Editorial

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Acknowledgement to Reviewers of Metals in 2013

by Metals Editorial Office

Metals 2014, 4(1), 64; https://doi.org/10.3390/met4010064 - 27 Feb 2014

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The editors of Metals would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...] Full article

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942 KiB

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A Concept for the Control of Pore Size in Superalloy Membranes

by Joachim Rösler, Waldemar Krause and Björn Hinze

Metals 2014, 4(1), 1-7; https://doi.org/10.3390/met4010001 - 09 Jan 2014

Cited by 6 | Viewed by 5406

Abstract

A new method to adjust the pore size in superalloy membranes is shown, utilizing controlled cooling from solution heat treatment of the solid superalloy. Hereby, the nucleation rate and, thus, the size of the γ'-precipitates can be varied to a large extent. This [...] Read more.

A new method to adjust the pore size in superalloy membranes is shown, utilizing controlled cooling from solution heat treatment of the solid superalloy. Hereby, the nucleation rate and, thus, the size of the γ'-precipitates can be varied to a large extent. This leads to a corresponding variation in the pore size once the membrane material is produced by directional coarsening of the γ'-phase to an interconnected network and subsequent selective extraction of the γ-phase. Furthermore, it was found that coherent and incoherent γ'-precipitates can be used alike to fabricate superalloy membranes, and yet, result in vastly different pore morphologies. The findings widen the application range of this novel material class. Full article

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606 KiB

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Magnetism-Structure Correlations during the ε→τ Transformation in Rapidly-Solidified MnAl Nanostructured Alloys

by Felix Jiménez-Villacorta, Joshua L. Marion, John T. Oldham, Maria. Daniil, Matthew A. Willard and Laura H. Lewis

Metals 2014, 4(1), 8-19; https://doi.org/10.3390/met4010008 - 21 Jan 2014

Cited by 41 | Viewed by 7727

Abstract

Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn₅₅Al₄₅ ribbons from the as-quenched metastable antiferromagnetic (AF) ε-phase to the target ferromagnetic (FM) L1₀ τ-phase are investigated. The as-solidified material exhibits a majority hexagonal ε-MnAl phase revealing [...] Read more.

Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn₅₅Al₄₅ ribbons from the as-quenched metastable antiferromagnetic (AF) ε-phase to the target ferromagnetic (FM) L1₀ τ-phase are investigated. The as-solidified material exhibits a majority hexagonal ε-MnAl phase revealing a large exchange bias shift below a magnetic blocking temperature T_B~95 K (H_ex~13 kOe at 10 K), ascribed to the presence of compositional fluctuations in this antiferromagnetic phase. Heat treatment at a relatively low annealing temperature T_anneal ≈ 568 K (295 °C) promotes the nucleation of the metastable L1₀ τ-MnAl phase at the expense of the parent ε-phase, donating an increasingly hard ferromagnetic character. The onset of the ε→τ transformation occurs at a temperature that is ~100 K lower than that reported in the literature, highlighting the benefits of applying rapid solidification for synthesis of the rapidly-solidified parent alloy. Full article

(This article belongs to the Special Issue Manganese-based Permanent Magnets)

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Microstructure and Magnetic Properties of Bulk Nanocrystalline MnAl

by Anurag Chaturvedi, Rumana Yaqub and Ian Baker

Metals 2014, 4(1), 20-27; https://doi.org/10.3390/met4010020 - 22 Jan 2014

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Abstract

MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the effects of consolidation by back-pressure, assisted equal channel angular extrusion processing on mechanically-milled, gas-atomized Mn-46% at. Al powder. X-ray diffraction showed both that the extruded rod consisted mostly [...] Read more.

MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the effects of consolidation by back-pressure, assisted equal channel angular extrusion processing on mechanically-milled, gas-atomized Mn-46% at. Al powder. X-ray diffraction showed both that the extruded rod consisted mostly of metastable τ phase, with some of the equilibrium γ₂ and β phases, and that it largely retained the as-milled nanostructure. Magnetic measurements show a coercivity of ≤4.4 kOe and a magnetization at 10 kOe of ≤40 emu/g. In addition, extrusions exhibit greater than 95% of the theoretical density. This study opens a new window in the area of bulk MnAl magnets with improved magnetic properties for technological use. Full article

(This article belongs to the Special Issue Manganese-based Permanent Magnets)

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Influence of Annealing on Mechanical Properties of Al-20Si Processed by Selective Laser Melting

by Pan Ma, Konda G. Prashanth, Sergio Scudino, Yandong Jia, Hongwei Wang, Chunming Zou, Zunjie Wei and Jürgen Eckert

Metals 2014, 4(1), 28-36; https://doi.org/10.3390/met4010028 - 27 Jan 2014

Cited by 135 | Viewed by 14717

Abstract

The microstructure and mechanical properties of Al-20Si produced by selective laser melting (SLM) are investigated for different heat treatment conditions. As a result of the high cooling rate during processing, the as-built SLM material displays a microstructure consisting of a supersaturated Al(Si) solid [...] Read more.

