Artículo Melt Spinning

1. Microstructural characterization of rapidly solidified Cu50Zr40Ni5Ti5
amorphous alloy
Celal Kursun a,⇑
, Musa Gögebakan a
, Yucel Gencer b
a
Department of Physics, Faculty of Art and Sciences, Kahramanmaras Sutcu Imam University, Kahramanmaras 46100, Turkey
b
Department of Materials Science and Engineering, Gebze Institute of Technology, Gebze, 41400 Kocaeli, Turkey
a r t i c l e i n f o
Article history:
Available online xxxx
Keywords:
Rapid solidification
Microhardness
Copper based alloy
Crystallisation
Kissenger plot
a b s t r a c t
The amorphous Cu50Zr40Ni5Ti5 alloy was produced by melt-spinning at wheel speeds of 35, 38 and
41 m sÀ1
. The resulting melt-spun ribbons were characterised using X-ray diffraction (XRD), scanning
electron microscopy coupled with energy dispersive spectroscopy (SEM-EDX), differential scanning
calorimetry (DSC) and Vickers microhardness (HV) tester. The XRD and SEM results revealed that the
rapidly solidified ribbons have a fully amorphous structure. After partial or fully crystallisation of
Cu50Zr40Ni5Ti5 ribbons upon annealing, the microstructure had uneven and irregularly shaped features
with the existence of Cu10Zr7, Cu8Zr3, CuZr and FCC-Cu phases while as quenched ribbons had featureless
microstructure. The SEM-EDX analysis confirmed compositional homogeneity of the Cu50Zr40Ni5Ti5 alloy
ribbon. According to DSC results, the amorphous ribbons exhibited distinct glass transition temperature
(Tg) and wide supercooled liquid region (DTx = Tx À Tg) before crystallization. Accordingly, Tg and DTx are
around 409–414 °C and 37–54 °C, respectively. The microhardness of the as-quenched ribbons was about
522 HV while it decreased with increasing annealing temperature and had a value of 463 HV for 725 °C.
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
Amorphous alloys have drawn increasing attention, due to their
excellent corrosion resistant, ultrahigh strength and soft ferromag-
netic properties [1–4]. These outstanding features are attributed to
their chemically and structurally homogeneous nature [5,6]. More-
over, chemical compositions of the amorphous alloys are not lim-
ited by solubility limits in comparison with the crystalline
materials. Therefore, they can be produced on a wide composition
range. Amorphous alloys exhibiting high mechanical strength,
good electrical and thermal conductivity are continually needed
in various applications such as electrical, defence and automobile
industries. For these applications, copper based amorphous alloys
are promising materials as they also have superior corrosion
resistance in various environment, high ductility and simple
manufacturing process [7]. Copper alloys are widely used as the
high-performance switches, the condenser tubes of ships, the
welding electrodes, the rocket nozzles, the heat exchangers and
the pipeline network of desalination technology industry [7–9].
Many studies have been carried out on mechanical properties
and microstructural characterization of Cu–Ti and Cu–Zr [10,11]
binary alloys, Cu–Mg–Ni, Cu–Zr–Al [12,13], Cu–Zr–Ti [14],
Cu–Zr–Ni, Cu–Zr–Ag [15,16] ternary alloys, Cu–Ti–Zr–Ni [17], qua-
ternary alloys and also Cu–Ti–Zr–Ni–Be [18,19], Cu–Ti–Zr–Ni–Si
[20,21] quinary alloys which manufactured by different tech-
niques. Hence, the properties of Cu-based alloys have been
improved continuously.
The aim of this research is to systematically investigate the
effect of wheel speeds of melt spinning and different annealing
process of melt-spun ribbons on the microstructural and mechan-
ical properties of Cu50Zr40Ni5Ti5 amorphous alloy. Therefore, the
rapidly solidified Cu50Zr40Ni5Ti5 amorphous alloys were produced
by melt spinning at different wheel speeds and by annealing.
