Metals

298 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Metals in 2015

by Metals Editorial Office

Metals 2016, 6(1), 27; https://doi.org/10.3390/met6010027 - 21 Jan 2016

Viewed by 3243

The editors of Metals would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. [...] Full article

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Open AccessFeature PaperArticle

Probing Interfaces in Metals Using Neutron Reflectometry

by Michael J. Demkowicz and Jaroslaw Majewski

Metals 2016, 6(1), 20; https://doi.org/10.3390/met6010020 - 20 Jan 2016

Cited by 8 | Viewed by 8314

Abstract

Solid-state interfaces play a major role in a variety of material properties. They are especially important in determining the behavior of nano-structured materials, such as metallic multilayers. However, interface structure and properties remain poorly understood, in part because the experimental toolbox for characterizing [...] Read more.

Solid-state interfaces play a major role in a variety of material properties. They are especially important in determining the behavior of nano-structured materials, such as metallic multilayers. However, interface structure and properties remain poorly understood, in part because the experimental toolbox for characterizing them is limited. Neutron reflectometry (NR) offers unique opportunities for studying interfaces in metals due to the high penetration depth of neutrons and the non-monotonic dependence of their scattering cross-sections on atomic numbers. We review the basic physics of NR and outline the advantages that this method offers for investigating interface behavior in metals, especially under extreme environments. We then present several example NR studies to illustrate these advantages and discuss avenues for expanding the use of NR within the metals community. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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5744 KiB

Open AccessArticle

The Study of Heat Treatment Effects on Chromium Carbide Precipitation of 35Cr-45Ni-Nb Alloy for Repairing Furnace Tubes

by Nakarin Srisuwan, Krittee Eidhed, Nantawat Kreatsereekul, Trinet Yingsamphanchareon and Attaphon Kaewvilai

Metals 2016, 6(1), 26; https://doi.org/10.3390/met6010026 - 19 Jan 2016

Cited by 14 | Viewed by 7602

Abstract

This paper presents a specific kind of failure in ethylene pyrolysis furnace tubes. It considers the case in which the tubes made of 35Cr-45Ni-Nb high temperature alloy failed to carburization, causing creep damage. The investigation found that used tubes became difficult to weld [...] Read more.

This paper presents a specific kind of failure in ethylene pyrolysis furnace tubes. It considers the case in which the tubes made of 35Cr-45Ni-Nb high temperature alloy failed to carburization, causing creep damage. The investigation found that used tubes became difficult to weld repair due to internal carburized layers of the tube. The microstructure and geochemical component of crystallized carbide at grain boundary of tube specimens were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) with back-scattered electrons mode (BSE), and energy dispersive X-ray spectroscopy (EDS). Micro-hardness tests was performed to determine the hardness of the matrix and the compounds of new and used tube material. The testing result indicated that used tubes exhibited a higher hardness and higher degree of carburization compared to those of new tubes. The microstructure of used tubes also revealed coarse chromium carbide precipitation and a continuous carbide lattice at austenite grain boundaries. However, thermal heat treatment applied for developing tube weld repair could result in dissolving or breaking up chromium carbide with a decrease in hardness value. This procedure is recommended to improve the weldability of the 35Cr-45Ni-Nb used tubes alloy. Full article

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6886 KiB

Open AccessArticle

Porous γ-TiAl Structures Fabricated by Electron Beam Melting Process

by Ashfaq Mohammad, Abdulrahman M. Alahmari, Khaja Moiduddin, Muneer Khan Mohammed, Abdulrahman Alomar and Ravi Kottan Renganayagalu

Metals 2016, 6(1), 25; https://doi.org/10.3390/met6010025 - 18 Jan 2016

Cited by 12 | Viewed by 5923

Abstract

Porous metal structures have many benefits over fully dense structures for use in bio-implants. The designs of porous structures can be made more sophisticated by altering their pore volume and strut orientation. Porous structures made from biocompatible materials such as titanium and its [...] Read more.

Porous metal structures have many benefits over fully dense structures for use in bio-implants. The designs of porous structures can be made more sophisticated by altering their pore volume and strut orientation. Porous structures made from biocompatible materials such as titanium and its alloys can be produced using electron-beam melting, and recent reports have shown the biocompatibility of titanium aluminide (γ-TiAl). In the present work, we produced porous γ-TiAl structures by electron-beam melting, incorporating varying pore volumes. To achieve this, the individual pore dimensions were kept constant, and only the strut thickness was altered. Thus, for the highest pore volume of ~77%, the struts had to be as thin as half a millimeter. To accomplish such fine struts, we used various beam currents and scan strategies. Microscopy showed that selecting a proper scan strategy was most important in producing these fine struts. Microcomputed tomography revealed no major gaps in the struts, and the fine struts displayed compressive stiffness similar to that of natural bone. The characteristics of these highly-porous structures suggest their promise for use in bio-implants. Full article

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3823 KiB

Open AccessArticle

Aluminium Foam and Magnesium Compound Casting Produced by High-Pressure Die Casting

by Iban Vicario, Ignacio Crespo, Luis Maria Plaza, Patricia Caballero and Ion Kepa Idoiaga

Metals 2016, 6(1), 24; https://doi.org/10.3390/met6010024 - 15 Jan 2016

Cited by 18 | Viewed by 8062

Abstract

Nowadays, fuel consumption and carbon dioxide emissions are two of the main focal points in vehicle design, promoting the reduction in the weight of vehicles by using lighter materials. The aim of the work is to evaluate the influence of different aluminium foams [...] Read more.

