Thermodynamics and kinetics analyses - 國立中山大學材料科學研究所碩士論文

5. Discussions

5.3 Thermodynamics and kinetics analyses

From the non-isothermal analyses, the addition of boron really enhances the thermal stability in the Mg-based alloys. In the Mg65Cu25-xY10Bx alloy systems, all samples exhibit a sharp exothermic peak during continuous DSC heating. With increasing boron content from 0 to 3 at%, the ∆Tx can increase from 58 to 66 K and can further decrease the melting point.

The γ value for Mg65Cu25-xY10Bx (x = 0, 3, 5) also increase from 0.40 to 0.42 and 0.41, respectively, as shown in Table 5.2. In contrast, the multi-exothermic peaks of the Mg₆₅Cu₂₅Y_10-xB_x alloys system would appear along with the primary crystallization and ∆T_x would decrease with increasing B content.

The Kissinger plots have been shown in Figs. 4.19 and 4.20, the activation energy evaluated by the onset crystallization temperature (or the very initial stage) is lower than that by the peak temperature. Because of the different stages of crystallization, it causes the difference in activation energy. Normally, the derived activation energy by the onset crystallization temperature is considered to be the energy barrier for nucleation, and the derived activation energy by the peak temperature is though to involve both nucleation and growth of crystallization. Hence, the later was extracted to be a higher value of activation energy. Activation energies in the range of 160-240 kJ/mol for crystallization of Mg-based amorphous alloys were also reported ^[58].

Besides, the activation energy for any specific volume fraction of crystallization can also be obtained by the non-isothermal Kissinger equation. For instance, the volume fraction of transformed of Mg65Cu25Y10 for the peak temperatures at heating rate 10, 20 and 30 K/min are 58%, 50% and 40%, respectively. It does not have too much meaning on their Kissinger slope.

But according to the peak shift of the linear heating DSC curves for the same volume fraction

of transformed crystallization at different heating rates, the activation energy for any specific volume fraction of crystallization also can be obtained by the Kissinger slope. The Kissinger plots are shown in Figs. 5.4 to 5.6. It is apparent that the activation energy is almost constant below 60% transformed volume, then drop to small value when above 60% transformed volume. This phenomenon is consistent with the description for the modified Kissinger plots.

The nucleation saturation sites are observed nearly the 63% transformed volume at several heating rates. It means that the growth mechanism dominates the later crystallization stage due to the absence of nucleation. Hence, the activation energy will decrease until the amorphous phase is completely crystallized.

In isothermal analyses, it is found that the value of Avrami exponent n may be influenced by the determination procedures, such as the calibration of baselines in the isothermal DSC curve, the incubation time, and the degree of crystallization. Furthermore, the n value is not an fixed integral. In comparison with the exponent n of Mg65Cu25Y10 and Mg65Cu22Y10B3, the average values of n are all about 3. This result implies that two alloys exhibit similar crystallization process.

For the activation energy evaluated by the isothermal analyses, the average activation energy of the Mg₆₅Cu₂₅Y₁₀ and Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloys for the primary crystallization of Mg2Cu are 150 and 210 kJ/mol, respectively. Because Mg has the low activation energy for diffusion at low temperatures, it postulated that the growth of the Mg₂Cu phase is controller by the Mg diffusion.

As for the Mg65Cu22Y10B3 amorphous alloy, the growth of Mg2Cu phase during isothermal annealing involves more than Mg diffusion. Figures 5.2 and 5.3 show the overall crystallization of the Mg65Cu25Y10 and the Mg65Cu22Y10B3 amorphous alloys. Due to the

addition of boron, the first peak is not Mg₂Cu phase until heating to higher temperatures, it means that boron can restrain the growth of Mg2Cu. The Mg65Cu22Y10B3 amorphous alloy has the higher activation energy (210 kJ/mol) for crystallization, suggesting that the B diffusion away and the Cu diffusion toward the Mg2Cu nuclei are also important.

Chapter 6 Conclusions

(1) Using the melting spinning method, the Mg65Cu25Y10, Mg65Cu25-xY10Bx (x=0 ~ 5), and Mg₆₅Cu₂₅Y_10-xB_x (x=0 ~ 10) are all amorphous alloys except for the Mg₆₅Cu₂₅Y₅B₅ and Mg65Cu25B10 alloys which have the crystalline phases of Mg2Cu and MgB.

