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Glass-Forming Ability and Competitive Crystalline Phases
for Lightweight Ti-Be–Based Alloys
Y. ZHANG, W.G. ZHANG, J.P. LIN, G.J. HAO, G.L. CHEN, and P.K. LIAW
The glass-forming ability (GFA) for the Ti-Be–based alloys in the Ti-Be-Zr ternary system is
systematically studied. It was found that the best GFA obtained at a composition of Ti41Be34Zr25
(at. pct) in the Ti-Be-Zr ternary system, and the bulk-metallic-glass (BMG) rod samples with a
diameter of 5 mm were fabricated by Cu-mold casting. The competitive crystalline phases
around the composition of the best GFA materials were determined by scanning electron
microscopy (SEM) and X-ray diffractometry (XRD). The GFA of the ternary alloys was further
improved by an addition of 4 at. pct vanadium (V). The largest supercooled liquid region, DTx
(DTx = Tx Tg, Tg is the glass-transition temperature, and Tx the crystallization temperature),
in the ternary alloy system reaches about 110 K (110 C) for the Ti35Be32Zr33 alloy.
DOI: 10.1007/s11661-009-0122-9
The Minerals, Metals & Materials Society and ASM International 2010
I.
INTRODUCTION
BULK-METALLIC GLASSES (BMGs) have attracted
extensive interest due to their unique physical, chemical,
and mechanical properties attributed to the randomatomic configurations. Owing to their high glassforming ability (GFA), good processing ability, and
exceptional stability with respect to the crystallization,
along with many promising properties, such as high
strengths, elastic strain limits, wear resistance, fatigue
resistance, and corrosion resistant, BMGs have been the
focus of the scientific research over the past 20 years.[1–19]
Much more attention was paid to Ti-based amorphous
alloys because of their high specific strength and
relatively low cost. However, most currently available
Ti-based BMGs with high GFA contain a high portion
of late transition metals (LTMs) (e.g., Ni, Cu, and Sn),
which are necessary for glass formation, and the specific
strength of these BMGs is compromised of the high
density of these LTMs. In this article, we attempted to
exclude the LTMs in Ti-based BMGs to further improve
their specific strength. The reported scheme based on the
binary eutectic clusters is applied to predict a base alloy
in the Ti-Zr-Be system. As a result, there is a class of
Ti-based bulk amorphous alloys excluding LTMs with
Y. ZHANG, J.P. LIN, and G.L. CHEN, Professors, and G.J.
HAO, Research Associate, are with the State Key Laboratory for
Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China. Contact e-mail: [email protected] W.G. ZHANG, formerly Graduate Student, State
Key Laboratory for Advanced Metals and Materials, University of
Science and Technology Beijing, is with the Chinese Academy of Space
Technology, Beijing 100083, China. P.K. LIAW, Professor, is with the
Department of Materials Science and Engineering, The University of
Tennessee, Knoxville TN 37996-2200.
This article is based on a presentation given in the symposium
‘‘Bulk Metallic Glasses VI,’’ which occurred during the TMS Annual
Meeting, February 15–19, 2009, in San Francisco, CA, under the
auspices of TMS, the TMS Structural Materials Division, TMS/ASM:
Mechanical Behavior of Materials Committee.
METALLURGICAL AND MATERIALS TRANSACTIONS A
high GFA, exceptional thermal stability, very high
specific strength, and large compressive plasticity.
Tanner[20–23] reported that amorphous ribbons (typically 30-lm thick) in the Ti-Be, Zr-Be, and Ti-Zr-Be
systems could be prepared by splat-quenching or meltspinning techniques at high cooling rates of ~106 K s1.
Recently, Wiest et al.[24,25] reported a series of ZrBeTi
ternary BMGs with high GFA. By tailoring the primary
dendrite phase, a tensile ductility was achieved in the
Ti-based BMG composite.[26] In the present work, the
binary eutectic-cluster-rule[27] and eutectic-coupled-zone
methods[3,4] were applied to optimize the GFA in the
Ti-Be-Zr alloy system. The article intends to clarify
the glass-formation zone and its crystal phases.
II.
