Crystallization, neutron irradiation, and annealing studies in glassy Ti50Be40Zr10

We have studied the crystallization and the effects of neutron irradiation and annealing on glassy Ti₅₀Be₄₀Zr₁₀ (Metglas 2204) using resistivity measurements. The resistivity was measured from 2–1000 K for as-received Metglas 2204. Jumps in the resistivity were observed at the various stages during the crystallization process in agreement with previously reported results. Further, the negative temperature dependence of resistivity is affected by neutron irradiation and annealing. In both cases, interpretation of the results in terms of the Ziman theory of liquid metals indicates that the structure factor has sharpened. In the neutron irradiation case the structural relaxation is most likely the result of radiation enhanced diffusion due to the formation of vacancies.     

Glass formation ability and mechanical properties of Ti40Cu40Zr10Ni10 alloy

Melt-spun ribbon and bulk samples in cylindrical rod form with diameter ranging from 2 mm to 4 mm of Ti₄₀Cu₄₀Zr₁₀Ni₁₀ alloy were prepared by melt-spinning technique and copper mould casting method, respectively. The microstructure, thermal stability and mechanical properties of the bulk samples were investigated. A completely glassy single phase is formed in the 2 mm rod sample. Increasing the diameter of the rod samples resulted in the formation of CuTi crystalline phase in the 3 mm and 4 mm rod samples. The 2 mm single glassy rod sample exhibited a large supercooled liquid region ΔT_x = 58 K and γ = T_x/(T_g + T_l) is 0.390, which indicated that the alloy possessed a good glass-forming ability. The bulk samples also exhibited good mechanical properties. The 2 mm rod sample showed the highest yield strength of about 2086 MPa. The 3 mm rod sample not only showed high yield strength of about 2000 MPa, but also enhanced plastic strain of about 0.71%.     

Pressure and heating rate dependence of the crystallization temperature for amorphous (Fe65Ni35)75P16B6Al3 and Ti50Be40Zr10

The crystallization temperature, T_x, was determined at constant heating rate, $\text{R =}\text{T}\text{?}\text{? 7}\text{K min}{}^{\mathrm{?1}}$, by monitoring the electrical resistance. Such experiments were carried out under pressures up to 2.5 GPa, and the resulting dT_x/dP was 15.9 K GPa^?1 for (Fe₆₅Ni₃₅)₇₅P₁₆B₆Al₃ and 8.7 K GPa^?1, 8.1 K GPa^?1 for the two crystallization processes in Ti₅₀Be₄₀Zr₁₀. The activation energies of crystallization under atmospheric pressure were obtained from measurements of T_x at rates from 0.05 K min^?1 ?55 K min^?1, analysed by plotting ln(T_x²R^?1) versus T_x^?1.     

Crystallization of amorphous Cu60Zr40 prepared by magnetron sputter deposition

The crystallization of amorphous Cu₆₀Zr₄₀ prepared by magnetron sputter deposition was studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. Calorimetric results were similar to those reported in the literature for liquid-quenched Cu₆₀Zr₄₀, including the manifestation of a glass transition. Crystallization above and below the glass transition temperature, T_g, occurred by nucleation and growth of the equilibrium phase, Cu₁₀Zr₇. This phase was characterized by convergent beam electron diffraction. With isothermal annealing below T_g, the time scale for crystallization indicated that the vapor-quenched alloy was kinetically more stable than the liquid-quenched alloy. This was interpreted as a difference in the quenched-in structures, produced by the different synthesis methods. During longer anneals, TEM analysis indicated that the structure was being contaminated by oxygen.     

Structural relaxation of Ti40Zr25Ni8Cu9Be18 bulk metallic glass

Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ bulk metallic glass has a unique quenched-in nuclei/amorphous matrix structure. The crystallization of quenched-in nuclei, when the experimental isothermal annealing time is within its incubation time, may not disturb the enthalpy relaxation, which makes it have the accordingly common enthalpy relaxation behavior with amorphous materials. The alloy's annealing time dependence of recovery enthalpy follows a stretched exponential function with the mean relaxation time obeying an Arrhenius law. The equilibrium recovery enthalpy ΔH_T^eq, mean relaxation time τ and stretching exponent β are all dependent on the annealing temperature, and generally, a higher annealing temperature comes with a lower value of ΔH_T^eq, τ and a higher value of β. Two parameters, β_g and τ_g, representing the stretching exponent and the mean structural relaxation time at the calorimetric glass transition temperature, respectively, are correlated with glass forming ability and thermal stability, respectively. For Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ BMG, the high value of β_g, which is much higher than 0.84 and approaches unity, reveals its good glass forming ability, while, on the other hand, the low value of τ_g indicates a worse thermal stability compared with typical BMGs.     

