scholarly journals Analysis of the Crystallization Kinetics and Thermal Stability of the Amorphous Mg72Zn24Ca4 Alloy

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3583
Author(s):  
Bartosz Opitek ◽  
Janusz Lelito ◽  
Michał Szucki ◽  
Grzegorz Piwowarski ◽  
Łukasz Gondek ◽  
...  
Keyword(s):  
Metallic Glass ◽  
Crystallization Kinetics ◽  
Crystallization Process ◽  
Isothermal Annealing ◽  
Amorphous Structure ◽  
Avrami Equation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Human Body Temperature ◽  
End Times

The aim of this study was to analyze the crystallization of the Mg72Zn24Ca4 metallic glass alloy. The crystallization process of metallic glass Mg72Zn24Ca4 was investigated by means of the differential scanning calorimetry. The glass-forming ability and crystallization are both strongly dependent on the heating rate. The crystallization kinetics, during the isothermal annealing, were modelled by the Johnson–Mehl–Avrami equation. Avrami exponents were from 2.7 to 3.51, which indicates diffusion-controlled grain growth. Local exponents of the Johnson–Mehl–Avrami equation were also calculated. In addition, the Mg phase—being the isothermal crystallization product—was found, and the diagram of the time–temperature phase transformation was developed. This diagram enables the reading of the start and end times of the crystallization process, occurring in amorphous ribbons of the Mg72Zn24Ca4 alloy on the isothermal annealing temperature. The research showed high stability of the amorphous structure of Mg72Zn24Ca4 alloy at human body temperature.

scholarly journals Crystallization Kinetics Analysis of the Amorphouse Mg72Zn24Ca4 Alloy at the Isothermal Annealing Temperature of 507 K

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2815
Author(s):  
Janusz Lelito
Keyword(s):  
Metallic Glass ◽  
Crystallization Kinetics ◽  
Rate Constant ◽  
Crystallization Process ◽  
Annealing Temperature ◽  
Isothermal Annealing ◽  
Avrami Exponent ◽  
Induction Melting ◽  
Transformation Rate ◽  
Transformation Rate Constant

This paper presents tests of metallic glass based on Mg72Zn24Ca4 alloy. Metallic glass was made using induction melting and further injection on a rotating copper wheel. A differential scanning calorimeter (DSC) was used to investigate the phase transformation of an amorphous ribbon. The tests were carried out at an isothermal annealing temperature of 507 K. The Kolmogorov-Johnson-Mahl-Avrami-Evans model was used to analyze the crystallization kinetics of the amorphous Mg72Zn24Ca4 alloy. In this model, both Avrami’s exponent n and transformation rate constant K were analyzed. Both of these kinetic parameters were examined as a function of time and the solid fraction. The Avrami exponent n value at the beginning of the crystallization process has value n = 1.9 and at the end of the crystallization process has value n = 3.6. The kinetic constant K values change in the opposite way as the exponent n. At the beginning of the crystallization process the constant K has value K = 9.19 × 10−7 s−n (ln(K) = −13.9) and at the end of the crystallization process has the value K = 6.19 × 10−9 s−n (ln(K) = −18.9). These parameters behave similarly, analyzing them as a function of the duration of the isothermal transformation. The exponent n increases and the constant K decreases with the duration of the crystallization process. With such a change of the Avrami exponent n and the transformation rate constant K, the crystallization process is controlled by the 3D growth on predetermined nuclei. Because each metallic glass has a place for heterogeneous nucleation, so called pre-existing nuclei, in which nucleation is strengthened and the energy barrier is lowered. These nuclei along with possible surface-induced crystallization, lead to rapid nucleation at the beginning of the process, and therefore a larger transformed fraction than expected for purely uniform nucleation. These sites are used and saturated with time, followed mainly by homogeneous nucleation. In addition, such a high value of the Avrami exponent n at the end of the crystallization process can cause the impingement effect, heterogeneous distribution of nuclei and the diffusion-controlled grain growth in the Mg72Zn24Ca4 metallic glassy alloy.