EXPERIMENTAL PROCEDURES
Alloys were prepared using elements with purity
better than 99.9 wt pct. The elements were weighed to
be within ±0.1 pct of the calculated mass to ensure
accurate compositions and were ultrasonically cleaned
in acetone and ethanol before melting. Typically, 10-g
ingots were arc melted on a Cu hearth in a Ti-gettered
argon atmosphere and flipped at least 3 times to ensure
the chemical homogeneity. The mass deviation after
melting was maintained to be within ±0.1 pct from the
originally weighed alloy before melting. Alloy rods with
diameters of 3, 5, and 8 mm were prepared by means of
copper-mold-suction castings. The phase structural
identification of these alloys was carried out by means
of the X-ray diffractometry (XRD) on the sections of the
rods using Cu Ka radiation (k = 0.154 nm). The thermal properties associated with the glass transition and
crystallization of the amorphous phase were measured
using differential scanning calorimetry (DSC). The DSC
traces were monitored during continuous heating from
373 to 1273 K (100 to 1000 C) using a constant heating
rate of 0.33 K/s (0.33 C/s). The melting process of the
alloys was studied by Perkin Elmer differential temperature analysis (DTA), DTA-7, with a heating rate of
0.33 K/s (0.33 C/s); the experimental detail can be seen
in Reference 28. Specimens with a diameter of 2 mm and
an aspect ratio of 2 were compressed between two SiC
platens at an engineering strain rate of 10-4s-1. The
density of bulk glassy alloys was measured by the
Archimedean principle.
As for exploring the glass formation of Ti-Be–based
alloys, 20 Ti-Be-Cu ternary alloys, 10 Ti-Be-Si ternary
alloys, and 10 Ti-Be-Y ternary alloys were cast into
3-mm-diameter-rod samples. However, no glass phase
formed after being detected by the XRD analysis. After
that, the study focused on the ternary Ti-Be-Zr alloys.
Totally, more than 50 alloys along 8 composition lines
in the Ti-Be-Zr ternary alloy system were studied by arc
melting and suction casting into 3-mm-diameter-rod
samples, in which 17 alloys can form BMGs in 3-mm
rods. The glass-formation compositions were shown in
Figure 1. The alloy marked by red circles was found to
have the best GFA, which can form BMG with at least
5-mm-diameter-rod samples. The typical alloys studied
in this work were also listed in Table I. Figure 2 shows
the glass-formation zones of 3 and 5 mm in the partial
ternary-phase diagram. It is obvious that there are two
glass-formation zones in the Ti-rich Ti-Be-Zr ternary
phase diagram. The first one with higher Be and Ti
contents can form BMGs in a 5-mm diameter, while the
other one with the more Zr content can only form 3-mm
BMGs. Figure 3 presents the scanning electron microscopy (SEM) pictures of the casting 3-mm-diameter-rod
samples of the alloys of (a) and (b) Ti55Be30Zr15, (c)
Ti39Be30Zr31, (d) Ti52Be32Zr16, (e) Ti54Be34Zr12, and (f)
Ti55Be35Zr10. Figures 3(a) and (b) indicate that the
casting 3-mm rod of the alloy of Ti55Be30Zr15 is mainly
of the eutectic of a-Ti + BeTi. Figure 3(c) shows that
the alloys of Ti39Be30Zr31 are mainly composed of the
b-Ti solid-solution dendrite + amorphous phase.
Figure 3(d) demonstrates that the alloy of Ti52Be32Zr16
consists of the phases of a-Ti + BeTi + Be2Zr.
Figure 3(e) shows that the alloy of Ti54Be34Zr12 is
mainly composed of a-Ti + BeTi + amorphous phases.
Figure 3(f) shows that the alloy of Ti55Be35Zr10 mainly
consists of the a-Ti + BeTi phases. The amorphous
phase formation with the competitive crystalline phases
can be presented in Figure 4. Figure 4(a) presents the
amorphous phase and its competitive primary phases of
a-Ti, BeTi, and Be2Zr, while Figure 4(b) shows the
amorphous phase and its competitive crystalline phases
of a-Ti, Be2Zr, and b-Zr. The first glass-formation zone
contains two intermetallic compounds and one solid
solution. The second one includes only one intermetallic
compound and two solid solutions. The GFA of the first
one is better than that of the second one. This trend will
be further discussed later.[27,29]
Fig. 1—Alloys studied exhibiting GFA of forming 3-mm-diameterrod BMGs, and the two lines were the connections of the binary
glass-formation region in the Ti-Be and Zr-Be binary alloys.
Fig. 2—Glass-formation zones of 3-mm and 5-mm rods in the TiBe-Zr ternary alloy system.
III.
RESULTS
Table I.
Composition
Ti45Be30Zr25
Ti43Be32Zr25
Ti47Be34Zr19
Ti41Be34Zr25
Ti35Be32Zr33
Ti41Be30Zr25V4
Phase
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous Parameters for the Typical Ti-Be–Based Alloys
Tg (K)
566.1
585.7
590.1
573.9
588
572.3
(293.1 C)
(312.7 C)
(317.1 C)
(300.9 C)
(315 C)
(299.3 C)
TX1 (K)
616.0 (343 C)
658.8 (385.8 C)
645.5 (372.5 C)
627.9 (354.9 C)
702 (429 C)
645.2 (372.2 C)
DTX (K)
50
73.1
55.4
54.0
113
72.9
(50 C)
(73.1 C)
(55.4 C)
(54.0 C)
(113 C)
(72.9 C)
Size (mm)
3
5
5
5
3
8
METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 3—SEM pictures of the casting alloys of (a) and (b) Ti55Be30Zr15, (c) Ti39Be30Zr31, (d) Ti52Be32Zr16, (e) Ti54Be34Zr12, and (f) Ti55Be35Zr10.