Nowadays, fuel consumption and carbon dioxide emissions are two of the main focal points in vehicle design, promoting the reduction in the weight of vehicles by using lighter materials. The aim of the work is to evaluate the influence of different aluminium foams and injection parameters in order to obtain compound castings with a compromise between the obtained properties and weight by high-pressure die cast (HPDC) using aluminium foams as cores into a magnesium cast part. To evaluate the influence of the different aluminium foams and injection parameters on the final casting products quality, the type and density of the aluminium foam, metal temperature, plunger speed, and multiplication pressure have been varied within a range of suitable values. The obtained compound HPDC castings have been studied by performing visual and RX inspections, obtaining sound composite castings with aluminium foam cores. The presence of an external continuous layer on the foam surface and the correct placement of the foam to support injection conditions permit obtaining good quality parts. A HPDC processed magnesium-aluminium foam composite has been developed for a bicycle application obtaining a suitable combination of mechanical properties and, especially, a reduced weight in the demonstration part. Full article

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2092 KiB

Open AccessReview

Structural Dynamics of Materials under Shock Compression Investigated with Synchrotron Radiation

by Kouhei Ichiyanagi and Kazutaka G. Nakamura

Metals 2016, 6(1), 17; https://doi.org/10.3390/met6010017 - 15 Jan 2016

Cited by 19 | Viewed by 6722

Abstract

Characterizing material dynamics in non-equilibrium states is a current challenge in material and physical sciences. Combining laser and X-ray pulse sources enables the material dynamics in non-equilibrium conditions to be directly monitored. In this article, we review our nanosecond time-resolved X-ray diffraction studies [...] Read more.

Characterizing material dynamics in non-equilibrium states is a current challenge in material and physical sciences. Combining laser and X-ray pulse sources enables the material dynamics in non-equilibrium conditions to be directly monitored. In this article, we review our nanosecond time-resolved X-ray diffraction studies with 100-ps X-ray pulses from synchrotron radiation concerning the dynamics of structural phase transitions in non-equilibrium high-pressure conditions induced by laser shock compression. The time evolution of structural deformation of single crystals, polycrystals, and glass materials was investigated. In a single crystal of cadmium sulfide, the expected phase transition was not induced within 10 ns at a peak pressure of 3.92 GPa, and an over-compressed structure was formed. In a polycrystalline sample of Y₂O₃ stabilized tetragonal zirconia, reversible phase transitions between tetragonal and monoclinic phases occur within 20 ns under laser-induced compression and release processes at a peak pressure of 9.8 GPa. In polycrystalline bismuth, a sudden transition from Bi-I to Bi-V phase occurs within approximately 5 ns at 11 GPa, and sequential V–III–II–I phase transitions occur within 30 ns during the pressure release process. In fused silica shocked at 3.5 GPa, an intermediate-range structural change in the nonlinear elastic region was observed. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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Open AccessFeature PaperArticle

The Eh-pH Diagram and Its Advances

by Hsin-Hsiung Huang

Metals 2016, 6(1), 23; https://doi.org/10.3390/met6010023 - 14 Jan 2016

Cited by 86 | Viewed by 50478

Abstract

Since Pourbaix presented Eh versus pH diagrams in his “Atlas of Electrochemical Equilibria in Aqueous Solution”, diagrams have become extremely popular and are now used in almost every scientific area related to aqueous chemistry. Due to advances in personal computers, such diagrams can [...] Read more.

