Shear Banding in Metallic Glasses: Major Weakness or Potential Advantage?

Abstract

Metallic glasses (MGs) are metallic materials without long-range ordering structures, which endows them with unique properties such as ultrahigh strength and hardness, high wear and corrosion resistances. MGs can be plastically thermoformed like plastics because their viscosity drops with the increase of temperature in their supercooled liquid region (SLR), which is a temperature interval localized between glass transition temperature Tg and crystallization temperature Tx. MGs display good plasticity in the case of high temperature combined with low strain rate. In contrast, when the temperature is under the glass transition temperature (Tg), the deformation is localized into shear bands and fracture occurs immediately after the initiation of shear bands. The material shows an asymmetry between tension and compression. Shear-banding is a plastic-deformation mode in all materials. Particularly, shear-banding is a form of plastic instability that localizes large shear strains in a relatively thin band when a material is deformed. This shear banding behavior of bulk metallic glasses (BMGs) is usually a weakness for these materials but sometimes may be transformed in an advantage by using good engineering solutions. A well known engineering application is the kinetic energy penetrator (KEP), when is used the effect of “self-sharpening” penetration. Shear bands are of crucial importance for deformation behavior of (MGs). Controlling the shear-banding is quite equivalent with the controlling of plasticity and failure at room temperature. This work provides an up-to-date overview on the fundamentals of shear-banding in (MGs) and also of the progress achieved very recently on this subject.

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Recent Patents on Materials Science
ISSN: 1874-4648
eISSN: 1874-4656
Materials Science
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1874-4656/16 $100.00+.00 © 2016 Bentham Science Publishers
Shear Banding in
Metallic Glasses: Major Weakness or Potential
Advantage?
Eugen M. Axintea,*, Yan Wangb, Lucian L. Tabacarua and Neyara Radwanc,d
aGheorghe Asachi Technical University of Iasi, Faculty of Machine Manufacturing and Industrial
Management, Iasi, Romania; bSchool of Materials Science and Engineering, University of Jinan Uni-
versity of Jinan, Jinan, P.R. China; cMechanical Department, Faculty of Engineering, Suez Canal
University, Ismailia, Egypt; dIndustrial Engineering Department, Faculty of Engineering, King Abdu-
laziz University, Jeddah, Saudi Arabia
Received: December 02, 2015; Accepted: April 4, 2016; Revised: April 3, 2016
Abstract: Metallic glasses (MGs) are metallic materials without long-range ordering structures, which
endows them with unique properties such as ultrahigh strength and hardness, high wear and corrosion
resistances. MGs can be plastically thermoformed like plastics because their viscosity drops with the increase of tempera-
ture in their supercooled liquid region (SLR), which is a temperature interval localized between glass transition tempera-
ture Tg and crystallization temperature Tx. MGs display good plasticity in the case of high temperature combined with low
strain rate. In contrast, when the temperature is under the glass transition temperature (Tg), the deformation is localized
into shear bands and fracture occurs immediately after the initiation of shear bands. The material shows an asymmetry be-
tween tension and compression. Shear-banding is a plastic-deformation mode in all materials. Particularly, shear-banding
is a form of plastic instability that localizes large shear strains in a relatively thin band when a material is deformed. This
shear banding behavior of bulk metallic glasses (BMGs) is usually a weakness for these materials but sometimes may be
transformed in an advantage by using good engineering solutions. A well known engineering application is the kinetic en-
ergy penetrator (KEP), when is used the effect of “self-sharpening” penetration. Shear bands are of crucial importance for
deformation behavior of (MGs). Controlling the shear-banding is quite equivalent with the controlling of plasticity and
failure at room temperature. This work provides an up-to-date overview on the fundamentals of shear-banding in (MGs)
and also of the progress achieved very recently on this subject.
Keywords: Atomic ordering, fundamental models, metallic glasses, plastic instability, recent findings, shear bands.
INTRODUCTION
Metals and glasses have been known for a long time. The
first manmade iron objects are from Sumer and Antique
Egypt (appreciatively at 4000 B.C.). It is historically ac-
cepted the fact that the first manufactured glass was in the
form of a glaze on ceramic vessels, about 3000 B.C. The first
glass vessels were produced about 1500 B.C. in Egypt and
Mesopotamia. Mineral soda-alumina (m-Na-Al) glass has
been found across a vast area stretching from Africa to East
Asia [1-3]. Usually, these two categories of materials, metals
and glasses, have been considered to possess distinctly dif-
ferent properties, and explored and developed independently.
Metals are made of metallic elements via metallic bonding.
Atoms in metals are known to reside on a crystalline lattice
with long-range translational order. Glasses, in contrast, of-
ten involve covalent bonds or van der Waals interactions,
and are characterized by an amorphous structure without
long-range structural correlation. The different atomic and
electronic structures underlie the contrasting properties of
metals and glasses [4].
*Address correspondence to this author at the Gheorghe Asachi Technical
University of Iasi, Faculty of Machine Manufacturing and Industrial Man-
agement, 59 A -Prof. Dimitrie Mangeron Blvd, Romania;
Tel: +40722892926; Fax: +40232217290; E-mail: axintee@tcm.tuiasi.ro
Metallic glasses (MGs) look like metals and have the
intimate structure and sometimes the behavior of glasses.
The first reported scientifically obtained MG was the alloy
Au75Si25 produced at Caltech by Klement et al., in 1959, by
extremely rapid cooling of the Au-based melted alloy. Due
to the high solidification rate required to produce MGs, the
section thickness was small, i.e. only a few tens of microme-
ters, typically 20 to 50m [5-7].
1. THE INTIMATE STRUCTURE OF METALLIC
GLASSES
The liquid structure is a fascinating subject in the field of
materials science and condensed matter physics, but it still
has many unanswered questions to solve, such as the exis-
tence of liquid-liquid structure change and its nature, the
mechanisms of temperature-induced structure change.
According to their atomic ordering and arrangement, solids
are described as crystalline/quasi-crystalline or amorphous. By
comparison with crystalline solids, amorphous materials do
not possess long-range atomic order, but only short-range or-
der over a few atoms. Amorphous materials are usually in
nature: e.g. rubber, glass, plastic and asphalt [8].
The standard structural signature of glasses is the lack of
long-range order. That is, atoms in glasses are not coordi-
nated to form a periodic lattice as in crystals, where the equi-

