbauer spectra in the xNa2O·(1 − x − y)B2O3·yFe2O3 glass system

A Mössbauer spectroscopic study is made on xNa₂O·(1 ? x ? 7)B₂O₃·yFe₂O₃; 0.045 ? x ? 0.405 and y = 0.05, 0.10 and 0.15 samples quenched from the melt. The presence of two quadrupole doublets indicates that an amphoteric cation like Fe³⁺ occupies both the tetrahedral “network forming” and the octahedral “network modifying” sites in the glass structure. The observed variations of isomer shift and quadrupole splitting with the values of x are similar to the ones found earlier in lead borates but different from those observed earlier in soda borates and other alkali alumino borates. In samples with smaller values of x, an additional devitrified magnetic phase of Fe₂O₃ is seen. The distribution of Fe³⁺ ions in different sites and phases is also discussed.     

Magnetic and magnetoimpedance properties of Mn-doped FINEMET

In this study, the effect of substituting Mn for Fe on the magnetic and magnetoimpedance (MI) properties of amorphous and nanocrystalline Fe_73.5?xMn_xCu₁Nb₃Si_13.5B₉ (x = 1, 3, 5, 7) alloys has been investigated. A higher Mn content causes a decrease in the saturation magnetization and Curie temperature. For as-received Fe_73.5?xMn_xCu₁Nb₃Si_13.5B₉ (x = 0, 1, 3, 5, 7) ribbons, the measured values of the MI are 11%, 12%, 16%, 12% and 15% for x = 0, 1, 3, 5, 7, respectively. The magnitude of the MI ratio increases in annealed samples, indicating that they are magnetically softened by nanocrystallisation. The change in MI is found to be ～70% for the x = 3 sample annealed at 550 °C. It is also found that replacing a small amount of Fe by Mn improves the magnetic softness of Fe_73.5?xMn_xCu₁Nb₃Si_13.5B₉ alloys.     

Structural investigation of amorphous FeZr,CoZr and NiZr alloys with low zirconium concentration

A structural investigation has been made of alloy glasses a low concentration of zirconium: compositions M_100?xZr_x with M = Fe, Co and Ni, and x = 9 at.% using X-ray diffraction. The characteristic second peak splitting in the radial distribution function is found for all samples presently investigated. The partial radial distribution functions of amorphous FeZr and CoZr alloys were derived from the measured total distribution function data by applying the concentration method with the anomalous scattering technique. The amplitude in the oscillation of the radial distribution function for M-M and M-Zr pairs is more enhanced in comparison with that of glasses with high Zr content, x = 40–45 at.%. The estimated coordination number of nearest neighbor Fe atoms (11.6 ± 0.5) for iron in the Fe₈₄Zr₁₆ glass is larger than that (10.7 ± 0.5) found in the Fe₈₃B₁₇ glass. This is consistent with the measurements of magnetic properties of these glasses with low zirconium concentration. The possible structural features of intertransition metal alloy glasses with low zirconium concentration is also discussed based on the present experimental data.     

Effect of Mo element on the properties of Fe–Mo–P–C–B bulk metallic glasses

Bulk Fe_80?xMo_xP₁₀C_7.5B_2.5 (x = 5–10 at.%) metallic glasses are synthesized by copper mold casting, which have a critical diameter up to 3 mm, fracture strength over 3000 MPa, plastic strain up to 2.5% and saturation magnetization reaching 1.1 T. Results show that the glass forming ability and strength increase with increasing Mo content, while the plasticity and saturation magnetization do otherwise. These Mo content dependent properties are illuminated with the atomic interactions in the alloys that could be strengthened by suitable addition of Mo element. The effects of Mo on the properties of the alloys imply that proper Mo element should be chosen in designing Fe-based glassy alloys with desired properties.     

