Crystallization kinetics in Cu46Zr45Al7Y2 bulk metallic glass by differential scanning calorimetry (DSC)

Crystallization transformation kinetics in isothermal and non-isothermal (continuous heating) modes were investigated in Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass by differential scanning calorimetry (DSC). In isochronal heating process, activation energy for crystallization at different crystallized volume fraction is analyzed by Kissinger method. Average value for crystallization in Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass is 361 kJ/mol in isochronal process. Isothermal transformation kinetics was described by the Johnson-Mehl-Avrami (JMA) model. Avrami exponent n ranges from 2.4 to 2.8. The average value, around 2.5, indicates that crystallization mechanism is mainly three-dimensional diffusion-controlled. Activation energy is 484 kJ/mol in isothermal transformation for Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass. These different results were discussed using kinetic models. In addition, average activation energy of Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass calculated using Arrhenius equation is larger than the value calculated by the Kissinger method in non-isothermal conditions. The reason lies in the nucleation determinant in the non-isothermal mode, since crystallization begins at low temperature. Moreover, both nucleation and growth are involved with the same significance during isothermal crystallization. Therefore, the energy barrier in isothermal annealing mode is higher than that of isochronal conditions.     

Study on crystallization kinetics of Al65Cu20Ti15 amorphous alloy

The crystallization behavior and thermal stability of amorphous phases of Al₆₅Cu₂₀Ti₁₅ alloy obtained by mechanical alloying were investigated by using in-situ X-ray diffraction and differential scanning calorimetry (DSC) under non isothermal and isothermal conditions. The result of a Kissinger analysis shows that the activation energy for crystallization is 1131 kJ/mol. The higher stability against crystallization of Al₆₅Cu₂₀Ti₁₅ amorphous alloy is attributed to the stronger interaction of atoms in the Al-Cu-Ti system and formed of complicated compound like Al₅CuTi₂ and Al₄Cu₉ as primary phases. The isothermal crystallization was modeled by using the Johnson-Mehl-Avrami (JMA) equation. The Avarami exponents suggest that the isothermal crystallization is governed by a three-dimensional diffusion-controlled growth.     

Crystallization kinetics of the Zr61Al7.5Cu17.5Ni10Si4 alloy using isothermal DSC and TEM observation

The crystallization behavior and microstructure development of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During isothermal annealing of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy at 703 K, Zr₂Cu crystals with an average size of about 5 nm were first observed during the early stages (30% crystallization) of crystallization by TEM. The Zr₂Cu crystal size increased with annealing time and attained an average size of 20 nm corresponding to the stage of 80% crystallization. In addition, the change in particle size with increasing annealing time exhibited a linear relationship between grain growth time and the cube of the particle size for the Zr₂Cu type crystalline phase. This indicates that the crystal growth of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy belongs to a thermal activated process of the Arrhenius type. The activation energy for the grain growth of Zr₂Cu is 155 ± 20 kJ/mol in the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ amorphous alloy. The lower activation energy for grain growth in compared to that for crystallization in Zr₆₅Cu₃₅ 440 kJ/mol crystal corresponds to the rearrangement of smaller atoms in the metallic glass, Al or Si (compare to Zr).     

Isothermal and non-isothermal crystallization kinetics in amorphous Ni45.6Ti49.3Al5.1 thin films

The crystallization kinetics in Ni_45.6Ti_49.3Al_5.1 film were studied by differential scanning calorimetry through isothermal and non-isothermal approaches. The activation energy for crystallization was determined to be 374 and 280 kJ/mol by the Kissinger and the Augis & Bennett method, respectively, in non-isothermal methods. In the isothermal annealing study, the Avrami exponents were in the range of 2.78-3.80 between 793 and 823 K, suggesting that the isothermal annealing was governed by three dimensional diffusion-controlled growth for Ni_45.6Ti_49.3Al_5.1 thin films, in which the activation energy of nucleation is higher than that of growth. In addition, the transformation rate curves of Ni_45.6Ti_49.3Al_5.1 film were also constructed by isothermal methods. The crystallization kinetics of amorphous Ni_45.6Ti_49.3Al_5.1 film can thus be appreciated and the transformation rate also can be employed to control the degree of crystallization.     