Shear Bands i n Metallic Glasses Recent Patents on Materials Science 2016, Vol. 9, No. 1 3
librium position of each is predictable. However, this does
not mean that the atomic-level structure of glasses is com-
pletely random or featureless.
BMGs were seriously investigated due to their unique
properties, such as excellent corrosion resistance, high
strength and hardness, and large elastic limit, which ensure
their potential applications as structural, functional and bio-
compatible materials. It is known that the properties of
BMGs depend on the synergetic effect of atomic arrange-
ment and internal microstructure. Experimental and simu-
lated results have shown that there is nanometer scale me-
dium-range order (MRO) and long-range topological (LRO)
order in the BMGs. Moreover, increasing efforts have
claimed that the compositional and structural heterogeneities
can be formed in some BMGs and have advantages of the
plasticity of BMGs [8-15].
BMGs (and the amorphous materials) are characterized
by the four crucial points shown in Fig. (1). The four points
are: (1) long-range atomic disorder; (2) isotropic physical
and chemical properties; (3) are metastable, but could un-
dergo relaxation towards crystallinity with heat or pressure;
(4) melting point determined but not very precise, and have a
glass transition temperature [14].
In the great review paper [16], Cheng et al., revealed that
MGs consisted of metallic elements and metallic bonds and
had an amorphous internal structure. Such a combination of
metal and glass leads to unique properties and unprecedented
opportunities.
Direct observations [17] of the local atomic order of
BMGs revealed that they do not have any translational and
rotational symmetry down to the nanoscale because of their
disordered atomic arrangement.
For BMGs, the direct reconstruction of the locally 3-D
structure is robust, and several experimental techniques are
used to get statistical information about the common glass
structure. Structural studies have been transformed in the
recent years by acceleration in the acquisition of X-ray and
neutron scattering data, and by improved computational
methods, which are given in Table 1.
According to all researchers in MGs domain, there are
two challenges in the study of BMGs structures:
(1) How to construct a realistic three-dimensional (3-D)
amorphous structure, using experimental and computa-
tional tools
(2) How to efficiently characterize a given amorphous
structure and extract the key structural features relevant
to the fundamentals of glass formation and properties,
using appropriate structural parameters.
Bernal, Scott and Finney, the pioneers in solving the
structure of metallic liquids, assumed that densest packing
is the key factor governing the structure of metallic liquids
and glasses. In 1960, Bernal considered the structure of
monatomic metallic liquids to be dense random packing
[18]. The atoms in metals are approximated as hard
spheres. The problem was the packing method of the 3-D
space with identical hard spheres as densely as possible,
without introducing crystalline order. According to Chen
and Ma, "This is Bernal's original idea of dense random
packing (DRP) of hard spheres (DRPHS)" -excerpt with
permission from [16].
Bernal proposed that five types of holes with edges of
equal length (i.e., equilateral triangle faces) are likely the
basic structural units of monatomic liquids. Bernal' canonical
holes are schematized in Fig. (2).
Recently, intensive studies have shown that there exists
the nanoscale structural inhomogeneity in BMGs. Simula-
tions assisted by computer and practical experiments show
Fig. (1). Schematic characterization of amorphous materials.
Table 1. Experimental and Computational Methods Used for Study of Local Structure of BMGs [7].
Experimental Methods Simulatio n and Computationa l Techniques
X-ray/neutron Diffraction (XRD)
X-ray Absorption Fine Structure (XAFS)
Fluctuation Electron Microscopy (FEM)
Transmission Electron Microscopy (TEM)
Nuclear Magnetic Resonance (NMR)
Quantum Molecular Dynamics - also called ab initio MD or
first-principles MD
Reverse Monte Carlo modeling (RMC)
Molecular Dynamics Simulation (MD)

4 Recent Patents on Materials Science 2016, Vol. 9, No. 1 Axinte et al.
that liquid-like regions in BMGs with viscoelasticity flow
feature act as the flow units, accommodating the deformation
and initiating the shear banding. According to the perspec-
tive of the flow units model, the BMGs can be regarded as
elastic matrix combined with liquid-like flow units as in Fig.
(3). The red atom areas represent the flow unit, the blue atom
areas represent the densely packed elastic matrix, and the
green dotted circles represent the distribution of free vol-
umes [19].
2. SHEAR-BANDING AND SHEAR BANDS IN MGS
2.1. Introduction to Shear Banding Phenomenon
Shear-banding is a phenomenon of plastic instability that
localizes large shear strains in a relatively thin band when a
material is deformed. BMGs have some good mechanical
and physical properties, as extremely high strength (~5GPa),
hardness (~12GPa), and large elastic strain limit (~2%).
BMGs usually display good plasticity in the case of high
temperature combined with low strain rate. In contrast, when
the temperature is under the glass transition temperature Tg,
the deformation is localized into shear bands, and fracture
occurs immediately after the initiation of shear bands. The
material shows an asymmetry between tension and compres-
sion [20, 21].
This shear banding behavior of BMGs is usually consid-
ered a weakness for these materials but sometimes may be
transformed into an advantage by using good engineering
solutions. A well-known engineering application is the ki-
netic energy penetrator (KEP) when the effect of "self-
sharpening" penetration is used.
The nanometer level width of shear bands in BMGs (10-
20nm) is much smaller than that of the adiabatic shear bands
in the crystalline alloys (10-500m). This implies that the
intimate structure of BMGs may have a significant effect on
its shear banding process. In the present time, thermo-
mechanical models, which suggest that the free volume sof-
tening dominates the shear banding process in BMGs, are
relatively used successfully. For the yielding and failure of
BMGs, some macroscopic criterions had been proposed.
However, the corresponding micro-mechanism is still under
the exploration process, and the failure process is usually
analyzed according to the evolution of microstructure in
BMGs.
2.2. Historical Moments in Shear Banding Studies
The first studies of MGs were limited by the small di-
mensions and irregular forms of samples and were dedicated
to thermal, electrical, magnetic and structural properties.
Fig. (2). The Bernal’s canonical holes [7, 16].
Fig. (3). Schematics of the free volume and flow units in BMGs [19].

