Glass formation and magnetic properties of Fe-based metallic glasses fabricated by low-purity industrial materials

Fe-based metallic glasses of (Fe₇₄Nb₆B₂₀)_100-xCr_x (x=1, 3, 5) with high glass forming ability (GFA) and good magnetic properties were prepared using low-purity raw materials. Increasing Cr content does not significantly change glass transition temperature and onset crystallization temperature, while it enhances liquidus temperature. The addition of Cr improves the GFA of the (Fe₇₄Nb₆B₂₀)_100-xCr_x glassy alloys compared to that in Cr-free Fe-Nb-B alloys, in which the supercooled liquid region (ΔT_x), T_rg and γ are found to be 50–54 K, 0.526–0.538, and 0.367–0.371, respectively. The (Fe₇₄Nb₆B₂₀)_100–xCr_x glassy alloys exhibit excellent soft magnetic properties with high saturation magnetization of 139–161 A·m²/kg and low coercivity of 30.24–58.9 A/m. Present Fe-Nb-B-Cr glassy alloys exhibiting high GFA as well as excellent magnetic properties and low manufacturing cost make them suitable for magnetic components for engineering application.     

Compositional dependence of thermal stability, glass-forming ability and fragility index in some Se-Te-Sn glasses

Non-isothermal DSC thermograms were obtained for the ternary Se₉₀Te_10−xSn_x (x = 2, 4, 6 and 8) chalcogenide glasses in order to determine the melting temperature T_m, glass transition temperature T_g, onset T_c and peak T_p temperatures of crystallization. These temperatures were utilized to investigate the thermal stability through the calculations of temperature difference (T_c − T_g), the glass transition activation energy E_t, the parameter S and the average value of crystallization rate factor 〈K_p〉. In addition, the glass forming ability was estimated by the criteria of reduced glass transition temperature, T_rg and Hruby parameter H_R. The fragility index m for the present glasses was determined in order to see whether these materials are obtained from strong or fragile glass-forming liquid. Results reveal that, both thermal stability and glass forming ability exhibit a maximum at x = 4 at.% of Sn. Meanwhile, the prepared glasses were obtained from strong glass-forming liquid as evident from the fragility index calculations. The compositional dependence of the above parameters was discussed on the basis of Philips and Thorpe topological model and the critical composition occurs at an average coordination number 〈r〉 = 2.16 but not 2.40. This is due to the formation of iono-covallent bonds when the glass doped with heavy elements like Sn.     

Thermal, mechanical, and upconversion properties of Er/Yb co-doped titanate glass prepared by levitation method

A novel Er³⁺/Yb³⁺ co-doped titanate glass sphere with diameter of 3.5 mm has been successfully fabricated by levitation method. Its thermal stability, mechanical property and upconversion behavior were investigated. The glass transition temperature T_g, onset crystallization temperature T_c, and peak crystallization temperature T_p, are as high as 820, 895 and 902 °C, respectively. Its Vickers hardness is found to be up to 7.85 GPa. Intense green and red upconversion emissions were obtained in this glassy sample upon 980 nm excitation. The results illustrate good potential of this class of material for practical application in frequency upconversion device. In addition, it is found that heating treatment above T_p can reduce the efficiency of upconversion fluorescence as well as deteriorate the mechanical property, due to the occurrence of La₄Ti₉O₂₄ crystals.     

Thermal behaviour of Pd40Cu30Ni10P20 bulk metallic glass

The thermal behaviour of differently milled Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk metallic glass through the glass transition has been investigated by in situ high-energy synchrotron X-ray diffraction. Repeated heating and cooling were performed between the glassy and the supercooled liquid state. The changes in positions and intensities of the first and second diffraction maxima of the as-milled powder indicate irreversible changes during first heating up to the glass transition temperature T_g due to structural relaxation. After annealing, reversible structural changes with temperature are observed upon heating and cooling in the glassy phase, and in the supercooled liquid state respectively. The shift in the position of the first maximum scales approximately with the linear thermal expansion for the glassy state; however, this relation does not hold for the supercooled liquid. The structural transition from the glass to the supercooled liquid at the glass transition temperature is reflected by the intensity of the diffraction maxima and by a reversed temperature dependence of the position of the second diffuse maximum below and above T_g. The changes of the glass structure for the decrease of free volume by annealing are found to be different from those observed for the reversible volume expansion or shrinkage by varying the temperature. Therefore, the shift of the first diffuse maximum position of bulk metallic glasses cannot be used as a measure of the change in free volume.     