Since Pourbaix presented Eh versus pH diagrams in his “Atlas of Electrochemical Equilibria in Aqueous Solution”, diagrams have become extremely popular and are now used in almost every scientific area related to aqueous chemistry. Due to advances in personal computers, such diagrams can now show effects not only of Eh and pH, but also of variables, including ligand(s), temperature and pressure. Examples from various fields are illustrated in this paper. Examples include geochemical formation, corrosion and passivation, precipitation and adsorption for water treatment and leaching and metal recovery for hydrometallurgy. Two basic methods were developed to construct an Eh-pH diagram concerning the ligand component(s). The first method calculates and draws a line between two adjacent species based on their given activities. The second method performs equilibrium calculations over an array of points (500 × 800 or higher are preferred), each representing one Eh and one pH value for the whole system, then combines areas of each dominant species for the diagram. These two methods may produce different diagrams. The fundamental theories, illustrated results, comparison and required conditions behind these two methods are presented and discussed in this paper. The Gibbs phase rule equation for an Eh-pH diagram was derived and verified from actual plots. Besides indicating the stability area of water, an Eh-pH diagram normally shows only half of an overall reaction. However, merging two or more related diagrams together reveals more clearly the possibility of the reactions involved. For instance, leaching of Au with cyanide followed by cementing Au with Zn (Merrill-Crowe process) can be illustrated by combining Au-CN and Zn-CN diagrams together. A second example of the galvanic conversion of chalcopyrite can be explained by merging S, Fe–S and Cu–Fe–S diagrams. The calculation of an Eh-pH diagram can be extended easily into another dimension, such as the concentration of a given ligand, temperature or showing the solubility of stable solids. A personal computer is capable of drawing the diagram by utilizing a 3D program, such as ParaView, or VisIt, or MATLAB. Two 3D wireframe volume plots of a Uranium-carbonate system from Garrels and Christ were used to verify the Eh-pH calculation and the presentation from ParaView. Although a two-dimensional drawing is still much clearer to read, a 3D graph can allow one to visualize an entire system by executing rotation, clipping, slicing and making a movie. Full article

(This article belongs to the Special Issue Hydrometallurgy)

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1194 KiB

Open AccessArticle

Study on Sintering Mechanism of Stainless Steel Fiber Felts by X-ray Computed Tomography

by Jun Ma, Aijun Li and Huiping Tang

Metals 2016, 6(1), 18; https://doi.org/10.3390/met6010018 - 13 Jan 2016

Cited by 9 | Viewed by 5667

Abstract

The microstructure evolution of Fe-17 wt. % Cr-12 wt. % Ni-2 wt. % Mo stainless steel fiber felts during the fast sintering process was investigated by the synchrotron radiation X-ray computed tomography technique. The equation of dynamics of stable inter-fiber neck growth was [...] Read more.

The microstructure evolution of Fe-17 wt. % Cr-12 wt. % Ni-2 wt. % Mo stainless steel fiber felts during the fast sintering process was investigated by the synchrotron radiation X-ray computed tomography technique. The equation of dynamics of stable inter-fiber neck growth was established for the first time based on the geometry model of sintering joints of two fibers and Kucsynski’s two-sphere model. The specific evolutions of different kinds of sintering joints were observed in the three-dimensional images. The sintering mechanisms during sintering were proposed as plastic flow and grain boundary diffusion, the former leading to a quick growth of sintering joints. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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10656 KiB

Open AccessFeature PaperReview

π-Conjugated Materials as the Hole-Transporting Layer in Perovskite Solar Cells

by Alexandre Gheno, Sylvain Vedraine, Bernard Ratier and Johann Bouclé

Metals 2016, 6(1), 21; https://doi.org/10.3390/met6010021 - 12 Jan 2016

Cited by 41 | Viewed by 13880

Abstract

Hybrid organometal halide perovskites have attracted much attention these past four years as the new active layer for photovoltaic applications. Researches are now intensively focused on the stability issues of these solar cells, the process of fabrication and the design of innovative materials [...] Read more.

Hybrid organometal halide perovskites have attracted much attention these past four years as the new active layer for photovoltaic applications. Researches are now intensively focused on the stability issues of these solar cells, the process of fabrication and the design of innovative materials to produce efficient perovskite devices. In this review, we highlight the recent progress demonstrated in 2015 in the design of new π-conjugated organic materials used as hole transporters in such solar cells. Indeed, several of these “synthetic metals” have been proposed to play this role during the last few years, in an attempt to replace the conventional 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD) reference. Organic compounds have the benefits of low production costs and the abundance of raw materials, but they are also crucial components in order to address some of the stability issues usually encountered by this type of technology. We especially point out the main design rules to reach high efficiencies. Full article

(This article belongs to the Special Issue Synthetic Metals)

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2228 KiB

Open AccessArticle

Deformation in Metallic Glasses Studied by Synchrotron X-Ray Diffraction

by Takeshi Egami, Yang Tong and Wojciech Dmowski

Metals 2016, 6(1), 22; https://doi.org/10.3390/met6010022 - 11 Jan 2016

Cited by 17 | Viewed by 6384

Abstract

High mechanical strength is one of the superior properties of metallic glasses which render them promising as a structural material. However, understanding the process of mechanical deformation in strongly disordered matter, such as metallic glass, is exceedingly difficult because even an effort to [...] Read more.