Shear Bands i n Metallic Glasses Recent Patents on Materials Science 2016, Vol. 9, No. 1 5
Studies of mechanical properties became possible in the time
when the techniques for the production of rapidly solidified
samples were improved.
In [21], is revealed that the first comprehensive study of
mechanical properties was performed by Masumoto and Mad-
din. The tensile tests were conducted over a broad range of
temperature and strain rate. It was found that despite the high
value of strength and the macroscopically brittle behavior, the
fracture stress was independent of sample volume. Greer,
et al., assumed that “this appears to be the first observation of
what are now known as shear bands” [21].
The shear nature of plastic deformation in MGs was es-
tablished in 1972 by Leamy, Wang, and Chen and was
communicated as “Plastic flow and fracture of metallic
glass” [22]. Examination of the tensile deformation and frac-
ture behavior of several amorphous and microcrystalline
alloys has shown that: a) Tensile stress is accommodated by
high hardening rate plastic shear deformation; b) Fracture
occurs on surfaces of maximum shear stress and is preceded
by plastic shear strain c) Fracture is accompanied by local
heating and viscous flow necking of material between
propagating cracks or voids. These observations form the
basis for speculation that plastic flow occurs via motion of
localized strain concentrations, and that fracture is initiated
by macroscopic adiabatic shear [22].
Spaepen in [23] realized the first empirical deformation-
mechanism map for a metallic glass. In this study, the two
modes of deformation- homogeneous and inhomogeneous
flow are reviewed. All these early studies revealed unani-
mously the essential characteristics of the mechanical prop-
erties of MGs, which are summarized in Table 2.
2.3. Why to Study the Shear Bands in BMGs?
However, below the glass transition temperature and at
high stresses, BMGs undergo inhomogeneous deformation
by concentrating severe plastic strain into nanoscale shear
bands [24]. The shear-banding-mode plastic flow of MGs at
ambient temperature continues to fascinate and challenge
scientists because of its physical origin and practical implica-
tions. The free volume creation and local heating generation,
in which shear-band thickness is a major factor, are two po-
tential causes of shear-banding instability in MGs [25, 26].
The formation and evolution of shear bands control the
yielding and plasticity of almost all MGs at room tempera-
ture, and in many cases, the formation of dominant shear
bands quickly leads to failure. In considering the mechanical
behavior of MGs, the key is to understand fully shear bands,
their initiation, propagation, evolution, consequences, and
control.
Several key aspects of shear banding importance for
MGs are summarized in Table 3.
2.4. Scenarios for Shear Band Occurrence
Following the models of Spaepen and Argon, plastic flow is
considered as a net balance of shear-induced atomic rear-
rangement creating free volume and diffusive-like processes
annihilating free volume [27]. Argon proposed the term of
"shear transformation." A shear transformation involves a
group of atoms with much larger atomic displacements than
in the surrounding matrix, and the local region including
these atoms is often called a shear transformation zone
(STZ). Takeuchi et al., provides an extensive study about
shear deformation in MGs [28]. In this article, author re-
Table 2. The Characteristics of the Mechanical Properties of BMGs [21].
The characteristics of the
mechanical properties of
MGs
High flow stress (when normalized to Young’s or shear modulus)
Low Young’s modulus (relative to crystalline counterparts)
Very limited ductility in tension
Two regimes of plastic flow: homogeneous at low strain rate and high temperature, inhomogeneous (in the form of
shear bands) at high strain rate and low temperature
High strength and high elastic limit
Table 3. Some Key Aspects of Shear Bands Importance for BMGs (Adapted From [21]).
Key aspects
of shear bands importance
They form along planes that closely approximate those of maximum shear stress;
While cohesion is maintained across them (they are not cracks), they do show a flow stress much lower than that of
the bulk, and may develop into cracks;
After deformation has ended, shear bands remain distinct from the bulk, being favored planes for further yielding and
undergoing preferential etching;
Such effects can be attributed to local disordering (associated with dilation, often describable as the generation of free
volume) and can be erased by annealing;
The lowering of the flow stress in shear bands has been attributed to local heating and to disordering;
Shear bands appear to be very thin (cca.20 nm)
Fracture surfaces often show a vein pattern associated with instability in a liquid-like layer that must be some mi-
crometers thick.

6 Recent Patents on Materials Science 2016, Vol. 9, No. 1 Axinte et al.
views atomistic simulation studies of deformation processes
in MGs, i.e., local shear transformation (LST), structural
characterization of the local shear transformation zones
(STZs), deformation-induced softening, shear band forma-
tion and its development, by using elemental and metal–
metal alloy models. Authors also review representative mi-
croscopic models so far proposed for the deformation
mechanism in early dislocation model, Spaepen's free-
volume model, Argons' STZ model and in some recent two-
state STZ models. Authors revealed that two pioneering de-
formation models were proposed in the late 1970's. “One of
these models is the free volume model by Spaepen. The con-
cept of the free volume was originally proposed by Cohen
and Turnbull to model the transport processes in the liquid of
hard spheres. Despite possible limitations, the free volume
concept was further employed and developed by Spaepen to
model the diffusion and plastic flow in MGs under different
levels of external stress. The other one is the shear transfor-
mation zone (STZ) model by Argon" (excerpt with permis-
sion from [28]). These two fundamental models are based on
the fact that the basic unit process of deformation is a local
rearrangement of atoms which accommodates the local shear
strain.
These processes are schematically represented in the scheme
from Fig. (4). The group of atoms changes its configuration
under a shear stress from one relatively small energy con-
figuration to a next such configuration by thermal activation.
Greer et al., [20] identified three scenarios for shear
bands formation summarized in Table 4.
The third scenario that assumed the formation of a shear
band in two consecutive stages was validated by experiments
and by computer simulations. This model also removes con-
fusion in understanding the shear-band speed. It was consid-
ered that a shear band runs very fast at, or near to, the speed
of sound, while others claim that the rate is much lower, of
the order of mm/s. Both experimental findings can be ration-
alized using the two-stage description: the rejuvenating front
in the first stage does propagate at, or near to, the speed of
sound, while the synchronized sliding of the shear band in
the second phase is much slower, with the exact rate depend-
ing on loading conditions and sample size [20].
Fig. (4). The schematization of Spaepen and Argon concepts
(adapted with permission from [7] ©2012Elsevier and from [21]).
3. RECENT FINDINGS AND EXPERIMENTAL ON
SHEAR BANDING PHENOMENON
To deeply explain the plastic deformation of BMGs be-
low Tg value, recently, a cooperative shearing model (CSM)
has been proposed which is based on the idea of potential
energy landscape [29]. The parameters such as activation
energy and volume () are necessary to describe the mecha-
nism of microscopic plastic, macroscopic mechanical proper-
ties and the structural heterogeneities of BMGs. However, it
is hard to calculate activation energy and volume of flow
units experimentally. In [29], Wang et al. revealed that the
activation energy of flow units of BMGs can be directly de-
termined by using dynamic mechanical analysis. The aver-
age volume of flow units and the number of atoms in a flow
unit for various BMGs are then experimentally obtained
based on CSM theory. The authors also evaluate the relation-
ship between the volume of the plastic units and the Pois-
son's ratio, which is correlated with the mechanical proper-
Table 4. Scenarios for Shear Band Formation (Adapted After [20]).
1. Percolation of homogeneously activated STZs to form a shear band
With the activation of a sufficiently large population of STZs in the glass matrix, they would eventually exceed the per-
colation limit. The percolated STZs, along the plane of maximum shear stress, form a deformation band, which is sof-
tened due to the activation of STZs and, therefore, would concentrate subsequent shear strains. A shear band then devel-
ops from this
2. The imperfections of fabrication are triggers of shear band formations
The inevitable micro/nano voids or surface notches serve as stress concentrators when the sample is under external load-
ing. It is then likely that shear bands preferentially initiate from these sites where the local stress can be higher than the
global average
Scenarios for
shear-ba nd formation
3. The formation of a shear band in two consecutive stages
Stage 1 is the creation of a viable band for shearing by structural rejuvenation
Stage 2 is the synchronized sliding and shear off along the rejuvenated plane. The shear-band material experiences large
plastic strains so that significant local heating is now possible