Magnetic properties of Fe-Co-Nd-Y-B magnet prepared by suction casting

The magnetic properties of Fe_67−xCo₁₀Nd₃Y_xB₂₀ (x = 0, 2, 6, 10) alloys prepared by suction casting had been investigated. It was found that a small addition of Y (6%) was very effective in improving glass-forming ability (GFA) of Fe-Co-Nd-Y-B alloys. The as-cast Fe₆₁Co₁₀Nd₃Y₆B₂₀ alloy presented soft magnetic behavior. However, the alloy showed the hard magnetic behavior due to exchange coupling between soft and hard magnetic phases after annealing at 948 K for 30 min. The results provide a promising approach for the production of bulk magnets by the simple process of copper mold casting and subsequent heat treatment.     

The shoulder in the second peak of the pair correlation function of superheated liquid Fe80B20 alloy

By referencing to a series of superheated liquid Fe_100 ? xB_x (x = 0 to 100) alloys, the existence of the shoulder in the second peak of the pair correlation functions of liquid Fe₈₀B₂₀ alloy is confirmed. The shoulder is caused by the unequal opportunity of connection modes rather than the occurrence of particular types of B-centered clusters. Our model predicts that vertex sharing and face sharing of the B-centered structure units are the two significant connection modes responsible for the shoulder. This picture may fill the gap in understanding the widely different shapes of the second peak in superheated liquid and amorphous Fe₈₀B₂₀ alloy.     

Mössbauer characterization of an amorphous steel with optimal Mo content

Three amorphous steel alloys, Fe_71.2?xC_7.0Si_3.3B_5.5P_8.7Cr_2.3Al_2.0Mo_x (x = 0, 4.5 and 6.5 at.%), have been produced by the melt-spinning technique and characterized by X-ray diffraction and transmission Mössbauer spectrometry (TMS). TMS allows us to study the local environments of the Fe atoms in the glassy state, showing the changes in the amorphous structure due to the addition of Mo. A reduction of the mean hyperfine field is observed as the amount of Mo increases. With intermediate Mo content, this reduction is associated to the substitution of Fe by Mo in a disordered magnetic Fe-rich structure, whereas for high Mo content, this structure is destroyed leading to an increase of paramagnetic environments. Finally, the relationship between the glass forming ability (GFA) of these alloys and their local structure determined by TMS will be discussed.     

Effect of Mo–Fe substitution on glass forming ability and thermal stability of Fe–C–B–Mo–Cr–W bulk amorphous alloys

Amorphous Fe_67?xC₁₀B₉Mo_7+xCr₄W₃ (x = 1–7 at.%) plates with 0.64 mm thickness were prepared by copper mold casting. The thermal properties and microstructural development during heat treatments were investigated by a combination of differential scanning calorimetry, differential thermal analysis, and X-ray diffraction. The glass forming ability (GFA) and activation energy for crystallization have a distinct dependence on Mo content. Fe₆₂C₁₀B₉Mo₁₂Cr₄W₃ was the best glass former in this study, demonstrating a supercooled liquid region, ΔT_x = 51 K, and an activation energy for crystallization, Q = 453 kJ/mol. The GFA of alloys in this system was governed by elastic strain optimization resulting directly from the variation in Mo content. Heat treatments were performed to demonstrate resistance to crystallization under typical processing conditions. Alloys in this system exhibited a three phased evolution during crystallization. A second set of heat treatments was performed to identify each phase. An analysis of phase evolution revealed a distinct dependence of phase evolution with stepwise substitution of Mo for Fe in this system.     

Effect of Al substitution on the magnetic properties of amorphous Fe73.5Cu1Mo3Si13.5−xAlxB9 alloy

We have synthesized FINEMET type amorphous Fe_73.5Cu₁Mo₃Si_13.5−xAl_xB₉ alloy by the single wheel melt spinning technique. The effect of Al substitution on the magnetic properties has been studied using a vibrating sample magnetometer, SQUID and Mössbauer spectroscopy. Magnetization and Curie temperature of the amorphous phase of the alloys were found to decrease with Al concentration. The results are attributed to the dilution effect of Al on the magnetic moment of Fe and to the increase in Fe–Fe interaction distance resulting in the weakening of exchange interaction.     

