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Metals, Volume 4, Issue 3 (September 2014), Pages 314-464

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Research

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Open AccessArticle Effect of Cu, Zn, and Mg Concentration on Heat Treating Behavior of Squeeze Cast Al-(10 to 12)Zn-(3.0 to 3.4)Mg-(0.8 to 1)Cu
Metals 2014, 4(3), 314-321; doi:10.3390/met4030314
Received: 16 May 2014 / Revised: 10 June 2014 / Accepted: 24 June 2014 / Published: 30 June 2014
Cited by 1 | PDF Full-text (878 KB) | HTML Full-text | XML Full-text
Abstract
Aluminum Alloy AA-7034 is a high strength wrought alloy with reasonable ductility containing 10–12 wt% Zn, 2–3 wt% Mg, and 0.8–1.2 wt% Cu. This work investigates the effect of varying the concentration of Zn (10–12 wt%) and Cu (0.8–1 wt%) on the [...] Read more.
Aluminum Alloy AA-7034 is a high strength wrought alloy with reasonable ductility containing 10–12 wt% Zn, 2–3 wt% Mg, and 0.8–1.2 wt% Cu. This work investigates the effect of varying the concentration of Zn (10–12 wt%) and Cu (0.8–1 wt%) on the solutionizing and aging behavior of squeeze cast AA-7034 samples. The same behaviors were investigated when Mg content was increased beyond 3 wt%. The solutionizing heat treatment dissolved much of the macroscopic second phases present in the as-cast AA-7034 alloys, but a significant amount of second phases remain after solutionizing in alloys with >3 wt% Mg. The behaviors of the various Al-Zn-Mg-Cu alloys are compared to squeeze cast Al-A206 casting alloy heat-treated to the T7 condition. All Al-Zn-Mg-Cu alloys obtained higher hardness values than those obtained by Al-A206-T7. Full article
Open AccessArticle Mineralogical Transformation and Electrochemical Nature of Magnesium-Rich Primers during Natural Weathering
Metals 2014, 4(3), 322-334; doi:10.3390/met4030322
Received: 15 May 2014 / Revised: 14 June 2014 / Accepted: 23 June 2014 / Published: 3 July 2014
Cited by 1 | PDF Full-text (2627 KB) | HTML Full-text | XML Full-text
Abstract
Magnesium-rich primers (MgRP) have generated great interest as a promising alternative to chromium-based primers for the protection of aluminum substrates but their performance during exterior exposure has not been well documented. This paper focuses on the evaluation of MgRP during natural weathering [...] Read more.
Magnesium-rich primers (MgRP) have generated great interest as a promising alternative to chromium-based primers for the protection of aluminum substrates but their performance during exterior exposure has not been well documented. This paper focuses on the evaluation of MgRP during natural weathering to gain insight into its mineralogical phase transformation and electrochemical nature. Control studies were conducted on Mg and AA2024-T3 coupons. The results indicate that Mg particles in MgRP transform into a variety of hydroxide, carbonate, and hydroxy carbonates. During natural weathering, CO2 inhibited the dissolution of both Mg and AA2024-T3 as a result of protective carbonate layer formation in the coating. Full article
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Open AccessArticle On the Physics of Machining Titanium Alloys: Interactions between Cutting Parameters, Microstructure and Tool Wear
Metals 2014, 4(3), 335-358; doi:10.3390/met4030335
Received: 9 May 2014 / Revised: 19 June 2014 / Accepted: 30 June 2014 / Published: 7 July 2014
Cited by 3 | PDF Full-text (2631 KB) | HTML Full-text | XML Full-text
Abstract
The current work deals with the analysis of mechanisms involved during the machining process of titanium alloys. Two different materials were chosen for the study: Ti-6Al-4V and Ti-55531. The objective was to understand the effect of all cutting parameters on the tool [...] Read more.