High mechanical strength is one of the superior properties of metallic glasses which render them promising as a structural material. However, understanding the process of mechanical deformation in strongly disordered matter, such as metallic glass, is exceedingly difficult because even an effort to describe the structure qualitatively is hampered by the absence of crystalline periodicity. In spite of such challenges, we demonstrate that high-energy synchrotron X-ray diffraction measurement under stress, using a two-dimensional detector coupled with the anisotropic pair-density function (PDF) analysis, has greatly facilitated the effort of unraveling complex atomic rearrangements involved in the elastic, anelastic, and plastic deformation of metallic glasses. Even though PDF only provides information on the correlation between two atoms and not on many-body correlations, which are often necessary in elucidating various properties, by using stress as means of exciting the system we can garner rich information on the nature of the atomic structure and local atomic rearrangements during deformation in glasses. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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1817 KiB

Open AccessArticle

Monitoring of Bainite Transformation Using in Situ Neutron Scattering

by Hikari Nishijima, Yo Tomota, Yuhua Su, Wu Gong and Jun-ichi Suzuki

Metals 2016, 6(1), 16; https://doi.org/10.3390/met6010016 - 9 Jan 2016

Cited by 8 | Viewed by 5134

Abstract

Bainite transformation behavior was monitored using simultaneous measurements of dilatometry and small angle neutron scattering (SANS). The volume fraction of bainitic ferrite was estimated from the SANS intensity, showing good agreement with the results of the dilatometry measurements. We propose a more advanced [...] Read more.

Bainite transformation behavior was monitored using simultaneous measurements of dilatometry and small angle neutron scattering (SANS). The volume fraction of bainitic ferrite was estimated from the SANS intensity, showing good agreement with the results of the dilatometry measurements. We propose a more advanced monitoring technique combining dilatometry, SANS and neutron diffraction. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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127 KiB

Open AccessEditorial

Casting Alloy Design and Modification

by Anders E.W. Jarfors

Metals 2016, 6(1), 15; https://doi.org/10.3390/met6010015 - 8 Jan 2016

Cited by 2 | Viewed by 3066

Abstract

Castings and the cast metals are among the most important facets creating a foundation for modern life. [...] Full article

(This article belongs to the Special Issue Casting Alloy Design and Modification)

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Open AccessArticle

Effective Synthesis and Recovery of Silver Nanowires Prepared by Tapered Continuous Flow Reactor for Flexible and Transparent Conducting Electrode

by Hyung Duk Yun, Duck Min Seo, Min Yoeb Lee, Soon Yong Kwon and Lee Soon Park

Metals 2016, 6(1), 14; https://doi.org/10.3390/met6010014 - 8 Jan 2016

Cited by 14 | Viewed by 6416

Abstract

Silver nanowires (AgNWs) with high aspect ratio were obtained utilizing a tapered tubular reactor by the polyol process. The tapered tubular type flow reactor allowed us to obtain nanowires in high yield without defects that is generally encountered in a closed reactor due [...] Read more.

Silver nanowires (AgNWs) with high aspect ratio were obtained utilizing a tapered tubular reactor by the polyol process. The tapered tubular type flow reactor allowed us to obtain nanowires in high yield without defects that is generally encountered in a closed reactor due to excessive shearing for a long time. After reaction the AgNWs were precipitated in the aqueous solution with the aid of a hydrogen bond breaker and were recovered effectively without using a high-cost centrifugation process. Dispersion of the AgNWs were used to prepare transparent conducting electrode (TCE) films by a spray coating method, which showed 86% transmittance and 90 Ωsq⁻¹ sheet resistance. Full article

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Open AccessArticle

The Establishment of Surface Roughness as Failure Criterion of Al–Li Alloy Stretch-Forming Process

by Jing-Wen Feng, Li-Hua Zhan and Ying-Ge Yang

Metals 2016, 6(1), 13; https://doi.org/10.3390/met6010013 - 7 Jan 2016

Cited by 8 | Viewed by 6223

Abstract

Taking Al–Li–S4–T8 Al–Li alloy as the study object, based on the stretching and deforming characteristics of sheet metals, this paper proposes a new approach of critical orange peel state characterizations on the basis of the precise measurement of stretch-forming surface roughness and establishes [...] Read more.

Taking Al–Li–S4–T8 Al–Li alloy as the study object, based on the stretching and deforming characteristics of sheet metals, this paper proposes a new approach of critical orange peel state characterizations on the basis of the precise measurement of stretch-forming surface roughness and establishes the critical criterion for the occurrence of orange peel surface defects in the stretch-forming process of Al–Li alloy sheet metals. Stretching experiments of different strain paths are conducted on the specimens with different notches so as to establish the Al–Li–S4–T8 Al–Li alloy, forming limit diagram and forming limit curve equation, with the surface roughness of characteristic critical orange peel structure as the stretch-forming failure criterion. Full article

(This article belongs to the Special Issue Aluminum Alloys)

