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Metals, Volume 3, Issue 1 (March 2013), Pages 1-158

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Research

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Open AccessArticle Mechanical Properties and Tensile Failure Analysis of Novel Bio-absorbable Mg-Zn-Cu and Mg-Zn-Se Alloys for Endovascular Applications
Metals 2013, 3(1), 23-40; doi:10.3390/met3010023
Received: 22 November 2012 / Revised: 11 December 2012 / Accepted: 17 December 2012 / Published: 21 December 2012
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Abstract
In this paper, the mechanical properties and tensile failure mechanism of two novel bio-absorbable as-cast Mg-Zn-Se and Mg-Zn-Cu alloys for endovascular medical applications are characterized. Alloys were manufactured using an ARC melting process and tested as-cast with compositions of Mg-Zn-Se and Mg-Zn-Cu, being
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In this paper, the mechanical properties and tensile failure mechanism of two novel bio-absorbable as-cast Mg-Zn-Se and Mg-Zn-Cu alloys for endovascular medical applications are characterized. Alloys were manufactured using an ARC melting process and tested as-cast with compositions of Mg-Zn-Se and Mg-Zn-Cu, being 98/1/1 wt.% respectively. Nanoindentation testing conducted at room temperature was used to characterize the elastic modulus (E) and surface hardness (H) for both the bare alloys and the air formed oxide layer. As compared to currently available shape memory alloys and degradable as-cast alloys, these experimental alloys possess superior as-cast mechanical properties that can increase their biocompatibility, degradation kinetics, and the potential for medical device creation. Full article
Open AccessArticle Large Compressive Plasticity in a La-Based Glass-Crystal Composite
Metals 2013, 3(1), 41-48; doi:10.3390/met3010041
Received: 28 November 2012 / Revised: 16 December 2012 / Accepted: 18 December 2012 / Published: 27 December 2012
Cited by 6 | PDF Full-text (1164 KB) | HTML Full-text | XML Full-text
Abstract
La55Al25Cu10Ni10 metallic glass has been reinforced with 325-mesh Ta particles to obtain ex situ glass-crystal composites. The composites show a high compressive plasticity (40%) with a minor reduction (~8%) in yield strength—a combination unprecedented for La-based
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La55Al25Cu10Ni10 metallic glass has been reinforced with 325-mesh Ta particles to obtain ex situ glass-crystal composites. The composites show a high compressive plasticity (40%) with a minor reduction (~8%) in yield strength—a combination unprecedented for La-based systems and even surpassing some Zr-based glassy composites that utilize a tougher matrix. However, it is also found that the plastic strain is apparently sensitive to defects, like oxides, in the glassy matrix. Full article
(This article belongs to the Special Issue Amorphous Alloys)
Open AccessArticle Permeability of Aluminium Foams Produced by Replication Casting
Metals 2013, 3(1), 49-57; doi:10.3390/met3010049
Received: 18 September 2012 / Revised: 6 December 2012 / Accepted: 20 December 2012 / Published: 28 December 2012
Cited by 2 | PDF Full-text (783 KB) | HTML Full-text | XML Full-text
Abstract
The replication casting process is used for manufacturing open-pore aluminum foams with advanced performances, such as stability and repeatability of foam structure with porosity over 60%. A simple foam structure model based on the interaction between sodium chloride solid particles poorly wetted by
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The replication casting process is used for manufacturing open-pore aluminum foams with advanced performances, such as stability and repeatability of foam structure with porosity over 60%. A simple foam structure model based on the interaction between sodium chloride solid particles poorly wetted by melted aluminum, which leads to the formation of air pockets (or “air collars”), is proposed for the permeability of porous material. The equation for the minimum pore radius of replicated aluminum foam is derived. According to the proposed model, the main assumption of the permeability model consists in a concentration of flow resistance in a circular aperture of radius rmin. The permeability of aluminum open-pore foams is measured using transformer oil as the fluid, changing the fractions of initial sodium chloride. Measured values of minimum pore size are close to theoretically predicted ones regardless of the particle shape. The expression for the permeability of replicated aluminum foam derived on the basis of the “bottleneck” model of porous media agrees well with the experimental data. The obtained data can be applied for commercial filter cells and pneumatic silencers. Full article
Open AccessArticle Synthesis and Characterization of NanocrystallineMg-7.4%Al Powders Produced by Mechanical Alloying
Metals 2013, 3(1), 58-68; doi:10.3390/met3010058
Received: 28 November 2012 / Revised: 19 December 2012 / Accepted: 25 December 2012 / Published: 4 January 2013
Cited by 2 | PDF Full-text (1893 KB) | HTML Full-text | XML Full-text
Abstract
Nanocrystalline Mg-7.4%Al powder was prepared by mechanical alloying using a high-energy mill. The evolution of the various phases and their microstructure, including size and morphology of the powder particles in the course of milling and during subsequent annealing, were investigated in detail. Room
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Nanocrystalline Mg-7.4%Al powder was prepared by mechanical alloying using a high-energy mill. The evolution of the various phases and their microstructure, including size and morphology of the powder particles in the course of milling and during subsequent annealing, were investigated in detail. Room temperature milling leads to a rather heterogeneous microstructure consisting of two distinct regions: Al-free Mg cores and Mg-Al intermixed areas. As a result, the material is mechanically heterogeneous with the Mg cores displaying low hardness (40–50 HV) and the Mg-Al intermixed regions showing high hardness of about 170 HV. The Mg cores disappear and the microstructure becomes (also mechanically) homogeneous after subsequent cryo-milling. Rietveld structure refinement reveals that the crystallite size of the milled powders decreases with increasing the milling time reaching a minimum value of about 30 nm. This is corroborated by transmission electron microscopy confirming an average grain size of ~25 nm. Full article
Figures