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.     

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.     

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.     

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.     

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.     

Phase transformation and crystallization kinetics of melt-spun Ni60Nb20Zr20 amorphous alloy

The glass transition and crystallization kinetics of melt-spun Ni₆₀Nb₂₀Zr₂₀ amorphous alloy ribbons have been studied under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC). The dependence of glass transition and crystallization temperatures on heating rates was analyzed by Lasocka's relationship. The activation energies of crystallization, E_x, were determined to be 499.5 kJ/mol and 488.6 kJ/mol using the Kissinger and Ozawa equations, respectively. The Johnson–Mehl–Avrami equation has also been applied to the isothermal kinetics and the Avrami exponents are in the range of 1.92–2.47 indicating a diffusion-controlled three-dimensional growth mechanism. The activation energy obtained from the Arrhenius equation in the isothermal process was calculated to be E_x = 419.5 kJ/mol. The corresponding three dimensional (3D) time–temperature–transformation (TTT) diagram of crystallization for the alloy has been drawn which provides the information about transformation at a particular temperature. In addition, the intermetallic phases and morphology after thermal treatment have been identified by X-ray diffraction (XRD) and scanning electron microscope (SEM).     

Combined in-situ SAXS/WAXS and HRTEM study on crystallization of (Cu60Co40)1 − xZrx metallic glasses

CuZr as well as CoZr are well known metallic glass-formers in a wide compositional range. Since the binary Cu-Co system exhibits a metastable liquid-liquid miscibility gap, i.e. Cu and Co tend to separate from each other, the ternary Cu-Co-Zr system is a promising candidate to form phase separated glass-glass composites. In this work (Cu₆₀Co₄₀)_1 − xZr_x metallic glasses with relatively low Zr contents of x = 37 and x = 32 were prepared by melt spinning and investigated by in-situ small-angle and wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). Certain heat treated samples were additionally investigated by high-resolution transmission electron microscopy (HRTEM). Even for x = 32 there are no indications for any kind of phase separation in the as-quenched state within experimental resolution, i.e. the critical temperature T_c for a liquid-liquid phase separation has already decreased from 1556 K for binary Cu₆₀Co₄₀ to a temperature below the glass transition temperature T_g = 762(5)K found for (Cu₆₀Co₄₀)₆₈Zr₃₂. Combined in-situ SAXS/WAXS and HRTEM investigations reveal that thermal annealing also does not induce an amorphous-amorphous phase separation. Instead the formation of nano crystallites of a so far unknown Cu-rich/Zr-poor phase with relatively low activation energy for crystallization E_a = 116(7) kJ/mol at temperatures far below the crystallization temperature deduced from DSC measurements is observed.     

Crystallization kinetics of Fe73.5−xMnxCu1Nb3Si13.5B9 (x = 0, 1, 3, 5, 7) amorphous alloys

In this study, we have investigated the effect of substituting Mn for Fe on the crystallization kinetics of amorphous Fe_73.5−xMn_xCu₁Nb₃Si_13.5B₉ (x = 1, 3, 5, 7) alloys. The samples were annealed at 550 °C and 600 °C for 1 h under an argon atmosphere. The X-ray diffraction analyses showed only a crystalline peak belonging to the α-Fe(Si) phase, with the grain size ranging from 12.2 nm for x = 0 to 16.7 nm for x = 7. The activation energies of the alloys were calculated using Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The Avrami exponent n was calculated from the Johnson-Mehl-Avrami equation. The activation energy increased up to x = 3, then decreased with increasing Mn content. The values of the Avrami exponent showed that the crystallization is typical diffusion-controlled three-dimensional growth at a constant nucleation rate.     