The current work deals with the analysis of mechanisms involved during the machining process of titanium alloys. Two different materials were chosen for the study: Ti-6Al-4V and Ti-55531. The objective was to understand the effect of all cutting parameters on the tool wear behavior and stability of the cutting process. The investigations were focused on the mechanisms of the chip formation process and their interaction with tool wear. At the microstructure scale, the analysis confirms the intense deformation of the machined surface and shows a texture modification. As the cutting speed increases, cutting forces and temperature show different progressions depending on the considered microstructure (Ti-6Al-4V or Ti-55531 alloy). Results show for both materials that the wear process is facilitated by the high cutting temperature and the generation of high stresses. The analysis at the chip-tool interface of friction and contact nature (sliding or sticking contact) shows that machining Ti55531 often exhibits an abrasion wear process on the tool surface, while the adhesion and diffusion modes followed by the coating delamination process are the main wear modes when machining the usual Ti-6Al-4V alloy. Full article
(This article belongs to the Special Issue Titanium Alloys)
Open AccessArticle Crystallization of Supercooled Liquid Elements Induced by Superclusters Containing Magic Atom Numbers
Metals 2014, 4(3), 359-387; doi:10.3390/met4030359
Received: 30 April 2014 / Revised: 10 July 2014 / Accepted: 16 July 2014 / Published: 6 August 2014
Cited by 5 | PDF Full-text (849 KB) | HTML Full-text | XML Full-text
Abstract
A few experiments have detected icosahedral superclusters in undercooled liquids. These superclusters survive above the crystal melting temperature Tm because all their surface atoms have the same fusion heat as their core atoms, and are melted by liquid homogeneous and heterogeneous [...] Read more.
A few experiments have detected icosahedral superclusters in undercooled liquids. These superclusters survive above the crystal melting temperature Tm because all their surface atoms have the same fusion heat as their core atoms, and are melted by liquid homogeneous and heterogeneous nucleation in their core, depending on superheating time and temperature. They act as heterogeneous growth nuclei of crystallized phase at a temperature Tc of the undercooled melt. They contribute to the critical barrier reduction, which becomes smaller than that of crystals containing the same atom number n. After strong superheating, the undercooling rate is still limited because the nucleation of 13-atom superclusters always reduces this barrier, and increases Tc above a homogeneous nucleation temperature equal to Tm/3 in liquid elements. After weak superheating, the most stable superclusters containing n = 13, 55, 147, 309 and 561 atoms survive or melt and determine Tc during undercooling, depending on n and sample volume. The experimental nucleation temperatures Tc of 32 liquid elements and the supercluster melting temperatures are predicted with sample volumes varying by 18 orders of magnitude. The classical Gibbs free energy change is used, adding an enthalpy saving related to the Laplace pressure change associated with supercluster formation, which is quantified for n = 13 and 55. Full article
(This article belongs to the Special Issue Liquid Metals)
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Open AccessArticle Investigation of Effect of Milling Atmosphere and Starting Composition on Mg2FeH6 Formation
Metals 2014, 4(3), 388-400; doi:10.3390/met4030388
Received: 17 July 2014 / Revised: 1 August 2014 / Accepted: 8 August 2014 / Published: 14 August 2014
Cited by 1 | PDF Full-text (2734 KB) | HTML Full-text | XML Full-text
Abstract
In this study we investigated the synthesis and the hydrogen storage properties of Mg2FeH6. The complex hydride was prepared by ball milling under argon and hydrogen atmosphere from 2Mg + Fe and 2MgH2 + Fe compositions. The [...] Read more.
