lass forming ability of binary ZR CU and ternary ZR CU AL alloys

GLASS FORMING ABILITY OF BINARY ZR-CU AND
TERNARY ZR-CU-AL ALLOYS














WANG DONG
(M.Eng, HUST)

A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF MATERIALS SCIENCE & ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2008



i

Acknowledgments

I would like to express my sincere appreciation and thanks to my supervisor, Associate
Professor Li Yi., for his supervision, constructive advice and help throughout this project.
Special thanks to the technicians in Department of Materials Science and
Engineering, Mr. Chan Yew Weng, Mr. Chen Qun, Ms. Lim Agnes, and Ms. Yin Hong
for helping me make use of the Laboratory’s equipment.
To the members of the non-equilibrium processing Lab, past and present, I extend
my very sincere thanks. Their friendship and help during my study have been wonderful.
It is the opportunity to have met and worked with all of them that has made my studies
worthwhile.
Words cannot express the gratitude and debt I owe to my parents. Without their
encouragement and support I am sure I would not have had the strength to finish this
project.
Lastly, I would like to acknowledge the support of the National University of
Singapore for granting me a research scholarship.

2008

Singapore Dong WANG


ii

Table of Contents

Acknowledgement i

Table of Contents ii

Summary vi

List of Tables ix

List of Figures x

List of Publication xxiv

Chapter 1 Introduction 1
Chapter 2 Literature Review 5
2.1 Development and property of bulk metallic glasses 5
2.1.1 Development of bulk metallic glasses 5
2.1.2 Properties of bulk Metallic Glasses 11
2.2 Practical methods of preparing bulk metallic glasses 13
2.2.1 Water quenching 13
2.2.2 Casting method 14
(a) Chill casting method 14
(b) High-pressure die casting method 14
(c) Suction casting method 16

2.2.3. Bridgman solidification technique 16
2.3 Scaling parameters for glass forming ability 17
2.3.1 Reduced glass transition temperature T
rg
18
2.3.2 Extent of undercooled liquid region
∆
T
x
20


iii
2.3.3 Failure of GFA scaling parameters 21
2.4 Empirical rules to discover alloy systems forming BMGs 21
2.4.1 Thermodynamics consideration 22
2.4.2 Kinetics consideration 22
2.4.3 Structure consideration 23
2.5 Glass formation in Zr based alloys 25
Chapter 3 Experimental Procedure 29
3.1 Sample preparation 29
3.1.1 Alloy preparation 29
3.1.2 Chill casting 29
(a) 2 mm copper mould casting 29
(b) 5 mm and 8 mm copper mould casting 31
3.2 Microstructure characterization 32
3.2.1 X-ray diffraction 32
3.2.2 Optical microscopy and scanning electron microscopy 33
3.3 Thermal analysis 34
3.3.1 Differential scanning calorimeter 34

3.3.2 Differential thermal analysis 35
Chapter 4 Results 36
4.1 GFA study of alloys in Cu
8
Zr
3
-Cu
10
Zr
7
binary eutectic system 36
4.1.1 2 mm casting of alloys in Cu
8
Zr
3
-Cu
10
Zr
7
eutectic system 37
4.2 Melting study of alloys in τ
3
-Zr
2
Cu-ZrCu, τ
3
-τ
5
-ZrCu and τ
5

-ZrCu-Cu
10
Zr
7
ternary
eutectic systems 45
4.2.1 Eutectic point in τ
3
-τ
5
-ZrCu system 45
4.2.2 Eutectic points in τ
5
-ZrCu-Cu
10
Zr
7
and τ
3
-Zr
2
Cu-ZrCu systems 47
4.3 GFA study of alloys in τ
3
-τ
5
-ZrCu ternary eutectic system 49
4.3.1 5 mm casting of the eutectic alloy in τ
3
-τ

5
-ZrCu system 49
4.3.2 Formation of (τ
3
+ glass matrix) composite 50
4.3.3 Formation of (τ
5
+ glass matrix) composite 57
4.3.4 Formation of (ZrCu + glass matrix) composite 61


iv
4.3.5 Formation of 5 mm fully amorphous BMG 63
4.3.6 Formation of 8 mm fully amorphous BMG 70
4.4 GFA study of alloys in τ
5
-ZrCu-Cu
10
Zr
7
ternary eutectic system 72
4.5 GFA study of alloys in τ
3
-Zr
2
Cu-ZrCu ternary eutectic system 81
Chapter 5 Discussions 92
5.1 Correlation between GFA and T
rg
,

∆
T
x
in binary Cu
8
Zr
3
-Cu
10
Zr
7
system 92
5.2 A new strategy to pinpoint the optimum glass former in binary eutectic systems . 95
5.2.1 Concept of phase selection 95
5.2.2 Calculated optimum glass forming zone in Cu
8
Zr
3
-Cu
10
Zr
7
system 98
5.2.3 Establishment of a new strategy to pinpoint the optimum glass former in
binary eutectic systems 105
5.2.4 Confirmation of the microstructure-based strategy for pinpointing the optimum
glass former in binary eutectic by Cu
8
Zr
3

-Cu
10
Zr
7
system 109
5.2.5 Other Considerations 113
(a) Strong dependency of GFA on alloy composition in binary alloy systems 113
(b) Binary BMGs 113
5.3 Correlation between GFA and T
rg
,
∆
T
x
in ternary τ
3
-τ
5
-ZrCu, τ
5
-ZrCu-Cu
10
Zr
7
and
τ
3
-Zr
2
Cu-ZrCu systems 114

