Special Issue "Amorphous Alloys"

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A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 October 2012)

Special Issue Editor

Guest Editor
Prof. Dr. Hans-Jörg Fecht

Director Institute of Micro and Nanomaterials Ulm University Albert-Einstein-Allee 47, 89081 Ulm, Germany
Website | E-Mail
Interests: nanocrystalline materials; bulk metallic glasses; nucleation theory; design and growth of thin films and layers

Special Issue Information

Dear Colleagues,

Bulk metallic glasses BMGs have been discovered about 30 years ago and constitute a new class of engineering materials with an increasing interest world-wide. They lack the long-range atomic order of crystalline materials exhibiting only short range atomic order in a thermodynamically metastable frozen state. They can be obtained when nucleation and growth of crystalline phases are suppressed during cooling of liquid alloys as bulk material with several mm3 volume.

Good glass forming alloys are usually multicomponent and eutectic or near eutectic liquid compositions with relatively high viscosities and strongly depressed melting temperatures that result in critical cooling rates of about 1 K/sec, i.e. typical for the metal casting industries. Typical examples are complex Zr-, Ti-, Fe-, Ni- or Mg-based alloys as well as precious metal systems.

Due to the absence of dislocations and grain boundaries BMGs have considerably improved mechanical properties and often better resistance to wear and corrosion than conventional metals. As such, they show perfect elastic behavior up to 2% strain and possess mechanical resilience far greater than crystalline metals and alloys with mechanical strength up to 5 GPa, i.e., several times the strength of conventional steels.

Furthermore, due to its glassy nature and drastical reduction of viscosity above the glass transition temperature, BMGs can be plastically deformed or moulded like plastic material in a certain time-temperature window. This combination of several advantageous properties opens a new way of designing materials, metal surfaces and components with intricate shapes and 3-D geometries never seen before. Engineering applications therefore range from structural components in electronic devices, shielding, springs and other MEMS parts to optical components, metallic foams and medical devices.

Prof. Dr. Hans Fecht
Guest Editor

Keywords

  • bulk metallic glasses
  • eutectic alloys
  • critical cooling rate
  • high strength materials
  • plastic moulding
  • engineering applications

Published Papers (6 papers)

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Research

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Open AccessArticle Development of Fe-B Based Bulk Metallic Glasses: Morphology of Residual Phases in Fe50Ni16Mo6B18Zr10 Glass
Metals 2013, 3(2), 159-177; doi:10.3390/met3020159
Received: 30 November 2012 / Revised: 19 March 2013 / Accepted: 26 March 2013 / Published: 9 April 2013
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Abstract
Iron-boron based bulk metallic glasses (BMG) development has been initiated using Fe40Ni38Mo4B18 as precursor. Addition of zirconium up to 10 atomic % along with the reduction of Ni proportion improves the glass forming ability (GFA), which
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Iron-boron based bulk metallic glasses (BMG) development has been initiated using Fe40Ni38Mo4B18 as precursor. Addition of zirconium up to 10 atomic % along with the reduction of Ni proportion improves the glass forming ability (GFA), which is optimum when Ni is suppressed in the alloy. However melting instability occurred during the materials fabrication resulting in the formation of residual crystalline phases closely related to the amorphous phase. Microstructure study shows an evolution from amorphous structure to peculiar acicular structure, particularly for Fe50Ni16Mo6B18Zr10, suggesting the amorphous structure as interconnected atomic sheets like “atomic mille feuilles” whose growth affects the alloys’ GFA. Full article
(This article belongs to the Special Issue Amorphous Alloys)
Open AccessArticle Large Compressive Plasticity in a La-Based Glass-Crystal Composite
Metals 2013, 3(1), 41-48; doi:10.3390/met3010041
Received: 28 November 2012 / Revised: 16 December 2012 / Accepted: 18 December 2012 / Published: 27 December 2012
Cited by 6 | PDF Full-text (1164 KB) | HTML Full-text | XML Full-text
Abstract
La55Al25Cu10Ni10 metallic glass has been reinforced with 325-mesh Ta particles to obtain ex situ glass-crystal composites. The composites show a high compressive plasticity (40%) with a minor reduction (~8%) in yield strength—a combination unprecedented for La-based
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La55Al25Cu10Ni10 metallic glass has been reinforced with 325-mesh Ta particles to obtain ex situ glass-crystal composites. The composites show a high compressive plasticity (40%) with a minor reduction (~8%) in yield strength—a combination unprecedented for La-based systems and even surpassing some Zr-based glassy composites that utilize a tougher matrix. However, it is also found that the plastic strain is apparently sensitive to defects, like oxides, in the glassy matrix. Full article
(This article belongs to the Special Issue Amorphous Alloys)
Open AccessArticle Structural Irreversibility and Enhanced Brittleness under Fatigue in Zr-Based Amorphous Solids
Metals 2012, 2(4), 529-539; doi:10.3390/met2040529
Received: 16 August 2012 / Revised: 9 November 2012 / Accepted: 11 December 2012 / Published: 19 December 2012
Cited by 2 | PDF Full-text (1305 KB) | HTML Full-text | XML Full-text
Abstract
The effect of fatigue on ZrCuAl amorphous metals induced by mechanical cyclic loading is investigated using inelastic neutron scattering and the pair density function analysis of neutron diffraction data. With cooling, the local atomic structure undergoes reorganization under fatigue that is directly related
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The effect of fatigue on ZrCuAl amorphous metals induced by mechanical cyclic loading is investigated using inelastic neutron scattering and the pair density function analysis of neutron diffraction data. With cooling, the local atomic structure undergoes reorganization under fatigue that is directly related to the number of fatigue cycles. Also under fatigue, suppression in the atomic dynamics is observed as well. A structural restructuring occurs within a 4 Å radius and intensifies with increasing the compression cycles, whereas the vibrational density of states is attenuated as the intensity shifts towards the elastic, zero-energy transfer peak. The combined static and dynamic structural effects are a signature of the microscopic changes brought about by fatigue, and together may be the onset for subsequent behaviors following extended cyclic loading such as fracture. Even after the load is removed, the structural changes described here remain and increase with repeated cyclic loading which is an indication that the lattice deforms even before shear bands are formed. Full article
(This article belongs to the Special Issue Amorphous Alloys)
Open AccessArticle Comparative Study of Elastoplastic Constitutive Models for Deformation of Metallic Glasses
Metals 2012, 2(4), 488-507; doi:10.3390/met2040488
Received: 7 November 2012 / Revised: 20 November 2012 / Accepted: 29 November 2012 / Published: 4 December 2012
Cited by 3 | PDF Full-text (1974 KB) | HTML Full-text | XML Full-text
Abstract
We present and compare three elastoplastic models currently used for deformation of metallic glasses, namely, a von Mises model, a modified von Mises model with hydrostatic stress effect included, and a Drucker-Prager model. The constitutive models are formulated in conjunction with the free
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We present and compare three elastoplastic models currently used for deformation of metallic glasses, namely, a von Mises model, a modified von Mises model with hydrostatic stress effect included, and a Drucker-Prager model. The constitutive models are formulated in conjunction with the free volume theory for plastic deformation and are implemented numerically with finite element method. We show through a series of case studies that by considering explicitly the volume dilatation during plastic deformation, the Drucker-Prager model can produce the two salient features widely observed in experiments, namely, the strength differential effect and deviation of the shear band inclination angle under tension and compression, whereas the von Mises and modified von Mises models are unable to. We also explore shear band formation using the three constitutive models. Based on the study, we discuss the free volume theory and its possible limitations in the constitutive models for metallic glasses. Full article
(This article belongs to the Special Issue Amorphous Alloys)
Figures