(2) The addition of B would increase the hardness from 220 to 327 Hv for Mg65Cu25-xY10Bx

(x=0 ~ 5), and Mg₆₅Cu₂₅Y_10-xB_x (x=0 ~ 10) amorphous alloys.

(3) The density of the modified MgCuY amorphous alloys increases owing to the filling of free volume by the small B atoms. Nevertheless, the density value are all still below 4 kg/m³ considered as light weight amorphous alloys.

(4) In the Mg₆₅Cu₂₅Y₁₀ amorphous alloy, the replacement of Cu by B can further enhance the thermal stability and glass forming ability. The supercooled temperature range ∆T and the glass forming γ index is increased to 66 K and 0.420, respectively.

(5) The activation energy of the Mg₆₅Cu₂₅Y₁₀ amorphous alloy for crystallization determined by the non-isothermal Kissinger method is 138 kJ/mol. With increasing B content, it can be promoted to a high energy barrier against crystallization, and Mg₆₅Cu₂₂Y₁₀B₃ has a higher value of 156 kJ/mol.

(6) The modified Kissinger plot for the non-isothermal analyses can characterize the nucleation behavior and growth mechanism form the slope. It can also observe the site saturation at a given transformed volume fraction.

(7) The activation energy values of the Mg₆₅Cu₂₅Y₁₀ and Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloys for crystallization determined from the isothermal analysis are 150 and 200 kJ/mol, respectively. Due to the addition of boron, it can restrain the growth of Mg₂Cu and increase the activation energy.

(8) From the n exponent extracted from the isothermal JMA equation, it implies that the Mg- based amorphous alloys exhibit the similar crystallization processes.

(9) The crystallization products of the Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy measuring from 200 to 400 nm are observed in TEM. The Mg2Cu, solid solution and yttrium rich compound are traced.

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Table 1.1 Application filed for bulk metallic glasses [9].

Properties Application Field

High strength High hardness

High fracture toughness High impact fracture energy High fatigue strength High elastic energy High corrosion resistance High wear resistance High reflection ratio High hydrogen storage Good soft magnetism

High frequency permeability Efficient electrode

High viscous flowability Self-sharping property

High wear resistance and manufacturability

Machinery structural materials Cutting materials

Die materials Tool materials Bonding materials Sporting goods materials Corrosion resistance materials Writing appliance materials Optical precision materials Hydrogen storage materials High magnetostrictive materials Electrode materials

Composite materials

Acoustic absorption materials Penetrator

Medical device materials

Table 2.1 The classification of amorphous alloy systems [9].

Zr-Al-Ni、Zr-Al-Cu、Zr-Al-Ni-Cu、

Zr-Ti-Al-Ni-Cu、Zr-Nb-Al-Ni-Ln、Zr-Ga-Ni I ETM(or Ln) + Al + LTM

Ln-Al-Ni 、 Ln-Al-Cu 、 Ln-Al-Ni-Cu 、 Ln-Ga-Ni、Ln-Ga-Cu

II LTM + ETM + Metalloid

Fe-Zr-B 、 Fe-Hf-b 、 Fe-Zr-Hf-B 、 Fe-Co-Ln-B、Co-Zr-Nb-B

III LTM(Fe) + Al or Ga + Metalloid Fe-(Al,Ga)-Metalloid

Mg + Ln +LTM Mg-Ln-Ni、Mg-Ln-Cu

TM(Zr or Ti) + Be + LTM Zr-Ti-Be-Ni-Cu

V LTM + Metalloid Pd-Ni-P、Pd-Cu-Ni-P、Pt-Ni-p

ETM = IVB~VIB Group Transition Metal LTM = VIIB~VIIIB Group Transition Metal

Table 2.2 The annual of bulk amorphous alloy was first published [9].