5.3.1 τ
3
-τ
5
-ZrCu system 117
5.3.2 τ
5
-ZrCu-Cu
10
Zr
7
system 120
5.3.3 τ
3
-Zr
2
Cu-ZrCu system 121
5.4 A new strategy to pinpoint the optimum glass former in ternary eutectic systems
123
5.4.1 Establishment of a new strategy to pinpoint the optimum glass former in
ternary eutectic systems 123
5.4.2 Confirmation of the microstructure-based strategy for pinpointing the optimum
glass former in ternary eutectic by τ
3
-τ
5
-ZrCu, τ
5
-ZrCu-Cu
10

Zr
7
and τ
3
-Zr
2
Cu-ZrCu
systems 131
(a) Previously reported Zr-Cu-Al bulk metallic glasses 131
(b) τ
3
-τ
5
-ZrCu system 132


v
(c) τ
5
-ZrCu-Cu
10
Zr
7
system 134
(d) τ
3
-Zr
2
Cu-ZrCu system 137
5.4.3 Other considerations 139

(a) Composite formation 139
(b) Strong dependency of GFA on alloy composition in ternary alloy systems. 140
Chapter 6 Conclusions 142
Chapter 7 Future Work 144
Bibliography 146
Appendix 150










vi

Summary

Although since the 1960s, many metallic glasses and bulk metallic glasses (BMGs) have
been reported, the way to find the alloy composition with the optimum glass forming
ability (GFA) within an alloy system still remains unclear. The first purpose of the
present study is to establish a practical strategy to pinpoint the optimum glass forming
alloy precisely in an alloy system.
Zr based alloy systems have become one of the most promising to discover bulk
metallic glasses. Moreover, Zr based bulk metallic glasses have exhibited a combination
of various good mechanical properties, which cannot be obtained for conventional
crystalline alloys. The second purpose of the present study is to obtain bulk metallic
glasses in the Zr-Cu binary and the Zr-Cu-Al ternary systems.

In this work, based on the principle of the competition of the formation/growth of
glass and crystalline phases, a metallographic strategy to pinpoint the optimum glass
former within a binary eutectic alloy system was established. The essence of this
metallographic strategy is that by monitoring the microstructure evolution with
composition and finding the junction where two composite (glass + primary phase ,
glass + primary phase ) zones meet, one can precisely pinpoint the optimum glass
former in the binary eutectic system. With the implementation of this strategy in the
binary Cu
8
Zr
3
-Cu
10
Zr
7
eutectic system, we successfully found the optimum glass forming


vii
alloy in this system and obtained 2 mm Zr
35.5
Cu
64.5
bulk metallic glass. This breaks the
empirical condition previously believed necessary for BMG formation, i.e. a multi-
component recipe with at least three components.
By extending the metallographic strategy for pinpointing the optimum glass
former within a binary eutectic alloy system to ternary systems, a metallographic strategy
to pinpoint the optimum glass former within a ternary eutectic alloy system was also
established. This metallographic strategy was applied to three adjacent eutectic systems,

τ
3
(Zr
51
Cu
28
Al
21
)-τ
5
(Zr
38
Cu
36
Al
26
)-ZrCu, τ
5
-ZrCu-Cu
10
Zr
7
and τ
3
-Zr
2
Cu-ZrCu, and three
optimum glass forming alloys (region) were precisely pinpointed. The discovered
optimum glass forming alloy in the τ
3

-τ
5
-ZrCu eutectic system can even form 8 mm bulk
metallic glass.
During the implementation of these metallographic strategies, we found that GFA
has a strong dependency on the alloy composition in both binary and ternary eutectic
systems. For example, in the binary Cu
8
Zr
3
-Cu
10
Zr
7
eutectic system, only Cu
64.5
Zr
35.5
can
obtain 2 mm fully glass cast rod; deviations of only 0.5 at% caused the appearance of
crystalline in 2 mm cast rods. Moreover, the 2 mm BMG composite zone (encompassing
the optimum glass forming composition, Cu
64.5
Zr
35.5
) was only from Cu
63
Zr
37
to

Cu
65.5
Zr
34.5
, a mere 2.5 at% range. In the τ
3
(Zr
51
Cu
28
Al
21
)-τ
5
(Zr
38
Cu
36
Al
26
)-ZrCu eutectic
system, 1 at% compositional deviation away from the optimum glass forming alloy,
Zr
48
Cu
45
Al
7
, decreased the BMG size from 8 mm to 5 mm. This narrow bulk-glass-
forming range and strong composition dependency of GFA explains why our discovered

binary bulk metallic glasses and ternary bulk metallic glasses were missed before. It also


viii
manifests the advantage of our microstructure-based strategies to pinpoint optimum glass
formers.

ix
List of Tables

Summary of results of morphology observations, DSC
and DTA analysis of 5 mm cast rods of typical Zr-Cu-
Al alloys in the τ
3
-Zr
2
Cu-ZrCu eutectic system.
Table 4.4
Page 82
Summary of results of morphology observations, DSC
and DTA analysis of 5 mm cast rods of typical Zr-Cu-
Al alloys in the τ
5
-ZrCu-Cu
10
Zr
7
eutectic system.
Table 4.3
Page 75
Summary of results of morphology observations, DSC
and DTA analysis of 5 mm cast rods of typical Zr-Cu-
Al alloys in the τ
3
-τ

5
-ZrCu eutectic system.
Table 4.2
Page 69
Results of DSC analysis of 2 mm cast rods of binary
alloys in the Cu
8
Zr
3
-Cu
10
Zr
7
eutectic system. The
liquidus temperature T
l
was obtained from Zr-Cu phase
diagram [Ref. 89].
Table 4.1
Page 51
Properties of Vit1 BMGs compared with some
crystalline metal alloys. (adapted from Ref. [11])
Table 2.4
Page 28
Typical Zr based ternary bulk metallic glasses.
Table 2.3
Page 27
Summary of bulk metallic glass’s application and
expected application in the future. (adapted from Ref.
[10])

