M. NABIALEK et al.: MAGNETIC PROPERTIES AND MICROSTRUCTURE OF A BULK AMORPHOUS ...
189–193
MAGNETIC PROPERTIES AND MICROSTRUCTURE OF A BULK
AMORPHOUS Fe61Co10Ti3Y6B20 ALLOY, FABRICATED AS RODS
AND TUBES
MAGNETNE LASTNOSTI IN MIKROSTRUKTURA MASIVNE
AMORFNE ZLITINE Fe61Co10Ti3Y6B20 V OBLIKI PALIC IN CEVI
Marcin Nabia³ek1, Katarzyna Bloch1, Karol Szl¹zak2, Micha³ Szota1
1Czestochowa University of Technology, Institute of Physics, Faculty of Production Engineering and Materials Technology,
19 Armii Krajowej Av., 42-200 Czêstochowa, Poland
2Warsaw University of Technology, Faculty of Materials Science and Engineering, 141 Woloska, 02-507 Warsaw, Poland
23kasia1@wp.pl
Prejem rokopisa – received: 2014-07-31; sprejem za objavo – accepted for publication: 2015-03-10
doi:10.17222/mit.2014.144
In this paper, studies are presented that characterize a bulk amorphous Fe61Co10Ti3Y6B20 alloy. Samples were fabricated in two
forms: as a rod of 1 mm in diameter and as a tube of 1 mm in the outer diameter. The investigated material was obtained using
the injection method, whereby the liquid alloy was injected into a copper mould. Using an X-ray diffractometer, a scanning
electron microscope and computer tomography, the microstructures of these rapidly cooled samples were studied. Based on the
obtained results, it was found that both the rod and the tube were fully amorphous. The cross-sections of the broken rod and tube
were characterized by a mixed rupture consisting of smooth chevron and river patterns. This shows that there are regions of
different ductility distributed throughout the volume of a sample. Three-dimensional images of the investigated materials,
obtained with computer tomography, allowed the determination of the contribution of the pores (and their size) to the total
volumes of the samples. The investigated alloy is a ferromagnetic material exhibiting good soft-magnetic properties such as a
high saturation magnetization, a high magnetic permeability and a low value of the coercive field. The technique of injecting the
liquid alloy into a copper mould, combined with the suction-casting method, can be used to produce toroidal cores that exhibit
highly promising properties for a successful application in the construction of electric motors.
Keywords: bulk amorphous alloys, X-ray diffractometry, electron scanning microscopy, computer tomography, saturation
magnetization, coercivity
^lanek prikazuje {tudijo zna~ilnosti masivne amorfne zlitine Fe61Co10Ti3Y6B20, katere vzorci so bili izdelani na dva na~ina: kot
palica premera 1 mm in kot cev z zunanjim premerom 1 mm. Preiskovani material je bil izdelan z vbrizgavanjem, saj je bila
talina vbrizgana v bakreno kokilo. Mikrostrukture hitro strjenih zlitin so bile prou~evane s pomo~jo rentgenskega difraktometra,
z vrsti~nim elektronskim mikroskopom in z ra~unalni{ko tomografijo. Na podlagi dobljenih rezultatov je bilo ugotovljeno, da
sta palica in cev popolnoma amorfni. Presek prelomljene palice in cevi ima me{an prelom, ki sestoji iz gladkih povr{in in
stopnic v obliki re~ic. To pomeni, da so razli~na podro~ja duktilnosti razporejena po volumnu vzorca. Trodimenzionalne slike
preiskovanih materialov, dobljenih s pomo~jo ra~unalni{ke tomografije, omogo~ajo dolo~itev dele`a por (in njihovih velikosti) v
celotnem volumnu vzorcev. Preiskovana zlitina je feromagnetna in ima dobre mehko magnetne lastnosti, kot so: visoko
nasi~enje pri magnetizaciji, visoka magnetna permeabilnost in majhna vrednost koercitivnega polja. Tehniko vbrizgavanja
teko~e litine v bakreno kokilo, v kombinaciji z livno metodo z vsesavanjem, se lahko uporabi za izdelavo toroidnih jeder, ki
imajo dobre lastnosti za uspe{no uporabo pri konstrukciji elektromotorjev.
