Abstract: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… Show more
“…This phenomenon is probably due to the large excess specific heat of the supercooled liquid relative to the solid and perhaps a small loss of enthalpy during heating to the crystallization temperature. The very low temperature of the beginning of crystallization of the two-component Mg-Zn alloy compared to the three-component Mg-Zn-Ca alloy (about 506 K) [ 15 , 16 ] suggests the low stability of the amorphous structure of the two-component alloy at ambient temperature. This may lead to spontaneous crystallization of this alloy at ambient temperature.…”
Section: Resultsmentioning
confidence: 99%
“…Metallic glasses, due to their amorphous structure, characterized by the lack of grain boundaries, can provide a material with better mechanical properties and higher corrosion resistance than crystalline materials. Numerous studies of the kinetics of crystallization of amorphous ternary Mg-Zn-Ca and Ca-Mg-Zn alloys with different chemical compositions can be found in the literature [ 15 , 16 , 17 , 18 , 19 , 20 ]. Unfortunately, the widespread use of amorphous alloys is limited due to their low plasticity [ 21 ].…”
The aim of the study was to analyze the crystallization kinetics of the Mg72Zn28 metallic glass alloy. The crystallization kinetics of Mg72Zn28 metallic glass were investigated by differential scanning calorimetry and X-ray diffraction. The phases formed during the crystallization process were identified as α-Mg and complex Mg12Zn13 phases. Activation energies for the glass transition temperature, crystallization onset, and peak were calculated based on the Kissinger model. The activation energy calculated from the Kissinger model was Eg = 176.91, Ex = 124.26, Ep1 = 117.49, and Ep2 = 114.48 kJ mol−1, respectively.
“…This phenomenon is probably due to the large excess specific heat of the supercooled liquid relative to the solid and perhaps a small loss of enthalpy during heating to the crystallization temperature. The very low temperature of the beginning of crystallization of the two-component Mg-Zn alloy compared to the three-component Mg-Zn-Ca alloy (about 506 K) [ 15 , 16 ] suggests the low stability of the amorphous structure of the two-component alloy at ambient temperature. This may lead to spontaneous crystallization of this alloy at ambient temperature.…”
Section: Resultsmentioning
confidence: 99%
“…Metallic glasses, due to their amorphous structure, characterized by the lack of grain boundaries, can provide a material with better mechanical properties and higher corrosion resistance than crystalline materials. Numerous studies of the kinetics of crystallization of amorphous ternary Mg-Zn-Ca and Ca-Mg-Zn alloys with different chemical compositions can be found in the literature [ 15 , 16 , 17 , 18 , 19 , 20 ]. Unfortunately, the widespread use of amorphous alloys is limited due to their low plasticity [ 21 ].…”
The aim of the study was to analyze the crystallization kinetics of the Mg72Zn28 metallic glass alloy. The crystallization kinetics of Mg72Zn28 metallic glass were investigated by differential scanning calorimetry and X-ray diffraction. The phases formed during the crystallization process were identified as α-Mg and complex Mg12Zn13 phases. Activation energies for the glass transition temperature, crystallization onset, and peak were calculated based on the Kissinger model. The activation energy calculated from the Kissinger model was Eg = 176.91, Ex = 124.26, Ep1 = 117.49, and Ep2 = 114.48 kJ mol−1, respectively.
“…The curves show the typical sigmoidal shape with their interpretation within the Kolmogorov-Johnson–Mehl–Avrami-Evans (KJMAE) model by two parameters: k—crystallization rate constant and n—Avrami exponent (average index describing the mechanism of crystallization). Both parameters were calculated using the equation 18 : where: α—degree of crystallization, k—crystallization rate constant, n—Avrami exponent, t—time. Figure 1 Isothermal kinetics results: ( a ) heat flows; ( b ) Avrami plot with calculated kinetic parameters n and k. …”
Section: Resultsmentioning
confidence: 99%
“…The k value is related to the rate of crystallization. Therefore its higher value at higher temperatures means a fast process of crystallization caused by the introduction of a higher energy into the system 18 . Because nucleation and growth change over time, the local Avrami exponent was calculated according to the formula 21 : …”
This work aims to investigate the isothermal crystallization behaviour, crystal structure and magnetic properties evolution of long-term (up to 300 h) low temperature (210 and 260 °C) vacuum- and air-annealed Fe80.3Co5Cu0.7B14 alloy. Before the α-Fe(Co) phase crystallization, the primary relaxation process has been identified at a temperature range up to 340 °C. The relaxation process performed under 210 °C for 300 h did not initiate the crystallization process. However, the topological and compositional short-range rearrangements improved magnetic properties remarkably. Annealing 150 h at 260 °C helps to deliver enough energy to stabilize the glassy state and initiate the crystallization process fully. Structural and magnetic properties evolution of 150 h annealing at 260 °C corresponds to the evolution presented during isochronal 20 min annealing at 310 °C. Magnetic properties Bs = 1.75–1.79 T, Hc < 20 A/m and P10/50 are similar to those for 20 min of annealing at 310 °C. Comparison of core power losses from up to 400 kHz frequency dependences of long-term low temperature annealed alloy with 20 min classical annealing at 310 °C shown that presented here long-term annealing is energetically insufficient to bring the glassy state system into the same low level of core power losses efficiency.
“…In general, systems of three or more components were observed to undergo glass transition more easily than binary systems [11]. Various Mg-Zn-based metallic glasses have been analyzed in the literature, but these with the addition of Ca are the most popular and investigated ones [1,2,4,[12][13][14][15][16][17]. As mentioned, a small change in the chemical composition can significantly affect the strength parameters, the ability to undergo glass transition, and the crystallization mechanism [4].…”
In this study, thin ribbons of amorphous Mg72Zn27Pt1 and Mg72Zn27Ag1 alloys with potential use in biomedicine were analyzed in terms of the crystallization mechanism. Non-isothermal annealing in differential scanning calorimetry (DSC) with five heating rates and X-ray diffraction (XRD) during heating were performed. Characteristic temperatures were determined, and the relative crystalline volume fraction was estimated. The activation energies were calculated using the Kissinger method and the Avrami exponent using the Jeziorny–Avrami model. The addition of platinum and silver shifts the onset of crystallization towards higher temperatures, but Pt has a greater impact. In each case, Eg > Ex > Ep (activation energy of the glass transition, the onset of crystallization, and the peak, respectively), which indicates a greater energy barrier during glass transition than crystallization. The highest activation energy was observed for Mg72Zn27Pt1 due to the difference in the size of the atoms of all alloy components. The crystallization in Mg72Zn27Ag1 occurs faster than in Mg72Zn27Pt1, and the alloy with Pt has higher (temporary) thermal stability. The Avrami exponent (n) values oscillate in the range of 1.7–2.6, which can be interpreted as one- and two-dimensional crystal growth with a constant/decreasing nucleation rate during the process. Moreover, the lower the heating rate, the higher the nucleation rate. The values of n for Mg72Zn27Pt1 indicate a greater number of nuclei and grains than for Mg72Zn27Ag1. The XRD tests indicate the presence of α-Mg and Mg12Zn13 for both Mg72Zn27Pt1 and Mg72Zn27Ag1, but the contribution of the Mg12Zn13 phase is greater for Mg72Zn27Ag1
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