Influence of nickel content on the electrochemical behavior of Finemet type amorphous and nanocrystalline alloys

The aim of this work has been the systematic study of the influence of partial substitution of Fe by Ni in the Ni_xFe_73.5−xSi_13.5B₉Nb₃Cu₁ alloy within the range 0 ⩽ x ⩽ 10% atom (x = 0, 2, 4, 6, 8, 10) on electrochemical behavior, corrosion rate and the structural changes in amorphous and nanocrystalline alloys. The amorphous nature of the alloys was confirmed by X-ray diffraction and the chemical compositions were determined by ICP. The glass transition and kinetic crystallization of amorphous alloys were studied by DSC. The technique of XPS was used for evaluating the chemical states of elements present in native oxide films. The electrochemical behavior of amorphous and nanocrystalline alloys have been investigated in 0.5 M KOH using cyclic voltammetry. The experimental results show that the formation of different nanocrystalline phases is not excessively transformed by the addition of small amount of nickel and the electrochemical behavior is improved as nickel content increased.     

XAS and XMCD studies of amorphous FeCo-based ribbons

This paper reports x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies at Fe L_3,2 and Co L_3,2-edges to investigate the electronic structure of (Fe_100 ? xCo_x)₇₈Si₉Nb₃B₉Cu₁ (0 < x < 95) alloys. The influence of controlled Co addition on electronic structural and magnetic properties of (Fe_100 ? xCo_x)₇₈Si₉Nb₃B₉Cu₁ (x = 0, 20, 40, and 60) alloys has been investigated and it has been observed that Co exists as Co²⁺/Co³⁺, while Fe exists as a mixture of Fe⁰ (metallic) and Fe²⁺. The XMCD studies confirm these results and reveal that Co-ions are responsible for the room temperature ferromagnetism (RTFM) in the system, while at Fe L_3,2-edge it shows a diamagnetic behavior.     

Corrosion behavior of Fe-based ferromagnetic (Fe,Ni)–B–Si–Nb bulk glassy alloys in aqueous electrolytes

Fe-based ferromagnetic [(Fe_1?xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ (x = 0, 0.2 and 0.4) bulk glassy alloys (BGAs) with a diameter of 2 mm were prepared by copper mold casting. The corrosion behavior of glassy alloy rods obtained was investigated in 0.5 M NaCl, 0.5 M NaOH and 0.5 M H₂SO₄ aqueous electrolytes, respectively, using weight loss and electrochemical polarization measurements. It was found that the corrosion rates significantly decrease with an increase in Ni content in all examined solutions. The Ni-containing BGAs are spontaneously passivated with wide passive regions and low passive current densities in NaCl and NaOH solutions, but exhibit the active–passive–transpassive behavior in H₂SO₄ solution. The partial substitution of Ni for Fe results in a considerable improvement on the corrosion resistance of [(Fe_1?xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ BGAs, because of the structural and chemical homogeneousness of the amorphous phase and the effect of Ni on promoting the formation of a passive film. Besides their high glass-forming ability (GFA), excellent soft-magnetic properties and good mechanical performance, which have been reported before, these FeNi-based BGAs also feature rather high corrosion resistance.     

Compositional dependence of crystallization temperature of Fe80−xMxB20 glasses

The effect of the first group of periodic elements M on the crystallization temperature and heat of crystallization of Fe_80?xM_xB₂₀ alloys has been investigated, where M stands for Ti, V, Cr, Mn, Co or Ni. The addition of the alloying elements, except for large amounts of cobalt and nickel (? 40 at.%), enhances the thermal stability of the glasses, in particular, titanium and vanadium in small amounts significantly increases the crystallization temperature. Elements possessing fewer outer electrons and higher cohesive energies tend to increase the thermal stability of the glasses. The heat of crystallization of the glasses decreases effectively by an addition of titanium or nickel.     