Bulk glassy Fe-Cr-Mo-C-B alloys with high corrosion resistance

The preparation of bulk glassy alloys with high glass-forming ability and high corrosion resistance in Fe-based system was succeeded by means of copper-mold casting. The temperature interval of supercooled liquid region (ΔT_x) is as large as 53-62 K and the reduced glass transition temperature (T_g/T_m) is as high as 0.62-0.63 for the cast Fe_50−xCr₁₆Mo₁₆C₁₈B_x (x=4, 6, 8 at.%) glassy alloys. The corrosion rates of the Fe_50−xCr₁₆Mo₁₆C₁₈B_x glassy alloys with a diameter of 1.2 mm were in the range of 10⁻³-10⁻² mm year⁻¹ in 1, 6 and 12 N HCl solutions at 298 K. The bulk glassy alloys are spontaneously passivated in 1 and 6 N HCl solutions with wide passive region and low passive current density. They do not suffer pitting corrosion even when polarized anodicly in 12 N HCl solution up to 1.0 V (Ag/AgCl). The high corrosion resistance is due to the formation of chromium-rich passive films during immersion in HCl solutions. In addition, the increase of boron content in alloys improves the corrosion resistance of the bulk glassy alloys within the composition range examined.     

Properties of the Ti<Subscript>40</Subscript>Zr<Subscript>10</Subscript>Cu<Subscript>36</Subscript>Pd<Subscript>14</Subscript> BMG Modified by Sn and Nb Additions

The results of investigation of the influence of additions of 2 and 3 at.% of Sn and simultaneously of Sn and 3 at.% Nb on microstructure and properties of the bulk metallic glasses of composition (Ti₄₀Cu_36?x Zr₁₀Pd₁₄Sn _x )_100?y Nb _y are reported. It was found that the additions of Sn increased the temperatures of glass transition (T _g), primary crystallization (T _x ), melting, and liquidus as well as supercooled liquid range (ΔT) and glass forming ability (GFA). The nanohardness and elastic modulus decreased in alloys with 2 and 3 at.% Sn additions, revealing similar values. The 3 at.% Nb addition to the Sn-containing amorphous phase decreased as well all the T _g, T _x , T _L, and T _m temperatures as ΔT and GFA; however, relatively larger values of this parameters in alloys containing larger Sn content were preserved. In difference to the previously published results, in the case of the amorphous alloys containing small Nb and Sn additions, a noticeable amount of the quenched-in crystalline phases was not confirmed, at least of the micrometric sizes. In the case of the alloys containing Sn or both Sn and Nb, two slightly different amorphous phase compositions were detected, suggesting separation in the liquid phase. Phase composition of the alloys determined after amorphous phase crystallization was similar for all compositions. The phases Cu₈Zr_3, CuTiZr, and Pd₃Zr were mainly identified in the proportions dependent on the alloy compositions.     

Zr-Co(Cu)-Al bulk metallic glasses with optimal glass-forming ability and their compressive properties

The formation of bulk metallic glasses (BMGs) in the ternary Zr₅₆Co₂₈Al₁₆ and quaternary Zr₅₆Co_28–xCu_xAl₁₆ (x=2, 4, 5, 6, 7, mole fraction, %) glassy alloys was investigated via the copper mold suction casting method. The main purpose of this work was to locate the optimal BMG-forming composition for the quaternary ZrCo(Cu)Al alloys and to improve the plasticity of the parent alloy. The X-ray diffractometry (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) were used to investigate the glassy alloys structure and their glass forming ability (GFA). In addition, the compression test, microhardness, nano-indentation and scanning electron microscopy (SEM) were utilized to discuss the possible mechanisms involved in the enhanced plasticity achievement. The highest GFA among Cu-containing alloys was found for the Zr₅₆Co₂₂Cu₆Al₁₆ alloy, which was similar to that of the base alloy. Furthermore, the plasticity of the base alloy increased significantly from 3.3% to 6% for the Zr₅₆Co₂₂Cu₆Al₁₆ BMG. The variations in the plasticity and GFA of the alloys were discussed by considering the positive heat of mixing within Cu and Co elements.     