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2782 KiB

Open AccessArticle

Investigation of Elastic Deformation Mechanism in As-Cast and Annealed Eutectic and Hypoeutectic Zr–Cu–Al Metallic Glasses by Multiscale Strain Analysis

by Hiroshi Suzuki, Rui Yamada, Shinki Tsubaki, Muneyuki Imafuku, Shigeo Sato, Tetsu Watanuki, Akihiko Machida and Junji Saida

Metals 2016, 6(1), 12; https://doi.org/10.3390/met6010012 - 5 Jan 2016

Cited by 4 | Viewed by 5047

Abstract

Elastic deformation behaviors of as-cast and annealed eutectic and hypoeutectic Zr–Cu–Al bulk metallic glasses (BMG) were investigated on a basis of different strain-scales, determined by X-ray scattering and the strain gauge. The microscopic strains determined by Direct-space method and Reciprocal-space method were compared [...] Read more.

Elastic deformation behaviors of as-cast and annealed eutectic and hypoeutectic Zr–Cu–Al bulk metallic glasses (BMG) were investigated on a basis of different strain-scales, determined by X-ray scattering and the strain gauge. The microscopic strains determined by Direct-space method and Reciprocal-space method were compared with the macroscopic strain measured by the strain gauge, and the difference in the deformation mechanism between eutectic and hypoeutectic Zr–Cu–Al BMGs was investigated by their correlation. The eutectic Zr₅₀Cu₄₀Al₁₀ BMG obtains more homogeneous microstructure by free-volume annihilation after annealing, improving a resistance to deformation but degrading ductility because of a decrease in the volume fraction of weakly-bonded regions with relatively high mobility. On the other hand, the as-cast hypoeutectic Zr₆₀Cu₃₀Al₁₀ BMG originally has homogeneous microstructure but loses its structural and elastic homogeneities because of nanocluster formation after annealing. Such structural changes by annealing might develop unique mechanical properties showing no degradations of ductility and toughness for the structural-relaxed hypoeutectic Zr₆₀Cu₃₀Al₁₀ BMGs. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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3770 KiB

Open AccessArticle

In situ Investigation of Titanium Powder Microwave Sintering by Synchrotron Radiation Computed Tomography

by Yu Xiao, Feng Xu, Xiaofang Hu, Yongcun Li, Wenchao Liu and Bo Dong

Metals 2016, 6(1), 9; https://doi.org/10.3390/met6010009 - 4 Jan 2016

Cited by 12 | Viewed by 5843

Abstract

In this study, synchrotron radiation computed tomography was applied to investigate the mechanisms of titanium powder microwave sintering in situ. On the basis of reconstructed images, we observed that the sintering described in this study differs from conventional sintering in terms of [...] Read more.

In this study, synchrotron radiation computed tomography was applied to investigate the mechanisms of titanium powder microwave sintering in situ. On the basis of reconstructed images, we observed that the sintering described in this study differs from conventional sintering in terms of particle smoothing, rounding, and short-term growth. Contacted particles were also isolated. The kinetic curves of sintering neck growth and particle surface area were obtained and compared with those of other microwave-sintered metals to examine the interaction mechanisms between mass and microwave fields. Results show that sintering neck growth accelerated from the intermediate period; however, this finding is inconsistent with that of aluminum powder microwave sintering described in previous work. The free surface areas of the particles were also quantitatively analyzed. In addition to the eddy current loss in metal particles, other heating mechanisms, including dielectric loss, interfacial polarization effect, and local plasma-activated sintering, contributed to sintering neck growth. Thermal and non-thermal effects possibly accelerated the sintering neck growth of titanium. This study provides a useful reference of further research on interaction mechanisms between mass and microwave fields during microwave sintering. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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3708 KiB

Open AccessArticle

Influence of Loading Rate on the Hydrogen-Assisted Micro-Damage in Bluntly Notched Samples of Pearlitic Steel

by Jesús Toribio, Diego Vergara and Miguel Lorenzo

Metals 2016, 6(1), 11; https://doi.org/10.3390/met6010011 - 4 Jan 2016

Cited by 16 | Viewed by 4974

Abstract

The influence of loading rate (crosshead speed) on the fracture process of bluntly notched samples of pearlitic steel under hydrogen environment is analyzed in this paper. Results indicate that the location of the zone where fracture initiates (fracture process zone) in pearlitic steel [...] Read more.