Klju~ne besede: masivne amorfne zlitine, rentgenski difraktometer, vrsti~ni elektronski mikroskop, ra~unalni{ka tomografija,
nasi~ena magnetizacija, koercitivnost
1 INTRODUCTION
The 21st century could be called the šage of miniatu-
rization and proliferation of the cutting-edge techno-
logy’. Currently, the rapid development of subassemblies
for electronic devices is on the increase, featuring
increasingly compact physical dimensions. Of particular
importance are the component parts for miniature
motors, targeted at specialist applications. The magnetic
material used in micro-motors should have a good
coefficient of fulfilment and, of course, excellent magne-
tic and mechanical properties.1–6 Bulk amorphous alloys
include highly promising materials for electrical-engi-
neering applications.7–10 Conventional amorphous alloys,
manufactured in the form of a strip (ribbon), cannot be
used for the construction of micro-motors because the
strip shape is not suitable for the application.
Through the selection of the right chemical compo-
sition for an alloy, the amorphous state can be obtained
using a relatively slow cooling rate (102 K/s – 100 K/s).11
This feature has been utilized in the production of the
so-called bulk amorphous alloys. The bulk amorphous
alloys consist of many components (more than three
chemical elements). In order to obtain a high value of the
glass-forming ability (GFA) the atomic radii of the main
alloy components must vary by more than 12 % and
these components should be characterized by the nega-
tive mixing heat.11 Moreover, the bulk amorphous alloys
are characterized by a wide range of the so-called
super-cooled liquid region, Tx ( = Tx – Tg), where Tx is
Materiali in tehnologije / Materials and technology 50 (2016) 2, 189–193 189
UDK 537.622:544.23:66.017:669.055 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(2)189(2016)
the crystallization-onset temperature and Tg is the glass-
transition temperature.12 Due to the facts that the bulk
amorphous alloys consist of many components of va-
rious atomic radii and are obtained using a slow cooling
rate, their density is higher than that typical of the
classical amorphous alloys. The relatively slow cooling
rate, used in the manufacture of the bulk amorphous
alloys, yields a more relaxed structure in the resulting
as-cast state.
This paper presents the results of the studies of the
microstructure and magnetic properties of the
Fe61Co10Ti3Y6B20 bulk amorphous alloy in the forms of a
rod and a tube.
2 METHOD
The samples used in the investigations were produced
of high-purity elements (greater than 99.95 % of amount
fraction), using a combination of the injection- and
suction-casting methods. The molten liquid was sucked
into a water-cooled, copper die. The initial material was
melted by arc melting (current range: 240–300 A; volt-
age: 80 V) under a protective atmosphere of inert gas. In
addition, immediately prior to the suction process, pure
titanium was re-melted in order to avoid a sample oxi-
dation.
The structure and microstructure of the resulting
material were investigated by means of an X-ray
diffractometer (Bruker Advanced D8), scanning electron
microscope (SEM – Zeiss, Supra 35) and computer
tomograph (Bruker, SkyScan 1172 Micro-CT). X-ray
diffraction patterns (Cu-K) were taken in a 2-theta
range from 30° to 120°, with a measurement step of
0.05° and time per step of 2 s. Images of the surfaces of
the samples were obtained using the SEM, with a
constant electron-acceleration voltage of 25 kV and the
maximum magnification of 12 × 103. A three-dimensio-
nal visualization of the scanned samples was performed
using the SkyScan software (Bruker). This kind of
equipment is commonly used in amorphous and nano-
crystalline materials investigations.13 The X-ray para-
meters such as the voltage, the type of filter, the
exposure time and the pixel size were optimized in order
to obtain the best image contrast. The X-ray tube voltage
was 100 kV and the current was 100 μA. The X-ray
projections were obtained at 0.3° intervals with a
scanning angular rotation of 360° and 6 frames were
averaged for each rotation. The obtained resolution
yielded a pixel size of 2.38 μm. In addition, ring artefacts
were reduced through the selection of the
random-movement amplitude of 50. The exposure time
was 1200 ms. The images were reconstructed and
analysed using the Bruker NRecon and CTAn software.
DataViewer (Bruker) and CTVol (Bruker) were used to
reveal the microstructural features of the samples. Static
hysteresis loops were taken by means of a Lake Shore
7301 vibrating-sample magnetometer (VSM), using a
magnetic field of up to 2 T.
3 RESULTS AND DISCUSSIONS
In Figure 1, X-ray diffraction patterns, obtained from
the powdered alloy samples, are presented. A wide maxi-
mum, typical for the amorphous materials, can be ob-
served on the X-ray diffraction patterns at 2 	50°.
Figure 2 shows SEM images of the investigated
samples. Images showing the cross-sectional structures
of the investigated samples are presented in Figure 3.
