Local Avrami Exponent Research Articles

Non-isothermal crystallization behavior of Cr50Fe6Co7Mo14C15B6Y2 metallic glass with super high content of Cr and integrated merits

In present work, non-isothermal crystallization behavior for novel Cr50Fe6Co7Mo14C15B6Y2 metallic glass (MG) with super high content of Cr and excellent merits was investigated by differential scanning calorimeter and X-ray diffraction. Both of the Kissinger and Ozawa methods show that the present glass transition is much harder than other transitions for a much larger apparent activation energy (E). While, the growth process of present second crystallization event is the easiest process, since it possesses the smallest E. Meanwhile, the local activation energy established by Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall methods both exhibit a trend of increasing to the maximum value at first and then gradual decrease until the finish of the crystallization, indicating that the difficulty increases until to the maximum at first and then gradually decreases during crystallization. Moreover, all the local Avrami exponent n(x) possesses a value of about 0 <n(x) < 1.5, implying a crystallization with pre-existing nuclei for present non-isothermal crystallization. Furthermore, the glass formation melt of present MG is considered as an intermediate one with moderate thermal stability. Additionally, the alloy firstly changes from monolithic MG to a composite of amorphous matrix superimposed with the main crystalline phases ((Fe,Cr)23(C,B)6, (Cr2.5Fe4.3Mo0.1)C3, Fe3Mo3C, FeC and some unknown phases), and then the remained amorphous matrix thoroughly changes to these crystalline phases with enriched crystal planes and fraction during crystallization. The results can supply basic data for designing valid crystallization strategy to tune performances of metallic glasses with high content of Cr.

Crystallization kinetics and structural development of Bi2GeO5 glass-ceramics fabricated by the modified incorporation technique

This study focuses on the fabrication and crystallization kinetics of bismuth germanate (Bi2GeO5) crystals in glass ceramics. Bismuth germanate glass-ceramics were produced from a base glass containing 58.4 mol% Bi2O3, 23.4 mol% GeO2, and 18.2 mol% B2O3 using a modified incorporation technique. Differential thermal analysis was used to determine the crystallization temperature. The X-ray diffraction results showed a dominant peak corresponding to the pure Bi2GeO5 phase, which has an orthorhombic crystal structure. The local Avrami exponent (n(x)) and local crystallization activation energy (Ec(x)) were determined using a non-isothermal method with heating rates ranging from 5 to 20 °C/min. The results indicated that the crystal growth process of the glass-ceramics occurred in all three dimensions, with Avrami exponent values ranging from 1.79 to 2.5. The microstructure also revealed uniform crystallization across the surface and bulk diffusion of crystallites. The modified incorporation method successfully enhanced the crystallization of Bi2GeO5 glass-ceramics, resulting in the transition from one-dimensional needle-like crystals to the desired crystal dimensions.

Crystallization kinetics and nanoindentation studies of Cu46Zr40Ti8.5Al5.5 glassy alloy

Crystallization kinetics of Cu46Zr40Ti8.5Al5.5 metallic glass is investigated in non-isothermal and isothermal conditions. In non-isothermal condition, the crystallization activation energy is determined using Kissinger's method. Further, activation energy of reported Cu-Zr-Al metallic glasses are compared with Cu46Zr40Ti8.5Al5.5 alloy to understand the effect of Ti addition on crystallization kinetics. Detailed investigation on activation energy through the crystallization process is studied. To understand the influence of nucleation and growth mechanism during the crystallization steps, samples are heated in isothermal conditions at various annealing temperatures in supercooled liquid region to determine the local Avrami's exponent using Johnson-Mehl-Avrami equation. Additionally, small scale mechanical response is noted on metallic glass sample to determine the influence of structure on hardness and elastic modulus. Nanoindentation results showed hardness value of 5.39 ± 0.09 GPa and Young's modulus of 92.81± 0.52 GPa.