I. Nonferrous metal base II. Ferrous metal base

Constituents Year Constituents Year

Mg-Ln-M Ln-Al-TM Ln-Ga-TM Zr-Al-TM Zr-Ti-Al-TM Ti-Zr-TM Zr-Ti-TM-Be Zr-(Nb, Pd)-Al-TM Pd-Cu-Ni-P

Pd-Ni-Fe-P Pd-Cu-B-Si Ti-Ni-Cu-Sn Zr-Nb-Cu-Fe-Be

1988 1989 1989 1990 1990 1993 1993 1995 1996 1996 1997 1998 2000

Fe-(Al, Ga)-(P, C, B, Si, Ge) Fe-(Nb, Mo)-(Al, Ga)-(P, B, Si) Co-(Al, Ga)-(P, B, Si)

Fe-(Zr, Hf, Nb)-B Co-Fe-(Zr, Hf, Nb)-B Ni-(Zr, Hf, Nb)-(Cr, Mo)-B Fe-Co-Ln-B

Ni-Ti-P

Ni-(Nb, Cr, Mo)-(P, B) Fe-Mn-Mo-Cr-C-B

1995 1995 1996 1996 1996 1996 1998 1999 1999 2002

Ln = Lanthanide Metal, M = Ni, Cu, Zn TM = VIB~VIIIB Group Transition Metal

Table 2.3 Summary of △T_x, T_rg, γ, critical cooling rate Rc and critical section thickness Zc

for typical bulk amorphous alloys [32].

Table 2.4 The exponent n for the JMA equation for different kinds of crystallization mechanisms [48-51].

Table 3.1 The alloy systems selected in this study.

Mg Cu Y B at% wt% at% wt% at% wt% at% wt%

Mg65Cu25Y10 65 9.74 25 9.78 10 5.48 0 0

Mg₆₅Cu₂₅Y₉B₁ 65 9.93 25 9.98 9 5.02 1 0.07

Mg65Cu25Y7B3 65 10.33 25 10.38 7 4.07 3 0.22

Mg65Cu25Y5B5 65 10.77 25 10.83 5 3.03 5 0.37

Mg65Cu25B10 65 12.06 25 12.12 0 0 10 0.82

Mg65Cu24Y10B1 65 9.86 24 9.52 10 5.55 1 0.07

Mg65Cu22Y10B3 65 10.13 22 8.96 10 5.70 3 0.21

Mg65Cu20Y10B5 65 10.41 20 8.37 10 5.86 5 0.36

Mg₆₅Cu₁₅Y₁₀B₁₀ 65 11.19 15 6.75 10 6.30 10 0.76

Table 4.1 Summary of the density for various alloy combinations _____________________________________________________________

Composition Theoretical density True density

Mg/m³ Mg/m³

_____________________________________________________________

Mg65Cu25Y10 3.82 3.09

---

Mg65Cu24Y10B1 3.82 --

Mg65Cu22Y10B3 3.62 3.46

Mg65Cu20Y10B5 3.49 3.24

Mg65Cu15Y10B10 3.16 --

---

Mg65Cu25Y7B3 3.76 3.81

Mg65Cu25Y5B5 3.71 3.74

Mg65Cu25B10 3.61 --

_____________________________________________________________

Pure elements:

* Mg: 1.74 Mg/m³; Cu: 8.96 Mg/m³; Y: 4.48 Mg/m³; B: 2.35 Mg/m³

Table 5.1 Summary of bonding parameter ∆x and δ for Mg-Cu-Y-B alloys.

_____________________________________________________________

Compositions ∆x δ ∆x．δ

_____________________________________________________________

Mg65Cu25Y10 0.305 0.07 0.021

--- Mg65Cu24Y10B1 0.306 0.08 0.025

Mg65Cu22Y10B3 0.307 0.10 0.031 Mg65Cu20Y10B5 0.309 0.11 0.034 Mg65Cu15Y10B10 0.321 0.14 0.045

--- Mg65Cu25Y7B3 0.316 0.09 0.028

Mg65Cu25Y5B5 0.323 0.10 0.032 Mg65Cu25B10 0.334 0.12 0.040

______________________________________________________________

Table 5.2 Summary of Tg , Tx , ∆Tx and γ value for the Mg-Cu-Y-B amorphous alloys at a heating of 20 K/min.