Structural and Phase Transformations During Crystallization of Pd43Ni10Cu27P20 Metallic Glass

2000 ◽  
Vol 644 ◽  
Author(s):  
Evgenia Pekarskaya ◽  
Jan Schroers ◽  
William L. Johnson
Keyword(s):  
Electron Microscopy ◽  
Amorphous Alloy ◽  
Metallic Glass ◽  
Temperature Region ◽  
Isothermal Annealing ◽  
P System ◽  
Scanning Calorimetry ◽  
Structural And Phase Transformations ◽  
Temperature Transformation ◽  
Nose Temperature

AbstractCrystallization of the Pd43Ni10Cu27P20 amorphous alloy during isothermal annealing in the undercooled temperature region is studied by electron microscopy and diffrential scanning calorimetry (DSC). It is established that different crystallization processes take place above and below the nose temperature of the time-temperature-transformation (TTT) diagram. Detailed analysis of the microstructural evolution at the early stages of the crystallization is performed. In addition, the stable phases in the Pd-Ni-Cu-P system are identified.

scholarly journals EFFECT OF STRUCTURAL RELAXATION ON THE DEFORMATION BEHAVIOR OF A Zr64.13Cu15.75Ni10.12Al10 BULK METALLIC GLASS UNDER NANOINDENTATION

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2320-2325 ◽  
Author(s):  
JIANSHENG GU ◽  
BINGCHEN WEI ◽  
TAIHUA ZHANG ◽  
YIHUI FENG ◽  
YANPING HU ◽  
...  
Keyword(s):  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Structural Relaxation ◽  
Deformation Behavior ◽  
Isothermal Annealing ◽  
Flow Behavior ◽  
Thermal And Mechanical Properties ◽  
Scanning Calorimetry ◽  
Obvious Effect ◽  
Dsc Curves

Structural relaxation by isothermal annealing below the glass transition temperature is conducted on a Zr 64.13 Cu 15.75 Ni 10.12 Al 10 bulk metallic glass. The effect of structural relaxation on thermal and mechanical properties was investigated by differential scanning calorimetry and instrumented nanoindentation. The recovery of the enthalpy in the DSC curves indicates that thermally unstable defects were annihilated through structural relaxation. During nanoindentation, the structural relaxation did not have a significant influence on the serrated plastic flow behavior. However, Structural relaxation shows an obvious effect in increasing both the hardness and elastic modulus, which is attributed to the annihilation of thermally unstable defects that resulted from the relaxation.

Effect of Heat Treatment on the Properties of (Fe0.6Co0.4)71Si5Nb4B20 Bulk Metallic Glass

2021 ◽  
Vol 875 ◽  
pp. 70-75
Author(s):  
Syed Zameer Abbas ◽  
Rashid Ali ◽  
Syed Muttahir Shah ◽  
Owais Jan ◽  
Munim Awan
Keyword(s):  
Glass Transition ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Cast Alloy ◽  
Amorphous Structure ◽  
Indentation Hardness ◽  
Alloy Sample ◽  
Scanning Calorimetry ◽  
Heat Treated Sample ◽  
Heat Treated

Bulk metallic glasses (BMGs) are an important class of materials with unique set of properties. A bulk metallic glass with composition of (Fe0.6Co0.4)71Nb4Si5B20 was cast in the form of a 1 mm thick strip in a water cooled copper mold. The BMG produced was characterized for structure, thermal and mechanical properties. The X-ray diffraction performed on the as cast alloy has shown completely amorphous structure. The glass transition and crystallization peak temperatures obtained through differential scanning calorimetry scan were 542 °C and 588.4 °C, respectively. Some cast amorphous alloy sample was annealed below glass transition (450 °C for 30 mi93nutes) and others above glass transition (580 °C for 5 minutes) temperatures. Nano- indentation hardness of 13.3 GPa was obtained for as cast alloy while a hardness values of 12.8 and 15.84 GPa were measured for heat treated alloys at temperature of 450 °C and 580 °C, respectively. Increase in hardness was attributed to formation of crystals in an amorphous matrix whereas decrease in hardness was due to relaxation of quenching residual stresses. The maximum value of elastic modulus obtained through indentation was 255 GPa for 580 °C heat treated sample.

scholarly journals A novel analytical approach to estimate isothermal and dynamic crystallization Avrami kinetic parameters

e-Polymers ◽  
2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Hossein Ali Khonakdar ◽  
Masoud Shiri ◽  
Ahmad Asadinezhad ◽  
Seyed Hassan Jafari ◽  
Mahdi Golriz
Keyword(s):  
Kinetic Parameters ◽  
Analytical Approach ◽  
Crystallization Process ◽  
Avrami Equation ◽  
Maximum Point ◽  
Scanning Calorimetry ◽  
Avrami Model ◽  
Dynamic Crystallization ◽  
Crystallization Mode ◽  
Evaluation Of Kinetic Parameters