Tuning Non-Isothermal Crystallization Kinetics between Fe20Co20Ni20Cr20(P0.45B0.2C0.35)20 High-Entropy Metallic Glass and the Predecessor Fe75Cr5P9B4C7 Metallic Glass

In the present work, comparisons of non-isothermal crystallization kinetics between Fe20Co20Ni20Cr20(P0.45B0.2C0.35)20 high-entropy metallic glass (HEMG) and the predecessor Fe75Cr5P9B4C7 metallic glass (MG) were performed with X-ray diffraction and differential scanning calorimetry approaches. The HEMG possesses a harsher crystallization process compared with the predecessor MG, deriving from a higher triggering energy for all the characteristic transitions and local activation energy along with a smaller local Avrami exponent and a growth with pre-existing nuclei. Meanwhile, the glass transition is the easiest process, but the nucleation of the second crystallization case is the hardest transition for the HEMG. However, the predecessor MG possesses distinctly different crystallization features of a moderate difficulty for the glass transition, the harshest process for the growth transition of the second crystallization case, and a crystallization of growth with a diverse nucleation rate. These results conclusively prove that the non-isothermal crystallization kinetics can be significantly changed after the present high-entropy alloying with the substitution of similar solvent elements Co, Ni, and Cr with Fe in Fe75Cr5P9B4C7 MG. Moreover, the two alloys possess a strong glassy formation melt with high thermal stability and diverse crystallized products after non-isothermal crystallization.

Kinetics of Austenite Decomposition in 54SiCr6 Steel during Continuous Slow Cooling Conditions

In this study, dilatometry and metallography were used to investigate the effect of silicon and copper alloying on the decomposition kinetics of 54SiCr6 steel during continuous slow cooling. It is different from the published literature for using the approach of the local activation energy of the austenite decomposition Ef and the local Avrami exponent n of the volume fraction of the transformed phase f to study the kinetics of austenite-pearlitic transformation in cooled 54SiCr steel at slow cooling rates. The Johnson–Mehl–Avrami equation was used to determine the dependence of the local activation energy for austenite decomposition Ef and the local Avrami exponent n on the volume fraction of the transformed phase f. The mechanism of the austenite decomposition was analysed based on the calculated values of n. Both the local and average activation energies were used to evaluate the alloying effect, and the results were compared with those obtained from other methods. The type of microstructure formed as a result of cooling at rates of 0.5 K/s, 0.3 K/s, 0.1 K/s and 0.05 K/s was determined. The effects of changes in the cooling rate and the content of silicon (1.5–2.5 wt.%) and copper (0.12–1.47 wt.%) on the dimension of nucleation and growth kinetics of the transformed phase were studied. It was revealed that the pearlite microstructure was formed predominantly in 54SiCr6 steel as a result of continuous cooling at slow cooling rates. It was also found that alloying this steel with copper led to a significant decrease in the value of Ef, as well as to a change in the mechanism of the kinetics of the austenite-pearlite transformation, which was realised in predominantly two- and three-dimensional nucleation and growth at a constant nucleation rate. At the same time, alloying this steel with silicon led only to a slight change in Ef. The results of the study of 54SiCr steel presented the dependence of the activation energy of transformation and the local Avrami exponent on the volume fraction of the transformed phase at a given cooling rate at different copper and silicon contents. In addition, the study provides insight into the mechanism of kinetics in cooled 54SiCr steel as a function of the cooling rate.

Non-isothermal crystallization behavioral analysis of detonation sprayed Fe-based amorphous coating

The non-isothermal crystallization behaviors of a detonation sprayed Fe-based amorphous coating (AMC) was systematically investigated through differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. The crystallization mechanism of the Fe-based AMC is analyzed and discussed in detail using a combination of the Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall approaches, as well as the local Avrami exponent. The results indicate that the crystallization process of the Fe-based AMC is affected by the non-isothermal heating rate with a significantly higher initial crystallization activation energy (917.7 kJ mol−1) and first peak activation energy (479.6 kJ mol−1), indicating excellent thermal stability. After four stages of amorphous crystallization and phase transformation, the crystallization products of the equilibrium state were primarily composed of 78.5%, 11.3%, and 5.8% (Cr, Fe)23(C, B)6, α-Fe phases, and FeMo2B2 phases, respectively.

Mechanical properties and non-isothermal crystallization kinetics of novel Ti-based high-entropy bulk metallic glasses

In this work, five novel Ti- and TiZr-based high entropy bulk metallic glasses (HE-BMGs) with good glass forming ability (GFA) were developed, among which the (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Ni6 alloy possesses the largest critical diameter of 9 mm. All developed HE-BMGs exhibit high yield strength and good compressive plasticity at room temperature. Especially, the (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 alloy with large GFA has suitable density and high specific strength (3.90 × 105 N m/kg), showing great potential in the aerospace sector. Moreover, the activation energies at characteristic temperatures of three HE-BMGs were obtained using the Kissinger method. The local Avrami exponents were calculated to analyze the crystallization mechanism of these HE-BMGs, revealing that the first crystallization process is mostly dominated by diffusion-controlled three-dimensional growth of pre-existing nuclei. In addition, all three HE-BMGs can be classified as “intermediate glasses” according to their fragility index values.

