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

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Editorial

Jump to: Research, Review

Open AccessEditorial Acknowledgement to Reviewers of Metals in 2013
Metals 2014, 4(1), 64; doi:10.3390/met4010064
Received: 27 February 2014 / Accepted: 27 February 2014 / Published: 27 February 2014
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Abstract The editors of Metals would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...] Full article

Research

Jump to: Editorial, Review

Open AccessArticle A Concept for the Control of Pore Size in Superalloy Membranes
Metals 2014, 4(1), 1-7; doi:10.3390/met4010001
Received: 29 November 2013 / Revised: 19 December 2013 / Accepted: 23 December 2013 / Published: 9 January 2014
Cited by 1 | PDF Full-text (942 KB) | HTML Full-text | XML Full-text
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. [...] 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
Open AccessArticle Magnetism-Structure Correlations during the ε→τ Transformation in Rapidly-Solidified MnAl Nanostructured Alloys
Metals 2014, 4(1), 8-19; doi:10.3390/met4010008
Received: 13 December 2013 / Revised: 14 January 2014 / Accepted: 16 January 2014 / Published: 21 January 2014
Cited by 6 | PDF Full-text (606 KB) | HTML Full-text | XML Full-text
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 [...] 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 TB~95 K (Hex~13 kOe at 10 K), ascribed to the presence of compositional fluctuations in this antiferromagnetic phase. Heat treatment at a relatively low annealing temperature Tanneal ≈ 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)
Open AccessArticle Microstructure and Magnetic Properties of Bulk Nanocrystalline MnAl
Metals 2014, 4(1), 20-27; doi:10.3390/met4010020
Received: 18 December 2013 / Revised: 10 January 2014 / Accepted: 17 January 2014 / Published: 22 January 2014
Cited by 6 | PDF Full-text (1085 KB) | HTML Full-text | XML Full-text
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 [...] 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)
Open AccessArticle Influence of Annealing on Mechanical Properties of Al-20Si Processed by Selective Laser Melting
Metals 2014, 4(1), 28-36; doi:10.3390/met4010028
Received: 17 December 2013 / Revised: 12 January 2014 / Accepted: 22 January 2014 / Published: 27 January 2014
Cited by 14 | PDF Full-text (1532 KB) | HTML Full-text | XML Full-text
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) [...] 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
Open AccessArticle The Strengthening Effect of Phase Boundaries in a Severely Plastically Deformed Ti-Al Composite Wire
Metals 2014, 4(1), 37-54; doi:10.3390/met4010037
Received: 26 November 2013 / Revised: 16 January 2014 / Accepted: 23 January 2014 / Published: 7 February 2014
Cited by 2 | PDF Full-text (5734 KB) | HTML Full-text | XML Full-text
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 [...] 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
Open AccessArticle Effect of ECAP Deformation Route on the Degree of Anisotropy of Microstructure of Extremely Low CN Fe-20mass%Cr Alloy
Metals 2014, 4(1), 55-63; doi:10.3390/met4010055
Received: 20 December 2013 / Revised: 13 February 2014 / Accepted: 20 February 2014 / Published: 27 February 2014
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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 [...] 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

Review

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Open AccessReview Metal Matrix Composites Reinforced by Nano-Particles—A Review
Metals 2014, 4(1), 65-83; doi:10.3390/met4010065
Received: 16 December 2013 / Revised: 26 February 2014 / Accepted: 4 March 2014 / Published: 10 March 2014
Cited by 42 | PDF Full-text (649 KB) | HTML Full-text | XML Full-text
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 [...] 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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