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Ghafari et al., J Material Sci Eng 2016, 5:6
DOI: 10.4172/2169-0022.1000299
ISSN: 2169-0022
Research
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Research Article
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Are Transition Metal-Rich Metallic Glasses Made Up of Distorted BCC
Clusters?
Ghafari M1*, Gleiter H1,2, Feng T1, Ohara K3 and Hahn H1,2
Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology, Nanjing, China
Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany
3
Japan Synchrotron Radiation Research Institute (JASRI), Hyogo, Japan
1
2
Abstract
A structural model of metal-rich amorphous alloys is proposed. This model differs from the known models of
the atomic structure of amorphous metal-rich alloys consisting of transition metal-early transition metal components
or of transition metal-metalloid components. The atomic structures of these kinds of alloys were studied by means
of synchrotron high energy X-ray diffraction. The results obtained are presented in the form of radial distribution
functions suggesting that the atomic structures of amorphous transition metal-rich alloys consist of clusters with
chemically disordered and structurally distorted bcc cells, irrespective of the crystal structure of the corresponding
pure metallic elements.
Keywords: Amorphous alloys; Atomic structure; Radial distribution
function; Transition metals; X-ray diffraction
Introduction
Numerous experimental studies [1] of metallic glasses indicate that
the arrangement of atoms in metallic glasses is aperiodic and isotropic.
The presence of Short Range Order (SRO) and Medium Range Order
(MRO) indicates that the atomic positions are correlated up to few
interatomic distances.
Since the discovery of amorphous metallic alloys the following
prominent structural models have been proposed: (a) The Dense
Random Packing of Hard Spheres (DRPHS) [2-4], (b) the model
based on the formation of structural units, such as trigonal prisms or
icosahedral arrangements [5-9], and (c) the Cluster Model (CM) of
glasses [10,11].
In fact, the analysis of the structure provides the suggestion that
a uniform structure model of amorphous alloy is ineligible. In some
cases, the chemical bonding is the decisive factor [12,13], then other
factors such as metallic binding [13].
Recent reports on the structure of metal-rich amorphous alloys
[1] as well as of the structure of isolated nanometer-sized Fe crystals
[14] suggest that new insight into the structure of amorphous metallic
materials consisting of transition metal-early transition metal
components or of transition metal-metalloid components may be
obtained by investigating (e.g., by means of the Radial Distribution
Function, RDF of these materials as well as of some of their physical
properties) the atomic arrangements in these materials. In fact, metalrich amorphous alloys consisting of transition metal-early transition
metal components or of transition metal–metalloid components seem
promising model systems for such studies. This view is supported by the
following observations reported in the literature.
The results of Mössbauer measurements show that the distribution
of the internal magnetic hyperfine fields and the quadrupole splitting
distribution of pure nanometer-sized Fe crystals [14] and amorphous
Fe90Sc10 [15] or Fe90Zr10 [16] are similar if the Fe crystals have a size of
2 nm or less. These observations indicate that the atomic environments
of 57Fe-atoms in both materials are similar because the quadrupole
splitting, which is caused by the interaction of electrical field gradient
and the quadrupole moment of nucleus is directly related to the
atomic environment. Furthermore, Mössbauer experiments measured
J Material Sci Eng, an open access journal
ISSN: 2169-0022
in external magnetic fields and at various temperatures have verified
the existence of magnetic clusters in a-Fe90Sc10 with average cluster
sizes close to the interatomic spacing as deduced from the Radial
Distribution Function, RDF [17,18].
Moreover, additional structural information may be obtained
by studying the photon energy because the photon energy is directly
related to the vibrational dynamics of the atoms and hence to their
structural arrangement. The shape and the position of the maximum
of the phonon DOS amorphous Fe-rich alloys [19] and amorphous Fe
[20] were found to be similar to nano-crystalline-Fe [21] indicating that
the atomic environments of 57Fe-atoms in both materials are similar
Using genetic algorithm calculations, Nguyen et al., [22] have
shown that by starting of random configurations, the structure of
minimum-energy of the FeCo alloy is the bcc atomic arrangement. All
of these observations suggest a structural similarity between crystalline
Fe and amorphous Fe-rich alloys. Based on this observation, it is the
aim of the study reported in this paper to investigate of the following
two questions:
1- Is the atomic arrangement in transition metal–rich amorphous
alloys similar to the atomic arrangement in transition metal–
rich crystalline metals?