Figure 5 exhibits the typical DSC heating curves of (a)
the Ti68–xBe32Zrx alloys and (b) the Ti66–xBe34Zrx alloys.
All the curves present glass-transition and crystallization
events. The glass-transition temperature (Tg) and first
crystallization temperature (Tx1) are 573.9 (300.9 C) and
627.9 K (354.9 C), respectively, for the Ti41Be34Zr25
alloy. The data about the other glass formers are listed in
Table I. The largest supercooled liquid region DTx
(DTx = Tx1 Tg) is obtained at the composition of
Ti35Be32Zr33, and the DTx is about 113.5 K (113.5 C).
It is interesting that after adding a small amount
of vanadium (V), the GFA of the ternary alloys was
METALLURGICAL AND MATERIALS TRANSACTIONS A
further improved. Figure 6(a) presents the XRD
patterns of Ti41Be34–xZr25Vx alloys. It can be seen that
the alloy of Ti41Be30Zr25V4 can form BMGs in an
8-mm-diameter-rod sample. Thus, a small amount of
the V addition enhanced the GFA of Ti-Be-Zr ternary
alloys. Figure 6(b) presents the DSC heating curves of
the crystallization process. It can be seen that the best
glass former, Ti41Be30Zr25V4, has the largest DTx value
among the other V-containing alloys, which is about
73 K (73 C). Figure 6(c) exhibits the melting process
of the Ti41Be34–xZr25Vx alloys. It can be seen that the
best glass former, the Ti41Be30Zr25V4 alloy, has the
Fig. 4—Schematic pictures of the two glass-formation zones with
its competitive crystalline phases: (a) a-Ti, BeTi and Be2Zr; and
(b) a-Ti, b-Zr, and Be2Zr.
lowest liquidus temperature as well as the lowest
solidus temperature.
Figure 7 shows the typical compressive stress-strain
curves of the TiBeZr ternary BMGs. It is clear that some
of the TiBeZr ternary alloys can have compressive
plasticity and high fracture strength (rb). The highest
specific strength can be 448 MPa/g/cm3 for the alloy of
Ti45Be35Zr20. Figure 8 exhibits the typical shear bands
on the side surface of the BMG samples. It can be found
that the primary shear bands are along a direction,
45 deg, to the compressive stress, while the secondary
shear bands are normal to the compressive stress.
IV.
DISCUSSION
A. GFA of the Ti-Be–Based Alloys
Inoue[30] has proposed that the BMG-forming alloys
should be composed of the LTM and early-transition
metal (ETM) and simple metal (SM), namely, ETM +
LTM + SM. A typical example should be TiCuBe.
However, our experiments showed that the TiBeCualloy system has a lower GFA than that of the TiBeZralloy system. It has been reported that the elements of Y
and Si are good for the GFA improvement in the
Zr- and Cu-based alloys,[31–36] but the GFA of the
TiBeY and TiBeSi is not so high to form the 3-mm
BMGs. As for the ternary system of Ti-Be-Zr, it was
found to have a much better GFA than the other three.
The ternary Ti-Be-Zr can be written as a pseudo-binary
Fig. 5—DSC heating curves of (a) Ti68–xBe32Zrx and (b) Ti66–xBe34Zrx
BMG alloys.
of (Ti, Zr)-Be, because Ti and Zr are of the same group
in the element Periodic table. The TiBeZr alloys without
containing the LTM would make the BMG lightweighted, because the LTM usually has a high density. For
example, Cu, Fe, or Ni has a density greater than
7 g/cm3. It is interesting that a small amount of V can
improve the GFA of the TiBeZr greatly. Wiest et al.
also reported that Cr has similar effects.[24,25]
B. Compositions of the Ti-Be-Zr–Based BMGs
Tanner[20–23] has found the glass-formation regions
for the binary of Ti-Be and Zr-Be alloys and, thus,
linked them to the binary glass-formation terminal
points, as shown in Figure 2. Tanner reported a ternary
glassy alloy with a composition of Ti50Be40Zr10, which
has a trademark of METGLAS 2204 (Allied Chemical
Corp., Morristown, NJ). Wiest et al.[24,25] observed the
glass-formation composition of Ti45Be35Zr20, which can
form 6-mm-diameter-rod samples. The binary-eutectic
METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 7—Compressive stress-strain curves of the Ti41Be32Zr27 and
Ti37Be32Zr31 alloys.