Viscosity and fragility of the supercooled liquids and melts from the Fe–Co–B–Si–Nb and Fe–Mo–P–C–B–Si glass-forming alloy systems

The dynamic viscosity of four Fe-based bulk metallic glass-forming alloys, [(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]₉₆Nb₄ (alloy A), {[(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]_0.96Nb_0.04}_99.5Cu_0.5 (alloy B), Fe₇₄Mo₄P₁₀C_7.5B_2.5Si₂ (alloy C) and (Fe_0.9Ni_0.1)₇₇Mo₅P₉C_7.5B_1.5 (alloy D), was investigated as a function of temperature in the supercooled liquid region, as well as above the melting point. The alloy B is Cu-added alloy A, while the alloy D was obtained upon fine-tuning the alloy C composition. All these alloys may form bulk metallic glasses upon copper mold casting. The viscosities in the supercooled liquid region were calculated using the data obtained upon parallel plate rheometry measurements, as well as upon differential scanning calorimetry (DSC). The values of the supercooled fragility parameter m, 61, 66, 52 and 60 for the alloys A, B, C and D respectively, indicate that these alloys are intermediate glass formers. The behavior of the same alloys, in the molten state, was studied using a high temperature torsional oscillation cup viscometer. The values of the corresponding fragility parameter M was calculated as 5.03, 5.91, 4.25, 4.93 for the alloys A, B, C and D, respectively. They confirm the supercooled liquid behavior and predict that the alloys A and C may form glasses easier than the fine-tuned compositions B and D. Angell plot is constructed for the entire range of viscosities and the values from both regions, i.e. above melting point and supercooled liquid region, fit well with the model.     

Thermodynamics of equilibrium and partitionless solidifications in glass forming binary eutectic alloys

T₀ curves in the phase diagrams have been proven useful to understand thermodynamically glass formation in metallic alloys, emphasizing the importance of the metastable solid solutions crystallized partitionlessly. Here we focus on four typical binary eutectic alloys with distinct glass-forming abilities and interatomic interactions, Ag₆₀Cu₄₀, Sb_17.5Pb_82.5, Au_81.4Si_18.6, and Ni₂₄Zr₇₆. The thermodynamics involved in the liquid–solid solution transition at T₀ temperatures for the alloys of eutectic compositions are quantified, and the validity of the thermodynamic properties is evaluated. The comparison of the melting entropies for the equilibrium and partitionless solidifications reveals a basic relation. Based on the thermodynamics of the equilibrium phases and the solid solutions, an understanding of the glass formation of metallic alloys is proposed.     

Compositional optimization of glass forming alloys based on critical dimension by using artificial neural network

An artificial neural network (ANN) model was developed for simulating and predicting critical dimension d_c of glass forming alloys. A group of Zr-Al-Ni-Cu and Cu-Zr-Ti-Ni bulk metallic glasses were designed based on the d_c and their d_c values were predicted by the ANN model. Zr-Al-Ni-Cu and Cu-Zr-Ti-Ni bulk metallic glasses were prepared by injecting into copper mold. The amorphous structures and the determination of the d_c of as-cast alloys were ascertained using X-ray diffraction. The results show that the predicted d_c values of glass forming alloys are in agreement with the corresponding experimental values. Thus the developed ANN model is reliable and adequate for designing the composition and predicting the d_c of glass forming alloy.     