Shear Bands i n Metallic Glasses Recent Patents on Materials Science 2016, Vol. 9, No. 1 7
ties of BMGs. Figure 5 presents a schematized flow units in
BMGs. The BMGs can be considered as a random distribu-
tion of flow units (regions with pink atoms) in an atomically
disordered continuum.
Fig. (5). Schematic of flow units in BMGs (adapted with permis-
sion from [29]) ©2015 Elsevier).
The authors also provided the correlation between Pois-
son’s ratio and the size of flow units (shown in Fig. (6)).
Fig. (6). The correlation between Poisson’s ratio and the size of
flow units (reproduced with permission from [29] ©2015 Elsevier).
Based on the critical energy dissipated within the shear
band, the shear-band toughness is proposed by [30] to quan-
titatively measure the susceptibility of the shear band to
catastrophic fracture in BMGs. The schematic diagram of
shear band initiating in local plastic regions in a BMG sub-
jected to external loading is proposed in Fig. (7).
Molecular dynamics simulations of shear band formation
in homogenous BMGs, nano-composites, and nano-glasses
are presented in [31]. The authors observed shear banding in
a defect-free sample without free surfaces and, therefore,
confirmed that strain localization is an intrinsic metallic
glass property, independent of the presence of extrinsic
stress concentrators. Comparing homogeneous and heteroge-
neous SB nucleation, it was found that the mechanisms for
the formation of an SB nucleus are rather similar and involve
the percolation of STZs along a viable shear path (Fig. (8))
[31].
The displacements in x-direction at the SB-nucleation
site (Fig. (8)) reveals the processes leading to SB formation
(A-C):
A. The surface roughness is low and no surface defects are
present that could serve as stress concentrator.
B. At 9% strain an embryonic STZ is activated at the sur-
face, since STZ operation involves the rearrangement of
atoms (as marked by the circle).
C. This embryonic STZ serves as a stress concentrator and
leads to shear localization (indicated by arrows).
The collective behavior of multiple shear bands under in
situ four-point bending tests of a Zr-based BMG over a
broad range of sample scales was investigated [32]. This
study might offer a fundamental picture of collective evolu-
tion dynamics of multiple shear bands in BMGs and provide
new insights into its fixed size and pressure sensitivity.
The developed analytical model can be adopted for a
range of loading conditions and not only for the round case.
For dynamic loading, the thermal effect on shear band evolu-
tion should be considered and the coupled free volume-
Fig. (7). The schematic diagram of shear band initiating and fracture features of Vitreloy 1 under quasi-static tension (a) Schematic diagram
of shear band initiating in local plastic regions in a BMG subjected to external loading. (b) Schematic diagram of experimental setup with a
specimen detail (reproduced with permission from [30] ©2011 Elsevier).

8 Recent Patents on Materials Science 2016, Vol. 9, No. 1 Axinte et al.
thermo-softening need to be rated. Also, the authors provide
a map of the shear band (SB) nucleation and growth depend-
ing on the sample thickness. This competition (nucleation
/propagation) can be depicted by a map of both the dissipa-
tion energies * and * (Fig. (9)) [32].
Fig. (9). Competing map of shear band (SB) nucleation and growth
depending on sample thickness (adapted with permission from [32]
©2013 Elsevier).
In [33], indentation techniques were used to study the
elastic deformation of a Zr-Cu-based BMG alloy, followed
by a systematic analysis of initiation and evolution of shear
band localization in the indented material. The results ob-
tained demonstrate the initiation of shear bands in the mate-
rial volume. Some results of initial numerical simulations of
deformation processes show that a maximum-shear-stress
criterion can, in developing constitutive models of BMG,
characterize shear band localization in BMGs (Fig. (10))
[33].
In [34], an essential feature of inhomogeneous micro-
scopic plastic deformation for Vitreloy BMG samples sub-
jected to macroscopic shear by high-pressure torsion (HPT)
has been researched. In HPT, a thin disk-shaped sample is
placed between two anvils and subjected to simultaneous
compressive force and torsional straining. Specifically, the
inhomogeneity of the plastic deformation has been investi-
gated at different characteristic length scales by analyzing
the distortion of a marker grid etched on an internal surface
of the HPT disks (Fig. (11)) [34].
Fig. (10). Indentation load-displacement curves of Zr-Cu-based
BMG for incremental loading-unloading at loading rate of 2mN/s.
The insets show evolution of shear-band patterns with increasing
load (reproduced with permission from [33] ©2014 Elsevier).
Atomistic simulations were performed to study the ef-
fects of size and shape of a slight or inner notch on the
strength and failure mechanism of CuZr metallic glass (MG)
under tensile loading. The results show that plastic deforma-
tion originating at the indent root reduces the stress concen-
tration there and leads to a notch-insensitive normalized ten-
sile strength [35]. Zhao et al., successfully demonstrated that
the micro-cracks in a ductile Zr-based BMG may originate
from the local planar faults or defects within the shear plane
along the shear direction [36]. The process was divided into
four stages which are schematized in Fig. (12) [36].
By using the elastic contact solutions and the Rudnicki-
Rice model, the authors identified regimes under the two-
dimensional cylindrical (three-dimensional spherical) contact
where different shear-band directions may occur (Fig. (13))
[37].
A two-dimensional cold rolling was performed on a Zr-
based BMG. The average shear band density continuously
increased with plastic strain. Based on an analysis of the
measured shear band densities and enthalpy changes, authors
Fig. (8). Shear band nucleation at a surface defect resulting from a STZ. The atoms are colored according to their displacement in x-direction
(adapted from [31] ©2013 Elsevier).

Shear Bands i n Metallic Glasses Recent Patents on Materials Science 2016, Vol. 9, No. 1 9
concluded that the free volume of both the matrix and the
shear bands must evolve continuously during deformation
(Fig. (14) [38].
In [39], Wang reviewed the formation and properties of a
series of high-mixing entropy BMGs. A high entropy BMG
sample (Zn20Ca20Sr20Yb20 (LixMgy)20 can be compressed to
70% of its original height without observable cracking and
shear banding. Such a heavy deformation without shear
bands and fracture, and the dependence of strain-rate of the
steady-state flow stress indicate the same flowability of the
MG at room temperature (Fig. (15) [40]).
Fig. (11). Shear bands in a BMG subjected to macroscopic shear by high pressure torsion (adapted with permission from [34] ©2014 El-
sevier).
Fig. (12). Shear bands evolve into cracks in BMGs with single dominant shear band deformation (stages1-4) Compressive load–displacement
curve of a fractured BMG sample (F1) with single dominant shear band deformation. In detail - the SEM micrograph of the fracture surface
and lateral surface of the F1 sample (adapted with permission from [36] ©2015 Elsevier).
Fig. (13). Radial and semicircular shear bands in Zr-based BMG are produced using the bonded-interface technique and spherical indenta-
tion: (a) top view; (b) side view of one quarter-space specimen beneath the indent (adapted with permission from [37] ©2011 Elsevier).