Figure 3a corresponds to the rod sample and reveals
a visible mixed rupture, consisting of a smooth cleavage,
a poorly developed chevron and river patterns. This is a
sign of a varying degree of the structural relaxation of
M. NABIALEK et al.: MAGNETIC PROPERTIES AND MICROSTRUCTURE OF A BULK AMORPHOUS ...
190 Materiali in tehnologije / Materials and technology 50 (2016) 2, 189–193
Figure 3: SEM images of the surfaces of the: a) rod and b), c), d) tube
for the Fe61Co10Ti3Y6B20 alloy
Slika 3: SEM-posnetki povr{ine palice: a) palica in b), c), d) cevka iz
Fe61Co10Ti3Y6B20
Figure 1: X-ray diffraction patterns for the Fe61Co10Ti3Y6B20 alloy
Slika 1: Rentgenogram zlitine Fe61Co10Ti3Y6B20
Figure 2: SEM images for the investigated samples: a) rod of a 1 mm
diameter, b) tube of a 1 mm diameter
Slika 2: SEM-posnetka preiskovanih vzorcev: a) palica premera 1 mm,
b) cev premera 1 mm
the rod-shaped sample. Similar patterns were observed
across the whole of the surface of the rod sample (Fig-
ure 3a). The cross-sectional images obtained for the
tube-shaped sample (Figures 3b to 3d) were more
inhomogeneous and different characters of the ruptures
were observed for different sections of the tube. In Fig-
ure 3b, a well-developed band can be observed, dividing
the regions of smooth and scale-like breakthroughs. At
the top of this band, and situated perpendicularly to it,
fine and poorly developed scales are visible. In another
area of the investigated tube-like sample (Figure 3c), a
band separating the regions of the smooth cleavage was
also observed, with well-developed scales that are pa-
rallel to each other. In the lower part of the band deter-
mining the border of the scales, numerous breakthroughs
appeared, indicating the direction of the created scale-
like structure. In Figure 3d, the cross-section of the tube
(with the parallel band of well-developed scales) can be
seen. However, the character of this breakthrough is not
typical. A further expansion of the scale-like structure is
limited by the areas that feature different degrees of
stress, and, as a result, double-graded scales can be ob-
served.
On the basis of the SEM investigations, it can be
stated that the quenching time (and, related with this, the
cooling speed) has a significant influence on the struc-
tures of the breakthroughs featured in the investigated
samples. The microstructures of the investigated rod- and
tube-shaped samples are shown, with a 3-D visualisation,
in Figures 4 to 6. On the basis of computed-tomography
investigations of the rod-shaped sample of
Fe61Co10Ti3Y6B20 alloy, it was found that its structure is
uniform and free from defects in the form of pores; this
is in agreement with the results of the SEM investiga-
tions (Figure 3a).
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Materiali in tehnologije / Materials and technology 50 (2016) 2, 189–193 191
Figure 7: 3-D microstructure of the tube (in grey) with pores
Slika 7: 3-D mikrostruktura cevi (siva barva) s porami
Figure 4: Three different cross-sectional views of the rod microstruc-
ture: a) coronal, b) transaxial, c) sagittal
Slika 4: Trije razli~ni prikazi mikrostrukture preseka palice: a) koro-
nalni, b) transaksialni, c) sagitalni
Figure 6: Three different cross-sectional views of the tube micro-
structure with open pores: a) coronal, b) transaxial, c) sagittal
Slika 6: Trije razli~ni prikazi mikrostrukture preseka cevi z odprtimi
porami: a) koronalni, b) transaksialni, c) sagitalni
Figure 5: Three different cross-sectional views of the tube microstruc-
ture: a) coronal, b) transaxial, c) sagittal
Slika 5: Trije razli~ni prikazi mikrostrukture preseka cevi: a) koro-
nalni, b) transaksialni, c) sagitalni
The microstructure of the tube was found to be
mostly continuous (Figure 5) but there were some open
and closed pores (Figure 6) that were visualized in 3-D
(Figure 7). The volume-equivalent sphere diameter of
the pores (Figure 8) revealed that there were only five
pores of a volume of 0.0170 % in the range of 23 μm –
63.7 μm (Figure 9). The largest quantity of the pores
(19) was in the range of 3.8 μm to 17 μm, but the volume
was only 0.0014 % (Figure 9). In addition, various
breakthrough structures, related with the varying thick-
ness of the tube, can be observed in the SEM images
(Figure 6).
The microstructure of the rod was continuous. To
analyse the rod thickness, the distribution of maximum
intensity projection (MIP) was used (Figure 10a). The
differences, related to the main diameter (1082.2 μm),
and their distribution are shown in Figure 10b. To cal-
culate the thickness distribution of the rod, this area was
divided into eight parts (Figure 10c) and analysed
(Figure 11). The average shell thickness was found to be
47.4 μm.