AbstractThe Avrami equation has been extensively used to describe the polymer crystallization kinetics. Evaluation of kinetic parameters of this equation is quite troublesome, calling for properly predetermining induction time. To avoid this problem, an analytical approach in terms of differential scanning calorimetry exotherm maximum point was adopted here so as to conveniently estimate the Avrami equation kinetic parameters both in isothermal and dynamic crystallization mode. In the case of dynamic crystallization under isokinetic conditions, a modified version of the Avrami model by Nakamura was employed and adequate predictions based on the derived formulas were obtained. However, due to the simplified assumptions of the Avrami theory, our adopted relations are only applicable to earlier stages of crystallization process and do not account for secondary crystallization.

Precipitation of icosahedral quasicrystalline phase in Hf69.5Al7.5Ni11Cu12 metallic glass

2001 ◽  
Vol 16 (4) ◽  
pp. 1190-1194 ◽  
Author(s):  
Chunfei Li ◽  
Akihisa Inoue
Keyword(s):  
Metallic Glass ◽  
Melt Spinning ◽  
Crystallization Process ◽  
Exothermic Reaction ◽  
Quasicrystalline Phase ◽  
Scanning Calorimetry ◽  
Exothermic Reactions ◽  
Transmission Electron ◽  
Icosahedral Quasicrystalline Phase ◽  
Icosahedral Quasicrystalline

A Hf69.5Al7.5Ni11Cu12 metallic glass was prepared by a single roller melt-spinning method, and the crystallization process was studied by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The metallic glass crystallizes through three exothermic reactions. The low-temperature exothermic reaction corresponded to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature led to the decomposition of the icosahedral quasicrystalline phase to other stable crystalline phases, indicating that the precipitated icosahedral quasicrystalline phase was in a metastable state. The crystallization process of the present alloy was compared with that of other Hf–Al–Ni–Cu alloys, and the reason for the precipitation of the icosahedral quasicrystalline phase was discussed.

scholarly journals Stability of ZrTiCuNiBe Bulk Metallic Glass upon Isothermal Annealing Near the Glass Transition Temperature

2002 ◽  
Vol 17 (6) ◽  
pp. 1385-1389 ◽  
Author(s):  
Wei Hua Wang ◽  
Ru Ju Wang ◽  
W. T. Yang ◽  
B. C. Wei ◽  
P. Wen ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Isothermal Annealing ◽  
Scanning Calorimetry ◽  
The Stability ◽  
Property Changes ◽  
Overlap Method

The stability of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) upon isothermal annealing near the glass transition temperature has been investigated by using x-ray diffraction, differential scanning calorimetry, and the pulse echo overlap method. The density, elastic constants, and thermodynamic parameters as well as their annealing time dependence have been determined. The microstructural and properties changes of the annealed BMG were checked by acoustic measurement. Obvious structural and property changes were observed with prolonged annealing of the BMG near the glass transition temperature.

Crystallization Kinetics in Cu64.5Zr35.5 Binary Metallic Glass

2017 ◽  
Vol 727 ◽  
pp. 233-238 ◽  
Author(s):  
Qian Gao ◽  
Zeng Yun Jian ◽  
Jun Feng Xu ◽  
Man Zhu
Keyword(s):  
Activation Energy ◽  
Grain Growth ◽  
Crystallization Kinetics ◽  
Crystallization Process ◽  
Crystallization Kinetic ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Growth Activation ◽  
Local Activation Energy ◽  
Kinetics Of

The crystallization kinetics of melt-spun Cu64.5Zr35.5 amorphous alloy ribbons was investigated using differential scanning calorimetry (DSC) at different heating rates. Besides, the Kissinger and isoconversional approaches were used to obtain the crystallization kinetic parameters. As shown in the results, the activation energies for glass transition and crystallization process at the onset, peak and end crystallization temperatures were obtained by means of Kissinger equation to be 577.65 ± 34, 539.86 ± 54, 518.25 ± 20 and 224.84 ± 2 kJ/mol, respectively. The nucleation activation energy Enucleation is greater than grain growth activation energy Egrowth, indicating that the nucleation process is harder than grain growth. The local activation energy Eα decreases in the whole crystallization process, which suggests that crystallization process is increasingly easy.

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