Diffusion and viscous flow in bulk glass forming alloys

We review radiotracer diffusion and isotope measurements in bulk glass forming alloys from the glassy state to the equilibrium melt and compare diffusion and viscous flow. In the glassy as well as in the deeply supercooled state below the critical temperature T_c, where the mode coupling theory predicts a freezing-in of liquid-like motion, very small isotope effects indicate a highly collective hopping mechanism. Not only in the glassy state but also in the supercooled state below T_c the temperature dependence of diffusion is Arrhenius-like with an effective activation enthalpy. A clear decoupling takes place between the diffusivities of the individual components of the alloys and between time scales related to diffusive transport and viscous flow. While the component decoupling is small for the smaller components a vast decoupling of more than 4 orders of magnitude is observed in Pd–Cu–Ni–P alloys between the diffusivity of the large majority component Pd and of the smaller components at the glass transition temperature T_g. The diffusivities of all components merge close to the critical temperature T_c of mode coupling theory. Above T_c, the onset of liquid-like motion is directly evidenced by a gradual drop of the effective activation energy. This strongly supports the mode coupling scenario. The isotope effect measurements show atomic transport up to the equilibrium melt to be far away from the regime of uncorrelated binary collisions. For Pd, in contrast to the behavior of single component molecular glass formers, the Stokes–Einstein equation even holds in the entire temperature range below T_c over at least 14 orders of magnitude. Apparently, the majority component Pd forms a slow subsystem in which the other elements move fast. Rearrangement of the Pd atoms thus determines the viscous flow behavior. The decoupling of atomic mobility seems to arise from a complex interplay between chemical short order and atomic size effects that gets more pronounced on approaching the glass transition temperature. The ability of the bulk glass forming alloys to form a slow subsystem in the liquid state appears to be a key to the understanding of their excellent glass forming properties.     

Topological instability and glass forming ability of Al–Ni–Sm alloys

The thermal crystallization of Al-based metallic glasses can be described in association with the topological instability λ criterion. In the present work, we report on the crystallization behavior and glass forming ability of Al-rich, Al–Ni–Sm alloys, designed with compositions corresponding to the same topological instability condition of λ ≈ 0.1. Amorphous melt-spun alloys were prepared with the following compositions, varying the ratio of Ni and Sm elements: Al_87.5Ni₄Sm_8.5, Al_83.5Ni₁₀Sm_6.5, Al_80.5Ni_14.5Sm₅ and Al_76.5Ni_20.5Sm₃. The glass forming ability of each alloy composition was evaluated based on the thermal parameters obtained from DSC runs and on X-ray diffraction patterns. Better glass forming ability was observed in compositions whose Sm content was increased and Ni content reduced. Thermal crystallization of the alloys with low Sm content showed only one crystallization peak and no glass transition event. In alloys with higher rare-earth content, a glass transition event was clearly detected before the crystallization event. The results are interpreted considering the different types and proportions of Sm–Al and Ni–Al clusters that can be formed in the alloys along the λ ≈ 0.1 line. They also emphasize the relevance of these different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallization.     

Development of FeNiNbSiBP bulk metallic glassy alloys with excellent magnetic properties and high glass forming ability evaluated by different criterions

Fe₃₈Ni₃₈Nb_2.5B_21.5−x−yP_xSi_y (x, y = 1–8) bulk metallic glassy alloys with high glass forming ability and excellent magnetic properties were developed. Bulk samples with maximum diameters of 3 mm are fabricated by copper mold casting method. The glassy alloys have large ΔT_x of 40–70 K. The alloys exhibit excellent magnetic properties like extremely low H_c of 0.5–0.8 A/m, high μ_e of 1.6–2.85 × 10⁴ and comparatively high B_s of 0.6–0.8 T which changes regularly with the content variations of P, B and Si. By ascertaining applicability of the empirical GFA criterions, T_rg, α, β and γ can be used in evaluating the GFA of FeNiBSiPNb system alloys.     