Non-isothermal crystallization kinetics study of sodium niobium phosphate glasses

Sodium niobium phosphate (SNP) glasses of composition xNb2O5–(50-x/2)Na2O–(50-x/2) P2O5 (x = 20, 30, 40 mol. %) are prepared by the conventional melt–quench technique. The non-isothermal kinetics of glass transition & crystallization of SNP glasses are studied by a differential scanning calorimeter (DSC). The dependence of glass transition temperature on the heating rate is used to deduce the activation energy of glass transition. The average activation energies of crystallization are calculated by model-free peak kinetic methods (Kissinger, Boswell, Augis-Bennet, and Ozawa). The local activation energies for crystallization with the volume fraction crystallized is estimated by linear iso-conversional methods (Kissinger-Akahira-Sunose, Starink, Tang, Flynn-Wall-Ozawa, and Various heating rates (VHR)) and by Friedman differential method. Avrami exponents are deduced to understand the nucleation and growth of various crystalline phases formed on heat treatment of SNP glasses. The change in the local Avrami exponent with the crystallized volume fraction confirms that the crystallization process occurs through volume nucleation, mainly with 3D growth. SEM analysis explored the crystalline morphologies and revealed the evolution of sheaf-like crystals.

Anomalous Avrami index recorded during the non-isothermal crystallization of borotitanosilicate glass powders

We investigated the crystallization kinetics of 24.5CaO-24.5SrO-3.7B2O3-6TiO2-41.3SiO2 and 25CaO-25SrO-3.8B2O3-8TiO2-42.2SiO2 (mol%) borotitanosilicate glass powders (≤ 43µm), herein referred as T6 and T8, respectively, using differential scanning calorimetry (DSC - β = 2.5°C/min – 40°C/min) and scanning electron microscopy (SEM). The kinetic parameters were calculated through model-free and model-fitting approaches. Despite minor variations in the corresponding activation energy, it was found that the local Avrami exponents changed significantly, and multiple-step reactions govern the crystallization process (with n ≥ 2 for 0.05 ≤ α ≤ 0.95). These unexpected n values were attributed to the complexity of the crystallization process, where crystals grow individually and three-dimensionally in the early stages, thereafter tending to grow in a single direction (1D) after meeting each other.

Comparative study of thermal stability and crystallization kinetics between melt-spun and bulk Pd77.5Cu6Si16.5 metallic glasses

A comparative study on the thermal stability and kinetics of crystallization of both melt–spun and bulk Pd77.5Cu6Si16.5 metallic glasses was performed. Rapidly quenched Pd77.5Cu6Si16.5 ribbon and as–cast bulk metallic glass (BMG) sample were produced by melt spinning and copper mold casting, respectively. Phase identification and transformation were studied by X–ray diffraction (XRD), transmission electronic microscopy (TEM), and differential scanning calorimeter (DSC) measurements. In non-isothermal conditions, the activation energies were calculated by Moynihan and Kissinger methods, respectively. The nucleation and growth during the crystallization were investigated in the frame work of the local activation energy and the local Avrami exponent. The local activation energy was calculated by Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Vyazovkin methods. The local Avrami exponent was calculated. The experimental results indicated that the characteristic temperatures depend on the heating rate. The obtained activation energies indicated that the Pd77.5Cu6Si16.5 amorphous alloys exhibit excellent thermal stability. The thermal stability of Pd77.5Cu6Si16.5 BMG is better than that of ribbon. The local activation energy Ea increases to a maximum and then decreases. It is indicated by local Avrami exponent that the crystallization processes of both Pd77.5Cu6Si16.5 amorphous ribbon and BMG are controlled by volume nucleation with three-dimensional growth with various nucleation rates. The crystallization process of Pd77.5Cu6Si16.5 amorphous ribbon is close to that of BMG. The isothermal crystallization kinetics of Pd77.5Cu6Si16.5 amorphous ribbon is investigated and compared with the results of non-isothermal crystallization kinetics.