Kinetic analysis of the isochronal crystallization of Ti40Zr25Ni8Cu9Be18 metallic glass

The isochronal crystallization kinetics of the Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ metallic glass has been investigated by differential scanning calorimetry (DSC). Results indicate that the two crystallization events of this metallic glass cannot be well-described by the classic Johnson-Mehl-Avrami (JMA) kinetic equation. The kinetic equation considering the impingement effect has been found more applicable for describing the isochronal crystallization kinetics of this amorphous alloy. Accurate values of kinetic parameters were determined by fitting the theoretical DSC data to experimental curves. The kinetic parameters change in different crystallization stages and show strong heating rate dependence. Reasons of the deviation from the JMA kinetics for the isochronal crystallization of Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ metallic glass were discussed.     

Crystallization of amorphous Ni35Zr65 and Fe40Ni40P14B6 under proton irradiation

Two amorphous alloys, Ni₃₅Zr₆₅ and Fe₄₀Ni₄₀P₁₄B₆, were irradiated using 400 keV protons at several temperatures below the crystallization temperature, T_x, to peak doses in the neighborhood of 3.5 to 4.5 dpa. Irradiation at 250°C resulted in the crystallization of both alloys, which were examined by transmission electron microscopy of samples electrolytically polished to various distances from the irradiated surface to study the effect of dose. Samples masked from the proton beam remained amorphous during irradiation. In the Ni₃₅Zr₆₅ alloy crystallization of the equilibrium phases propagated throughout the entire sample, while the in the Fe₄₀Ni₄₀P₁₄B₆ alloy crystallization was observed only in those parts of the samples lying within the proton range. Neither alloy crystallized during irradiation at 100°C. In both these alloys the amorphous phase is therefore evidently stable at irradiation temperatures below approximately 0.6 T_x. An examination of the literature on irradiation damage of binary alloys and intermetallic compounds suggests that there is a tendency for initially amorphous alloys to remain amorphous at irradiation temperatures, T_irr < 0.3 T_L, where T_L (≈T_x) is the “melting” temperature (either a eutectic, peritectic or congruent melting temperature). Also, these same alloys, even when they are initially crystalline, transform to the amorphous state during irradiation at T < 0.3 T_L. Some other crystalline alloys have also been shown to transform to the amorphous state at T_irr < 0.3 T_L even though they have never been prepared in this condition by rapid quenching techniques. The temperature 0.3 T_L appears to be a lower limit, however, since the crystalline to amorphous transformation occurs in many of these alloys at temperatures greater than 0.3 T_L. It is suggested, by analogy with results on void formation in irradiated metals, that this low temperature limit is related to the low mobility of vacancies in these materials, although the mechanism of crystallization, or conversely amorphization, is not fully understood.     

Crystallization processes in amorphous Zr54Cu46 alloy

The crystallization of amorphous Zr₅₄Cu₄₆ alloy was investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The experimental results show that an endothermic peak in DSC traces for amorphous Zr₅₄Cu₄₆ alloy exists at about 1006 K, indicating following eutectoid reaction occurs, namely, Cu₁₀Zr₇+CuZr₂↔CuZr in amorphous Zr₅₄Cu₄₆ alloy during heating. With increasing the heating rate, the glass transition temperature T_g and onset crystallization temperature T_x of amorphous Zr₅₄Cu₄₆ alloy increase in parallel, and the supercooled liquid region ΔT_x (=T_x−T_g) holds almost constant with an average value of 44 K. Both XRD and TEM results prove that Cu₁₀Zr₇ and CuZr₂ are main crystallization products for amorphous Zr₅₄Cu₄₆ alloy under continuous heating conditions. No CuZr phase is identified because of its small precipitation amount. Finally, the crystallization processes of amorphous Zr₅₄Cu₄₆ alloy were summarized.     

Influence of outphase Cu50Ti50 amorphous alloy addition on microstructural evolution of mechanically alloyed Zr66.7Ni33.3 amorphous alloy

The influence of outphase Cu₅₀Ti₅₀ amorphous alloy addition on microstructural evolution of Zr_66.7Ni_33.3 amorphous alloy has been investigated using a mechanical alloying method. It has been found that the milling induced microstructural evolution is related to the change of peak positions of the first maximum on X-ray diffraction patterns of the as-obtained amorphous alloys. With increasing milling time, the 3 wt.% Cu₅₀Ti₅₀ addition can give rise to the cyclic amorphization transformation of the as-milled alloy. The mechanical stability of the mixing amorphous phase can be greatly enhanced with increasing Cu₅₀Ti₅₀ addition up to 10 wt.%. Moreover, the addition of outphase Cu₅₀Ti₅₀ amorphous alloy not only increases the onset crystallization temperature of Zr_66.7Ni_33.3 amorphous alloy but also alters its crystallization mode. The effect of outphase amorphous addition on the mechanical stability of the Zr_66.7Ni_33.3 amorphous phase has been discussed based upon the bond order theory.     

