Metals

1305 KiB

Open AccessArticle

Structural Irreversibility and Enhanced Brittleness under Fatigue in Zr-Based Amorphous Solids

by Peng Tong, Despina Louca, Gongyao Wang, Peter K. Liaw, Yoshihiko Yokoyama, Anna Llobet, Hiroshi Kawaji, Yiming Qiu and Yunfeng Shi

Metals 2012, 2(4), 529-539; https://doi.org/10.3390/met2040529 - 19 Dec 2012

Cited by 4 | Viewed by 6407

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 [...] Read more.

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)

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797 KiB

Open AccessArticle

Applicability of Solid Solution Heat Treatments to Aluminum Foams

by Jaime Lázaro, Eusebio Solórzano, Javier Escudero, Jose Antonio De Saja and Miguel Rodríguez-Pérez

Metals 2012, 2(4), 508-528; https://doi.org/10.3390/met2040508 - 14 Dec 2012

Cited by 11 | Viewed by 7055

Abstract

Present research work evaluates the influence of both density and size on the treatability of Aluminum-based (6000 series) foam-parts subjected to a typical solid solution heat treatment (water quenching). The results are compared with those obtained for the bulk alloy, evaluating the fulfilment [...] Read more.

Present research work evaluates the influence of both density and size on the treatability of Aluminum-based (6000 series) foam-parts subjected to a typical solid solution heat treatment (water quenching). The results are compared with those obtained for the bulk alloy, evaluating the fulfilment of cooling requirements. Density of the foams was modeled by tomography analysis and the thermal properties calculated, based on validated density-scaled models. With this basis, cooling velocity maps during water quenching were predicted by finite element modeling (FEM) in which boundary conditions were obtained by solving the inverse heat conduction problem. Simulations under such conditions have been validated experimentally. Obtained results address incomplete matrix hardening for foam-parts bigger than 70 mm in diameter with a density below 650 kg/m³. An excellent agreement has been found in between the predicted cooling maps and final measured microhardness profiles. Full article

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1974 KiB

Open AccessArticle

Comparative Study of Elastoplastic Constitutive Models for Deformation of Metallic Glasses

by Ming Zhao and Mo Li

Metals 2012, 2(4), 488-507; https://doi.org/10.3390/met2040488 - 4 Dec 2012

Cited by 15 | Viewed by 9355

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 [...] Read more.

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)

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104 KiB

Open AccessArticle

Analysis of Heavy Metal in Electrocoagulated Metal Hydroxide Sludge (EMHS) from the Textile Industry by Energy Dispersive X-Ray Fluorescence (EDXRF)

by Tanveer Mehedi Adyel, Syed Hafizur Rahman, Mala Khan and S.M. Nazrul Islam

Metals 2012, 2(4), 478-487; https://doi.org/10.3390/met2040478 - 3 Dec 2012

Cited by 9 | Viewed by 7157

Abstract

Environmental pollution due to discharges of heavy metal containing sludge from textile industries is a common nuisance in Bangladesh, where no treatment of sludge is carried out before final disposals. Energy Dispersive X-ray Fluorescence (EDXRF) was employed in the present study to analyze [...] Read more.

Environmental pollution due to discharges of heavy metal containing sludge from textile industries is a common nuisance in Bangladesh, where no treatment of sludge is carried out before final disposals. Energy Dispersive X-ray Fluorescence (EDXRF) was employed in the present study to analyze the heavy metal content of Electrocoagulated Metal Hydroxide Sludge (EMHS) collected from a composite textile industry. Thirteen heavy metals, viz., Mn, Ti, Cu, Zn, Ni, Sr, V, Cr, Zr, Hg, Cd, Nb and Ga, were detected. Mn, Ni, Cu, Zn and Cd exceeded the permissible limit to apply the EMHS in agricultural land. Cr, Ni, Cu and Zn were compared to the values of the European legislation to evaluate the environmental risk and to classify the wastes as inert wastes or as wastes that have to be control landfilled. EMHS was categorized as class I and needs to be deposited in controlled landfills. Full article

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1917 KiB

Open AccessArticle

Corrosion Protection of Electrically Conductive Surfaces

by Jian Song, Liangliang Wang, Andre Zibart and Christian Koch

Metals 2012, 2(4), 450-477; https://doi.org/10.3390/met2040450 - 15 Nov 2012

Cited by 106 | Viewed by 21703

Abstract

The basic function of the electrically conductive surface of electrical contacts is electrical conduction. The electrical conductivity of contact materials can be largely reduced by corrosion and in order to avoid corrosion, protective coatings must be used. Another phenomenon that leads to increasing [...] Read more.