Tuning crystallization kinetics by high-content solvent element substitution between Cr45Fe11Co7Mo14C15B6Y2 and Fe41Cr15Co7Mo14C15B6Y2 metallic glasses

In this work, the effects of high-content (30 at.%) solvent element (denoted as HC30SE) substitution of Cr for Fe on crystallization kinetics between Cr45Fe11Co7Mo14C15B6Y2 metallic glass (MG) and the precursor Fe41Cr15Co7Mo14C15B6Y2 MG were studied by Johnson-Mehl-Avrami, Arrhenius, Kissinger and Ozawa approaches using differential scanning calorimeter. Under the isothermal crystallization, the incubation period, local activation energy and the diversity of the crystallized phase are improved by HC30SE substitution of Cr for Fe. Additionally, the crystallization characteristics established by Avrami exponent change from a combination of growth with retarding nucleation rate and growth with promoting nucleation rate to only a growth with promoting nucleation rate after HC30SE substitution of Cr for Fe. Moreover, the local Avrami exponent for the two MGs possesses nearly opposite trend with each other. Furthermore, the difficulty of the non-isothermal crystallization events is enhanced after HC30SE substitution of Cr for Fe as the enhanced apparent activation energy.

Tuning isothermal crystallization kinetics by minor similar solute element substitution in novel La‐(AlGa)‐C metallic glasses

AbstractIn the present text, the effects of minor similar solute element Ga substitution for Al on the isothermal crystallization kinetics of novel light RE‐based La‐(AlGa)‐C metallic glasses (MGs) were systematically investigated between La60Al26Ga4C10 MG and the precursor La60Al30C10 MG by using phase analysis, Johnson–Mehl–Avrami and Arrhenius using x‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The incubation period, the accomplishment time of the whole process, and the diversity of both the precipitated phases and the varying trend of the local Avrami exponent are elevated by minor similar solute element Ga substitution for Al, respectively. Additionally, the Avrami exponent of different isothermal crystallization temperature changes from g n &gt; 2.5 to a combination of values 1.5 &lt; n &lt; 2.5 and a value n &gt; 2.5 given by minor similar solute element Ga substitution for Al, corresponding to the crystallization characteristics changing from crystallization with promoting nucleation rate to a combination of crystallization with a reducing nucleation rate and crystallization with promoting nucleation rate. Moreover, the isothermal crystallization process becomes more difficult after minor similar solute element Ga substitution for Al, due to the reduced Avrami exponent and the intensified local activation energy.

Non-isothermal crystallization kinetics of Ge-Cu-Te thin films for phase-change memory

We investigated the crystallization kinetics of Ge-Cu-Te ternary system phase-change thin films using non-isothermal differential scanning calorimetry and estimated the kinetic triplet (activation energy, pre-exponential factor, and reaction model) by the combined application of isoconversional and model-fitting approaches at different heating rates over a range of 10–40 K/min for GeCu2Te2 thin films. The results indicate a multi-step crystallization process where the activation energy of crystallization is not constant but decreases via three recognizable stages with crystallization fraction α. The local Avrami exponents suggest that two crystallization mechanisms containing three-dimensional growth with increasing nucleation rates in the range of crystallization fraction α ≤ 0.4 and three- and two-dimensional growths at a decreasing nucleation rate over the wide range of α > 0.4 are responsible for the whole crystallization process. Furthermore, the reaction model displays dependence on the heating rates for the GeCu2Te2 thin films, where heating rates of 10–30 K/min drive a second-order reaction while a three-halve order reaction occurs for a heating rate of 40 K/min, which is different from the second-order reaction for the GeCu2Te3 thin films. Also, both GeCu2Te2 and GeCu2Te3 thin films provide better data retention capability than the Ge2Sb2Te5 thin films without sacrificing the crystallization time. The results indicate that Ge-Cu-Te ternary system thin films have great potentiality in phase-change memory applications.

Nonisothermal crystallization kinetics of Cr‐rich metallic glass Cr29.4Fe29.4Mo14.7C14.7B9.8Y2 with desirable properties