High-strength Cu-based bulk glassy alloys in Cu–Zr–Ti and Cu–Hf–Ti ternary systems

New Cu-based bulk glassy alloys were formed in Cu–Zr–Ti and Cu–Hf–Ti systems by the copper mold casting method. The critical diameter is 4 mm for the Cu₆₀Zr₃₀Ti₁₀ and Cu₆₀Hf₂₅Ti₁₅ alloys which are larger than 1 mm for the Cu₆₀Zr₄₀ and Cu₆₀Hf₄₀ glassy alloys. The substitution of Zr or Hf for Ti causes an increase in the glass-forming ability (GFA). As the Ti content increases, the glass transition temperature (T_g), crystallization temperature (T_x), and the supercooled liquid region ΔT_x(=T_x−T_g) decrease for both Cu₆₀Zr_40−xTi_x and Cu₆₀Hf_40−xTi_x alloys. In contrast, the liquid temperature (T_l) has a minimum value of 1127 K for the Cu₆₀Zr₂₀Ti₂₀ alloy and 1175 K for the Cu₆₀Hf₂₀Ti₂₀ alloy, resulting in a maximum T_g/T_l of 0.63 and 0.62, respectively. The alloys with the highest T_g/T_l value showed the highest GFA for these Cu-based alloys. The bulk glassy alloys exhibit high tensile fracture strength of 2000–2160 MPa, compressive fracture strength of 2060–2150 MPa and compressive plastic elongations of 0.8–1.7%. The finding of the new Cu-based bulk glassy alloys with high GFA, high fracture strength above 2000 MPa and distinct plastic elongation is encouraging for the future development of a new type of bulk glassy alloy which can be used for structural materials.     

Thermal, structural and magnetic properties of some zinc phosphate glasses doped with manganese ions

(MnO)_x·(P₂O₅)₄₀·(ZnO)_60−x glasses containing different concentrations of MnO ranging from 0 to 20 mol% were prepared by the melt-quenching technique. The samples had a fixed P₂O₅ content of 40 mol% and the MnO:ZnO ratio was varied. The thermal, structural and magnetic properties of these glasses were investigated by means of differential thermal analysis (DTA), electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Compositional dependence of the glass transition (T_g), crystallization (T_p) and melting temperatures were determined by DTA investigations. From the dependence of the T_g on the heating rate (a), the activation energy of the glass transition (E_g) was calculated. The fragility index (F) for the studied glasses was determined to see whether these materials are obtained from kinetically strong-glass-forming (KS) or kinetically fragile-glass forming (KF) liquids. The EPR spectra of the studied glasses revealed absorptions centered at g ≈ 2.0, 3.3 and 4.3. The compositional variations of the intensity and line width of these absorption lines was interpreted in terms of the variation in the concentration of the Mn²⁺ and Mn³⁺ ions in the glass and the interaction between the manganese ions. EPR and magnetic susceptibility data reveal that both Mn²⁺ and Mn³⁺ ions are present in the studied glasses, their relative concentration being dependent on the glass composition. Magnetic susceptibility data reveal an antiferromagnetic interaction between the manganese ions for the glasses containing 20 mol% MnO.     

Effect of oxygen impurity on long-term thermal stability of Zr-based metallic glasses below glass transition temperature

1Introduction Metallic glasses as disordered solids are thermo-dynamically metastable at the temperature below theirglass transition temperatures,Tg.Phase transformation ofdevitrification being activated by time and temperaturecan occur not only above Tg …     

Fe-Co-Ni-Cr-Mo-C-B-Y系大块金属玻璃的热稳定性、晶化行为、维氏硬度和磁性能

研究Fe41Co7-xNixCr15Mo14C15B6Y2(x=0,1,3,5)大块金属玻璃的热稳定性、晶化行为、维氏硬度和磁性能.通过铜模铸造法制备Fe41Co7-xNixCr15Mo14C15B6Y2(x=0,1,3,5)大块金属玻璃.利用差示扫描量热法和等温热处理法研究这些金属玻璃的热稳定性和晶化行为.在室温下利用维氏硬度计测量试样经过不同温度和时间退火后的硬度,并对它们的磁学性质进行表征.实验结果表明,少量Ni元素的加入没有增大过冷液相区间和玻璃形成能力,但是改变合金的初始晶化行为,增大晶化激活能.少量Ni元素的加入能够细化最终晶化组织中的晶粒大小.初晶相使合金的硬度降低,但随着热处理温度的升高,所有合金的硬度都明显提高,原因是析出了大量的碳化物和硼化物.退火温度对合金的磁性能有很大影响,少量Ni元素的加入阻止了合金在高温退火后从顺磁态向铁磁态的转变.     