2. Experimental
An ingot with nominal composition Cu50Zr40Ni5Ti5 (at.%) alloy was prepared
from the pure elements, Cu (99.7%), Zr (99.9%), Ni (99.5%), and Ti (99.99%) by arc
melting in a titanium-gettered argon atmosphere. The ingot was remelted four
times in order to obtain chemically homogenous Cu50Zr40Ni5Ti5 alloy. The rapidly
solidified ribbons were manufactured from the ingot in a single-roller Edmund
Bühler melt spinner at wheel surface velocities of 35, 38 and 41 m sÀ1
. The
melt-spun ribbons were typically 4–5 mm wide and 20–80 lm thickness. The phase
content of the melt-spun ribbons was characterized by XRD using a Philips X’Pert
powder diffractometer with Cu Ka radiation generated at 40 kV and 30 mA. The
thermal behaviour was examined by Perkin-Elmer Sapphire DSC unit under inert
gas atmosphere using continuous heating mode with the heating rate of 40 K minÀ1
for all melt-spun ribbons. A further DSC analysis was carried out for the melt-spun
http://dx.doi.org/10.1016/j.jallcom.2014.10.041
0925-8388/Ó 2014 Elsevier B.V. All rights reserved.
⇑ Corresponding author. Tel.: +90 344 280 1438; fax: +90 344 219 1042.
E-mail addresses: celalkursun@ksu.edu.tr, celalkursun@hotmail.com (C. Kursun).
Journal of Alloys and Compounds xxx (2014) xxx–xxx
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2. ribbon at wheel speed of 35 m sÀ1
using continuous heating mode with the heating
rates of 5–40 K minÀ1
. The cross section of the melt-spun ribbons was examined by
Zeiss Evo LS10 SEM and SEM-EDX after conventional metallographic preparation.
The melt-spun ribbons were annealed under vacuum/inert gas atmosphere at
the temperatures of 200, 470, 500, 550, 600, 725 and 800 °C for 30 min. The
annealed samples were characterised by XRD from surface, SEM from cross-section
with the same conditions used for as-quenched ribbons. The Vickers microhardness
measurements of the as-quenched and subsequently annealed ribbons were per-
formed using a Shimadzu HMV-2 by an applied load of 0.98 N with a dwell time
of 10 s at ten different locations.
3. Results and discussion
Fig. 1 shows typical XRD spectrum of the melt-spun Cu50Zr40-
Ni5Ti5 ribbons obtained using wheel surface velocities of 35, 38
and 41 m sÀ1
. The XRD spectrums of the melt-spun ribbons show
the broad maxima characteristic for amorphous material without
the evidence of any crystalline peaks within the sensitivity limits
of XRD. It is concluded from the XRD results that these 3 surface
velocities of 35, 38 and 41 m sÀ1
are high enough to obtain the
Cu50Zr40Ni5Ti5 alloy as completely amorphous state.
Fig. 2 shows the DSC curves of the rapidly solidified Cu50Zr40Ni5-
Ti5 alloys at wheel speeds of 35, 38 and 41 m sÀ1
during continuous
heating at a heating rate of 40 K minÀ1
. As seen in Fig. 2, the DSC
traces exhibit distinct and similar glass transition temperature fol-
lowed by a wide supercooled liquid temperature range. There is an
obvious exothermic reaction for all the samples according to the
crystallization behaviour of Cu50Zr40Ni5Ti5 ribbons. Table 1 sum-
marises thermal values obtained from DSC curves for melt-spun
Cu50Zr40Ni5Ti5 ribbons with the characteristic values of the glass
transition temperature Tg, crystallization temperature Tx, super-
cooled liquid region DTx (DTx = Tx À Tg), and crystallization tem-
perature Tp. Table 1 shows that Tx, DTx and Tp decrease while Tg
increases with increasing melt-spun wheel surface velocity. It is
concluded that the amorphous phase obtained at the highest wheel
speeds is the least stable for Cu50Zr40Ni5Ti5 alloy. This finding is
similar to the result which was reported by Yang et al., for amor-
phous Cu52.5Ti30Zr11.5Ni6 alloy [22].