10 Recent Patents on Materials Science 2016, Vol. 9, No. 1 Axinte et al.
Fig. (14). The experimentally determined values for the shear band
line density logarithmically plotted vs. the true plastic strain to
which the material has been deformed (reproduced with permission
from [38] ©2014 Elsevier).
Fig. (15). The photo image of the compressed MG, which can be
compressed up to 70% of its original height without shear banding
and cracking (reproduced with permission from [40]).
The compressive behavior of a Zr-based (Zr39.6Ti33.9Nb7.6
Cu6.4Be12.5) BMG composite was extensively studied in [41].
The results demonstrate that the propagation behavior of
shear bands and the fracture of this material are strongly af-
fected by the strain rate. The multiplication of shear bands
was observed under quasistatic strain rate, while single shear
banding occurs in the dynamic case (Fig. (16)).
An intrinsic transition was observed (at room tempera-
ture) from catastrophic shear failure to more uniform plastic-
ity and complete ductile necking of a BMG when the sample
diameter is reduced to below 500 nanometers. The main
condition is that the sample to be prepared and tested in a
manner to avoid extrinsic effects. According to the theoreti-
cal analysis, the plasticity of BMGs is mediated by the STZ
catalyzed by the local dilatation (Fig. (17)) [42].
Micropillars with different diameters (3.8, 1 and 0.7m)
were fabricated from a Zr-based metallic glass using focus
ion beam (FIB), and then tested in micro-compression at
different strain rates. At all sizes, the plastic flow is localized
in shear bands and manifested as strain bursts to release the
energy. There are more shear bands in the Zr-based BMG as
compared to that in Mg-based BMG, which is consistent
with the fact that Zr-based BMG is more ductile than Mg-
based BMG [43].
In [44], a modified expanding cavity model developed
for Vickers indentation-induced shear bands appears to
Fig. (16). The deformation and fracture of the quasistatic specimen
(a, c) and dynamic specimen (b, d) (reproduced with permission
from [41] ©2013 Elsevier).
Fig. (17). Transition from catastrophic shear fracture to ductile
necking of Pd-based glassy wires with reduction in sample diameter
(reproduced with permission from [42] ©2015 Elsevier).
successfully describe the deformation behaviors of the Mg-
based BMGs. The experimental results obtained from the
Vickers indentation evidently confirmed the model predic-
tions.
The dynamic fragmentation in a Zr-based BMG, induced
by network-like shear bands was observed by [45]. The
authors proposed a theoretical model that takes into account
the influence of elastic strain energy on the shear-band evo-
lution. It is shown that, with the increase of strain rates,
shear-band patterns transfer from one dominated mode to
multiple modes. Dynamic fragmentation is given by the
competition between the energy dissipated within a shear
band and the elastic strain energy in a momentum diffusion
zone. The authors claim that the similarities between experi-
mental observations and their theoretical analysis indicate that
the elastic strain energy plays a significant role in shear band-
ing phenomenon (see Fig. (18)). As shown in Fig. (18b),
however, there is an elastic region and the energy per unit
area is supplied by elastic strain energy stored in the area.

Shear Bands in Metallic Gla sses Recent Patents on Materials Science 2016, Vol. 9, No. 1 11
A Pd-based BMG (Pd40Ni40P20) was rolled at room tem-
perature up to 99% in thickness reduction. The evolution of
the shear bands, free volume content, and structure of the
subjected BMG vs. plastic deformation were studied. A high
density of shear bands with an average spacing of 31nm in-
troduced in the room temperature (RT) rolled sample with a
strain of 99% exhibits a nano glass microstructure. Com-
pared with the as-cast sample, about 34% more free volume
is introduced into the RT-rolled sample with a strain of 99%.
It was also observed that phase separation or crystallization
did not occur [46].
Quasi-in situ compression-compression fatigue experi-
ments at the high-stress level were performed. The crack
start-up, propagation, and the shear banding processes were
observed at different stages of the fatigue test. The investiga-
tion directly confirms that fatigue crack initiates from the
shear band and propagates along the major shear bands
(MSB) at high-stress level. The mechanisms of fatigue
cracking and fracture of the MGs can be readily clarified by
the good correspondence between the stages of crack fatigue
evolution on the sample surface and the regions on the fa-
tigue fracture surface, i.e. the crack propagation region, the
fast fracture region and the stable region.
The authors also provide a comprehensive diagram of the
fatigue damage processes and fatigue fracture morphologies
varying with the crack length L (Fig. (19)) [47].
MD simulations of tension–compression fatigue in
Cu50Zr50 MGs under strain-controlled cyclic loading were
performed. Under cyclic loading, SB initiation takes place
when aggregates of shear transformation zones (STZs) ac-
cumulating at the MG surface reach a critical size compara-
ble to the SB width, and the accumulation of STZs follows a
power law with rate depending on the applied strain. It is
shown that almost the entire fatigue life of nanoscale MGs
under low cycle fatigue is utilized in the SB-initiation stage,
similar to that of crystalline materials [48]. A spatially strain
map of a plastically deformed BMG has been created by
using high-energy X-ray diffraction. The results revealed
that plastic deformation produces a spatially heterogeneous
atomic arrangement, consisting of high compressive and
tensile strain fields. Also, the significant shear strain is intro-
duced in the samples. Plastic deformation was carried out
through imprinting, which has been proven to be useful for
enhancing the room-temperature tensile ductility of brittle
MGs [49].
A technique of indentation at nanoscale level was devel-
oped to examine the strain rate sensitivity and its dependence
on the structural state of Vitreloy1. The free volume content
in the BMG was varied by testing samples in the as-cast,
shot-peened, and structurally relaxed states. The experimen-
tal results show that m is always negative at room tempera-
ture and also at slightly higher temperatures [50].
Based on atomic-level stress theory, atomic strain energy
and von Mises shear stress were correlated with the local
dynamic and mechanical properties of MGs. Molecular dy-
namics simulations of CuxZr100x MGs were performed to
study the dynamic and mechanical behaviors of structural
defects [51].
In [52], the authors examined experimentally structural
rejuvenation concerning the strain rate and deformation
stage. It was demonstrated that the atomistic mechanism of
structural renewal is due to topological rearrangement in the
atomic connectivity network.
Electrodeposition was used into coat copper films on the
surface of the BMG pillars of Vitleroy 105 with two differ-
ent film thicknesses (of 71.5m and 161.1m) [53]. The re-
sults of the compression tests of the BMG pillars and the
coated BMG pillars revealed that the copper coating in-
creased the density of shear bands in the pillars formed dur-
ing the trials, resulting in the improvement of the plasticity.
The technique developed by the authors of this work pro-
vides an effective way to enhance the resilience of BMGs at
room temperature (Fig. (20)) [53].
Recently, a Zr-based metallic glass (ZrxCuyAg8 Al8Be7.5)
which can be cast into a glassy rod with 73mm in diameter by
conventional copper mold casting, was successfully developed
[54]. Unfortunately, this BMG still suffers from low plasticity.
The excellent glass forming ability (GFA) of this alloy pro-
vides an enough wide window for the compositional optimiza-
tion with good flexibility and high GFA simultaneously.
Mechanical size effects in ZrxNi100x thin metallic glass
films are investigated for thicknesses from 200 to 900nm.
Local order, elastic properties and rate sensitivity are shown
to be thickness independent, while hardness and fracture
resistance are not. The increase of hardness with decreasing
thickness is related to the substrate constraint on shear band-
ing [55].
Fig. (18). Schematic of the shear-band evolution at (a) Its initial and (b) Evolving stages. (c) Illustration of the competition between the criti-
cal energy dissipated within a shear band and the applied energy near it (reproduced with permission from [45] ©2015 Elsevier).