Table 2.2
Page 12
Summary of Bulk Metallic Glass Alloys with critical
size bigger that 10 mm. (Adapted from Ref. [37])
Table 2.1
Page 9


x
List of Figures
















Vit1 BMGs combine higher strength than crystalline metal
alloys with the elasticity of polymers. (adapted from Ref.
[11])
Figure 2.5.2

Page 28
Calculated phase diagram of Zr-Cu, experimentally
observed glass forming range of the Zr-Cu alloy system
and calculated glass forming range of the Zr-Cu alloy
system under the cooling rate of 10
7
K/s. (adapted from
Ref. [74-76])

Page 25
Figure 2.5.1
A simplified binary alloy phase diagram showing the T
g

and T
l
as a function of compositions. (T
g
is the glass
transition temperature, T
m
is the onset melting temperature
and T
l
is the liquidus temperature)
Figure 2.3.2
Page 20
Critical cooling rates for glass formation of several alloys
based on Pd, Zr, La, Mg, rare-earth and several inorganic
glasses as a function of T

rg
values. (adapted from Ref.
[57])
Figure 2.3.1
Page 19
Schematic diagram of the apparatus used in some
laboratories for Bridgman direction solidification.
Figure 2.2.2
Page 17
Schematic illustration of high-pressure die casting
equipment used for bulk metallic glass formation.
Figure 2.2.1
Page 15
Five groups of BMG forming alloy systems categorized by
Inoue. ETM and LTM represent the transition metals
belonging to groups IV-VI and VII-VIII in the periodic
table respectively. (Adapted from Ref. [10])
Figure 2.1.3
Page 10
Maximum thickness, t
max
, of a variety of bulk metallic
glasses discovered in the last five decades.
Figure 2.1.2
Page 10
Gun technique of Duwez for rapid solidification of melts.
Figure 2.1.1
Page 6

xi

















SEM micrographs showing (a) the transversal cross
section of 2 mm cast rod of Zr
35.5
Cu
64.5
and (b) the
featureless morphology of this 2 mm cast rod at high
magnification.
Figure 4.1.6
Page 40
SEM micrographs showing the transversal cross section of
2 mm cast rods of (a) Zr

36.5
Cu
63.5
, (b) Zr
36
Cu
66
and the
morphology of the crystalline “islands” in amorphous
matrix of 2 mm rods of (c) Zr
36.5
Cu
63.5
, (d) Zr
36
Cu
64
at high
magnification.
Figure 4.1.5
Page 40
SEM micrographs showing (a) the transversal cross
section of 2 mm cast rod of Zr
37
Cu
63
and (b) the
morphology of the crystalline “islands” in amorphous
matrix of this 2 mm rod at high magnification.
Figure 4.1.4

Page 39
SEM micrographs showing the transversal cross section of
2 mm cast rods of (a) Zr
38.2
Cu
61.8
, (b) Zr
37.5
Cu
62.5
and the
morphology of the fully crystalline region in the center of
2 mm rods of (c) Zr
38.2
Cu
61.8
, (d) Zr
37.5
Cu
62.5
at high
magnification.
Figure 4.1.3
Page 39
XRD patterns of 2 mm cast rods of Zr
38.2
Cu
61.8
,
Zr

37.5
Cu
62.5
, Zr
37
Cu
63
, Zr
36.5
Cu
63.5
,

Zr
36
Cu
64
, Zr
35.5
Cu
64.5
,
Zr
35
Cu
65
and Zr
34.5
Cu
65.5.

Figure 4.1.2
Page 38
Phase diagram of Zr-Cu. (Adapted from Ref. [89])
Figure 4.1.1
Page 37
Photo of the 8 mm copper mould and crucible in the
chamber of the LSG-400 arc-melting system.
Figure 3.1.3
Page 32
Photo of the 2 mm casting equipment modified from the
Edmund Buhler D-7400 MAM-1 mini arc melting system.
Figure 3.1.2
Page 31
Schematic diagram of the 2 mm casting equipment.
Figure 3.1.1
Page 30


xii

XRD pattern of 5 mm cast rod of alloy 3 (Zr
48
Cu
38
Al
14
).
(inset: DSC curve of this 5 mm cast rod)
Figure 4.3.1
Page 49
DTA melting curves of alloy 6 (Zr
52
Cu
38
Al
10
), and its three
surrounding alloys, Zr
50
Cu
40

Al
10
, Zr
52
Cu
36
Al
12
and
Zr
54
Cu
38
Al
8
.
Figure 4.2.4
Page 48
DTA melting curves of alloy 47 (Zr
45
Cu
49
Al
6
), and its
three surrounding alloys, Zr
45
Cu
47
Al

8
, Zr
47
Cu
49
Al
4
and
Zr
43
Cu
51
Al
6
.
Figure 4.2.3
Page 48
DTA melting curves of Zr
48
Cu
38
Al
14
(alloy 3) and its three
surrounding alloys, Zr
46
Cu
38
Al
16

, Zr
50
Cu
36
Al
14
and
Zr
48
Cu
40
Al
12
.
Figure 4.2.2
Page 47
Experimentally determined liquidus isotherms of the τ
3
-
Zr
2
Cu-ZrCu, τ
3
-τ
5
-ZrCu and τ
5
-ZrCu-Cu
10
Zr

7
systems
with three corresponding eutectics points found at
Zr
52
Cu
38
Al
10
(alloy 6),