The influence of loading rate (crosshead speed) on the fracture process of bluntly notched samples of pearlitic steel under hydrogen environment is analyzed in this paper. Results indicate that the location of the zone where fracture initiates (fracture process zone) in pearlitic steel samples with a blunt notch directly depends on the loading rate or crosshead speed. For slow testing rates, such a zone is placed in the specimen center due to hydrogen diffusion towards the prospective fracture places located in the central area of the section. On the other hand, in the case of high testing rates, the process of hydrogen-assisted fracture initiates near the sample periphery, i.e., in the vicinity of the notch tip, because in such quick tests hydrogen does not have enough time to diffuse towards inner points of the specimen. Full article

(This article belongs to the Special Issue The Role of MnS Inclusions in the Localized Corrosion of Carbon Steel)

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2724 KiB

Open AccessReview

In Situ Characterization Techniques Based on Synchrotron Radiation and Neutrons Applied for the Development of an Engineering Intermetallic Titanium Aluminide Alloy

by Petra Erdely, Thomas Schmoelzer, Emanuel Schwaighofer, Helmut Clemens, Peter Staron, Andreas Stark, Klaus-Dieter Liss and Svea Mayer

Metals 2016, 6(1), 10; https://doi.org/10.3390/met6010010 - 4 Jan 2016

Cited by 32 | Viewed by 10345

Abstract

Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density and high stiffness constitute a profile [...] Read more.

Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density and high stiffness constitute a profile perfectly suitable for their application as advanced aero-engine turbine blades or as turbocharger turbine wheels in next-generation automotive engines. As the properties of TiAl alloys during processing as well as during service are dependent on the phases occurring, detailed knowledge of their volume fractions and distribution within the microstructure is of paramount importance. Furthermore, the behavior of the individual phases during hot deformation and subsequent heat treatments is of interest to define reliable and cost-effective industrial production processes. In situ high-energy X-ray diffraction methods allow tracing the evolution of phase fractions over a large temperature range. Neutron diffraction unveils information on order-disorder transformations in TiAl alloys. Small-angle scattering experiments offer insights into the materials’ precipitation behavior. This review attempts to shine a light on selected in situ diffraction and scattering techniques and the ways in which they promoted the development of an advanced engineering TiAl alloy. Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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5465 KiB

Open AccessArticle

Study on Austenitization Kinetics of SA508 Gr.3 Steel Based on Isoconversional Method

by Xiaomeng Luo, Lizhan Han and Jianfeng Gu

Metals 2016, 6(1), 8; https://doi.org/10.3390/met6010008 - 29 Dec 2015

Cited by 15 | Viewed by 6027

Abstract

The austenitization kinetics of SA508 Gr.3 steel during heating was studied using the isoconversional method combined with continuous thermal dilatometric tests for the first time. The model-free austenitization kinetics was built and the effective activation energy as a function of transformed austenite fraction [...] Read more.

The austenitization kinetics of SA508 Gr.3 steel during heating was studied using the isoconversional method combined with continuous thermal dilatometric tests for the first time. The model-free austenitization kinetics was built and the effective activation energy as a function of transformed austenite fraction was determined without transformation models. Then, the corresponding regression validation was carried out. The time-temperature-austenitization (TTA) diagram of SA508 Gr.3 steel, which is very difficult to be obtained using experiment measures, was constructed. Finally, the austenitization kinetics in a more realistic case, i.e., under non-constant heating rates, was predicted, which is found to agree well with the experimental results. Full article

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1120 KiB

Open AccessFeature PaperArticle

Spectral Shift Amplification and Polarization-Controlled Spectral Shift with Silver Metal

by Pin Han and Yung-Chieh Tseng

Metals 2016, 6(1), 7; https://doi.org/10.3390/met6010007 - 26 Dec 2015

Cited by 3 | Viewed by 5036

Abstract

The spectral shift amplification effect and polarization-controlled spectral shifts are studied using silver (Ag) metal. The spectral shift amplification factor can be doubled by using silver compared with using water. The solid Ag metal surface also provides orientation freedom for polarization-controlled spectral shifts, [...] Read more.

The spectral shift amplification effect and polarization-controlled spectral shifts are studied using silver (Ag) metal. The spectral shift amplification factor can be doubled by using silver compared with using water. The solid Ag metal surface also provides orientation freedom for polarization-controlled spectral shifts, benefiting data transmission applications in any direction. The liquid water interface provides only limited direction at the Brewster angle. Besides those advantages, the higher reflectivity of Ag reflects higher spectral intensity, which makes the signal easier to detect. The spectral switch phenomenon that depends on the central wavelength variation is also presented. Full article

(This article belongs to the Special Issue Refractory Metals and Alloys)

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3414 KiB

Open AccessArticle

Residual Stress Distribution and Microstructure at a Laser Spot of AISI 304 Stainless Steel Subjected to Different Laser Shock Peening Impacts

by Wenquan Zhang, Jinzhong Lu and Kaiyu Luo

Metals 2016, 6(1), 6; https://doi.org/10.3390/met6010006 - 25 Dec 2015

Cited by 35 | Viewed by 6045

Abstract

The effects of different laser shock peening (LSP) impacts on the three-dimensional displayed distributions of surface and in-depth residual stress at a laser spot of AISI 304 stainless steel were investigated by X-ray diffraction technology with the sin²φ method and MATLAB [...] Read more.

