scholarly journals Specific Features of Structure Transformation and Properties of Amorphous-Nanocrystalline Alloys

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 358 ◽  
Author(s):  
Alexandr Aronin ◽  
Galina Abrosimova
Keyword(s):  
Amorphous Phase ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Structural Changes ◽  
Shear Bands ◽  
Component Composition ◽  
Amorphous Structure ◽  
Structure Evolution ◽  
Current State ◽  
Heterogeneous Phase

This work is devoted to a brief overview of the structure and properties of amorphous-nanocrystalline metallic alloys. It presents the current state of studies of the structure evolution of amorphous alloys and the formation of nanoglasses and nanocrystals in metallic glasses. Structural changes occurring during heating and deformation are considered. The transformation of a homogeneous amorphous phase into a heterogeneous phase, the dependence of the scale of inhomogeneities on the component composition, and the conditions of external influences are considered. The crystallization processes of the amorphous phase, such as the homogeneous and heterogeneous nucleation of crystals, are considered. Particular attention is paid to a volume mismatch compensation on the crystallization processes. The effect of changes in the amorphous structure on the forming crystalline structure is shown. The mechanical properties in the structure in and around shear bands are discussed. The possibility of controlling the structure of fully or partially crystallized samples is analyzed for creating new materials with the required physical properties.

scholarly journals Influence of HPT Deformation on the Structure and Properties of Amorphous Alloys

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 415 ◽  
Author(s):  
Dmitry Gunderov ◽  
Vasily Astanin
Keyword(s):  
Amorphous Phase ◽  
Amorphous Alloys ◽  
Amorphous Materials ◽  
Structural Changes ◽  
High Pressure Torsion ◽  
Shear Bands ◽  
Physical And Mechanical Properties ◽  
Chemical Separation ◽  
Structure And Properties ◽  
Processing Regimes

Recent studies showed that structural changes in amorphous alloys under high pressure torsion (HPT) are determined by their chemical composition and processing regimes. For example, HPT treatment of some amorphous alloys leads to their nanocrystallization; in other alloys, nanocrystallization was not observed, but structural transformations of the amorphous phase were revealed. HPT processing resulted in its modification by introducing interfaces due to the formation of shear bands. In this case, the alloys after HPT processing remained amorphous, but a cluster-type structure was formed. The origin of the observed changes in the structure and properties of amorphous alloys is associated with the chemical separation and evolution of free volume in the amorphous phase due to the formation of a high density of interfaces as a result of HPT processing. Amorphous metal alloys with a nanocluster structure and nanoscale inhomogeneities, representatives of which are nanoglasses, significantly differ in their physical and mechanical properties from conventional amorphous materials. The results presented in this review show that the severe plastic deformation (SPD) processing can be one of the efficient ways for producing a nanocluster structure and improving the properties of amorphous alloys.

Bulk Metallic Glasses

2008 ◽  
Vol 604-605 ◽  
pp. 229-238
Author(s):  
Marcello Baricco ◽  
Tanya A. Başer ◽  
Gianluca Fiore ◽  
Rafael Piccin ◽  
Marta Satta ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Shear Bands ◽  
Bulk Metallic Glasses ◽  
Rapid Quenching ◽  
Second Phase ◽  
Research Activity ◽  
Long Time ◽  
Geometrical Constraints

Rapid quenching techniques have been successfully applied since long time for the preparation of metallic glasses in ribbon form. Only in the recent years, the research activity addressed towards the synthesis of bulk metallic glasses (BMG), in form of ingots with a few millimetres in thickness. These materials can be obtained by casting techniques only for selected alloy compositions, characterised by a particularly high glass-forming tendency. Bulk amorphous alloys are characterised by a low modulus of elasticity and high yielding stress. The usual idea is that amorphous alloys undergo work softening and that deformation is concentrated in shear bands, which might be subjected to geometrical constraints, resulting in a substantial increase in hardness and wear resistance. The mechanical properties can be further improved by crystallisation. In fact, shear bands movement can be contrasted by incorporating a second phase in the material, which may be produced directly by controlled crystallisation. Soft magnetic properties have been obtained in Fe-based systems and they are strongly related to small variations in the microstructure, ranging from a fully amorphous phase to nanocrystalline phases with different crystal size. The high thermal stability of bulk metallic glasses makes possible the compression and shaping processes in the temperature range between glass transition and crystallisation. Aim of this paper is to present recent results on glass formation and properties of bulk metallic glasses with various compositions. Examples will be reported on Zr, Fe, Mg and Pd-based materials, focussing on mechanical and magnetic properties.