Zr
48
Cu
38
Al
14
(alloy 3) and
Zr
45
Cu
49
Al
6
(alloy 47) respectively.
Figure 4.2.1
Page 46
GFA change of alloys in the Cu
8
Zr

3
-Cu
10
Zr
7
binary
eutectic system.
Figure 4.1.11
Page 44
values of H
x
(enthalpy of crystallization) of 2 mm cast
rod as a function of Cu content in the Cu
8
Zr
3
-Cu
10
Zr
7

eutectic system.
Figure 4.1.10
Page 44
DSC curves of 2 mm cast rods

of Zr
35.5
Cu
64.5

, Zr
35
Cu
65
and
Zr
34.5
Cu
65.5
.
Figure 4.1.9
Page 43
DSC curves of 2 mm cast rods of Zr
38.2
Cu
61.8
, Zr
37.5
Cu
62.5
,
Zr
37
Cu
63
, Zr
36.5
Cu
63.5
,

Zr
36
Cu
64
and Zr
35.5
Cu
64.5
.
Figure 4.1.8
Page 42
SEM micrographs showing the transversal cross section of
2 mm cast rods of (a)

Zr
35
Cu
65
, (b)

Zr
34.5
Cu
65.5
and the
morphology of the crystalline “islands” in amorphous
matrix of 2 mm rods of (c) Zr
35
Cu

65
, (d) Zr
34.5
Cu
65.5
at high
magnification.
Figure 4.1.7
Page 41


xiii














XRD patterns of 5 mm cast rods of alloy 11
(Zr
46
Cu

42
Al
12
), alloy 39 (Zr
46
Cu
44
Al
10
)

and alloy 40
(Zr
47
Cu
45
Al
8
) showing the decrease of the intensity of
crystalline diffraction peaks from alloy 11 to alloy 40.
Figure 4.3.8
Page 57
DSC curves of 5 mm cast rods of alloy 8 (Zr
50
Cu
34
Al
16
),
alloy 2 (Zr

50
Cu
36
Al
14
), alloy 1 (Zr
50
Cu
38
Al
12
), alloy 7
(Zr
50
Cu
40
Al
10
) and alloy 55 (Zr
50
Cu
43
Al
7
).
Figure 4.3.7
Page 56
Schematic summarization of the morphology evolution of
the transversal cross sections of alloys 8, 2, 1, 7 and 55 (5
mm copper mould casting).

Figure 4.3.6
Page 55
SEM micrographs showing (a) the fully crystalline region
in the central part of 5 mm cast rod of alloy 2
(Zr
50
Cu
36
Al
14
), (b) the bordering part between the central
fully crystalline region and the surrounding composite
region (τ
3
distributed in amorphous matrix) of 5 mm cast
rod of alloy 2, and the composite region (τ
3
distributed in
amorphous matrix) in the central part of 5 mm cast rods of
(c) alloy 1 (Zr
50
Cu
38
Al
12
), (d) alloy 7 (Zr
50
Cu
40
Al

10
), (e)
alloy 55 (Zr
50
Cu
43
Al
7
) at high magnification.
Figure 4.3.5
Page 54
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloy 8 (Zr
50
Cu
34
Al
16
),
alloy 2 (Zr
50
Cu
36
Al
14
), alloy 1 (Zr
50
Cu
38
Al

12
), alloy 7
(Zr
50
Cu
40
Al
10
) and alloy 55 (Zr
50
Cu
43
Al
7
) macroscopically,
indicating the increase of volume percentage of amorphous
phase from alloy 8 to alloy 55.
Figure 4.3.4
Page 53
XRD patterns of 5 mm rods of alloy 8 (Zr
50
Cu
34
Al
16
),
alloy 2 (Zr
50
Cu
36

Al
14
), alloy 1 (Zr
50
Cu
38
Al
12
), alloy 7
(Zr
50
Cu
40
Al
10
) and alloy 55 (Zr
50
Cu
43
Al
7
) showing the
decrease of the intensity of crystalline diffraction peaks
from alloy 8 to alloy 55.
Figure 4.3.3
Page 51
Alloys in the
τ
3
-

τ
5
-ZrCu eutectic system in the present
study.
Figure 4.3.2
Page 50


xiv















XRD patterns of 5 mm cast rods of alloys 64
(Zr
49
Cu
44
Al

7
), 67 (Zr
48
Cu
45
Al
7
), 56 (Zr
49
Cu
45
Al
6
) and 45
(Zr
48
Cu
46
Al
6
), showing a typical broad hump without any
visible crystalline diffraction peaks.
Figure 4.3.16
Page 64
DSC curves of 5 mm cast rods of alloy 57 (Zr
49
Cu
46
Al
5

)
and alloy 62 (Zr
49
Cu
47
Al
4
).
Figure 4.3.15
Page 63
SEM micrographs showing the morphology of the
crystalline “islands” in the composite region of 5 mm cast
rods of (a) alloy 57 (Zr
49
Cu
46
Al
5
) and (b) alloy 62
(Zr
49
Cu
47
Al
4
) at high magnification.
Figure 4.3.14
Page 62
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloy 57 (Zr

49
Cu
46
Al
5
)
and alloy 62 (Zr
49
Cu
47
Al
4
) macroscopically, indicating the
decrease of volume percentage of amorphous phase from
alloy 57 to alloy 62.
Figure 4.3.13
Page 62
XRD patterns of 5 mm cast rods of alloy 57 (Zr
49
Cu
46
Al
5
)
and alloy 62 (Zr
49
Cu
47
Al
4