In this study we investigated the synthesis and the hydrogen storage properties of Mg2FeH6. The complex hydride was prepared by ball milling under argon and hydrogen atmosphere from 2Mg + Fe and 2MgH2 + Fe compositions. The samples were characterized by X-ray powder diffraction and scanning electron microcopy. Kinetics of hydrogen absorption and desorption were measured in a Sievert’s apparatus. We found that the milling atmosphere plays a more important role on Mg2FeH6 synthesis than the starting compositions. Ball milling under hydrogen pressure resulted in smaller particles sizes and doubled the yield of Mg2FeH6 formation. Despite the microstructural differences after ball milling, all samples had similar hydrogen absorption and desorption kinetics. Loss of capacity was observed after only five cycles of hydrogen absorption/desorption. Full article
Open AccessArticle Fabrication and Mechanical Characterisation of Titanium Lattices with Graded Porosity
Metals 2014, 4(3), 401-409; doi:10.3390/met4030401
Received: 3 July 2014 / Revised: 22 July 2014 / Accepted: 8 August 2014 / Published: 14 August 2014
Cited by 10 | PDF Full-text (872 KB) | HTML Full-text | XML Full-text
Abstract
Electron Beam Melting (EBM) is an Additive Manufacturing technique which can be used to fabricate complex structures from alloys such as Ti6Al4V, for example for orthopaedic applications. Here we describe the use of EBM for the fabrication of a novel Ti6Al4V structure [...] Read more.
Electron Beam Melting (EBM) is an Additive Manufacturing technique which can be used to fabricate complex structures from alloys such as Ti6Al4V, for example for orthopaedic applications. Here we describe the use of EBM for the fabrication of a novel Ti6Al4V structure of a regular diamond lattice incorporating graded porosity, achieved via changes in the strut cross section thickness. Scanning Electron Microscopy and micro computed tomography analysis confirmed that generally EBM reproduced the CAD design of the lattice well, although at smaller strut sizes the fabricated lattice produced thicker struts than the model. Mechanical characterisation of the lattice in uniaxial compression showed that its behaviour under compression along the direction of gradation can be predicted to good accuracy with a simple rule of mixtures approach, knowing the properties and the behaviour of its constituent layers. Full article
Open AccessArticle A Multi-Scale Numerical Method for the Study of Size-Scale Effects in Ductile Fracture
Metals 2014, 4(3), 428-444; doi:10.3390/met4030428
Received: 9 June 2014 / Revised: 30 July 2014 / Accepted: 18 August 2014 / Published: 27 August 2014
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Abstract
The use of a stress-strain constitutive relation for the undamaged material and a traction-separation cohesive crack model with softening for cracking has been demonstrated to be an effective strategy to predict and explain the size-scale effects on the mechanical response of quasi-brittle [...] Read more.
The use of a stress-strain constitutive relation for the undamaged material and a traction-separation cohesive crack model with softening for cracking has been demonstrated to be an effective strategy to predict and explain the size-scale effects on the mechanical response of quasi-brittle materials. In metals, where ductile fracture takes place, the situation is more complex due to the interplay between plasticity and fracture. In the present study, we propose a multi-scale numerical method where the shape of a global constitutive relation used at the macro-scale, the so-called hardening cohesive zone model, can be deduced from meso-scale numerical simulations of polycrystalline metals in tension. The shape of this constitutive relation, characterized by an almost linear initial branch followed by a plastic plateau with hardening and finally by softening, is in fact the result of the interplay between two basic forms of nonlinearities: elasto-plasticity inside the grains and classic cohesive cracking for the grain boundaries. Full article
Open AccessArticle Closed-Cell Aluminum Foam of Improved Sound Absorption Ability: Manufacture and Properties
Metals 2014, 4(3), 445-454; doi:10.3390/met4030445
Received: 19 April 2014 / Revised: 14 July 2014 / Accepted: 7 August 2014 / Published: 28 August 2014
Cited by 1 | PDF Full-text (1814 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents a new method for the production of the closed-cell Al foams of improved sound absorbing ability. Final heat treatment procedure including heating below the solidus temperature followed by water quenching is proposed as an alternative method to machining, which [...] Read more.