Dynamic indentation response of ZrHf-based bulk metallic glasses

2007 ◽  
Vol 22 (2) ◽  
pp. 478-485 ◽  
Author(s):  
Ghatu Subhash ◽  
Hongwen Zhang
Keyword(s):  
Shear Band ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Shear Bands ◽  
Indentation Hardness ◽  
Strain Rates ◽  
Dynamic Indentation ◽  
Confinement Pressure ◽  
Static Indentation ◽  
Deformation Features

Static and dynamic Vickers indentations were performed on ZrHf-based bulk amorphous alloys. A decrease in indentation hardness was observed at higher strain rates compared with static indentation hardness. For equivalent loads, dynamic indentations produced more severe deformation features on the loading surface than static indentations. Using bonded interface technique, the induced shear band patterns beneath the indentations were studied. In static indentations, the majority of the deformation was primarily accommodated by closely spaced semicircular shear bands surrounding the indentation. In dynamic indentations two sets of widely spaced semicircular shear bands with two different curvatures were observed. The observed shear band patterns and softening in hardness were rationalized based on the variations in the confinement pressure, strain rate, and temperature within the indentation region during dynamic indentations. It is also proposed that free volume migration and formation of nano-voids leading to cracking are favored due to adiabatic heating and consequently cause the observed softening at high strain rates.

Conchoidal Fracture of Zr- and Mg-Based Amorphous Glass

2017 ◽  
Vol 891 ◽  
pp. 504-508
Author(s):  
Jozef Miškuf ◽  
Kornel Csach ◽  
Alena Juríková ◽  
Mária Huráková ◽  
Martin Miškuf ◽  
...  
Keyword(s):  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Shear Bands ◽  
High Strength ◽  
Fracture Surfaces ◽  
Conchoidal Fracture ◽  
Final Failure ◽  
Complex Shear ◽  
Amorphous Glass ◽  
Surface Morphologies

In metallic glasses plastic deformation occurs via the creation and the propagation of a softened region in the shear bands. Some of the high strength metallic glasses (as Zr-based metallic alloys) exhibit complex shear band topography and the final failure respects the allocation of the shear bands. We studied the differences in the fracture surfaces of Zr-and Mg-based amorphous alloys. Ductile behaviour of the shear bands in Zr-based amorphous alloy tends to the dimple creation during the failure. On the fracture surfaces the vein pattern morphology manifestations were present. Conchoidal fracture was typical for Mg-based amorphous glass. Two different surface morphologies, plumes and rib marks ornament the fracture surfaces.

Structure Evolution of Fe- and Co-Based Amorphous Alloys Studied by the Electrical Resistivity Measurements

2014 ◽  
Vol 215 ◽  
pp. 185-189 ◽  
Author(s):  
Aleksandr Kotvitckii ◽  
Galina Kraynova ◽  
Anatoly Frolov ◽  
Vitaly Ivanov ◽  
Vladimir Plotnikov
Keyword(s):  
Electrical Resistivity ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Residual Resistivity ◽  
Structure Evolution ◽  
Crystalline Materials ◽  
Conduction Electrons ◽  
Structure Sensitive ◽  
The Subject ◽  
Temperature Coefficient Of Resistivity

The subject of this study is the change of the electrical resistivity of Fe-based metallic glasses during heat treatment. Electrical resistivity is a structure-sensitive characteristic of materials. In metallic glasses, the scattering of conduction electrons on the disordered structure is the main mechanism responsible for the electrical resistivity. Hence amorphous metallic alloys have a much higher residual resistivity as compared to their crystalline analogs. It is typical for metallic glasses that the temperature coefficient of resistivity (TRC) is smaller than for the corresponding crystalline materials, and it can be either positive or negative.