).
Figure 4.3.12
Page 61
DSC curves of 5 mm cast rods of alloy 11 (Zr
46
Cu
42
Al
12
),
alloy 39 (Zr
46
Cu
44
Al
10
)

and alloy 40 (Zr
47
Cu
45
Al
8
).
Figure 4.3.11
Page 60
SEM micrographs showing (a) the fully crystalline region
in the central part of 5 mm cast rod of alloy 11
(Zr

46
Cu
42
Al
12
), and the composite region (τ
5
distributed in
amorphous matrix) in the central part of 5 mm cast rods of
(b) alloy 39 (Zr
46
Cu
44
Al
10
), (c) alloy 40 (Zr
47
Cu
45
Al
8
).
Figure 4.3.10
Page 60
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloy 11 (Zr
46
Cu
42
Al

12
),
alloy 39 (Zr
46
Cu
44
Al
10
)

and alloy 40 (Zr
47
Cu
45
Al
8
)
macroscopically, indicating the increase of volume
percentage of amorphous phase from alloy 11 to alloy 40.
Figure 4.3.9
Page 59


xv

SEM micrographs showing (a) the morphology of τ
3
distributed in amorphous matrix of 8 mm cast rod of alloy
64 at high magnification, (b) the featureless transversal
cross section morphology of 8 mm cast rod of alloy 67
macroscopically, (c) the featureless fully amorphous
morphology of 8 mm cast rod of alloy 67 at high
magnification and (d) the transversal cross section
morphology of 8 mm cast rod of alloy 56 macroscopically.
Figure 4.3.23
Page 71
XRD patterns of 8 mm cast rods of alloys 64
(Zr
49
Cu
44
Al
7
), 67 (Zr
48
Cu
45

Al
7
), 56 (Zr
49
Cu
45
Al
6
) and 45
(Zr
48
Cu
46
Al
6
), showing that a typical broad hump without
any visible crystalline diffraction peaks was observed only
for alloy 67.
Figure 4.3.22
Page 70
Schematic summary of the morphology change of the
transversal cross sections of 5 mm cast rods as the
composition moved to the 5 mm-glass-composition region
(alloys 64, 67, 56 and 45).
Figure 4.3.21
Page 68
Trend in GFA change of alloys in the
τ
3
-

τ
5
-ZrCu eutectic
system and the discovered 5 mm-glass-composition region
in this system. (A: Amorphous)
Figure 4.3.20
Page 67
DSC curves of 5 mm cast rods of alloys 64 (Zr
49
Cu
44
Al
7
),
67 (Zr
48
Cu
45
Al
7
), 56 (Zr
49
Cu
45
Al
6
) and 45 (Zr
48
Cu
46

Al
6
),
exhibiting a strong crystallization event.
Figure 4.3.19
Page 65
SEM micrographs showing a featureless fully amorphous
morphology of 5 mm cast rods of (a) alloy 64
(Zr
49
Cu
44
Al
7
), (b) alloy 67 (Zr
48
Cu
45
Al
7
), (c) alloy 56
(Zr
49
Cu
45
Al
6
) and (d) alloy 45 (Zr
48
Cu

46
Al
6
) under high
magnification.
Figure 4.3.18
Page 65
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 64 (Zr
49
Cu
44
Al
7
),
67 (Zr
48
Cu
45
Al
7
), 56 (Zr
49
Cu
45
Al
6
) and 45 (Zr
48
Cu

46
Al
6
)
macroscopically, showing a featureless appearance of
amorphous phase with no crystalline inclusion under low
magnification.
Figure 4.3.17
Page 64


xvi
















XRD patterns of 5 mm cast rods of alloys 65 (Zr
47

Cu
49
Al
4
)
and 66 (Zr
46
Cu
49
Al
5
).
Figure 4.4.8
Page 78
DSC curves of 5 mm cast rods of alloys 43 (Zr
45
Cu
47
Al
8
)
and 49 (Zr
45
Cu
48
Al
7
).
Figure 4.4.7
Page 77

(a) SEM micrographs showing the composite region (τ
5
distributed in amorphous matrix) in the central part of 5
mm cast rods of alloy 43 (Zr
45
Cu
47
Al
8
) and (b) alloy 49
(
Z
r
45
Cu
48
Al
7
)
at hi
g
h ma
g
nification.
Figure 4.4.6
Page 77
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 43 (Zr
45
Cu

47
Al
8
)
and 49 (Zr
45
Cu
48
Al
7
) macroscopically, indicating the
increase of volume percentage of amorphous phase from
alloy 43 to alloy 49.
Figure 4.4.5
Page 77
XRD patterns of 5 mm cast rods of alloys 43 (Zr
45
Cu
47
Al
8
)
and 49 (Zr
45
Cu
48
Al
7
), showing the decrease of the intensity
of crystalline diffraction peaks from alloy 43 to alloy 49.

Figure 4.4.4
Page 76
(a) Optical photo showing about a quarter part of the
transversal cross section of 5 mm cast rod of alloy 47
(Zr
45
Cu
49
Al
6
) macroscopically and (b) SEM micrograph
showing the featureless fully amorphous morphology of
this 5 mm cast rod at high magnification.
Figure 4.4.3
Page 76
XRD pattern of 5 mm cast rod of alloy 47 (Zr
45
Cu
49
Al
6
),
showing a typical broad hump without any visible
crystalline diffraction peaks. (inset: DSC curve of this 5
mm cast rod)
Figure 4.4.2
Page 76
Trend in GFA change in the
τ
5