The effects of different laser shock peening (LSP) impacts on the three-dimensional displayed distributions of surface and in-depth residual stress at a laser spot of AISI 304 stainless steel were investigated by X-ray diffraction technology with the sin²φ method and MATLAB 2010a software. Microstructural evolution in the top surface subjected to multiple LSP impacts was presented by means of cross-sectional optical microscopy (OM) and transmission electron microscopy (TEM) observations. Experimental results and analysis indicated that residual stress distribution and microstructure at a laser spot depended strongly on the number of multiple LSP impacts, and refined grain and ultra-high strain rate play an important role in the improvement of compressive residual stress of AISI 304 stainless steel. The analysis of treatment of the extended surface was presented to obtain uniform surface properties on the top surface of AISI 304 stainless steel. Full article

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5422 KiB

Open AccessArticle

Evolution of the Annealing Twin Density during δ-Supersolvus Grain Growth in the Nickel-Based Superalloy Inconel™ 718

by Yuan Jin, Marc Bernacki, Andrea Agnoli, Brian Lin, Gregory S. Rohrer, Anthony D. Rollett and Nathalie Bozzolo

Metals 2016, 6(1), 5; https://doi.org/10.3390/met6010005 - 24 Dec 2015

Cited by 33 | Viewed by 7576

Abstract

Grain growth experiments were performed on Inconel™ 718 to investigate the possible correlation of the annealing twin density with grain size and with annealing temperature. Those experiments were conducted at different temperatures in the δ supersolvus domain and under such conditions that only [...] Read more.

Grain growth experiments were performed on Inconel™ 718 to investigate the possible correlation of the annealing twin density with grain size and with annealing temperature. Those experiments were conducted at different temperatures in the δ supersolvus domain and under such conditions that only capillarity forces were involved in the grain boundary migration process. In the investigated range, there is a strong inverse correlation of the twin density with the average grain size. On the other hand, the twin density at a given average grain size is not sensitive to annealing temperature. Consistent with previous results for pure nickel, the twin density evolution in Inconel™ 718 is likely to be mainly controlled by the propagation of the pre-existing twins of the growing grains; i.e., the largest ones of the initial microstructure. Almost no new twin boundaries are created during the grain growth process itself. Therefore, the twin density at a given average grain size is mainly dependent on the twin density in the largest grains of the initial microstructure and independent of the temperature at which grains grow. Based on the observations, a mean field model is proposed to predict annealing twin density as a function of grain size during grain growth. Full article

(This article belongs to the Special Issue Superalloys)

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3518 KiB

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Establishment of Heat Treatment Process for Modified 440A Martensitic Stainless Steel Using Differential Scanning Calorimetry and Thermo-Calc Calculation

by Huei-Sen Wang and Pei-Ju Hsieh

Metals 2016, 6(1), 4; https://doi.org/10.3390/met6010004 - 23 Dec 2015

Cited by 5 | Viewed by 8487

Abstract

To provide a suitable microstructure and mechanical properties for modified Grade 440A martensitic stainless steel (MSS), which could facilitate the further cold deformation process (e.g., cold rolling), this work used differential scanning calorimetry (DSC) and Thermo-Calc software to determine three soaking temperatures for [...] Read more.

To provide a suitable microstructure and mechanical properties for modified Grade 440A martensitic stainless steel (MSS), which could facilitate the further cold deformation process (e.g., cold rolling), this work used differential scanning calorimetry (DSC) and Thermo-Calc software to determine three soaking temperatures for annealing heat treatment processes (HT1, HT2 and HT3). To verify the feasibility of the proposed annealing heat treatment processes, the as-received samples were initially heated to 1050 °C (similar to the on-line working temperature) for 30 min and air quenched to form a martensitic structure. The air-quenched samples were then subjected to three developed annealing heat treatment conditions. The microstructure and mechanical properties of the heat-treated samples were then investigated. Test results showed that considering the effects of the microstructure and the hardness, the HT1, the HT2 or the soaking temperatures between the HT1 and HT2 were the most recommended processes to modified Grade 440A MSS. When using the recommended processes, their carbides were fine and more evenly distributed, and the microhardness was as low as 210 Hv, which can be applied to the actual production process. Full article

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975 KiB

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Biodegradable Behaviors of Ultrafine-Grained ZE41A Magnesium Alloy in DMEM Solution

by Jinghua Jiang, Fan Zhang, Aibin Ma, Dan Song, Jianqing Chen, Huan Liu and Mingshan Qiang

Metals 2016, 6(1), 3; https://doi.org/10.3390/met6010003 - 23 Dec 2015

Cited by 14 | Viewed by 5089

Abstract

The main limitation to the clinical application of magnesium alloys is their too-fast degradation rate in the physiological environment. Bio-corrosion behaviors of the ZE41A magnesium alloy processed by multi-pass equal channel angular pressing (ECAP) were investigated in Dulbecco's Modified Eagle Medium (DMEM) solution, [...] Read more.