Crystallization kinetics of (Ni0.75Fe0.25)78Si10B12 amorphous alloy

Amorphous ribbon specimen of (Ni_0.75Fe_0.25)₇₈Si₁₀B₁₂ has been prepared by a single roller melt-spinning technique in the air atmosphere. The crystallization kinetics of the alloy has been investigated using different thermal analysis by means of continuous heating and isothermal heating. The activation energy of the alloy has been calculated by using Kissinger plot method and Ozawa plot method based on differential thermal analysis data, respectively. The products of crystallization have been analyzed by X-ray diffraction. A single phase of γ-(Fe, Ni) solid solution with grain size of about 10.3 and 18.5 nm precipitates in the amorphous matrix after annealing at temperatures 715 and 745 K, respectively. The crystallized phases are γ-(Fe, Ni) solid solution, Fe₂Si, Ni₂Si, Fe₃B and unidentified phase after annealing at 765 K. The details of nucleation and growth during the isothermal crystallization are expatiated in terms of local Avrami exponent and local activation energy.     

Crystallization of amorphous Ni55Pd35P10 alloys

The crystallization of Ni₅₅Pd₃₅P₁₀ alloys was examined by isochronal resistivity and hardness measurements, along with observations of the phase transformation in the heating stage of a transmission electron microscope (TEM). The resistivity temperature coefficient between 26 and 250°C is low (9.38 × 10^?5/°C); a few metastable phases form on crystallization. The hardness-temperature curve shows the hardness to increase as the metastable phases appear.     

Thermal stability of amorphous Mg50Ni50 alloy produced by mechanical alloying

Amorphous Mg₅₀Ni₅₀ alloy was produced by mechanical alloying (MA) of the elemental powders Mg and Ni using a SPEX 8000D mill. The alloyed powders were microstructurally characterized by X-ray diffraction (XRD). The thermal transformation of amorphous Mg₅₀Ni₅₀ into stable intermetallics (Mg₅₀Ni₅₀ → remaining amorphous + Mg₂Ni → Mg₂Ni + MgNi₂) was analyzed using the Kissinger and isoconversional methods based on the non-isothermal differential scanning calorimetry (DSC) experiments. The apparent activation energies (E_a) and the transformation diagrams, temperature-time-transformation (T-T-T) and temperature-heating rate-transformation (T-HR-T), were obtained for both processes. A good agreement was observed between the calculated transformation curves and the experimental data, which verifies the reliability of the method utilized.     

Potentiodynamic polarization studies on amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr65Cu17.5Ni10Al7.5, Zr67Ni33 and Ti60Ni40 in aqueous HNO3 solutions

Potentiodynamic polarization studies were carried out on virgin specimens of Zr-based bulk amorphous alloys Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 and Zr₆₅Cu_17.5Ni₁₀Al_7.5, and conventional-type binary amorphous alloys Zr₆₇Ni₃₃ and Ti₆₀Ni₄₀ in solutions of 0.2 M, 0.5 M and 1.0 M HNO₃ at room temperature. The values of the corrosion current density (I_corr) for the bulk amorphous alloy Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 were found to be comparable with those of Zr₆₅Cu_17.5Ni₁₀Al_7.5 in 0.2 M and 0.5 M HNO₃, but the value of I_corr for the former was almost three times more than that of the latter in 1.0 M HNO₃. In the case of conventional binary amorphous alloys, Ti₆₀Ni₄₀ showed lower value of I_corr as compared to Zr₆₇Ni₃₃ in 0.5 M and 1.0 M HNO₃ and a comparable value of I_corr in 0.2 M HNO₃. In general, the binary Ti₆₀Ni₄₀ displayed the best corrosion resistance among all the alloys in all the cases and the corrosion current density (I_corr) for all the alloys was found to increase with the increasing concentration of nitric acid. It is noticed that the bulk amorphous alloys do not possess superior corrosion resistance as compared to conventional binary amorphous alloys in aqueous HNO₃ solutions. The observed differences in their corrosion behavior are attributed to different alloy constituents and composition of the alloys investigated.     