2- Does the atomic arrangement in transition metal-rich
amorphous alloys depend on their chemical composition?
Experimental
The materials systems chosen for the investigations that will be
reported in this paper were the following two families of alloys. (1)
*Corresponding author: Ghafari M, Herbert Gleiter Institute of Nanoscience,
Nanjing University of Science and Technology, Nanjing 210094, China, Tel:
862584303409; E-mail: [email protected]
Received October 28, 2016; Accepted November 14, 2016; Published November
24, 2016
Citation: Ghafari M, Gleiter H, Feng T, Ohara K, Hahn H (2016) Are Transition
Metal-Rich Metallic Glasses Made Up of Distorted BCC Clusters? J Material Sci
Eng 5: 299. doi: 10.4172/2169-0022.1000299
Copyright: © 2016 Ghafari M, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Volume 5 • Issue 6 • 1000299
Citation: Ghafari M, Gleiter H, Feng T, Ohara K, Hahn H (2016) Are Transition Metal-Rich Metallic Glasses Made Up of Distorted BCC Clusters? J
Material Sci Eng 5: 299. doi: 10.4172/2169-0022.1000299
Page 2 of 4
Transition metals-early transition alloys and (2) Transition metal-rich
and metalloid alloys (produced by Hitachi Metals Ltd., Vacuumschmelze
GmbH & Co. KG and in our laboratory by electrochemical deposition
methods). Early transitions metals (such as Sc) and metalloids (such as
P, B, and Si) are known as glass forming element.
All the metallic glasses studied by us - except of amorphous Ni86P14
and Co80P20 alloys - were prepared by melt spinning. The preparation of
Ni90Sc10, Co90Sc10 and Fe90Sc10 alloys was performed in a high vacuum
chamber. The amorphous Ni86P14 and Co80P20 alloys were prepared by
the electrochemical deposition methods [23,24].
The atomic structures of the metallic glass were studied using highenergy XRD (HE-XRD) with a photon wavelength of 0.21 Å at the
beamline BL04B2 at SPring-8. The beamline BL04B2 is designed for
diffraction and scattering experiments at photon energies larger than
37 keV. The main advantage of the beamline is the ability to structurally
characterize disordered samples by employing a wide range of scattering
vectors Q and a low instrumental background. Further advantages
are small correction terms (especially for absorption correction) and
reduction of truncation errors. The analysis of High-Energy X-Ray
Diffraction (HE-XRD) data and the transformation from k space to the
real space is described elsewhere [18].
Results
Figure 1 shows the radial distribution function of crystalline bcc-Fe,
fcc-Ni and hcp-Co and of the amorphous transition metal-rich Fe90Sc10
alloy. As may be seen with the similarity exists between pattern of the
peaks of the RDF of amorphous Fe90Sc10 alloy and crystalline Fe with
a bcc structure. However, the peaks of the amorphous alloy (Figure 1)
are broader than the ones of the Fe bcc crystals and the positions of
the peaks are shifted which indicates different interatomic spacing in
the amorphous Fe90Sc10 alloy and crystalline Fe. The similarity between
pattern of the peaks of the RDF of amorphous Fe90Sc10 alloy and
crystalline Fe with a bcc structure indicates that the atomic structure
of the amorphous alloy can be described as arrangements of distorted
cluster with a bcc structure (the peaks of the amorphous alloy were
broader than the ones of the Fe bcc crystals) and a distribution of
interatomic spacing centered on those of bcc-Fe with a certain shift
of the peak positions. In pure bcc-Fe, the nearest neighbor (nn) and
the next nearest neighbor (nnn) atoms are located at 2.48 Å and
2.87 Å, respectively, with 8 atoms and 6 atoms as nn and nnn in the
corresponding distances. Due to the small difference between the
nn and nnn shells in bcc-Fe, the nn and nnn shells overlap in the
amorphous alloy so that the nn and nnn shells become - in amorphous
metal-rich alloy - indistinguishable.