-ZrCu-Cu
10
Zr
7
system and
the discovered optimum glass former (alloy 47, 5 mm fully
amorphous) in this system. (A: Amorphous)
Figure 4.4.1
Page 74


xvii

















XRD patterns of 5 mm cast rods of alloys 12

(Zr
54
Cu
38
Al
8
), 75 (Zr
55
Cu
37
Al
8
) and 14 (Zr
56
Cu
36
Al
8
),
showing a typical broad hump without any visible
crystalline diffraction peaks.
Figure 4.5.2
Page 84
Trend in GFA change in the
τ
3
-Zr
2
Cu-ZrCu system and the
discovered optimum glass formers (alloys 12, 75 and 14, 5

mm fully amorphous) in this system. (A: Amorphous)
Figure 4.5.1
Page 81
DSC curves of 5 mm cast rods of alloys 59 (Zr
45
Cu
50
Al
5
)
and 73 (Zr
44
Cu
51
Al
5
).
Figure 4.4.15
Page 80
SEM micrographs showing the morphology of the
crystalline “islands” in the composite region of 5 mm cast
rods of (a) alloy 73 (Zr
44
Cu
51
Al
5
) and (b) alloy 59
(Zr
45

Cu
50
Al
5
) at high magnification.
Figure 4.4.14
Page 80
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 73 (Zr
44
Cu
51
Al
5
)
and 59 (Zr
45
Cu
50
Al
5
) macroscopically, indicating the
increase of volume percentage of amorphous phase from
alloy 73 to alloy 59.
Figure 4.4.13
Page 79
XRD patterns of 5 mm cast rods of alloys 73 (Zr
44
Cu
51

Al
5
)
and 59 (Zr
45
Cu
50
Al
5
) showing the decrease of the intensity
of crystalline diffraction peaks from alloy 73 to alloy 59.
Figure 4.4.12
Page 79
DSC curves of 5 mm cast rods of alloys 65 (Zr
47
Cu
49
Al
4
)
and 66 (Zr
46
Cu
49
Al
5
).
Figure 4.4.11
Page 79
SEM micrographs showing the morphology of the

crystalline “islands” in the composite region of 5 mm cast
rods of (a) alloy 65 (Zr
47
Cu
49
Al
4
) and (b) alloy 66
(Zr
46
Cu
49
Al
5
) at high magnification.
Figure 4.4.10
Page 78
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 65 (Zr
47
Cu
49
Al
4
)
and 66 (Zr
46
Cu
49
Al

5
) macroscopically, indicating the
increase of volume percentage of amorphous phase from
alloy 65 to alloy 66.
Figure 4.4.9
Page 78


xviii

















XRD patterns of 5 mm cast rods of alloys 28 (Zr
54
Cu
42

Al
4
)
and 71 (Zr
54
Cu
40
Al
6
), showing the increase of the intensity
of crystalline diffraction peaks from alloy 71 to alloy 28.
Figure 4.5.10
Page 88
DSC curves of 5 mm cast rods of alloys 10 (Zr
54
Cu
34
Al
12
)
and 72 (Zr
54
Cu
36
Al
10
).
Figure 4.5.9
Page 88
SEM micrographs showing the composite region (τ

3
distributed in amorphous matrix) in the central part of 5
mm cast rods of (a) alloy 10 (Zr
54
Cu
34
Al
12
) and (b) alloy
72
(
Z
r
54
Cu
36
Al
10
)
at hi
g
h ma
g
nification.
Figure 4.5.8
Page 87
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 10 (Zr
54
Cu

34
Al
12
)
and 72 (Zr
54
Cu
36
Al
10
) macroscopically, indicating the
increase of volume percentage of amorphous phase from
alloy 10 to 72.
Figure 4.5.7
Page 87
XRD patterns of 5 mm cast rods of alloys 10
(Zr
54
Cu
34
Al
12
) and 72 (Zr
54
Cu
36
Al
10
), showing the
decrease of the intensity of crystalline diffraction peaks

from alloy 10 to alloy 72.
Figure 4.5.6
Page 87
DSC curves of 5 mm cast rods of alloys 12 (Zr
54
Cu
38
Al
8
),
75 (Zr
55
Cu
37
Al
8
) and 14 (Zr
56
Cu
36
Al
8
), exhibiting a strong
crystallization event.
Figure 4.5.5
Page 86
SEM micrographs showing the featureless fully
amorphous morphology of 5 mm cast rods of (a) alloy 12
(Zr
54

Cu
38
Al
8
), (b) alloy 75 (Zr
55
Cu
37
Al
8
) and (c) alloy 14
(Zr
56
Cu
36
Al
8
) at high magnification.
Figure 4.5.4
Page 86
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 12 (Zr
54
Cu
38
Al
8
),
75 (Zr
55

Cu
37
Al
8
) and 14 (Zr
56
Cu
36
Al
8
) macroscopically,
showing a featureless appearance of amorphous phase with
no crystalline inclusion under low magnification.
Figure 4.5.3
Page 85


xix

XRD pattern of 5 mm cast rod of alloy 6 (Zr
52
Cu
38
Al
10
).
(inset: DSC curve of this 5 mm cast rod)
Figure 4.5.18
Page 91
DSC curves of 5 mm cast rods of alloys 17 (Zr
58
Cu
36
Al
6
)
and 20 (Zr
60
Cu
36
Al
4
).
Figure 4.5.17
Page 90

SEM micrographs showing the morphology of the fully
crystalline region in the central part of 5 mm cast rods of
(a) alloy 17 (Zr
58
Cu
36
Al
6
) and (b) alloy 20 (Zr
60
Cu
36
Al
4
) at
high magnification.
Figure 4.5.16
Page 90
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 17 (Zr
58
Cu
36
Al
6
)
and 20 (Zr
60
Cu
36