_____________________________________________________________________

Compositions Tg Tx ∆Tx Tmsolid

Tmliquid γ _____________________________________________________________________

Mg₆₅Cu₂₅Y₁₀ 410 468 58 728 760 0.40 Mg₆₅Cu₂₂Y₁₀B₃ 410 476 66 715 738 0.42 Mg₆₅Cu₂₀Y₁₀B₅ 420 470 50 712 736 0.41 Mg₆₅Cu₁₅Y₁₀B₁₀420 465 45 --- --- --- --- Mg₆₅Cu₂₅Y₇B₃ 420 457 37 Mg₆₅Cu₂₅Y₅B₅ 408 430 22 --- --- ---

Mg₆₅Cu₂₅B₁₀ Not amorphous alloy

_____________________________________________________________________

Fig. 1.1 The atomic arrangements of crystal and amorphous alloy [1].

Figs. 2.1 Schematic drawings of four quenching methods from the melt: (a) piston and anvil, (b) melt spinning, (c) melt extraction, and (d) twin roller quenching.

Fig. 2.3 Relationship between the critical cooling rate (R_c), the maximum sample thickness (tmax) and reduced glass transition temperature (Tg/Tm) for bulk amorphous systems [9].

Fig. 2.4 Relationship between the critical cooling rate (Rc) and the maximum sample thickness (t_max) for bulk amorphous alloy systems [9].

G F A

Liquid phase stability

Resistance to crystallization

Stability at equilibrium

state

Stability at metastable

state

Upon heating

1( TL+ Tg)

TTT position along temperature axis

TTT position along time axis

Fig. 2.5 The parameter of γ for glass forming ability (GFA) [32].

Fig. 2.6 The atomic arrangement of the different atomic size system.

Fig. 2.7 The three empirical rules was proposed by Inoue [33].

Figs. 2.8 The relationship between the bond parameters, including electronegativity difference (∆X) and atomic size parameters (δ), and the widths of supercooled liquid region (∆Tx) in Mg-Based bulk metallic glasses [38].

Figs. 2.9 Relationship between the Young’s modulus, tensile strength and hardness for various metallic glass systems [9].

Fig. 3.1 Flow chart showing the experiment procedures.

Fig. 3.2 Photograph of the arc melting device.

Fig. 3.3 Photography of the melt spinning device.

Fig. 3.4 The DSC trace for amorphous alloy at heating.

30 ^oC, 600s 10^oC/min

400^oC, 300s

oC/min

30 ^oC, 600s

T em p era tu re (

C )

Time (sec.)

(a)

20^oC/min

min

30 ^oC, 600s 10^oC/min

oC,

30 ^oC, 600s

T em p erature (

C )

Time (sec.)

(b)

Fig. 3.5 The DSC programs for (a) non-isothermal, and (b) isothermal analyses.

Fig. 4.1 The experiment procedures for Mg-based amorphous alloys.

Fig. 4.2 Surface appearance of the melt spun Mg-Cu-Y-B amorphous alloy.

Fig. 4.3 Bending behavior of the Mg-Cu-Y amorphous alloy.

20 30 40 50 60 70 80

∗ MgB₄

∗

^Mg²^Cu

X = 5

X = 3

X = 1

X = 0

Intensity

2θ

Fig. 4.4 X-ray diffraction patterns for the melt spun Mg65Cu25Y10-xBx alloy.

10 20 30 40 50 60 70 80

MgB₄ Mg₂Cu

Intensity

2θ

Fig. 4.5 X-ray diffraction patterns of the melt spun Mg65Cu25B10 alloy.

20 30 40 50 60 70 80 X = 10

X = 5 X = 3

X = 1 X = 0

Intensity

2θ

Fig. 4.6 X-ray diffraction patterns for the melt spun Mg₆₅Cu_25-xY₁₀B_xalloy.

(a)

(b)

Fig. 4.7 SEM/EPMA micrographs of the Mg₆₅Cu₂₅Y₁₀ metallic glass: (a) BEI image (b) mapping image.

0 2 4 6 8 1 220

240 260 280 300 320 340

0 Mg65Cu

25-xY

10B

Mg₆₅Cu₂₅Y_10-xB_x 290

270 258

327 325 310

280

220 Vicker hardness (H V)

B (at.%)

Fig. 4.8 Hardness as a function of B content for the Mg65Cu25-xY10Bx and Mg65Cu25Y10-xBx alloys.