12 Recent Patents on Materials Science 2016, Vol. 9, No. 1 Axinte et al.
The thickness effect on the mechanical properties of a
thin film metallic glass (TFMG) is investigated by using the
nano-indentation. Mechanical size effects in Zr65Ni35 TFMG
were studied with an emphasis on a transition in failure
mechanisms occurring below 500nm. XRD and TEM analy-
ses confirmed the absence of any crystalline phase [56]. Fi-
nite-element simulations unravel the origin of the size effect
and the transition of failure mode from the constraint on
plastic dissipation. The fracture toughness of submicron
Zr65Ni35 sputter-deposited films is thickness dependent. The
failure mechanism involves corrugations for the thickest
films and a transition at 500nm thickness to an absolutely
flat fracture surface. Both mechanisms are brittle-type, even
though the elastic and plastic properties are independent of
thickness and similar to the expected ductile bulk response
[57].
Fig. (19). Diagram of the fatigue damage processes and fatigue fracture morphology vs. the crack length L (reproduced with permission from
[47] ©2015 Elsevier).
Fig. (20). Diagram of the fatigue damage processes and fatigue fracture morphology vs. the crack length L (reproduced with permission from
[53] ©2015 Elsevier).

Shear Bands in Metallic Gla sses Recent Patents on Materials Science 2016, Vol. 9, No. 1 13
Fig. (21). Schematic illustrations of the microscopic (a) Shearing,
(b) Volume dilatation mechanisms for the destabilization of amor-
phous structures and (c) Relationship between the failure mode
factor  and Poisson's ratio in MGs (reproduced with permission
from [58]).
By adopting an ellipse failure criterion, the authors of
[58] precisely described the strength and failure behaviors of
MGs, according to their shear modulus and Poisson's ratio.
Quantitative relations are established systematically and
verified by experimental results. Accordingly, the real sense
of non-destructive failure prediction can be achieved through
various MGs (Fig. (21)) [58].
In [59], the mechanical behaviors of BMG composites
were simulated by the numerical method, whereby the inter-
action between the shear banding and dislocation sliding was
analyzed, and the resulting toughening mechanisms were
elucidated. Free volume acts as an internal state variable for
describing the shear banding evolution in BMG matrix via
the free volume theory, and dislocation sliding was depicted
with the mechanism-based strain gradient plasticity theory.
The toughing micro-mechanism was clarified from the firm
interaction between the dislocation propagation and shear
bands. Also, the tensile ductility of a BMG composite is very
sensitive to the parameters of the back stress, Taylor factor,
and particle size (Fig. (22)) [59].
4. CURRENT & FUTURE DEVELOPMENT
The future of BMGs sounds well. BMGs, still "young"
materials, are considered to be among the materials of the
future. Dr. Marios Demetriou from Caltech declared ‘‘Ow-
ing to their attractive mechanical properties and unique proc-
essing capabilities, MGs have the potential to dominate
metal-hardware engineering in the 21st century'' (excerpt
with permission from [7]). Dr. Physicist Joerg Heber, Dep-
uty Chief Editor at Nature Communications and science
writer, says:" For centuries, researchers have exploited the
properties of crystals because their properties seemed easier
to control. But this doesn't necessarily hold true. In future,
we will see much more emphasis on amorphous materials''
(excerpt with permission from [7]). The using and industri-
alization of MGs are just at the start, and a long way of find-
ings is perspective in various industries (aerospace, automo-
tive, medicine, and biomedicine, defense, energy storage and
production, computer science).
In the last years, a continuous and constant increasing
interest in the magneto-caloric effect (MCE) and magnetic
refrigeration (MR) is observed. Compared with conventional
vapor cycle refrigeration, the magnetic refrigeration tech-
niques based on MCE have the advantages of both high en-
ergy efficiency and environmentally friendliness. It has been
found that these MGs manifested large MCE over much
wider temperature range, and directly lead to a much higher
refrigerant capacity (RC), which is an important parameter
that characterizes the refrigerant efficiency of a material [60-
66].
Due to their unique and surprising properties, MGs have
a brightness future as superhydrophobic materials. Superhy-
drophobic surfaces have aroused great interest for both aca-
demic pursuits and industrial applications. Superhydrophobic
surfaces have been extensively studied due to their impor-
tance in fundamental research and practical applications. In
nature, many biological materials exhibit excellent surface
superhydrophobicity, such as lotus leaves, rice leaves, butter-
fly wings, and mosquito compound eyes. The limited me-
chanical durability and corrosion resistance have been identi-
Fig. (22). Detailed evolutions of dislocation sliding in ductile particles and shear banding in BMG matrix with the applied macroscopic de-
formation for BMG composites (adapted with permission from [59] ©2015 Elsevier).