A new glass-forming ability criterion for bulk metallic glasses

A new indicator of glass-forming ability (GFA) for bulk metallic glasses (BMGs) is proposed based on crystallization processes during cooling and reheating of the supercooled liquid. The interrelationship between this new parameter and the critical cooling rate or critical section thickness is elaborated and discussed in comparison with two other representatives, i.e. reduced glass transition temperature T_rg (=T_g/T_l, where T_g and T_l are the glass transition temperature and liquidus temperature, respectively) and supercooled liquid range ΔT_xg (=T_x−T_g, where T_x is the onset crystallization temperature and T_g the glass transition temperature). Our results have shown that ΔT_xg alone cannot infer relative GFA for BMGs while the new parameter γ, defined as T_x/(T_g+T_l), has a much better interrelationship with GFA than T_rg. An approximation of the critical cooling rate and critical section thickness for glass formation in bulk metallic glasses is also formulated and evaluated.     

Local atomic arrangements and their topology in Ni–Zr and Cu–Zr glassy and crystalline alloys

Different experimental techniques (X-ray diffraction, neutron diffraction with isotopic substitution, extended X-ray absorption spectroscopy) and theoretical methods (reverse Monte-Carlo simulation, molecular dynamics modelling, Voronoi analysis) were applied to elucidate the atomic structure of Ni–Zr and Cu–Zr alloys in glassy and crystalline states and to explain differences in the glass-forming abilities of the Ni₆₄Zr₃₆ and Cu₆₅Zr₃₅ compositions. Both glasses show similar strong topological ordering, but it is established that the degree of chemical ordering is much more pronounced in Ni₆₄Zr₃₆ glass than in Cu₆₅Zr₃₅ glass. The short-range atomic order and topology in the glassy and crystalline structures are remarkably different, and these differences are presumed to hinder crystal nucleation and growth, hence promoting glass formation upon fast cooling of the Ni₆₄Zr₃₆ and Cu₆₅Zr₃₅ liquid alloys. The larger differences observed for the Cu₆₅Zr₃₅ alloy in glassy and crystalline states are suggested to play a decisive role in increasing its bulk-glass-forming ability.     

On calorimetric study of the fragility in bulk metallic glasses with low glass transition temperature: (Ce0.72Cu0.28)90−x Al10Fex (x = 0, 5 or 10) and Zn38Mg12Ca32Yb18

Compared with conventional bulk metallic glasses, Ce-based and Zn-based bulk metallic glasses have received considerable attention because of their possible application as structural and functional materials. Kinetic fragility parameter m in amorphous material presents degree of deviations from the Arrhenius law above the glass transition temperature (T_g) of the material. Kinetic fragility parameter (m) and Kauzmann temperature (T_K) in (Ce_0.72Cu_0.28)_90?x Al₁₀Fe_x (x = 0, 5 or 10) and Zn₃₈Mg₁₂Ca₃₂Yb₁₈ bulk metallic glasses have been determined by differential scanning calorimetry (DSC). Results show that Zn₃₈Mg₁₂Ca₃₂Yb₁₈ presents a higher m than (Ce_0.72Cu_0.28)_90?x Al₁₀Fe_x (x = 0, 5 or 10). The activation energies E_g for glass transition are 1.51 eV (x = 0), 1.59 eV (x = 5) and 1.83 eV (x = 10) in (Ce_0.72Cu_0.28)_90?x Al₁₀Fe_x (x = 0, 5 or 10), and 3.59 eV in Zn₃₈Mg₁₂Ca₃₂Yb₁₈, respectively. The values of E_g increase with increasing the Fe content in (Ce_0.72Cu_0.28)_90?x Al₁₀Fe_x (x = 0, 5 or 10) bulk metallic glasses. Kinetic fragility parameter m of bulk metallic glasses increases with the glass transition temperature T_g of bulk metallic glasses, in agreement with previous investigations.