Fig. 4.9 SEM/BEI micrograph showing the shear bands in the Mg-Cu-Y-B alloy.

400 450 500 550 600 650 30 K/min

20 K/min 10 K/min Mg₆₅Cu₂₅Y₁₀

Exothermic

Temperature (K)

Fig. 4.10 DSC curves of the amorphous Mg65Cu25Y10 alloy.

400 450 500 550 600 650

30 K/min 20 K/min 10 K/min

Exothermic

Temperature (K)

Mg65Cu

22Y

10B

Fig. 4.11 DSC curves of the amorphous Mg65Cu22Y10B3 alloy.

400 450 500 550 600 650 30 K/min

20 K/min 10 K/min Mg₆₅Cu₂₀Y₁₀B₅

Exothermic

Temperature (K)

Fig. 4.12 DSC curves of the amorphous Mg65Cu20Y10B5 alloy.

400 450 500 550 600 650

30 K/min 20 K/min 10 K/min Mg65Cu

15Y

10B

Exothermic

Temperature (K)

Fig. 4.13 DSC curves of the amorphous Mg65Cu15Y10B10 alloy.

400 450 500 550 600 650 Mg

Cu

25-X

Y

B

T_x1 T_g

X = 0 X = 10 X = 5 X = 3

Ex ot h er m ic

Temperature (K)

Fig. 4.14 DSC curves of the amorphous Mg₆₅Cu_25-xY₁₀B_x (x = 0, 3, 5, 10) alloy at a heating rate of 20 K/min.

0 2 4 6 8 10 400

420 440 460 480 500

465 470

476 468

420 420 410 410

onset glass transition temperature onset crystallization temperature

Temperature (K)

B (at.%)

Fig. 4.15 Glass transition and crystallization temperature as a function of B content for the Mg₆₅Cu_25-xY₁₀B_x alloys.

400 450 500 550 600 650 Mg

Cu

Y

10-X

B

T_x1 T_g

E xot herm ic

Temperature (K)

X = 5 X = 3 X = 0

Fig. 4.16 DSC curves of the amorphous Mg65Cu25Y10-xBx (x = 0, 3, 5) alloys at a heating rate of 20 K/min.

400 450 500 550 600 650

Exothermic

Temperature (K)

Mg₆₅Cu₂₂Y₁₀B₃

Mg65Cu

25Y

Fig. 4.17 DSC curves of the amorphous Mg65Cu25Y7B3 and Mg65Cu22Y10B3 alloys at a heating rate of 20 K/min.

650 675 700 725 750

Exothermic

Temperature (K)

T

^liq_m

T

^Sol_m

X = 5 X = 3

Fig. 4.18 DSC traces showing the melting endotherms obtained from the Mg65Cu25Y10-xBx (x = 3, 5) alloy at a heating rate of 20 K/min.

2.04 2.08 2.12 2.16 2.20 -10.0

-9.6 -9.2 -8.8

E_p=166 kJ/mol

E_x=138 kJ/mol

ln(φ/T2 )

(1/T x 10³) (1/K) (a)

2.04 2.08 2.12 2.16 2.20

-10.0 -9.6 -9.2 -8.8

ln(φ/T2 )

(1/T x 10³) (1/K)

E_x=156 kJ/mol

E_p=164 kJ/mol

(b)

Fig. 4.19 Kissinger plots for the melt spun alloys: (a) Mg65Cu25Y10 and (b) Mg65Cu22Y10B3.

2.04 2.08 2.12 2.16 2.20 -10.0

-9.6 -9.2 -8.8

E_p=164 kJ/mol

E_x=149 kJ/mol

ln(φ/T2 )

(1/T x 10³) (1/K) (a)

2.04 2.08 2.12 2.16 2.20

-10.0 -9.6 -9.2 -8.8

ln(φ/T2 )

(1/T x 10³) (1/K)

E_x=151 kJ/mol

E_p=162 kJ/mol

(b)

Fig. 4.20 Kissinger plots for the melt spun alloys: (a) Mg65Cu20Y10B5 and (b) Mg₆₅Cu₁₅Y₁₀B_10.