14 Recent Patents on Materials Science 2016, Vol. 9, No. 1 Axinte et al.
fied as the main barriers to the industrial application of su-
perhydrophobic materials. The mechanical wear and the cor-
rosion of the superhydrophobic surfaces could destroy the
surface roughness features that are essential for superhydro-
phobicity [67-73].
Pd-based MG surfaces with hierarchical structures at
nanometric scale are fabricated by thermoplastic forming.
The resultant MG surface with well-defined hierarchical
structures consisting of nanoscale protrusions on the mi-
croscale textures showed superhydrophobicity without low
surface energy modification. These hydrophobic MG sur-
faces have superior mechanical stability and corrosion resis-
tance. A schematic of the fabrication of micro-nano scale
structured superhydrophobic metallic glass surface is pre-
sented in Fig. (23) [68].
Recently, the hybrid of CeH2.73 and CeO2 with low cata-
lytic effect exhibits surprisingly high catalytic activity for
dehydrogenation of MgH2. A simple strategy to generate a
novel symbiotic CeH2.73/CeO2 catalyst in Mg-based hydrides
with exact size by simple conventional hydriding and heat
treatment process exempting long-time ball milling and so-
phisticated chemical process has been proposed. The free
hydrogen release effect on the interface region of the symbi-
otic CeO2/CeH2.73 nanoparticles accounts for its role as effi-
cient hydrogen pump. The symbiotic CeO2/CeH2.73 catalyst is
suitable for large-scale productions due to the easy fabrica-
tion technology. These findings might open a novel approach
to explore the advanced catalysts for alloy-based hydrogen
storage materials [74]. Wang et al., studied the effects of
annealing treatment on the microstructure, corrosion behav-
ior and mechanical properties of the RE-based BMG. The
results indicate that the annealing treatment causes changes
of distance between the neighboring atoms of the amorphous
matrix, which results in the variation of the thermal stability
and crystallization behavior of the studied BMG [75]. Also,
some studies on the graphene (Gr) addition on the amor-
phous formation and thermal stability of the Al-based BMG
were performed. The Gr addition enhances the thermal sta-
bility of the as-milled Al88Ni6Y6 alloy, which is useful to
fabricate Al-based BMG composites using sinter method
(Fig. (24)) [76].
Since current time, the vitrification of single-element
metallic liquids was considered almost impossible. A labora-
tory demonstration of the formation of monatomic metallic
glass has been successfully performed [77, 78]. The authors
report an experimental approach to the vitrification of mona-
tomic metallic liquids by achieving a high liquid-quenching
rate of 1014Ks-1. Liquid tantalum and vanadium, are suc-
cessfully vitrified to form MGs suitable for property interro-
gations. This technique also shows excellent control over the
reversible vitrification-crystallization processes, suggesting
its potential in micro-electromechanical applications [78].
High-entropy alloys (HEAs) are defined as multicomponent
equiatomic or almost equiatomic metallic systems in nature,
which have the tendency to form solid solutions with face-
centered cubic (FCC) or body centered cubic (BCC) crystal
structures as well as a rarely formed amorphous structure. It
is a quasi-known fact that HEAs exhibit great potential for
engineering applications in hardness, wear resistance, corro-
sion resistance, high-temperature softening resistance and
magnetism. HE -BMGs can be referred to BMGs with an
equal-atomic or near equal atomic composition. These
BMGs have not only large high GFA, but also very high
entropy of mixing. The high-entropy BMGs are a special
class of BMGs which have both strong topological disorder
and chemical disorder. Due to the lack of the long-range
chemical order, the high-entropy BMGs may have special
properties which do not exhibit in either normal BMGs (i.e.
the good fatigue resistance of the studied high-entropy
BMGs may be attributed to the formation of protective oxide
films on the surface of the specimen in high-temperature
water, leading to good overall corrosion resistance) In [79],
the behavior of high-entropy HE-BMGs was seriously
investigated. Recently, Huo et al, developed a series of HE-
BMGs which are based on the traditional RE-based BMGs.
The developed MGs exhibits a large MCE [80, 81]. Dynamic
Fig. (23). Diagram of the fabrication of micro-nano scale structured superhydrophobic metallic glass surface. (a) Nano scale fabrication with
anodic aluminum oxide template; (b) Micro scale fabrication with silicon mold; (c) SEM images of the as-fabricated MG surface and the
magnified details(reproduced with permission from [68]).

Shear Bands in Metallic Gla sses Recent Patents on Materials Science 2016, Vol. 9, No. 1 15
double-notched experiments by using Split Hopkinson Pres-
sure Bars (SHPB) and high-speed camera were performed on
bulk metallic glass in [82]. Shear crack propagating process
was captured with the high temporal resolution of high-speed
camera and the crack front propagating velocity was esti-
mated to be 1137m/s, the shear strain/shear stress curve of
BMG under dynamic loading was also obtained.
A promising remedy to the failure of MGs by shear band-
ing is the use of a dense network of glass-glass interfaces,
i.e., a nanoglass (NG). In [83], the effect of grain size (d) on
the failure of NG by performing molecular dynamics simula-
tions of tensile-loading on Cu 50Zr50 NG with d= 5 to 15nm
was investigated. The results suggest that grain size can be
an effective design parameter to tune the mechanical proper-
ties of MGs.
The effect of a small rare earth (RE) metal addition on
GFA and mechanical properties of (Cu47Zr45Al8)100-xREx
(RE = Ce, Nd, Gd, Y, Dy, Lu, x = 0-4; at.%) BMGs have
been studied in [84]. It has been found that a small amount
of rare-earth addition in the Cu-rich (Cu-Zr-Al) alloys can
decrease the temperature of glass transition (Tg) and improve
the GFA. The (Cu47Zr45Al8)97Lu3 bulk metallic glass exhib-
ited good plasticity 4.65% at room temperature during com-
pression test, which was applied to high yield strength of
1840MPa. With the increase of rare-earth elements addition
up to 4 at.%, the fracture strength of the alloy reduced obvi-
ously and no more plastic deformation can be observed on
the fracture surface [84].
Schroers performed molecular dynamics (MD) simula-
tions of the crystallization process in binary Lennard-Jones
systems during heating and cooling to investigate atomic-
scale crystallization kinetics in glass-forming materials. The
results are consistent with the prediction from classical nu-
cleation theory [85].
Generally, at temperatures below the Tg, the failure of
MGs is induced by shear banding. Recent findings show that
shear banding can be totally suppressed under extreme low
temperature, high strain rates or by a long time annealing of
samples. Also, the cavitation can provoke the brittle fractures
[86]. It was demonstrated experimentally that, upon cooling
down to liquid helium temperature (4.2K), a Zr-based BMG
under quasi-static uniaxial tension can fracture via cavita-
tion, rather than by shear banding. In these conditions, the
Zr-based BMG showing a transition from shear failure to
dilatation failure [87].
The observation of a shear direction alternatively
changed the crack path in a thin Fe78Si9B13 metallic glassy
sheet with high strength and elasticity as provided in [88].
This configuration of the crack path in the thin sheet under
tension is discussed in the framework of the thin elastic sheet
with high strength.
Most recently, researches established a quantitative para-
bolic relationship between the atomic local shear and hydro-
static volumetric strains by carrying out statistical analysis
on a deformed glass model. The atomistic demonstration of
shear-dilatation correlation collaborates with a few percent
volume change in shear bands as observed experimentally. It
brings quantitative insights into the unique correlation be-
tween shear transformation and cavitation in MGs [89].
Nanoscale periodic patterns in the fracture surfaces of
various MGs were investigated. A comprehensive picture of
nanoscale near-tip events and associated energy dissipation
in MG breaking was provided. Two competing failure
mechanisms of current meniscus instability and cavitation
mechanism near the crack tip control the fracture process of
MGs were observed by investigation of the progressive evo-
lution of fine corrugation features along the crack path and
the formation process of nanostripes near the crack tip. A
model that can capture the essential characteristics of the
observed nanoscale periodic stripes was proposed [90].
Recent research [91] shows that by application of an
electric current pulse in the presence of a normally directed
magnetic field can heat (by electrical resistance) a metallic
glass to a softened state, while simultaneously inducing a
large enough magnetic body force to plastically shape it. The
heating and shaping is performed on millisecond timescales,
effectively bypassing crystallization producing fully amor-
phous-shaped parts. This electromagnetic forming process
may become a promising manufacturing platform for strong
metals.
5. RECENT PATENTS IN MGS INDUSTRIALIZA-
TION
MGs have aroused interest for industrialization and pro-
duction. The main directions of development are observed in
the domain of medical and bio-medical devices, in military
and aerospace devices, microelectronics devices. Unfortu-
nately, due to the military and defense industry applications,
the list of patents in the field of MGs is not very generous.
Some of the patents that we have at our disposal are listed
and described in this section. US7998286 [92] describes a
subset of Zr-Ti-based MGs with improved corrosion resis-
tance properties. BMGs are designed by carefully controlling
concentration of, or completely removing highly electro-
negative elements (Ni and Cu) from Zr-Ti-based bulk solidi-
fying amorphous alloys. There are producing BMG materials
with corrosion resistance properties that far exceed those of
current commercially available MGs and most conventional
alloys. The invention described in US patent [93] is an artifi-
Fig. (24). SEM image of additional grapheme (reproduced with
permission from [76] ©2015 Elsevier).