The main limitation to the clinical application of magnesium alloys is their too-fast degradation rate in the physiological environment. Bio-corrosion behaviors of the ZE41A magnesium alloy processed by multi-pass equal channel angular pressing (ECAP) were investigated in Dulbecco's Modified Eagle Medium (DMEM) solution, in order to tailor the effect of grain ultrafining on the biodegradation rate of the alloy implant. Hydrogen evolution tests indicated that a large number of ECAP passes decreased the stable corrosion rate of the alloy after the initial incubation period. Potentiodynamic polarization curves showed that more ECAP passes made the corrosion potential nobler and the corrosion tendency lower. Corroded surfaces of the ECAPed alloy indicated a higher resistance toward localized corrosion due to the homogeneous redistribution of broken second phases on the ultrafine-grained Mg matrix. It suggests that grain ultrafining can decrease the biodegradable rate of the magnesium alloy-containing rare-earth elements and tailor the lifetime of the biodegradable material. Full article

(This article belongs to the Special Issue Oxidation of Metals)

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3850 KiB

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Continuous Casting of Incoloy800H Superalloy Billet under an Alternating Electromagnetic Field

by Fei Wang, Lintao Zhang, Anyuan Deng, Xiujie Xu and Engang Wang

Metals 2016, 6(1), 2; https://doi.org/10.3390/met6010002 - 23 Dec 2015

Cited by 10 | Viewed by 6375

Abstract

We experimentally investigate the influence of an alternating electromagnetic field on the surface and internal qualities of Incoloy800H superalloy billets. The electromagnetic continuous casting experiments for Incoloy800H superalloy were successfully conducted and the billets (0.1 m × 0.1 m × 1.2 m) were [...] Read more.

We experimentally investigate the influence of an alternating electromagnetic field on the surface and internal qualities of Incoloy800H superalloy billets. The electromagnetic continuous casting experiments for Incoloy800H superalloy were successfully conducted and the billets (0.1 m × 0.1 m × 1.2 m) were obtained. We figure out that the high frequency (20.4 kHz) electromagnetic field which is applied in the mould region can improve the surface quality of Incoloy800H superalloy billet remarkably; the depth of oscillation mark decreases from 1.2 mm (without electromagnetic field) to 0.3 mm (with electromagnetic field). The internal quality of the billet was studied using a variety of characterization techniques. The low frequency (5 Hz) electromagnetic field which is applied in the second cooling region can improve the internal quality; the region of the equiaxed grain increases from 2.45% (without electromagnetic field) to 41.45% (with electromagnetic field). Furthermore, macro- and micro-segregation are suppressed and the TiN inclusion number is decreased as well. Full article

(This article belongs to the Special Issue Superalloys)

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3451 KiB

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Effect of Cold Rolling and Heat Treatment on the Mechanical Properties of GH4169 Alloy Sheet at Room Temperature

by Shi-Hong Zhang, Neng-Yong Ye, Ming Cheng, Hong-Wu Song, Hong-Wei Zhou and Ping-Bo Wang

Metals 2016, 6(1), 1; https://doi.org/10.3390/met6010001 - 23 Dec 2015

Cited by 16 | Viewed by 6206

Abstract

The mechanical properties of GH4169 alloy sheet after cold rolling (at 0%, 10%, 30%, 50% and 70%) and solid solution were investigated. The textures and Taylor factors were characterized using electron backscattering diffraction (EBSD). The fractions of δ phase were measured by X-ray [...] Read more.

The mechanical properties of GH4169 alloy sheet after cold rolling (at 0%, 10%, 30%, 50% and 70%) and solid solution were investigated. The textures and Taylor factors were characterized using electron backscattering diffraction (EBSD). The fractions of δ phase were measured by X-ray diffraction. The contributions of δ phase, grain size, texture, and work hardening on the mechanical properties were also discussed. The results showed increases in the yield strength (YS) (0.2%) as well as the ultimate tensile strength (UTS) of GH4169 superalloy sheet after cold rolling, when rolling reduction was increased. In contrast, following solid solution treatment, YS and UTS were increased then subsequently decreased. The changes of yield strength of GH4169 superalloy were attributed to the texture and work hardening, followed by the grain refinement and precipitation of δ phase. When the rolling reduction was below 30%, the influence of δ phase was greater than grain refinement and when the rolling reduction was larger than 50%, the controversial results occur. The precipitation of δ phase promoted the improvement of yield strength, the relationship between the fraction of δ phase and improved yield strength satisfactory fit to the following equation: σ_δ = 15.9W_δ + 59.7. Full article

(This article belongs to the Special Issue Superalloys)

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Metals, Volume 6, Issue 1 (January 2016) – 26 articles

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