Open AccessArticle Nanometer-Scale Heterogeneities of the Structure of Zirconium-Based Bulk Metallic Glasses
Metals 2012, 2(4), 441-449; doi:10.3390/met2040441
Received: 10 October 2012 / Revised: 26 October 2012 / Accepted: 29 October 2012 / Published: 15 November 2012
Cited by 3 | PDF Full-text (344 KB) | HTML Full-text | XML Full-text
Abstract
Structure of amorphous alloys ZrTiCuNiBe and ZrTiCuNiAl is studied by means of low-field ion and combined field-emission microscopy. In both alloys the structural heterogeneities of nanometer-scale are clearly revealed. The surface layers formed by field evaporation possess a cellular structure. The cells have
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Structure of amorphous alloys ZrTiCuNiBe and ZrTiCuNiAl is studied by means of low-field ion and combined field-emission microscopy. In both alloys the structural heterogeneities of nanometer-scale are clearly revealed. The surface layers formed by field evaporation possess a cellular structure. The cells have polygonal shape with transverse size ranging from 2 nm to 20 nm. It is established that variance of the local energy of field evaporation is of 0%–5% in the cell body. A local minimum of the field evaporation energy is observed within the cell boundaries (intercluster boundaries). In the minimum the depth is measured to be of 0.8 eV. Full article
(This article belongs to the Special Issue Amorphous Alloys)

Review

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Open AccessReview Mechanical Properties and Deformation Behavior of Bulk Metallic Glasses
Metals 2013, 3(1), 1-22; doi:10.3390/met3010001
Received: 2 November 2012 / Revised: 5 December 2012 / Accepted: 10 December 2012 / Published: 20 December 2012
Cited by 12 | PDF Full-text (418 KB) | HTML Full-text | XML Full-text
Abstract
Metallic glasses demonstrate unique properties, including large elastic limit and high strength, which make them attractive for practical applications. Unlike crystalline alloys, metallic glasses, in general, do not exhibit a strain hardening effect, while plastic deformation at room temperature is localized in narrow
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Metallic glasses demonstrate unique properties, including large elastic limit and high strength, which make them attractive for practical applications. Unlike crystalline alloys, metallic glasses, in general, do not exhibit a strain hardening effect, while plastic deformation at room temperature is localized in narrow shear bands. Room-temperature mechanical properties and deformation behavior of bulk metallic glassy samples and the crystal-glassy composites are reviewed in the present paper. Full article
(This article belongs to the Special Issue Amorphous Alloys)

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