16 Recent Patents on Materials Science 2016, Vol. 9, No. 1 Axinte et al.
cial heart component that includes amorphous metal alloy
parts. This invention may be applied to: sutures, implantable
surgical fabrics, stents, heart valves, implants for reconstruc-
tive surgery, orthodontic and dental implants, all of these
comprising amorphous metal alloys. In patent [94], the
authors describe an aluminum based prothesis, an implant
having a solid basic structure and a porous jacket structure.
The method of manufacturing such an implant is also de-
scribed. In [95], is described a metallic glass based orthodon-
tic bracket. A new method and apparatus for forming high
aspect ratio metallic glass, including metallic glass sheet and
tube, by a melt deposition process are provided in [96].
A new method of manufacturing parts from a metallic
glass alloy by applying a quantum of electrical energy using
a rapid capacitive discharge forming system to heat the feed-
stock to a temperature above the glass transition is developed
and revealed in [97]. By using this method, articles are ob-
tained as: the component of an electronics device, a medical
implant, a dental prosthetic, a watch component, a ferromag-
netic core, a sporting good, or a luxury good.
Methods were proposed to fabricate objects using bulk
metallic glass matrix composites. In such methods, soft me-
tallic glass matrix composites developed with variable non-
equilibrium inclusions. The softness of such composite was
deduced by the shear modulus, the elastic limit, and the
hardness [98].
Some method were reported to produce high-aspect-ratio
metallic glass articles using rapid capacitive discharge tech-
nique. It was found that the articles were of substantially low
defects and cosmetic imperfections [99]. Several methods
were suggest to form high aspect ratio metallic glass capital-
izing on melt deposition process. In Such deposition method,
the alloy being quenched, deposited and form without expe-
riencing considerable shear flow [100].
A metallic glass was prepared using Aluminum (Al) with
transition and rare earth metals. It was suggested that, the
prepared metallic glass could be utilized as conductive paste
and/or an electrode of an electronic device [101]. A layer by
layer method was described for construction of parts utiliz-
ing metallic glass alloys. The repeated deposition of metallic
glass-forming powder and fusing by laser heating or electron
beam heating technologies executed to construct the part. In
certain cases, non-metallic-glass-forming material layers
were integrated to form the composites [102]. Most recently,
different methods were reported to form multilayers metallic
glass by depositing metallic glass liquid layer above metallic
glass layer developing an alloy [103]. Such method could be
applied to produce multilayers glass articles. A new class of
alloys were also invented [104]. These alloys have structures
and properties which yield high elasticity corresponding to a
MG, high plasticity corresponding to a ductile crystalline
metal, and great strength as may be observed in nanoscale
materials. Due to the particular combination of favorable
properties, which involves the relatively high tensile strength
and hardness joined with significant tensile elongation and
high elasticity. These alloys are promising materials for fi-
bers, ribbons, foils, and microwires.
CONCLUSION
The shear-banding-mode plastic flow of MGs at ambient
temperature continues to fascinate and challenge scientists
because of its physical origin and practical implications. The
free volume creation and local heating generation, in which
shear band thickness is an important factor, are two potential
causes of shear-banding instability in MGs.
The formation and evolution of shear bands control the
yielding and plasticity of almost all MGs at room tempera-
ture and the formation of dominant shear bands quickly lead
to failure. In considering the mechanical behavior of MGs, it
is fundamental to strongly understand shear bands, their ini-
tiation, propagation, evolution, consequences, and control.
Controlling the shear -banding is quite equivalent with the
controlling of plasticity and failure at room temperature.
This shear banding behavior of BMGs is usually a weak-
ness for these materials but sometimes may be transformed
into an advantage by using good engineering solutions. Pro-
fessor Wei Hua Wang (Group EX4, Key Laboratory of Ex-
treme Conditions-Institute of Physics of Chinese Academy
of Science - Beijing) declared in this review paper: “The
plastic deformation is usually inhomogeneous with plastic
strain highly localized into nano-scale narrow regions termed
as shear bands. The shear band is usually 10-20nm in thick-
ness observed from the TEM observation. However, the
shear band can accommodate displacement nearly up to mil-
limeter scale, yielding an extremely large plastic strain
within them. Once initiated, shear bands become unstable
and propagate rapidly, often leading to the catastrophic frac-
ture of BMGs. Thus, the shear bands play a central role in
understanding the plastic deformation and fracture behavior
of BMGs as well as in controlling and designing the plastic
MGs”.
Some recent findings demonstrate that shear banding can
be entirely suppressed under extremely low temperature,
high strain rates or by a long time annealing of samples.
CONFLICT OF INTEREST
The authors confirm that this article content has no con-
flict of interest.
ACKNOWLEDGEMENTS
Dr. Physicist Joerg Heber, Deputy Chief Editor at Nature
Communications and science writer, for his friendly advices,
encouragements and for permission provided to use some
information from his scientific and editorial work.
Professor Dr. Wei Hua Wang (Institute of Physics of
Chinese Academy of Science - Beijing) for permission pro-
vided to reuse some information from his published work
and for the statement made for this review.
Elsevier Ltd., Nature Publishing Group, Springer for
copyright licenses and permissions provided via Copyright
Clearance Centre (CCC) - www.rightslink.com.
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