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 -12

-8 -4 0 4

ln[-ln(1-X)]

lnφ

470 K n=5.44 472 K n=4.86 474 K n=4.15 476 K n=3.38 478 K n=2.59 480 K n=1.81

Fig. 4.21 The extraction of the n value from the modified non-isothermal equation for Mg65Cu25Y10.

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6

-12 -8 -4 0 4

ln[-ln(1-X)]

lnφ

474 K n=9.38 476 K n=7.14 478 K n=5.73 480 K n=4.56 482 K n=3.53 484 K n=2.59 486 K n=1.76 488 K n=1.45 490 K n=1.43

Fig. 4.22 The extraction of the n value from the modified non-isothermal equation for Mg₆₅Cu₂₂Y₁₀B₃.

1.95 2.00 2.05 2.10 2.15 2.20 2.25 -16

-12 -8 -4 0 4

10 K/min 20 K/min 30 K/min

ln[-ln(1-X)]

1000/T (K^-1)

Fig. 4.23 Extraction of the activation energy from the modified non-isothermal DSC scan for Mg65Cu25Y10.

1.95 2.00 2.05 2.10 2.15 2.20 2.25

-16 -12 -8 -4 0 4

ln[-ln(1-X)]

1000/T (K^-1)

10 K/min 20 K/min 30 K/min

Fig. 4.24 Extraction of the activation energy from the modified non-isothermal DSC scan for Mg65Cu22Y10B3.

1.95 2.00 2.05 2.10 2.15 2.20 2.25 -16

-12 -8 -4 0 4

10 K/min 20 K/min 30 K/min

ln[-ln(1-X)]

1000/T (K^-1)

Fig. 4.25 Extraction of the activation energy from the modified non-isothermal DSC scan for Mg₆₅Cu₂₀Y₁₀B₅.

1.95 2.00 2.05 2.10 2.15 2.20 2.25

-16 -12 -8 -4 0 4

ln[-ln(1-X)]

1000/T (K^-1)

10 K/min 20 K/min 30 K/min

Fig. 4.26 Extraction of the activation energy from the modified non-isothermal DSC scan for Mg₆₅Cu₁₅Y₁₀B₁₀.

0 2000 4000 6000 8000

Ex oth erm ic

Tims (sec)

440 K 438 K 435 K 433 K

Fig. 4.27 DSC trace of isothermal annealing for Mg₆₅Cu₂₅Y₁₀ amorphous alloy.

0 2000 4000 6000 8000

440 K

438 K

435 K

433 K

Ex o the rm ic

Tims (sec)

Fig. 4.28 DSC trace of isothermal annealing for Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy.

Fig. 4.29 PeakFit software for Mg65Cu25Y10.

Fig. 4.30 PeakFit software for Mg₆₅Cu₂₂Y₁₀B₃.

0 1000 2000 3000 4000 5000 6000 7000 0

20 40 60 80

100 ^{440 K} ^{438 K} ^{435 K} ^{433 K}

F raction of crystalliz a tion (% )

Time (sec)

Fig. 4.31 The plot of transformed volume fraction versus time for Mg₆₅Cu₂₅Y₁₀.

0 1000 2000 3000 4000 5000 6000 7000 0

20 40 60 80

100 ^{440 K} ^{438 K} ^{435 K} ^{433 K}

Fraction of crystalliz a tion (% )

Time (sec)

Fig. 4.32 The plot of transformed volume fraction versus time for Mg65Cu22Y10B3.

6.0 6.5 7.0 7.5 8.0 8.5 -3

-2 -1 0 1

2 433 K

435 K 438 K 440 K

ln [-ln (1 -X )]

lnt (sec)

3.5

Fig. 4.33 The variation of Avrami exponent n for Mg₆₅Cu₂₅Y₁₀.

6.0 6.5 7.0 7.5 8.0 8.5

-3 -2 -1 0 1 2

ln[-ln (1-X)]

lnt (sec)

433 K 435 K 438 K 440 K

3.3

Fig. 4.34 The variation of Avrami exponent n for Mg65Cu22Y10B3.