XPS characterization of corrosion films formed on the crystalline, amorphous and nanocrystalline states of the alloy Ti60Ni40

X-ray photoelectron spectroscopy investigations were carried out on the crystalline, amorphous and nanocrystalline states of the alloy Ti₆₀Ni₄₀ after corrosion test in 1 M HNO₃ aqueous medium using potentiodynamic polarization method. Polarization plots revealed that the nanocrystalline state is more corrosion resistant than the amorphous and crystalline states of the alloy Ti₆₀Ni₄₀. The XPS characterization of the oxide film formed after corrosion tests revealed that a multiple phase oxide film is formed on the crystalline and amorphous specimens of the alloy Ti₆₀Ni₄₀ consisting of Ti²⁺, Ti³⁺ and Ti⁴⁺ species along with some unoxidized Ti in metallic form (Ti⁰) in the case of crystalline specimen whereas the oxide film formed on nanocrystalline specimen consists of only Ti²⁺ and Ti⁴⁺ species. The high corrosion resistance of nanocrystalline state is attributed to the presence of fewer oxide species in the oxide film than that of the amorphous and crystalline states of the alloy Ti₆₀Ni₄₀.     

Structure and magnetic properties of bulk amorphous Fe60Co10Ni10Zr7B13 alloy formed by mechanical synthesis and hot pressing

Formation and magnetic properties of the bulk amorphous Fe₆₀Co₁₀Ni₁₀Zr₇B₁₃ alloy are described. The amorphous powder was prepared by high-energy ball milling of the amorphous ribbon and then was pressed under high pressure and temperature to obtain a bulk alloy in the form of a disc 5 mm in diameter and 2.5 mm thick. The compacted discs are fully amorphous as confirmed by X-ray diffraction and Mössbauer spectroscopy measurements. Differential scanning calorimetry curve recorded for the amorphous ribbon shows two exothermal peaks related to two stages of crystallization. Similar thermal behavior is observed for the powder samples. Hysteresis loops obtained for the amorphous ribbon, as-milled and compacted powders reveal their soft magnetic properties.     

The effect of structural relaxation on the local structure of Cu40Zr60 amorphous alloys

Structural relaxation phenomena associated with heat treatments near the glass transition temperature range were investigated in liquid-quenched amorphous Cu₄₀Zr₆₀ alloys by means of differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and EXAFS. A kinetic study was performed by DSC in order to determine the evolution of the configurational enthalpy ($\text{3 H}{}_{\mathrm{\sigma }}$) against temperature (upon continuous heating or during isothermal annealing treatments) and to define the heat treatment suitable to obtain highly relaxed samples.SAXS results show that the structure of the relaxed samples remains homogeneous at the intermediate range of order up to at least 100 Å, whatever be the previous heat treatment. EXAFS detects a slight change in the local structure only for the most highly relaxed samples; this change could be interpreted by a variation of 0.5 atom in the coordination numbers (probably of the ZrZr pairs) or by a change of the disorder parameter of about 0.01 Å.No phase separation is detected in the relaxed amorphous Cu₄₀Zr₆₀ specimens.     

Crystallization of amorphous selenium and As0.005Se0.995

The effect of temperature on the crystallization kinetics of bulk amorphous selenium and the alloy As_0.005Se_0.995 has been studied using differential scanning calorimetry. A time-temperature-transformation (TTT) curve has been plotted from isothermal results over the temperature range 320 to 490 K, and shows the presence of two minima for both materials. Using the empirical Avrami expression for solid-state transformations, a number of kinetic parameters has been determined.     

Crystallization effects in amorphous Cd3As2 films

The amorphous to crystalline transformation due to electron beam or heat treatments was studied. From the results it was concluded that the temperature of the transformation is higher than 300°C - higher than the epitaxy temperature for the deposition process. The a→c transition proceeds in several stages. By using the “cross-cut” method the activation energy for crystallization was estimated to be 2 eV.     

Crystallization behavior of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass under the action of high-density pulsing current

The crystallization behavior of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (Vit1 BMG) under the action of high-density pulsing current (HDPC) have been studied experimentally. It has been found that high-density pulsing current can directly induce the rapid nanocrystallization of Vit1 BMG. The multiple crystallization processes of Vit1 BMG induced by HDPC have been confirmed as Amorphous → Amorphous + i-phase → Be₂Zr + Zr₂Cu + Ni₇Zr₂ + FCC phase + other phases → Zr₂Cu + Ni₇Zr₂ + FCC phase + other phases. By comparing to the crystallization behavior of Vit1 BMG induced by isothermal annealing, the crystallization temperature is reduced and crystallizing process is significantly shortened, while the sequence of crystallization process in both cases is basically same. The present results show that the HDPC has significantly influenced the crystallizing kinetics of Vit1 BMG due to that it can greatly promote the movement and rearrangement of atoms, which will result in a rapid nanocrystallization. It suggests that HDPC treatment can be an effective way to induce the rapid nanocrystallization of BMGs.