The measurements of the šmagnetization versus mag-
netic field’ were performed on the rod- and tube-shaped
samples of the Fe61Co10Ti3Y6B20 amorphous alloy (Fig-
ure 12). The static hysteresis loops were found to have
the shapes typical for the ferromagnetic materials that
exhibit soft-magnetic properties. The saturation-magne-
tization values for the rod- and tube-shaped samples of
the investigated alloy were found to be almost identical,
both being approximately 1.17 T. Moreover, the investi-
gated alloys are characterized by low values of coer-
civity: 0.37·10–4 T and 0.25·10–4 T for the tube- and
rod-shaped samples, respectively.
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192 Materiali in tehnologije / Materials and technology 50 (2016) 2, 189–193
Figure 12: a), b) Static hysteresis loops, c), d) inserts with the origin
of M-H system
Slika 12: a), b) Stati~ne histerezne zanke ter c), d) vlo`ki iz M-H
sistema
Figure 9: Ratio of the volume of the pores to the total volume
Slika 9: Razmerje volumna por glede na celotni volumen
Figure 10: Microstructure of the rod: a) maximum intensity pro-
jection, b) differences for the main diameter (in white) and their
distribution (in grey), c) thickness distribution divided into 8 parts
Slika 10: Mikrostruktura palice: a) projekcija najve~je intenzivnosti,
b) razlika med glavnim premerom (bela barva) in njihova razporeditev
(siva barva), c) razporeditev debeline, razdeljene na 8 delov
Figure 8: Volume-equivalent sphere diameter of the pores
Slika 8: Volumenski ekvivalent kroglastega premera por
Figure 11: Rod thickness distribution divided into 8 parts (Figure 7c)
Slika 11: Razporeditev debeline palice, razdeljene na 8 delov (Slika
7c)
4 CONCLUSIONS
The utilization of the combined injection-casting
method, which features the suction casting of a molten
alloy into a copper die, facilitated the fabrication of a
bulk amorphous Fe61Co10Ti3Y6B20 alloy. In the case of the
investigated alloy, the most important application para-
meters are the good soft-magnetic properties, attained
whilst preserving the amorphous structure. Elements Ti
and Y were used as the components facilitating the
amorphicity of the alloy. It is commonly known that the
addition of a small quantity of titanium (up to 5 % of
amount fraction), or a similar addition of yttrium, to the
Fe-based alloys improve their glass-forming ability (an
increase in Tx); however, usually this has a negative
impact on the soft-magnetic properties. As demonstrated
in this work, despite the addition of these components
(3 % of amount fraction of Ti and 6 % of amount frac-
tion of Y), the bulk amorphous Fe61Co10Ti3Y6B20 alloy is
characterized by good soft-magnetic properties; i.e., a
high value of the saturation magnetization (1.17 T) and
low values of coercivity (0.37·10–4 T and 0.25·10–4 T for
the tube and rod samples, respectively).
When carrying out a computer-tomography investi-
gation of the rod-shaped sample of the Fe61Co10Ti3Y6B20
alloy, no pores were observed in the structure. However,
during the production of the tube-shaped sample, pores
were found in the volume of the sample. The volume-
equivalent sphere diameter of the pores indicated that
there were only five pores within a range of 23–63.7 μm
with a volume of 0.0170 %. The largest quantity of the
pores was within a range of 3.8 μm to 17 μm, but their
volume comprised only 0.0014 %. The presence of the
pores within the volume of the tube-shaped sample
caused only a minor deterioration of the magnetic pro-
perties in comparison with the rod-shaped sample (an
increase in the coercivity). Despite this, the material can
be used for the magnetic cores in micromotors, for
applications involving miniature devices.
By regulating the technical parameters of the produc-
tion process, it was possible for the rod- or tube-shaped
samples to be obtained. On the basis of the performed
investigations, it can be stated that a variation in the
quenching speed of the molten alloy has a substantial
influence on the structure, the microstructure and some
of the magnetic properties of the investigated material.
Hitherto, the bulk amorphous alloys have been produced
mainly in the forms of rods and plates. The creation of
bulk samples in the form of closed rings is a major
technological step. During the production process, an
additional problem was the appearance of the pores in
the volume of the tube, which had deleterious effects on
the durability and soft-magnetic properties of the investi-
gated alloy. Given an appropriate chemical composition,
these rings could be used in the construction of the
magnetic cores in electronic and electric microdevices.
The results of the investigations presented in this
paper demonstrate that changes in the structural stresses
and quenching speed of the molten alloy have a major
influence on the value of the coercivity, which is a
measure of the energy required for demagnetizing the
material. Despite a minor increase in the value of the
coercivity for the tube-shaped sample, the material
formed in this shape can be used for the magnetic cores
of micromotors in miniaturized devices.
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