Al
4
) macroscopically, indicating the
decrease of volume percentage of amorphous phase from
alloy 17 to alloy 20.
Figure 4.5.15
Page 90
XRD patterns of 5 mm cast rods of alloys 17 (Zr
58
Cu
36
Al
6
)
and 20 (Zr
60
Cu
36
Al
4
), showing the increase of the intensity
of crystalline diffraction peaks from alloy 17 to alloy 20.
Figure 4.5.14
Page 89
DSC curves of 5 mm cast rods of alloys 28 (Zr
54
Cu
42
Al
4

)
and 71 (Zr
54
Cu
40
Al
6
).
Figure 4.5.13
Page 89
SEM micrographs showing the morphology of the
crystalline “islands” in the composite region of 5 mm cast
rods of (a) alloy 71 (Zr
54
Cu
40
Al
6
) and (b) alloy 28
(Zr
54
Cu
42
Al
4
) at high magnification.
Figure 4.5.12
Page 89
Optical photos of about a quarter part of the transversal
cross section of 5 mm cast rods of alloys 28 (Zr

54
Cu
42
Al
4
)
and 71 (Zr
54
Cu
40
Al
6
) macroscopically, indicating the
decrease of volume percentage of amorphous phase from
alloy 71 to alloy 28.
Figure 4.5.11
Page 88


xx

Schematic diagrams showing (a) glass forming zone and
glass matrix composite zones in a binary eutectic system,
(b) cross section of a casting mould with an appropriate
size and a cast sample inside resulting in a range of
cooling rate (
1
T

to
4
T

), (c) microstructure evolution of the
cast samples with the change of compositions (
1
C
α
,
2
C
α
, C
gl
,
2
C

β
,
1
C
β
).
Figure 5.2.5
Page 108
Schematic diagrams showing different compositions
(
1
C
α
,
2
C
α
,
2
C
β
,
1
C
β
and C
gl
) under the same range of cooling
rate (
1

T

to
4
T

) resulting in fully glass or glass matrix
composites. (
T

is cooling rate)
Figure 5.2.4
Page 106
Calculated optimum glass forming zone and
experimentally observed optimum glass former in the
Cu
8
Zr
3
-Cu
10
Zr
7
system.
Figure 5.2.3
Page 105
Linear fit of the liquidus line on the two sides of the
eutectic point (Zr
38.2
Cu

61.8
) in the binary Cu
8
Zr
3
-Cu
10
Zr
7

eutectic system.
Figure 5.2.2
Page 100
Schematic diagrams showing (a) glass forming zone and
glass matrix composite zones with a symmetrical eutectic
coupled zone, (b) glass forming zone and glass matrix
composite zones with a skewed eutectic coupled zone. (T


is cooling rate and C is composition)
Figure 5.2.1
Page 96
(a) Part of the phase diagram of the Cu
8
Zr
3
-Cu
10
Zr
7

system, and plot of the values of
T
g
and T
x
; (b) plot of the
volume percentage of glass phase in 2 mm cast rods and
the values of T
rg
(T
g
/T
l
) and T
x
(T
x
-T
g
).
Figure 5.1.1
Page 93
(a) Optical photo showing about a quarter part of the
transversal cross section of 5 mm cast rod of alloy 6
(Zr
52
Cu
38
Al

10
) macroscopically, (b) SEM micrograph
showing the composite region (τ
3
distributed in amorphous
matrix) in the central part of 5 mm cast rod of alloy 6 at
hi
g
h ma
g
nification.
Figure 4.5.19
Page 91


xxi

Positions of Line 1 and Line 2, along which approximate
critical sizes of fully glass formation versus compositions,
and values of
T
rg
and T
x
versus compositions are shown
in Figures 5.3.6 and 5.3.7.
Figure 5.3.5
Page 119
Representations of 2 mm, 5 mm and 8 mm full glass
forming range (black lines) and isolines of
T
x
values (blue
lines) of the τ
3
-Zr
2
Cu-ZrCu, τ
3
-τ
5
-ZrCu and τ
5
-ZrCu-
Cu
10
Zr

7
eutectic systems, showing T
x
values cannot
indicate the GFA change in these three eutectic systems.
Figure 5.3.4
Page 117
Representations of 2 mm, 5 mm and 8 mm full glass
forming range (black lines) and isolines of T
rg
values (red
lines) of the τ
3
-Zr
2
Cu-ZrCu, τ
3
-τ
5
-ZrCu and τ
5
-ZrCu-
Cu
10
Zr
7
eutectic systems, showing T
rg
values cannot
indicate the GFA change in these three eutectic systems.

Figure 5.3.3
Page 116
T
x
and T
l
isotherms of the
τ
3
-Zr
2
Cu-ZrCu,
τ
3
-
τ
5
-ZrCu and
τ
5
-ZrCu-Cu
10
Z
r
7
eutectic s
y
ste
m
s.

Figure 5.3.2
Page 115
T
g
and T
l
isotherms of the
τ
3
-Zr
2
Cu-ZrCu,
τ
3
-
τ
5
-ZrCu and
τ
5
-ZrCu-Cu
10
Z
r
7
eutectic s
y
ste
m
s.