AbstractThe nonisothermal crystallization kinetics for the first crystallization event of Cr‐rich metallic glass (MG) Cr29.4Fe29.4Mo14.7C14.7B9.8Y2 with desirable properties was systematically studied by Kissinger, Ozawa, Kissinger‐Akahira‐Sunose (KAS), Ozawa‐Flynn‐Wall (OFW), and Vogel‐Fulcher‐Tammann approaches using differential scanning calorimeter. The apparent activation energy (E) for characteristic temperatures deduced by Kissinger approach is comparable with that deduced by Ozawa approach. The Eg for the glass transition temperature is smaller than the Ep1 for the peak temperature of the first crystallization event and larger than E for other characteristic temperatures, exhibiting that the glass transition is easier than the growth process of the first crystallization event and more difficult than other processes. The local activation energy estimated by KAS and OFW approaches shows approximate tendency of increasing initially and then gradually decreasing, which indicates that the crystallization process is difficult at first and then gradually becomes easy. The local Avrami exponent (n(x)) changes from n(x) &gt; 2.5 to 1.5 &lt; n(x) &lt; 2.5 for crystallization under low heating rate and from n(x) &gt; 2.5 to 0 &lt; n(x) &lt; 1.5 for crystallization under high heating rate, corresponding to a diffusion‐governed crystallization changing from enhancing nucleation rate to reducing nucleation rate under low heating rate and from enhancing nucleation rate to preexisting nuclei under high heating rate, respectively. The kinetic fragility parameter shows that the glass‐forming liquid of the present MG is intermediate type with moderate glass‐forming ability. The results would provide comprehensive insights to understand the formation of Cr‐rich MG.

Studies of crystallization kinetics and optical properties of ZnO films prepared by sol–gel technique

The crystallization of ZnO prepared by sol–gel technique was investigated under nonisothermal conditions by differential scanning calorimetry (DSC) and prediction isothermal method. The transformation from the amorphous to crystalline state was investigated by X-ray diffraction (XRD). The influence of the annealing temperature on the structure of the ZnO was studied by Filed Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM). Two exothermic changes were reported between the temperature ranges 590–710 K and 645–750 K for first and second transition, respectively. The isoconversional methods of Friedman, Ozawa and Flynn and Wall (FWO), Kissinger–Akahira–Sunose and the Vyazovkin (minimizing) were used to determine the variation of the effective activation energy with the extent of crystallization, Eα (α) and hence, with temperature Eα (T). In addition, the activation energy was calculated from predicted isothermal results. Analysis of the obtained data shows that the activation energy of crystallization is not constant but varies with the degree of conversion and, hence, with temperature. The value of the local Avrami exponent, n (α), varies within 1.88–1.97 for isothermal study and within 2.35–2.4 for nonisothermal process. By using the Johnson–Mehl–Avrami (JMA) model, a good fit was achieved between experimental and theoretical calculation of the reaction (crystallization) rate. The optical energy gap decreased with increasing annealing temperature.

Isothermal and non-isothermal crystallization kinetics of novel metalloid-bearing light rare-earth-based La64Al26Ga4C6 metallic glass with high thermal stability

The crystallization kinetics of a novel metalloid-bearing light rare-earth (RE)-based La64Al26Ga4C6 metallic glass (MG) under isothermal and non-isothermal conditions were systematically researched by Johnson-Mehl-Avrami (JMA), Arrhenius, Kissinger, Ozawa, Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall approaches using differential scanning calorimeter. The present MG possesses higher thermal stability than other light RE-based MGs without metalloid. As the isothermal crystallization temperature increases, the Avrami exponent estimated by JMA equation ranges from 2.36 to 2.94, implying that the isothermal crystallization mechanism varies from a three-dimensional diffusion-governed growth with a decreasing nucleation rate to a three-dimensional diffusion-governed growth with an increasing nucleation rate. Meanwhile, the apparent activation energy determined by Kissinger and Ozawa methods for characteristic temperatures indicates that glass transition is more difficult than crystallization process. Additionally, the local Avrami exponents show various trends, implying a transformable crystallization mechanism with crystallization proceeding. Furthermore, the crystallization process becomes easier due to the decrease of local activation energy.

Effects of Si/B ratio on the isothermal crystallization behavior of FeNiSiBCuNb amorphous alloys

In the present work, (Fe40Ni40SixByCu1)0.97Nb0.03 (Si/B = 1:1, 1:2, and 1:3) alloys were prepared by the as-melt spun method. The effect of different Si/B ratios on the isothermal crystallization behavior of FeNiSiBCuNb glass alloys were investigated. The activation energies of the Si/B = 1:1, 1:2, and 1:3 alloys for nucleation and grain growth were calculated by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model as 123.6 kJ/mol and 207.3 kJ/mol, 151.0 kJ/mol and 251.3 kJ/mol, and 88.6 kJ/mol and 170.0 kJ/mol respectively; hence, crystal nuclei needed to cross a higher energy barrier in the growth process. The variation of local Avrami exponent n(α) with crystallization fraction α demonstrates that the crystallization mechanism was divided into three stages: i: initial crystallization stage with n＞2, indicating that α-Fe(Si) phase or γ-(Fe, Ni)Si phase with a high nucleation rate stage, ii: middle crystallization stage with n≈2, indicating that FeNiB phase with a stable nucleation stage, and iii: the end of crystallization stage with n＜2, indicating that γ-(Fe, Ni)Si and FeNiB phases with a growth stage; The crystallization process was transformed from diffusion-controlled one-dimensional growth to diffusion-controlled three-dimensional growth.