The basic function of the electrically conductive surface of electrical contacts is electrical conduction. The electrical conductivity of contact materials can be largely reduced by corrosion and in order to avoid corrosion, protective coatings must be used. Another phenomenon that leads to increasing contact resistance is fretting corrosion. Fretting corrosion is the degradation mechanism of surface material, which causes increasing contact resistance. Fretting corrosion occurs when there is a relative movement between electrical contacts with surfaces of ignoble metal. Avoiding fretting corrosion is therefore extremely challenging in electronic devices with pluggable electrical connections. Gold is one of the most commonly used noble plating materials for high performance electrical contacts because of its high corrosion resistance and its good and stable electrical behavior. The authors have investigated different ways to minimize the consumption of gold for electrical contacts and to improve the performance of gold plating. Other plating materials often used for corrosion protection of electrically conductive surfaces are tin, nickel, silver and palladium. This paper will deal with properties and new research results of different plating materials in addition to other means used for corrosion protection of electrically conductive surfaces and the testing of corrosion resistance of electrically conductive surfaces. Full article

(This article belongs to the Special Issue Advanced Corrosion Resistant Alloys for Energy Production, Storage, and Transportation Systems)

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344 KiB

Open AccessArticle

Nanometer-Scale Heterogeneities of the Structure of Zirconium-Based Bulk Metallic Glasses

by Alexander S. Bakai, Evgenij V. Sadanov, Vjacheslav A. Ksenofontov, Sergej A. Bakai, Julia A. Gordienko and Igor M. Mikhailovskij

Metals 2012, 2(4), 441-449; https://doi.org/10.3390/met2040441 - 15 Nov 2012

Cited by 5 | Viewed by 5297

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 [...] Read more.

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)

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3006 KiB

Open AccessReview

Microstructure and Fatigue Characteristic of AM60B Magnesium Alloy

by Farid Taheri, You Lu and Morteza Mehrzadi

Metals 2012, 2(4), 411-440; https://doi.org/10.3390/met2040411 - 13 Nov 2012

Cited by 3 | Viewed by 9273

Abstract

This paper summarizes and reviews the findings of our research on AM60B magnesium alloy conducted in past 8 years. It essentially covers three categories: microstructural study, environmental effect, and fatigue crack growth rate of AM60B. The experimental and numerical studies on the influence [...] Read more.

This paper summarizes and reviews the findings of our research on AM60B magnesium alloy conducted in past 8 years. It essentially covers three categories: microstructural study, environmental effect, and fatigue crack growth rate of AM60B. The experimental and numerical studies on the influence of casting defects on this particular material’s properties are reviewed in the first part. It has been shown that the non-uniform solidification of the casting results in variations of the microstructure in different layers (skin and core) of the alloy which affects the mechanical properties in those regions. Moreover, the influence of microstructure on fatigue crack initiation and propagation response of the alloy is presented. The influence of several casting defects on the failure mechanism of the material are also numerically analyzed and discussed. The influence of elevated and cold temperatures on the fatigue response of the alloy is reviewed in the second part. Our findings show that the temperature does not have a significant effect on the number of cycles to failure. However, but at some stress level, this effect cannot be dismissed. The fatigue crack growth rate (FCGR) response of the alloy at a wide range of stress ratios is also investigated in the last part. The FCGR of the alloy showed a noticeable dependency on the stress ratio. A model is proposed for estimating the FCGR of the alloy, which could provide a good prediction of alloy’s FCGR over a wide range of negative and positive stress ratios. The integrity of the new model is also compared against other models. Finally, the influence of compressive loading on fatigue life of the specimens under constant and random amplitude cyclic loading is investigated experimentally. Full article

(This article belongs to the Special Issue Magnesium Technology)

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493 KiB

Open AccessArticle

Characterization of Steel Foams for Structural Components

by Brooks H. Smith, Stefan Szyniszewski, Jerome F. Hajjar, Benjamin W. Schafer and Sanjay R. Arwade

Metals 2012, 2(4), 399-410; https://doi.org/10.3390/met2040399 - 1 Nov 2012

Cited by 28 | Viewed by 10410

Abstract

Experimentally measured mechanical properties of hollow sphere steel foam are the subject of this paper. The characterization of the hollow sphere foam encompasses compressive yield stress and densification strain, compressive plastic Poisson’s ratio, and compressive unloading modulus, as well as tensile elastic modulus, [...] Read more.

Experimentally measured mechanical properties of hollow sphere steel foam are the subject of this paper. The characterization of the hollow sphere foam encompasses compressive yield stress and densification strain, compressive plastic Poisson’s ratio, and compressive unloading modulus, as well as tensile elastic modulus, tensile unloading modulus, tensile yield stress, and tensile fracture strain. Shear properties are also included. These tests provide sufficient information to allow calibration of a macroscopic, continuum constitutive model. Calibrated foam plasticity parameters are tabulated, and unique feature of foam plasticity are explained. Also, initial development of mesoscale simulations, which explicitly model voids and sintered hollow spheres, is reported. This work is part of a larger effort to help the development of steel foam as a material with relevance to civil engineering applications. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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Metals, Volume 2, Issue 4 (December 2012) – 8 articles , Pages 399-539

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