The paper presents a new method for the production of the closed-cell Al foams of improved sound absorbing ability. Final heat treatment procedure including heating below the solidus temperature followed by water quenching is proposed as an alternative method to machining, which is used commonly for improvement of the sound absorption coefficient. Several kinds of foams based on AlZnMg-alloys comprising brittle eutectic domains of interdendritic redundant phase have been produced by the Alporas-like melting process to realize the method above. Opening of the closed cell structure required for ensuring high sound absorption ability has been achieved by cracking the walls between neighboring cells, making them gas permeable. They ultimately looked like Helmholtz micro-perforated resonators. Processing parameters and other variables that are favorable both for foaming regime and for final heat treatment are discussed and specified. Full article
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Open AccessArticle Electronic Structure and Maximum Energy Product of MnBi
Metals 2014, 4(3), 455-464; doi:10.3390/met4030455
Received: 30 June 2014 / Revised: 20 August 2014 / Accepted: 21 August 2014 / Published: 29 August 2014
Cited by 5 | PDF Full-text (1209 KB) | HTML Full-text | XML Full-text
Abstract
We have performed first-principles calculations to obtain magnetic moment, magnetocrystalline anisotropy energy (MAE), i.e., the magnetic crystalline anisotropy constant (K), and the Curie temperature (Tc) of low temperature phase (LTP) MnBi and also estimated the maximum [...] Read more.
We have performed first-principles calculations to obtain magnetic moment, magnetocrystalline anisotropy energy (MAE), i.e., the magnetic crystalline anisotropy constant (K), and the Curie temperature (Tc) of low temperature phase (LTP) MnBi and also estimated the maximum energy product (BH)max at elevated temperatures. The full-potential linearized augmented plane wave (FPLAPW) method, based on density functional theory (DFT) within the local spin density approximation (LSDA), was used to calculate the electronic structure of LPM MnBi. The Tc was calculated by the mean field theory. The calculated magnetic moment, MAE, and Tc are 3.63 μB/f.u. (formula unit) (79 emu/g or 714 emu/cm3), −0.163 meV/u.c. (or K = −0.275 × 106 J/m3) and 711 K, respectively. The (BH)max at the elevated temperatures was estimated by combining experimental coercivity (Hci) and the temperature dependence of magnetization (Ms(T)). The (BH)max is 17.7 MGOe at 300 K, which is in good agreement with the experimental result for directionally-solidified LTP MnBi (17 MGOe). In addition, a study of electron density maps and the lattice constant c/a ratio dependence of the magnetic moment suggested that doping of a third element into interstitial sites of LTP MnBi can increase the Ms. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)

Review

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Open AccessReview The Atomistic Structure of Metal/Ceramic Interfaces Is the Key Issue for Developing Better Properties
Metals 2014, 4(3), 410-427; doi:10.3390/met4030410
Received: 3 June 2014 / Revised: 9 August 2014 / Accepted: 11 August 2014 / Published: 20 August 2014
Cited by 2 | PDF Full-text (1444 KB) | HTML Full-text | XML Full-text
Abstract
Metal-metal-, ceramic-metal-composites (MMC, CMC) and related functional materials are steadily gaining interest for practical applications. This invited overview paper is divided into three parts. First, the importance of interfaces in material science is emphasized, then basics of computer modeling of interfaces on [...] Read more.
Metal-metal-, ceramic-metal-composites (MMC, CMC) and related functional materials are steadily gaining interest for practical applications. This invited overview paper is divided into three parts. First, the importance of interfaces in material science is emphasized, then basics of computer modeling of interfaces on atomic scale is outlined, followed by the description of some interface examples and their applications. Atomistic modeling requires the specific determination of the orientation relationship between both crystal lattices facing the heterogeneous interface, the interface plane, and translation vectors of two facing crystals. Examples of the atomistic structure are described in this paper for interfaces, such as MgO/Ag, MgO/TiN, Al2O3/Fe, and others. The trend in this research is gradually, but steadily shifting from structural towards functional materials, because atomic binding at interfaces offers a broad spectrum of new properties to be utilized for applications. Full article
(This article belongs to the Special Issue Advances in Cermets)
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