Fig. 3 shows the DSC plots of the alloy at the heating rates; 5, 10,
20 and 40 K minÀ1
. The values of the peak temperatures (Tg, Tx, Tp)
and the super-cooled liquid region (DTx) of Cu50Zr40Ni5Ti5 alloy are
listed Table 2. As shown in Table 2, peak temperatures and super-
cooled region are shifted to higher temperatures with increasing
heating rate. It reveals that the parameters of crystallization and
glass transition rely on the heating rate during continuous heating
[23]. Thus, it is possible to mention the importance of the kinetic
aspects of the glass transition for amorphous alloys [24].
The activation energy, E which affects the thermal stability of an
amorphous alloy is often estimated by the Kissinger equation (Eq.
(1)) by using data from different heating rates of the alloy [25].
Fig. 1. Typical XRD spectrum of the melt-spun Cu50Zr40Ni5Ti5 ribbons obtained
using wheel surface velocities of 35, 38 and 41 m sÀ1
as-quenched.
Fig. 2. The DSC curves of the rapidly solidified Cu50Zr40Ni5Ti5 alloys at wheel speeds
of 35, 38 and 41 m sÀ1
obtained with continuous heating at a heating rate of
40 K minÀ1
.
Table 1
Thermal values obtained from DSC curves for melt-spun Cu50Zr40Ni5Ti5 ribbons at
different wheel speed.
Wheel (speed/m sÀ1
) Tg (°C) Tx (°C) Tx (°C) Tp (°C)
35 409 463 54 472
38 412 459 47 472
41 414 451 37 467
Fig. 3. DSC analysis results for the melt-spun ribbon obtained at wheel speed of
35 m sÀ1
using continuous heating mode with the heating rates of 5–40 K minÀ1
.
Table 2
Thermal values obtained from DSC curves for melt-spun Cu50Zr40Ni5Ti5 amorphous
ribbons produced at wheel speed of 35 m sÀ1
at different heating rates.
/ (K/min) Tg (K) Tx (K) DTx (K) Tp (K)
5 665 714 49 722
10 673 724 51 732
20 678 731 53 740
40 682 736 54 745
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Please cite this article in press as: C. Kursun et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.10.041

3. ln
/
T2
¼ À
E
RT
þ A ð1Þ
where T is the specific temperature, such as glass transition tem-
perature Tg, onset temperature Tx, or peak temperature Tp, of crys-
tallization, / is the heating rate, R is the gas constant
(8.314 J/mol K), E is the activation energy, A is a constant.
Approximately a straight line is obtained by plotting ln(//T2
) versus
1/(RT). The corresponding activation energy Eg, Ex or Ep of the total
reaction of the certain peak temperatures (Tg, Tx, Tp) obtained from
the slope of this straight line. The Kissenger plots of amorphous
Cu50Zr40Ni5Ti5 alloy by manufactured at wheel speed of 35 m sÀ1
are shown in Fig. 4. According to the present results, the activation
energies of Eg, Ex and Ep are calculated 442.47 (±15), 393.24 (±8) and
381.13 (±11) kJ/mol, respectively from the DSC results in the pre-
sent study. These activation energy values are higher than the
amorphous alloys of Cu45Zr45Ag7Al3 (Eg = 377, Ex = 307, Ep = 340 -
kJ/mol) [26], Cu52.5Zr11.5Ti30Ni6 (Eg = 357, Ex = 297, Ep = 289 kJ/mol)
[22] and Cu54Zr37Ti8In1 (Eg = 321, Ex = 392 kJ/mol) [23]. Moreover,
the Ex values of Cu- or CuZr-based metallic glasses which have been
reported in previous studies are generally calculated above
250 kJ/mol [23]. This indicates the mentioned metallic glasses have
good thermodynamic stability [23], therefore, it can be concluded
that the Cu50Zr40Ni5Ti5 alloy with the calculated the Eg value of
393.24 kJ/mol has also good thermodynamic stability.