Mössbauer spectroscopic study of gamma-ray irradiated potassium phosphate glasses

A Mössbauer spectroscopic study was performed to investigate the effect of γ-ray irradiation on the formation of non-bridging oxygens in the potassium phosphate glasses denoted by the formula x K₂O · (100 ? x)P₂O₅ · 7 Fe₂O₃ (0 ? x ? 50 mol.%). Mössbauer spectra for these glass samples consisted of two kinds of doublets due to Fe²⁺ and Fe³⁺ ions of octahedral symmetries. Only small changes occurred in the Mössbauer parameters as a result of irradiation at room temperature in a dry nitrogen atmosphere, except for the decrease in the absorption area for the Fe²⁺ ions. The decrease in the absorption area was attributed to the electron transfer from the Fe²⁺ ions to the neighboring oxygens. Thermal annealing experiments for a few non-irradiated glass samples indicated that the decrease in the absorption area was confirmed to be due to γ-rays rather than heating during the irradiation.     

In-situ crystallization of amorphous Fe73−xNbxAl4Si3B20 alloys through synchrotron radiation

In the present work Fe_73−xNb_xAl₄Si₃B₂₀ (x = 5, 10) alloys have been processed by melt-spinning with the aim of studying the crystallization sequence through annealing in suitable temperatures. Melt-spun ribbons were characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) through Cu-Kα (λ = 1.54 Å) and synchrotron radiation (λ = 1.77 Å) and transmission electron microscopy (TEM). Soft magnetic properties were measured through the hysteresis loop tracer. In-situ XRD through synchrotron radiation was very accurate in phase identification. Fe_73−xNb_xAl₄Si₃B₂₀ (x = 5, 10) alloys showed the possibility of forming ferromagnetic amorphous alloys composed of commercial Fe-based master alloys with fine nanocrystalline structure and good soft magnetic properties.     

The small anomaly in the temperature dependence of the electrical conductivity of iron containing phosphate glasses

The dc conductivities, σ,of 2 CaO·K₂O·x Fe₂O₃·(5 - x)P₂O₅ glasses (1.4 ?x?2.2) [Fe³⁺/(Fe²⁺ + Fe³⁺)= constant (0.88±0.015)] have been measured in the temperature range from room temperature to 300°C. It has been found that the glass transition temperature increases rapidly with increasing Fe/P ratio and that mixed-valence hopping type electronic conduction takes place in these glasses and every log σ versus 1/T curve obtained shows a change in slope near 100°C, which produces a small increase, 0.14 (for x=2.2)?0.18 eV (for x=1.4), in activation energy at higher temperatures. Both the activation energy and pre-exponential factor for conduction display different dependences on the Fe/P ratio in the different temperature ranges on both sides of the anomaly temperature. These results are discussed in terms of the Mott's equation for small polaron hopping.     

Influence of composition in the crystallization process of Fe75−xNb10B15+x metallic glasses

The devitrification process of Fe_75−xNb₁₀B_15+x (x = 0, 5, 10) metallic glasses produced by melt-spinning has been analyzed by calorimetric, microstructural and magnetic measurements. The experimental results show large differences in the behavior of these alloys as a function of composition. The alloy x = 0 undergoes a primary crystallization process separated in two stages while only one is observed for alloys with x = 5 and x = 10. This difference, observed by DSC, is correlated with a microstructural change in the phases that precipitate. For alloys x = 5 and 10, Fe₂₃B₆ and bcc-Fe are identified after the first calorimetric peak. In the sample x = 0, bcc-Fe and an unidentified phase precipitate in the first peak but massive crystallization of bcc-Fe is observed after the second stage. Finally the thermal dependence of magnetization has been measured and the Curie temperatures for the metallic glasses are determined. The change of these quantities with heat treatment and composition is discussed.