scholarly journals Deformation and crystallization of Zr-based amorphous alloys in homogeneous flow regime

2010 ◽  
Vol 25 (6) ◽  
pp. 1137-1148 ◽  
Author(s):  
Min Tao ◽  
Atul H. Chokshi ◽  
Robert D. Conner ◽  
Guruswami Ravichandran ◽  
William L. Johnson
Keyword(s):  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Structural Changes ◽  
Strain Rates ◽  
Compression Tests ◽  
Scanning Calorimetry ◽  
Free Volume Theory ◽  
Transmission Electron ◽  
Deformation Behaviors ◽  
Zr Alloys

The purpose of this study is to experimentally investigate the interaction of inelastic deformation and microstructural changes of two Zr-based bulk metallic glasses (BMGs): Zr41.25Ti13.75Cu12.5Ni10Be22.5 (commercially designated as Vitreloy 1 or Vit1) and Zr46.75Ti8.25Cu7.5Ni10Be27.5 (Vitreloy 4, Vit4). High-temperature uniaxial compression tests were performed on the two Zr alloys at various strain rates, followed by structural characterization using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Two distinct modes of mechanically induced atomic disordering in the two alloys were observed, with Vit1 featuring clear phase separation and crystallization after deformation as observed with TEM, while Vit4 showing only structural relaxation with no crystallization. The influence of the structural changes on the mechanical behaviors of the two materials was further investigated by jump-in-strain-rate tests, and flow softening was observed in Vit4. A free volume theory was applied to explain the deformation behaviors, and the activation volumes were calculated for both alloys.

Granulation of Bulk Metallic Glass Forming Alloys as a Feedstock for Thermoplastic Forming and their Compaction into Bulk Samples

2016 ◽  
Vol 879 ◽  
pp. 589-594 ◽  
Author(s):  
David Geissler ◽  
Jacob Grosse ◽  
Sven Donath ◽  
David Ehinger ◽  
Mihai Stoica ◽  
...  
Keyword(s):  
Metallic Glasses ◽  
Shear Bands ◽  
Bulk Metallic Glasses ◽  
Supercooled Liquid ◽  
Amorphous Structure ◽  
Supercooled Liquid Region ◽  
Structural Defects ◽  
Liquid Region ◽  
Brittle Behavior ◽  
Technological Approach

The various technologically important properties of metallic glasses are intimately connected to their amorphous structure that lacks the archetypical structural defects of polycrystalline metals and alloys, i.e. dislocations and grain boundaries. However, the amorphous structure also limits the application potential of this class of materials because of a macroscopically brittle behavior and size limitations. Consequently, with some exceptions, at least one dimension for technological products is limited to a few millimeters or even less. With the presented technological approach this drawback will be addressed. Our first results on several alloys show that with a dedicated instrumentation amorphous granulates can be successfully produced. By hot pressing in the supercooled liquid region, these granulates can be compacted into bulk shapes in the cm range. Further, due to the low viscosity of the supercooled liquid state, this technology disposes of a high formability. It is demonstrated that not only compact samples but also complex shapes in near net shape geometry can be produced. Results on the mechanical properties and microstructure will be discussed and related to important processing issues. Even though this technological approach does not directly address the second drawback of bulk metallic glasses, i.e. catastrophic failure due to highly localized shear bands, it is believed that this route offers possible pathways to improve this issue as well and, most important, to offer a technological route for implementing bulk metallic glasses into products of rather arbitrary shape and larger size.

scholarly journals Magnetic properties optimization of Zr/Fe dual amorphous phase bulk metallic glasses

2020 ◽  
Vol 19 (1) ◽  
pp. 67-71
Author(s):  
Mircea Vodă ◽  
Cosmin Codrean ◽  
Viorel Aurel Şerban ◽  
Dacian Toṣa ◽  
Eugen Zặbavặ ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Amorphous Phase ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Glassy Alloy ◽  
Bulk Metallic Glasses ◽  
Volume Ratio ◽  
X Ray Diffraction ◽  
X Ray ◽  
Viable Method