2.26 2.28 2.30 2.32 6.8

7.2 7.6 8.0 8.4 8.8

lnt (sec)

1000/T (K^-1)

Q 10% 134 20% 144 30% 149 40% 153 50% 156 60% 159 70% 161 80% 164 90% 166

Fig. 4.35 Extraction of isothermal activation energy of the first crystalline phase for the Mg65Cu22Y10B3 amorphous alloy.

2.26 2.28 2.30 2.32

6.8 7.2 7.6 8.0 8.4 8.8

Q 10% 211 20% 211 30% 210 40% 210 50% 211 60% 210 70% 211 80% 211 90% 210

lnt (sec)

1000/T (K^-1)

Fig. 4.36 Extraction of isothermal activation energy of the first crystalline phase for the Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy.

2.26 2.28 2.30 2.32 5.2

5.6 6.0 6.4 6.8 7.2

lnt (sec)

1000/T (K^-1)

Q 10% 200 20% 202 30% 202 40% 204 50% 202 60% 202 70% 202 80% 206 90% 205

Fig. 4.37 Extraction of isothermal activation energy of the second crystalline phase for the Mg65Cu22Y10B3 amorphous alloy.

(a) (b)

Fig. 4.38 The TEM images of the as-melt-spun Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy:

(a) Bright field image and (b) Selected area diffraction pattern.

Fig. 4.39 The TEM images of the yttrium oxide particle in the as-melt-spun Mg65Cu22Y10B3 amorphous alloy: (a) Bright field image and (b) Selected area diffraction pattern.

(a) (b)

(c)

Fig. 4.40 The TEM images of the crystallization in the Mg65Cu22Y10B3 amorphous alloy annealed to 670 K then cooled to room temperature: (a) Bright field image, (b) Selected area diffraction pattern, and (c) EDS analysis.

(a) (b)

(c)

Fig. 4.41 The TEM images of the crystallization in the Mg65Cu22Y10B3 amorphous alloy annealed to 670 K then cooled to room temperature: (a) Bright field image, (b) Selected area diffraction pattern, and (c) EDS analysis.

(a) (b)

(c)

Fig. 4.42 The TEM images of the crystallization in the Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy annealed to 670 K then cooled to room temperature: (a) Bright field image, (b) Selected area diffraction pattern, and (c) EDS analysis.

(a) (b)

Fig. 4.43 The TEM images of the crystallization in the Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy annealed to 670 K then cooled to room temperature: (a) Bright field image and (b) Selected area diffraction pattern.

(a) (b)

Fig. 4.44 The TEM images of the crystallization in the Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy annealed to 670 K then cooled to room temperature: (a) Bright field image and (b) Selected area diffraction pattern.

(a) (b)

Fig. 4.45 The TEM images of the crystallization in the Mg₆₅Cu₂₂Y₁₀B₃ amorphous alloy annealed to 670 K then cooled to room temperature: (a) Bright field image and (b) Selected area diffraction pattern.

0 2 4 6 8 10 0.020

0.025 0.030 0.035 0.040 0.045

?x . δ

B (at. %)

Mg

Cu

25-x

Y

B

Mg

Cu

Y

10-x

B

Fig. 5.1 Bonding parameter for the Mg-based alloys against boron content.

20 30 40 50 60 70 80 600 K

560 K

500 K

Intensit y

2θ

Fig. 5.2 The overall crystallization in the Mg₆₅Cu₂₂Y₁₀B₃.

20 30 40 50 60 70 80

600 K

500 K

470 K

In ten sity

2θ

Fig. 5.3 The overall crystallization in the Mg65Cu15Y10B10.

2.00 2.04 2.08 2.12 2.16 -10.0

-9.6 -9.2 -8.8

(1/T x10

) (1/K) ln ( φ /T

)

Q 10% 154 20% 155 30% 156 40% 156 50% 154 60% 151 70% 145 80% 136 90% 123

Fig. 5.4 Extraction of non-isothermal activation energy for the Mg₆₅Cu₂₅Y₁₀.

2.00 2.04 2.08 2.12 2.16

-10.0 -9.6 -9.2 -8.8

ln ( φ /T

)

(1/T x10

) (1/K)

Q 10% 152 20% 153 30% 155 40% 154 50% 150 60% 146 70% 140 80% 131 90% 121

Fig. 5.5 Extraction of non-isothermal activation energy for the Mg65Cu22Y10B3.

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