Non-isothermal crystallization kinetics of La2CaB10O19 from glass

The non-isothermal crystallization kinetics of La₂CaB₁₀O₁₉ (LCB) from a La₂O₃-CaO-B₂O₃ glass was studied. Differential thermal analysis methods were performed on three glass powders to obtain the kinetic parameters of LCB crystallization mechanism. The activation energies for overall crystallization (E), obtained by the methods of Kissinger and Ozawa, were in the range of 479-569 kJ/mol. Multiple (five) analysis methods were used to estimate the Avrami exponent (n), which could consequently be reduced into the single value of n = 3.1 ± 0.3. The growth morphology index (m) of LCB was corroborated by microscopy (optical and electron) images, which revealed a three dimensional growth. Energy dispersive spectroscopy confirmed that LCB is the crystallizing phase from the glass by an interface controlled mechanism. The parameters of the Johnson-Mehl-Avrami kinetic model for the analysis of LCB crystallization from glass were found to be n = m = 3.     

Load relaxation behavior of a Zr41.2Ti13.8Cu12.5Ni10 Be22.5 bulk metallic glass

The load relaxation behavior within the supercooled liquid region of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass has been investigated. To explain the relationship between normalized stress and relaxation time, two different stress relaxation modes such as a Kohlrausch-Williams-Watts (KWW) behavior and a simple power law were applied to the short and long relaxation time regimes, respectively. The apparent activation energy for stress relaxation is 126 ± 10 kJ/mol. Flow curves were obtained by converting load-displacement data into a flow stress-strain rate relation, resulting in three different deformation characteristics through a wide strain rate region interpreted in terms of strain rate sensitivity. A prediction of hot workability has also been attempted by constructing a power dissipation map based on a dynamic materials model.     

A new composition zone of bulk metallic glass formation in the Cu-Zr-Ti ternary system and its correlation with the eutectic reaction

A new composition region of bulk metallic glass formation, around Cu₅₂Zr₄₀Ti₈, was discovered in the Cu-Zr-Ti ternary system, for which monolithic bulk metallic glass rods of 4 mm in diameter can be fabricated using copper mold casting. The solidification of the Cu₅₂Zr₄₀Ti₈ deeply-undercooled liquid mainly undergoes a univariant eutectic reaction, (L → Cu₁₀Zr₇ + CuZr), even though this composition was predicted to be a ternary eutectic point (L → Cu₁₀Zr₇ + CuZr + Cu₂ZrTi) by CALPHAD calculations. With respect to the deep-eutectic reaction of (L → Cu₁₀Zr₇ + CuZr) in the Cu-Zr binary alloys, alloying of Ti has a significant effect on further stabilizing the liquid, as indicated as a drop of the univariant eutectic groove, limiting the coupled growth of two crystalline phases, hence increasing the glass-forming ability.     

Crystallization kinetics determination of Pb15Ge27Se58 chalcogenide glass by using the various heating rates (VHR) method

The kinetics of crystallization of Pb₁₅Ge₂₇Se₅₈ was studied by differential scanning calorimetry non-isothermally. Various experimental methods are currently employed for determining the kinetic parameters of crystallization in a glassy system. These parameters include the activation energy of crystallization E (kJ/mol), the kinetic exponent n and the frequency factor K_o (s⁻¹). Recently, a new method (VHR method) has been derived from Johnson-Mehl-Avrami (JMA) transformation rate equation to calculate - in sequence - the crystallization kinetic parameters of a glassy system. The VHR technique has been used to estimate the crystallization parameters of Pb₁₅Ge₂₇Se₅₈ chalcogenide glass under non-isothermal conditions. The average value of E, n and K_o are found equal to 181.74 ± 0.58 (kJ/mol), 1.085 ± 0.023 and (9.196 ± 0.716) × 10¹² (s⁻¹), respectively. The kinetic exponent, n ≈ 1 indicates a surface nucleation mechanism.     