The microstructure and mechanical properties of Al-20Si produced by selective laser melting (SLM) are investigated for different heat treatment conditions. As a result of the high cooling rate during processing, the as-built SLM material displays a microstructure consisting of a supersaturated Al(Si) solid solution along with heavily refined eutectic Si and Si particles. The Si particles become coarser, and the eutectic Si gradually changes its morphology from fibrous to plate-like shape with increasing annealing temperature. The microstructural variations occurring during heat treatment significantly affect the mechanical behavior of the samples. The yield and ultimate strengths decrease from 374 and 506 MPa for the as-built SLM material to 162 and 252 MPa for the sample annealed at 673 K, whereas the ductility increases from 1.6 to 8.7%. This offers the possibility to tune microstructure and corresponding properties of the Al-20Si SLM parts to meet specific requirements. Full article

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5734 KiB

Open AccessArticle

The Strengthening Effect of Phase Boundaries in a Severely Plastically Deformed Ti-Al Composite Wire

by Tom Marr, Jens Freudenberger, Verena Maier, Heinz Werner Höppel, Mathias Göken and Ludwig Schultz

Metals 2014, 4(1), 37-54; https://doi.org/10.3390/met4010037 - 07 Feb 2014

Cited by 4 | Viewed by 6477

Abstract

An accumulative swaging and bundling technique is used to prepare composite wires made of Ti and an Al alloy. These wires show reasonable higher yield stresses than expected from the pure material flow curves. The additional strengthening in the composite is analyzed using [...] Read more.

An accumulative swaging and bundling technique is used to prepare composite wires made of Ti and an Al alloy. These wires show reasonable higher yield stresses than expected from the pure material flow curves. The additional strengthening in the composite is analyzed using nanoindentation measurements, tensile testings and investigations of the microstructure. In addition, these properties are analyzed in relation to the fracture surface of the mechanically tested wires. Additional strengthening due to the presence of phase boundaries could be verified. Indications for residual stresses are found that cause a global hardness gradient from the center to the wire rim. Finally, the yield stress of the wires are calculated based on local hardness measurements. Full article

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3106 KiB

Open AccessArticle

Effect of ECAP Deformation Route on the Degree of Anisotropy of Microstructure of Extremely Low CN Fe-20mass%Cr Alloy

by Muhammad Rifai, Hiroyuki Miyamoto and Hiroshi Fujiwara

Metals 2014, 4(1), 55-63; https://doi.org/10.3390/met4010055 - 27 Feb 2014

Cited by 5 | Viewed by 6192

Abstract

The effect of the deformation route on the microstructural evolution of low CN Fe-20%Cr alloy by ECAP has been investigated, with a focus on the anisotropy of the microstructure. This alloy was pressed at 423 K from one, two and four passes via [...] Read more.

The effect of the deformation route on the microstructural evolution of low CN Fe-20%Cr alloy by ECAP has been investigated, with a focus on the anisotropy of the microstructure. This alloy was pressed at 423 K from one, two and four passes via routes A, Bc and C, and the microstructure was observed three dimensionally. As has been acknowledged, overall grain fragmentation proceeded most effectively in route Bc, and the highest hardness was obtained following routes C and A. However, the degree of anisotropy of microstructural development is different among the three deformation routes. The fractions of the high angle grain boundary (HAGB) and mean grain boundary misorientation were high and nearly isotropic in route Bc, whereas they are considerably low in one direction and highly anisotropic in routes A and C. Most importantly, those two parameters and hardness are the highest in route C if limited to the transverse direction, i.e., normal to both the insert and extruding directions. This result contrasts with FCC materials which most papers report as having the highest fraction of HAGB in route Bc. This result can be interpreted by the slip irreversibility of screw dislocations which is predominant in BCC metals. Full article

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Review

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Metal Matrix Composites Reinforced by Nano-Particles—A Review

by Riccardo Casati and Maurizio Vedani

Metals 2014, 4(1), 65-83; https://doi.org/10.3390/met4010065 - 10 Mar 2014

Cited by 809 | Viewed by 36779

Abstract

Metal matrix composites reinforced by nano-particles are very promising materials, suitable for a large number of applications. These composites consist of a metal matrix filled with nano-particles featuring physical and mechanical properties very different from those of the matrix. The nano-particles can improve [...] Read more.

Metal matrix composites reinforced by nano-particles are very promising materials, suitable for a large number of applications. These composites consist of a metal matrix filled with nano-particles featuring physical and mechanical properties very different from those of the matrix. The nano-particles can improve the base material in terms of wear resistance, damping properties and mechanical strength. Different kinds of metals, predominantly Al, Mg and Cu, have been employed for the production of composites reinforced by nano-ceramic particles such as carbides, nitrides, oxides as well as carbon nanotubes. The main issue of concern for the synthesis of these materials consists in the low wettability of the reinforcement phase by the molten metal, which does not allow the synthesis by conventional casting methods. Several alternative routes have been presented in literature for the production of nano-composites. This work is aimed at reviewing the most important manufacturing techniques used for the synthesis of bulk metal matrix nanocomposites. Moreover, the strengthening mechanisms responsible for the improvement of mechanical properties of nano-reinforced metal matrix composites have been reviewed and the main potential applications of this new class of materials are envisaged. Full article

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Metals, Volume 4, Issue 1 (March 2014) – 8 articles , Pages 1-83

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