In order to characterise the crystallisation behaviour of the
melt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speed
of 35 m sÀ1
, the ribbon was annealed in the temperature range of
200–800 °C for 30 min. The typical XRD spectrum of Cu50Zr40Ni5Ti5
alloy shows the crystallization stages alloy depending on the
annealing temperature (Fig. 5). The XRD spectrum of Cu50Zr40Ni5-
Ti5 amorphous ribbons annealed at 200 °C, that is, before the
exothermic reaction, shows fully an amorphous phase. However,
several sharp diffraction peaks have been observed after heating
the Cu50Zr40Ni5Ti5 amorphous ribbons to the annealing tem-
perature of 470 °C, which is just above the crystallization peak in
DSC traces. This is directly related to formation of crystalline phas-
es. The determined crystalline phases in the XRD pattern were
mainly indexed as orthorhombic-Cu10Zr7 and Cu8Zr3, monoclinic-
CuZr and f.c.c-Cu phases. It was reported in the literature that Cu10-
Zr7, Cu8Zr3 and CuZr phases were also observed after annealing for
copper based Cu45Zr45Ag7Al3 bulk metallic glass [26], Cu54.8Zr39.7-
Ag5.5 [16] and Cu50ÀxCoxZr50 (x = 2, 5 at. pct) alloys [27]. With
increasing annealing temperature (up to 800 °C), no change in
the crystallization peaks occurred. Thus, it may be suggested that
the thermal stability of the crystallized Cu50Zr40Ni5Ti5 alloy is high.
Fig. 6 shows typical SEM images from the cross-section of the
melt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speed
of 35 m sÀ1
and annealed in the temperature range of 200–800 °C
for 30 min. It can be seen clearly in Fig. 6 that the microstructure
of Cu50Zr40Ni5Ti5 alloy changes with increasing annealing tem-
perature. In Fig. 6a and b, the ribbons display featureless mor-
phology. This morphology is typical characteristic of the
amorphous ribbons which was reported in previous many similar
studies previously as well [28–30]. The SEM results in (Fig. 6a
and b) are in accord with the XRD patterns which display fully
amorphous features for as quenched and annealed (200 °C) ribbons
of Cu50Zr40Ni5Ti5 alloy.
After partial or fully crystallisation these ribbons display
microstructure with uneven and irregularly shaped features which
have already been reported in previous works [16,23,31–33]. The
SEM images (Fig. 6c–e) of annealed (470, 600 and 800 °C) Cu50Zr40-
Ni5Ti5 alloy ribbon imply that the amorphous phase transforms
into the crystallite phases similar to the findings of the reported
previous works [16,23,31–33].
According to XRD results of the annealed (470, 600 and 800 °C
for 30 min) ribbons, the crystallite phases that are seen in
Fig. 6c–e are defined Cu10Zr7, Cu8Zr3 or CuZr phases. Furthermore,
in order to confirm the compositional homogeneity of the Cu50Zr40-
Ni5Ti5 alloy ribbons, the SEM-EDX analysis was performed. Fig. 7
shows the EDX analysis of the Cu50Zr40Ni5Ti5 alloy ribbon (pre-
pared at a wheel speed of 35 m sÀ1
). It can be seen clearly from
SEM-EDX results that the peaks in the spectrum belong to Cu, Zr,
Ni and Ti elements. As shown in Fig. 7, the nominal composition
of the amorphous alloy is also so close to the percentages of ele-
ment compositions.
The rapidly solidified Cu50Zr40Ni5Ti5 alloy ribbons as-quenched
and annealed at different temperature were examined by Vickers
HV measurements to study the effect of annealing temperature
on the hardness. The following Vickers HV formula was employed
to evaluate the microhardness of the Cu50Zr40Ni5Ti5 alloy ribbon:
HV ¼
2P sinðh=2Þ
d
2
¼
1:8544ðPÞ
d
2
ð2Þ
where P is the indentation force, d is the average diagonal length
and 1.8544 is the geometrical factor for the diamond pyramid
[34]. The change in Vickers microhardness values for Cu50Zr40Ni5Ti5
Fig. 4. Kissinger plots of the amorphous Cu50Zr40Ni5Ti5 alloy manufactured at
wheel speed of 35 m sÀ1
.