Effects of Sn addition on the glass forming ability and crystallization behavior in Ni-Zr-Ti-Si alloys

The effect of Sn substitution for Si on the glass forming ability (GFA) and crystallization behavior has been studied in Ni₅₉Zr₂₀Ti₁₆Si_5 − xSn_x (x=0, 3, 5) alloys. A bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy with diameter up to 3 mm can be fabricated by injection casting. Partial substitution of Si by Sn in Ni₅₉Zr₂₀Ti₆Si_5 − xSn_x alloys improves the glass forming ability. The improved GFA of the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy is can be explained based on the lowering of liquidus temperature. The crystallization sequence becomes completely different with addition of Sn. The amorphous Ni₅₉Zr₂₀Ti₁₆Si₅ alloy crystallizes via precipitation of only a cubic NiTi phase in the first crystallization step, whereas the amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy crystallizes via simultaneous precipitation of orthorhombic Ni₁₀(Zr,Ti)₇ and cubic NiTi phases. Addition of Sn in the Ni₅₉Zr₂₀Ti₁₆Si₅ alloy suppresses the formation of the primary cubic NiTi phase. The bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy exhibits high compressive fracture strength of about 2.7 GPa with a plastic strain of about 2%.     

An investigation of the kinetic transformation mechanism of Ge12.5Te87.5 chalcogenide glass under non-isothermal regime

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation in Ge_12.5Te_87.5 chalcogenide glass. The kinetic parameters of glassy Ge_12.5Te_87.5 under non-isothermal conditions are analyzed by the model-free and model-fitting approaches from a series of experiments at different constant heating rates (5-50 K/min). The effective activation energy of crystallization was determined by analyzing the data using the isoconversional methods of Kissinger-Akahira-Sunose (KAS), Tang, Starink, Flynn-Wall-Ozawa (FWO) and Vyazovkin. The analysis of the present data shows that the effective activation energy of crystallization is constant throughout the entire interval of conversions and hence with temperature. The transformation mechanism examined using the local Avrami exponents indicates that one mechanism (three-dimensional growth) is responsible for the transformation process for all heating rates used. The reaction model that may describe the transformation process of the Ge_12.5Te_87.5 chalcogenide glass is the Avrami-Erofeev model (g(α) = [− ln(1 − α)]^1/n) with n = 3 for all heating range at the whole range of crystallized fraction (α = 0.05-0.95). A good agreement between the experimental and the reconstructed (α-T) curves has been achieved. The transformation from amorphous to crystalline phase in Ge_12.5Te_87.5 chalcogenide glass demonstrates a single-step mechanism.     

Non-isothermal crystallization kinetics study on new amorphous Ga20Sb5S75 and Ga20Sb40S40 chalcogenide glasses

Bulk glasses of the system Ga₂₀Sb_xS_80−x (x = 5 and 40) were prepared for the first time by the known melt quenching technique. Non-isothermal differential scanning calorimetric (DSC) measurements of as-quenched Ga₂₀Sb_xS_80−x (x = 5 and 40) chalcogenide glasses reveal that the characteristic temperatures e.g. the glass transition temperature (T_g), the temperature corresponding to the maximum crystallization rate (T_p) recorded in the temperature range 400-650 K for x = 5 and 480-660 K for x = 40 are strongly dependent on heating rate and Sb content. Upon heating, these glasses show a single glass transition temperature (T_g) and double crystallization temperatures (T_p1 and T_p2) for x = 5 which overlapped and appear as a single crystallization peak (T_p) for x = 40. The activation energies of crystallization E_c were evaluated by three different methods. The crystallization data were examined in terms of recent analysis developed for non-isothermal conditions. The crystalline phases resulting from (DSC) have been identified using X-ray diffraction.     

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.