Figure 5.3.1
Page 115
Schematic diagram showing the 2 mm fully glass forming
zone and 2 mm glass matrix composite forming zones
(glass + Cu
8
Zr
3
, glass + Cu
10
Zr
7
) in the Cu
8
Zr
3
-Cu
10
Zr
7
eutectic system. (A: Amorphous).
Figure 5.2.7
Page 112
Morphological change of 2 mm cast rods from Zr
37
Cu
63
to
Zr
34.5

Cu
65.5
: the switch of the primary phase in glass matrix
(from Cu
10
Zr
7
in Zr
36
Cu
64
to Cu
8
Zr
3
of Zr
35
Cu
65
)

encompasses the optimum glass former (Zr
35.5
Cu
64.5
). (a)
and (b) The XRD patterns of Zr
37
Cu
63

and

Zr
34.5
Cu
65.5.
(c)
to (g) The cross section of Zr
37
Cu
63
, Zr
36
Cu
64
, Zr
35.5
Cu
64.5
,
Zr
35
Cu
65
and Zr
34.5
Cu
65.5
, (h) and (i) The morphology of
Cu

10
Zr
7
phase in Zr
36
Cu
64
and

Cu
8
Zr
3
phase in Zr
35
Cu
65
under high magnification.
Figure 5.2.6
Page 111


xxii

Fully glass forming zones superimposed on the ternary
phase diagram showing the composition regions of 2 and 5
mm full glass formation in the three eutectics. The dashed
line shows the
∆
T
x
isotherm from ref. [82]. A:
Zr
65
Cu
27.5
Al
7.5
, B: Zr
60
Cu
30
Al
10
, C: Zr
45
Cu

50
Al
5
, D:
Z
r
50
Cu
40
Al
10
,
E: Z
r
47
Cu
46
Al
7
.
Figure 5.4.5
Page 132
Schematic diagrams showing (a) cross section of a casting
mould with an appropriate size and a cast sample inside
resulting in a range of cooling rate above the critical
cooling rate for fully glass forming in the ternary alloy
system (T

is cooling rate), (b) microstructure evolution of
the cast samples with the change of compositions from

region 3a, region 3b and region 3c to region 1 in Figure
5.4.3.
Figure 5.4.4
Page 130
(a) Schematic representation of the composition ranges of
the various structure (considering formation of glass), (b)
to (e) Schematics of growth interface morphologies of
these regions.
Figure 5.4.3
Page 127
(a) Schematic representation of the composition ranges of
the various structure (adapted from Ref. [108], not
considering formation of glass), (b) to (e) Schematics of
growth interface morphologies of these regions.
Figure 5.4.2
Page 124
Ternary eutectic phase diagram.
Figure 5.4.1
Page 123
Values of T
rg
and T
x
versus compositions, and
approximate critical sizes of fully glass formation versus
compositions along Line 2 in Figure 5.3.5.
Figure 5.3.7
Page 122
Values of T
rg

and T
x
versus compositions, and
approximate critical sizes of fully glass formation versus
compositions along Line 1 in Figure 5.3.5.
Figure 5.3.6
Page 120


xxiii
















Morphological change of 5 mm cast rods in the
τ
3
-Zr

2
Cu-
ZrCu system: (a) The optimum glass forming region is at
the junction where the two composite (primary phase τ
3
,
ZrCu in glass matrix) zones meet. (b) The XRD patterns of
alloys 10, 75, 28 and 20. (c) The morphology of τ
3
in glass
matrix under high magnification. (d) to (j) A quarter of the
cross section of alloys 10, 72, 75, 17, 20, 71 and 28.
Figure 5.4.8
Page 138
Morphological change of 5 mm cast rods in the τ
5
-ZrCu-
Cu
10
Zr
7
system: (a) The optimum glass forming
composition is at the junction where the three composite
(primary phase τ
5,
ZrCu or Cu
10
Zr
7
in glass matrix) zones

meet. (b) The XRD patterns of alloys 43, 47, 73 and 65. (c)
The morphology of τ
5
in glass matrix under high
magnification. (d) to (j) A quarter of the cross section of
alloys 43, 49, 47, 66, 65, 59 and 73.
Figure 5.4.7
Page 136
Morphological change of 5 mm cast rods in the
τ
3
-τ
5
-ZrCu
system: (a) The optimum glass forming region is at the
junction where the three composite (primary phase τ
3
, τ
5
or
ZrCu in glass matrix) zones meet. (b) The XRD patterns of
alloys 1, 39, 67 and 57. (c) and (d) The morphology of τ
3
and τ
5
phases in glass matrix under high magnification. (e)
to (l) A quarter of the cross section of alloys 1, 55, 64, 39,
40, 67, 57 and 62.
Figure 5.4.6
Page 134

xxiv

List of Publications

1. D. Wang, H. Tan and Y. Li “Multiple maxima of GFA in three adjacent eutectics in
Zr-Cu-Al alloy system A metallographic way to pinpoint the optimum glass forming
alloys” in Acta materialia, Vol. 53, June 2005.

2. D. Ma, H. Tan, D. Wang, Y. Li and E. Ma “A Strategy for Pinpointing the Optimum
Glass-forming Alloys” in Applied Physics Letters, Vol. 86, May 2005.

3. D. Wang, Y. Li, B. B. Sun, M. L. Sui, K. Lu and E. Ma “Bulk Metallic Glass
Formation in the Binary Cu-Zr system” in Applied Physics Letters, Vol. 84, May 2004.

4. D. Wang, H. Tan and Y. Li “Pinpoint the Optimum Glass Forming Alloy by
Microstructure Study in Cu
8
Zr
3
-Cu
10
Zr
7
Eutectic System of Cu-Zr Binary System” in the
Proceedings of the 11
th
(2004) International Symposium on Metastable,
Mechanically Alloyed and Nanocrystalline Materials.

5. D. Wang, H. Tan and Y. Li “Optimum Glass Formation of Cu-Zr Alloys in Cu
8
Zr
3
-
Cu
10
Zr
7
Eutectic System” in the Proceedings of 13
th
(2004) International Conference
on Processing and Fabrication of Advanced Materials.