Fig. 5. Typical XRD spectrum of the melt-spun ribbon of Cu50Zr40Ni5Ti5 alloy
prepared at a wheel speed of 35 m sÀ1
and annealed in the temperature range of
200–800 °C for 30 min.
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4. alloy produced (the wheel speed of 35 m sÀ1
) with annealing
temperatures shown in Fig. 8.
The microhardness values decreased with the annealing tem-
perature, and they were calculated as 522–473 HV in the annealing
temperature range of 200–400 °C (Fig. 8). There are similar report-
ed results associated with this decline of the microhardness values
of Cu-based amorphous alloys with increasing annealing tem-
peratures [7,35–39]. The microhardness value of the alloy which
Fig. 6. Typical SEM images from the cross section of the melt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speed of 35 m sÀ1
(a) as quenched and annealed at the
temperatures (b) 200 °C, (c) 470 °C, (d) 600 °C, and (e) 800 °C.
Cu50Zr40Ni5Ti5 (at. %)
Element Element
(wt. %)
Element
(at. %)
Cu K 49.18 50.48
Zr L 43.67 39.61
Ni K 3.75 4.69
Ti K 3.40 5.22
Total 100.00 100.00
Fig. 7. Typical SEM-EDX analysis result of the melt-spun ribbon of Cu50Zr40Ni5Ti5 alloy prepared at a wheel speed of 35 m sÀ1
as quenched.
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5. annealed at the temperature range of 400–725 °C, was determined
as approximately 463 HV since the crystalline phases in the
microstructure of Cu50Zr40Ni5Ti5 alloy were the same. Therefore,
the highest microhardness value of 522 HV was measured for the
ribbons as-quenched state. This hardness value is also the highest
compared with the Cu-based alloys which have been produced by
different techniques [7,9,35–43]. It is very interesting that the all
compared Cu-based alloys have crystal structures. Thus, it may
be easily mentioned that the effect on the hardness of the amor-
phous structure for rapidly solidified Cu50Zr40Ni5Ti5 alloy is pretty
good. The decline in the microhardness of amorphous structure
may be attributed to the lack of slip system which would normally
exist in a material with crystallite structure. Therefore, amorphous
metallic materials show much greater resistance to plastic defor-
mation than crystalline metals. Thus, this behaviour leads to
greater Vickers microhardness, as well as yield stress and fracture
stress [44].
4. Conclusions
1. The amorphous Cu50Zr40Ni5Ti5 alloys were successfully synthe-
sized by melt-spinning at wheel speeds of 35, 38 and 41 m sÀ1
.
2. DSC traces of the Cu50Zr40Ni5Ti5 ribbons exhibited similar dis-
tinct glass transition followed by a wide super-cooled liquid
region. According to the results, Tg and DTx are around 409–
414 °C and 37–54 °C, respectively.
3. The activation energies of Eg, Ex and Ep were calculated 442, 393
and 381 kJ/mol, respectively.
4. The existence of the Cu10Zr7, Cu8Zr3, CuZr and FCC-Cu phases in
the microstructure were determined annealing temperature of
470 °C and higher while the amount of Cu8Zr3 phase decreases
slightly as the annealing temperature increases.
5. After partial or fully crystallisation of Cu50Zr40Ni5Ti5 ribbons,
the microstructure had uneven and irregularly shaped features
while as quenched ribbons had featureless microstructure.
6. SEM-EDX analysis confirmed the compositional homogeneity of
Cu50Zr40Ni5Ti5 amorphous ribbons.
7. The microhardness of the Cu50Zr40Ni5Ti5 ribbons decreased
with increasing annealing temperature. The highest value of
the microhardness was measured about 522 HV for the ribbons
as-quenched state.
Acknowledgments
We would like to thank Kahramanmaras Sutcu Imam University
for financial support of the research programme (Project No: 2013/
3-41M). C. Kursun, one of the authors, would like to thank Council
of Higher Education (YÖK) for graduate research support and Tech-
nische Universität Dresden, IFW, Germany for providing laboratory
facilities and also to Fatemeh A. Javid for assistance in the produc-
ing of the alloys.
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