As may be seen from Figures 2 and 3, the RDF’s of crystalline
bcc-Fe and the RDF’s of amorphous Co90Sc10 and Ni90Sc10alloys yields
the same result as for Fe90Sc10 alloy. The following two main features
of the peak pattern of all three alloys are as follows: (1) All the peak
patterns of the RDFs are identical; (2) The major differences between
them are the enhanced peak widths and the shifts of peaks of the
individual amorphous metal-rich alloys relative to the peaks of the
bcc-Fe. In other words, the SRO and MRO of metal-rich alloys can
be described to consist of chemically disordered and structurally
distorted clusters with a bcc atomic arrangement. Figure 4 shows a
schematic drawing of two-dimensional atomic arrangements of the
nn and the nnn in a bcc cluster and the corresponding arrangements
in a distorted bcc cluster with a Sc-atom in the center. Because of
the different electronegativity of Fe and Sc, the Sc-atoms have the
tendency to attract the Fe- atoms.
On the other hand, it may be noted that according to the results
reported above, the bcc clusters making up the amorphous structures
seem not to be correlated with the crystal structure of main transition
metal, i.e., bcc for Fe, fcc for Ni and hcp for Co.
Figure 2: RDF of crystalline bcc-Fe, and amorphous Co90Sc10 alloy.
Figure 1: RDF of crystalline hcp-Co, fcc-Ni. bcc-Fe, and amorphous Fe90Sc10
alloy. The values of RDF in y-axis are valid for bcc-Fe and hcp-Co. In order to
see the different RDFs, the values for amorphous alloy and fcc-Ni are shifted
with a constant.
J Material Sci Eng, an open access journal
ISSN: 2169-0022
Figure 3: RDF of bcc-Fe and distorted bcc structure of crystalline Ni90Sc10 alloy
with long-range order.
Volume 5 • Issue 6 • 1000299
Citation: Ghafari M, Gleiter H, Feng T, Ohara K, Hahn H (2016) Are Transition Metal-Rich Metallic Glasses Made Up of Distorted BCC Clusters? J
Material Sci Eng 5: 299. doi: 10.4172/2169-0022.1000299
Page 3 of 4
In summary, the similarities of the RDFs of amorphous transition
metal-rich alloys of Fe, Ni and Co, indicate that the structure of all of
these alloys consist of distorted bcc clusters. For amorphous alloys with
transition metal compositions larger ≥ 78 at percentage, the structure
seems independent of the second components of these alloys with
such as Sc, B, Si or P as presented in Figure 5. Finally, let’s address the
question: Why are the distorted bcc clusters the preferred structural
units of the amorphous metal–rich alloys. In order to discuss this
question, the structure factor, S(Q), of amorphous Fe90Sc10 alloy as a
function of Q=4Π⁄λ was compared, Figure 6 [25] by means of the pair
correlation functions with the S(Q) of molten Fe at T=1870 K and at
1830 K (the melting temperature of Fe is Tm=1811 K) and with the S(Q)
of an undercooled melt of Fe at T=1750 K, 1730 K and 1670 K. As may
be seen, the position of peaks in the S(Q) plots (up to about 1 Å) and
the number of the nn are similar in the amorphous Fe90Sc10, in the melt
and in the undercooled Fe melt. This experimental observation suggests
that in rapidly quenched melts bcc clusters are the preferred structural
units.
Acknowledgements
This work is supported by the National Natural Science Foundation of China
(Grant no. 51571119, 51520105001), the Natural Science Foundation of Jiangsu
Province and the Fundamental Research Funds for the Central Universities. T. F.
acknowledges the support by the innovation project and the specially-appointed
professor project of Jiangsu province. The synchrotron radiation experiment
was approved by the Japan Synchrotron Radiation Research Institute (proposal.
2015A1890).
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J Material Sci Eng, an open access journal
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Volume 5 • Issue 6 • 1000299
Citation: Ghafari M, Gleiter H, Feng T, Ohara K, Hahn H (2016) Are Transition Metal-Rich Metallic Glasses Made Up of Distorted BCC Clusters? J
Material Sci Eng 5: 299. doi: 10.4172/2169-0022.1000299
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Citation: Ghafari M, Gleiter H, Feng T, Ohara K, Hahn H (2016) Are Transition
Metal-Rich Metallic Glasses Made Up of Distorted BCC Clusters? J Material
Sci Eng 5: 299. doi: 10.4172/2169-0022.1000299
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ISSN: 2169-0022
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