The dual amorphous phase bulk metallic glasses (DAPBMGs) contain two distinct amorphous alloys in order to bring together all the favorable properties of each phase. A viable method for obtaining dual bulk amorphous alloys is powder metallurgy. A Zr/Fe DAPBMG were successfully prepared by hot-pressing of Zr –based and Fe –based glassy alloy powder in different volumetric proportions. The samples obtained were structural investigated by scanning electron microscopy and X-Ray diffraction. Magnetic properties were determined using hysteresis graph of integrator fluxmeter type. It was found that with increasing the volume ratio of the Fe-based alloy decreases the coercivity and increases saturation magnetization

scholarly journals The influence of rolling and high-pressure torsion in the Bridgman chamber on the quantitative characteristics of shear bands in an amorphous Zr-based alloy

2021 ◽  
pp. 67-74
Author(s):  
I. A. Khriplivets ◽  
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
High Pressure Torsion ◽  
Shear Bands ◽  
Quantitative Description ◽  
Polished Surface ◽  
Deformation Method ◽  
Quantitative Characteristics

Amorphous alloys based on metal components demonstrate a unique ability to realize plastic deformation under the influence of external mechanical stresses. Influenced by substantial degrees of plastic deformation in alloys, one can observe shear bands (SB) in the form of rough lines on the polished surface of the sample. The concept of shear band formation in amorphous metallic glasses varies greatly from plastic deformation processes in crystalline metals and alloys. Unlike crystalline metals, amorphous metallic glasses can exist in a spectrum of structural states with accompanying mechanical, thermodynamic, and physical properties of materials. The formation and evolution of shear bands control the fluidity and plasticity of almost all metallic glasses at room temperature, and in many cases, the formation of dominant shear bands rapidly leads to failure. The literature does not contain any rigorous quantitative description of SB main parameters, which could adequately describe in the analytical form the process of plastic deformation of amorphous alloys, similar to the dislocation and disclination theories of plastic deformation of crystals. An open question remains how the transition from macroscopic deformation to severe plastic deformations of amorphous alloys affects the key SB characteristics. In this work, using the method of optical profilometry, the author studied in detail the quantitative characteristics of the steps formed by shear bands on the surface of deformed samples of the massive amorphous alloy Zr60Ti2Nb2Cu18.5Ni7.5Al10 after high-pressure torsion (HPT) and after rolling. The study identified that the design of shear bands depends on the deformation method and showed that the magnitude of deformation had the controlling effect on the shear bands thickness (the height of the steps). The transition from deformation by rolling (e=0.4) to plastic deformation during HPT (e=2.6) leads to the threefold increase in the power of shear bands and the average distance between them.

Oxygen Distribution in Zr-Based Metallic Glasses

1998 ◽  
Vol 554 ◽  
Author(s):  
D. H. Ping ◽  
K. Hono ◽  
A. Inoue
Keyword(s):  
Amorphous Phase ◽  
Metallic Glasses ◽  
Amorphous Alloys ◽  
Atom Probe ◽  
Oxygen Distribution ◽  
Crystalline Phases ◽  
Kinetics Of Crystallization ◽  
Crystallization Reaction ◽  
Impurity Oxygen ◽  
Kinetics Of

AbstractThis paper reports the atom probe analysis results of the oxygen dissolved in the as-cast amorphous and crystallized Zr65Cu15Al10Pd10 and Zr65Cul17.5Ni10Al17.5 alloys. Impurity oxygen ranging from 0.1 to 1 at.% is dissolved uniformly in the as-quenched Zr65Cu15A110Pd10 and Zr65Cu17.5Ni10Al7.5 amorphous alloys even though the oxygen is not added intentionally. When the Zr65Cu15Al10Pd10 alloy is crystallized, oxygen redistribution occurs; it is rejected from the primary Zr2 (Cu, Pd) crystals and partitioned in the subsequently crystallized phases. Oxygen atoms are enriched in some of the crystalline phases up to approximately 4 at.%, and virtually no oxygen is dissolved in the remaining amorphous phase. In the partially crystallized Zr65Cu17.5Ni10Al7.5 alloy, fine oxygen enriched particles containing ∼ 15 at.%O have been detected in direct contacted with crystalline grains. This work demonstrates that oxygen redistribution occurs during the crystallization reaction, thereby influencing the kinetics of crystallization.

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