Fig. 6—(a) XRD patterns, (b) DSC heating curves showing the glass
transition and crystallization, and (c) DTA curves showing the melting process of Ti41Be34–xZr25Vx alloys.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 8—Typical shear bands on the side surface of the Ti41Be30Zr25V4 BMGs.
rule[27] was used to predict the glass-formation composition, CA, in the ternary eutectic of A-B-C:
CA ¼ a½EuðA-BÞ þ b½EuðB-CÞ þ c½EuðC-AÞ
The (Ti, Zr)-Be pseudo-binary system can be regarded
as an ideal glass-forming liquid, and its composition CA
can be obtained as follows:
CA ¼ a½EuðBe-TiÞ þ b½EuðBe-ZrÞ
½1
where a and b are constants, a + b = 1, and Eu
denotes the eutectic composition (e.g., Eu(Be-Ti)
denotes the eutectic composition of the Be-Ti binary
system). As suggested in Reference 27, a and b values
can be determined in a way that clusters with a large
negative heat of mixing should have a relatively low
concentration. Thus,
aDHTi-Be ¼ bDHZr-Be
½2
where DHTi-Be and DHZr-Be are heats of mixing for the
atomic pairs Ti-Be and Zr-Be, respectively. From the
binary-phase diagrams of Be-Ti and Be-Zr, Eu(Be-Ti) =
Ti70Be30 and [Eu(Be-Zr)] = Zr65Be35. Then a and b can
be calculated by substituting the heat of mixing of these
atomic pairs into Eq. [2], and the predicted glass former
is Ti41Be32Zr27. The best ternary BMG alloy was found
by experiments with a composition of Ti41Be34Zr25,
which is very close to the predicted composition.
C. Competition with Crystalline Phases
In this work, two glass-formation zones, glass-zone A
(GA) and glass-zone B (GB), were found. Each one
corresponds to a ternary-eutectic reaction (EA and EB).
The EA is L fi a-Ti + BeTi + Be2Zr, and the EB is
L fi a-Ti + b-Zr + Be2Zr. In the glass-formation zone
of GA, the largest glass-casting size is 5 mm, while the
GB is 3 mm. This trend may be due to the fact that the
EA is composed of two intermetallic compounds and
one solid solution, while the EB contains only one
intermetallic compound with two solid solutions. Previous work has shown that the intermetallic compounds
are easier to be suppressed, as they are usually the
ordered phases,[17,20] which need a longer time to order.
The interface between the liquid and the compounds
usually faceted, and the interface undercooling of the
faceted interface was deeper than that of the unfaceted
one. All of the preceding factors are beneficial for
suppressing the crystallization, thus improving the GFA
of the alloys.
D. GFA Indicators for the Ti-Be–Based Alloys
There have been many indicators for predicting the
GFA of the alloys. For example, Inoue[7–9] proposed
that the larger the DTx, the higher the GFA of the alloy
would be. However, in this work, the largest DTx is
reached at a composition of Ti35Be32Zr33, which is
about 113 K (113 C). While the best GFA is at a
composition of Ti41Be34Zr25, its DTx is about 54 K
(54 C). Moreover, after adding 4 at. pct V, the GFA of
the alloy increases from 5-mm to 8-mm-diameter rod of
BMG samples, but the DTx is about 73 K (73 C). From
the preceding facts, it is concluded that the GFA does
not have a direct relationship with the DTx, which has
also been reported in the La-based BMGs.[6]
V.
CONCLUSIONS
The Ti-Be-Zr ternary alloy system exhibits higher
GFA than those of the Ti-Be-Cu, Ti-Be-Y, and Ti-Be-Si
ternary alloy systems. The BMG composition predicted
by the binary-eutectic rule is very close to the experimental results. The ternary eutectic consisting of two
solid solution phases and one intermetallics exhibits
lower GFA than that of the one solid solution and two
intermetallics. The DTx has no direct relation with the
GFA of the alloys. The quaternary alloys of
Ti41Be30Zr25V4 can form BMGs with a diameter of
8 mm. The specific strength of the Ti45Be35Zr20 BMG is
448 MPa/g/cm3.
ACKNOWLEDGMENTS
The research is supported by the Program for New
Century Excellent Talents in University (Grant No.
NCET-05-0105) of China, and the ‘‘973 program’’
(Contract No. 2007CB613903), and in part by the
National Natural Science Foundation of China (Grant
No. 50571018). One of the authors (PKL) is supported
by the National Science Foundation International
Materials Insititutes (IMI) Program, Dr. C. Huher,
Dr. U. VenkEteswEren, and Dr. D. Finotello, as
program directors.
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