Crystallization Kinetics and Fragility of Al-Based Amorphous Alloy

Crystallization among amorphous alloy is a crucial study since it generally affects it properties, which may detrimental or beneficial, depending in the intended application of the materials. Controlling crystallization is crucial for obtaining the desired properties. The crystallization study was performed using differential scanning calorimeter (DSC). Samples were heated at heating rate between 20 and 40 K·min-1. Structural evolution during crystallization was studied under X-ray diffraction (XRD). Apparent activation energy for each temperature characteristics was determined using Kissinger’s equation. Local Avrami exponent was investigated using modified Johnson-Mehl-Avrami-Kolgomorov equation. Liquid fragility, which indicates the strength of the glass formation, was predicted using temperature characteristics instead of its viscosity. It was found that upon crystallization both as-cast samples crystallize to cubic-Al, Al2CuMg and Al2Cu and Al3Ni. Alloy with composition of (Al75Cu17Mg8)95Ni5 shows superior activation energy at every temperature characteristics than alloy with composition of Al75Cu10Mg8Ni7. Local Avrami exponent and local activation energy for (Al75Cu17Mg8)95Ni5 show high values at the beginning and at the end of crystallization process. From liquid fragility, it was predicted that the samples are stronger glass former than previous studied Al-amorphous alloys.

Abnormal isochronous crystallization behavior of Zr-Al-Ni-Cu-Fe-C bulk metallic glasses

(Zr53Al11.6Ni11.7Cu23.7)1-x(Fe77.1C22.9)x (x = 0–2.2 at.%) bulk metallic glasses (BMGs) were prepared by water cooling copper mold suction casting and their isochronous crystallization characteristics are investigated. The glass transition temperature, crystallization temperature, and crystallization peak temperature for all studied Zr-based BMGs firstly increase with increasing heating rate, and then decrease when the heating rate increases up to 60 K/min for the BMGs (0 ≤ x ≤ 0.88 at.%) and 80 K/min for the BMGs (1.32 ≤ x ≤ 2.20 at.%). The glass transition temperature, crystallization temperature, glass transition activiation energy, crystallization activiation energy, and activiation energy for crystallization peak temperature of the Fe- and C-free Zr-based BMG are the smallest among the studied BMGs, indicating that Fe and C additions are benificial to delaying the glass transition and the crystallization. Fe and C additions influence more significantly on the glass transition than on the crystallization. The local crystallization activiation energy for the Fe- and C-free BMG are the smallest among the studied BMGs, indicating that the crystallization is easy for the Fe- and C-free BMG. The peak height of local Avrami exponent and its corresponding crystallization fraction decrease with increasing heating rate except for the BMG (x = 1.32 at.%). The fragility indexes are 32–48 for the studied Zr-based BMGs. The present results are of guiding significance for preparing the excellent BMG composites by heat treatment and selecting suitable conditions for forming the BMGs.

Influence of substitution of Cu by Ni on the crystallization kinetics of TiZrHfBeCu high entropy bulk metallic glass

The crystallization kinetics of TiZrHfBe(Cu, Ni) high entropy bulk metallic glasses have been studied using differential scanning calorimetry. Each alloy possesses a complex multi-step crystallization process due to the high entropy effect. It was found that substitution of Cu by Ni significantly improves the glass-forming ability but deteriorates the thermal stability of the TiZrHfBeCu alloy. The activation energies of glass transition and crystallization together with the fragility parameter for the Ni-free and Ni-containing alloys have been calculated. According to the calculated values of local Avrami exponent, the first crystallization event for the studied TiZrHfBe(Cu, Ni) alloys is dominated by a direct growth of crystal nuclei. Substitution of Cu by Ni favors the precipitation of Ni-containing intermetallic compounds and inhibits the formation of CuHf2 phase, resulting in the improvement of glass-forming ability.