Abstract
This paper reports the crystallization kinetics of (Cu60Zr25Ti15)99.3Nb0.7 bulk metallic glass under isothermal conditions. Differential scanning calorimetry (DSC) has been employed for isothermal annealing at ten different temperatures prior to the onset of crystallization (To) temperature. X-ray diffraction and transmission electron microscopy have been used to confirm the amorphous structure of the as cast sample. Crystallized volume fractions (x) are calculated from the exothermic peaks of DSC scans. Crystallized volume fractions (x) against time show sigmoidal type of curves as well as the curves become steeper at higher annealing temperatures. Continuous heating transformation diagram has been simulated to understand the stability of the bulk metallic glass. Crystallization kinetics parameters are calculated using Arrhenius and Johnson–Mehl–Avrami equations. Activation energy (Ea) and Avrami exponential factor (n) have exhibited strong correlation with crystallized volume fraction (x). The average activation energy for isothermal crystallization is found to be 330 ± 30 kJ/mol by Arrhenius equation. Nucleation activation energy (Enucleation) is found to be higher than that of growth activation energy (Egrowth). The Avrami exponential factor (n) indicates about the diffusion controlled mechanism of the nucleation and three-dimensional growth.
Highlights
This paper reports the crystallization kinetics of (Cu60Zr25Ti15)99.3Nb0.7 bulk metallic glass under isothermal conditions
Isothermal crystallization kinetics can give an idea about the time and temperature for isothermal heating of bulk metallic glasses (BMGs) to create a second phase of the desired size which can result into a ductile BMG
The sigmoidal type curves of crystallized volume fraction against time become steeper with the higher annealing temperatures, and it demonstrates about the sharp crystallization with shorter time at the higher annealing temperatures
Summary
This paper reports the crystallization kinetics of (Cu60Zr25Ti15)99.3Nb0.7 bulk metallic glass under isothermal conditions. The magnetic properties have been reported to improve in Febased metallic glasses by the formation of nanocrystals inside the amorphous m atrix[14,15]. The improvement of the mechanical properties in BMG is reported by creating second phase inside the amorphous m atrix[17,18]. The crystallization kinetics in amorphous materials is sensitive to the parameters such as; activation energy, nucleation and growth mechanism, crystalline temperature and time, nature of the crystalline phases being formed[6]. Cu-based bulk metallic glasses (BMGs) have been of great research interest worldwide due to its high glass forming ability, good mechanical properties, high corrosion resistance and reasonable materials cost compare to other BMG s ystems[10,24,25,26]. A continuous heating transformation diagram has been plotted from the isothermal crystallization data to understand the stability of the (Cu60Zr25Ti15)99.3Nb0.7 BMG
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