Open AccessArticle Exchange Bias and Inverse Magnetocaloric Effect in Co and Mn Co-Doped Ni2MnGa Shape Memory Alloy
Metals 2013, 3(1), 69-76; doi:10.3390/met3010069
Received: 13 December 2012 / Revised: 8 January 2013 / Accepted: 17 January 2013 / Published: 25 January 2013
Cited by 4 | PDF Full-text (323 KB) | HTML Full-text | XML Full-text
Abstract
Exchange bias effect observed in the Ni1.68Co0.32Mn1.20Ga0.80 alloy confirms the coexistence of antiferromagnetic and ferromagnetic phases in the martensite phase. A large inverse magnetocaloric effect has been observed within the martensitic transformation temperature range, which is
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Exchange bias effect observed in the Ni1.68Co0.32Mn1.20Ga0.80 alloy confirms the coexistence of antiferromagnetic and ferromagnetic phases in the martensite phase. A large inverse magnetocaloric effect has been observed within the martensitic transformation temperature range, which is originated from modified magnetic order through magnetic-field-induced phase transformation from partially antiferromagnetic martensite to ferromagnetic austenite. The magnetic entropy change is 16.2 J kg−1 K−1 at 232 K under ΔH = 60 kOe, with the net refrigerant capacity of 68 J kg−1. These properties indicate Co and Mn co-doped Ni2MnGa alloy is a multifunctional material potentially suitable for magnetic refrigeration and spintronics applications. Full article
(This article belongs to the Special Issue Shape Memory Alloys)
Open AccessArticle Magnetic Moment of Cu-Modified Ni2MnGa Magnetic Shape Memory Alloys
Metals 2013, 3(1), 114-122; doi:10.3390/met3010114
Received: 4 January 2013 / Revised: 24 January 2013 / Accepted: 25 January 2013 / Published: 4 February 2013
Cited by 4 | PDF Full-text (192 KB) | HTML Full-text | XML Full-text
Abstract
The magnetization measurements at 5 K were carried out for Ni2Mn1xCuxGa (0 ≤ x ≤ 0.40) and Ni2MnGa1yCuy(0 ≤ y ≤ 0.25) alloys. All of the magnetization
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The magnetization measurements at 5 K were carried out for Ni2Mn1 xCuxGa (0 ≤ x ≤ 0.40) and Ni2MnGa1 yCuy (0 ≤ y ≤ 0.25) alloys. All of the magnetization curves are characteristic of ferromagnetism or ferrimagnetism. By using Arrott plot analysis the spontaneous magnetization of all samples was determined from the magnetization curves. The magnetic moment per formula unit, μs, at 5 K was estimated from the spontaneous magnetization. For Ni2Mn1 xCuxGa (0 ≤ x ≤ 0.40) alloys μs at 5 K decreases linearly with increasing x. On the other hand, the μs at 5 K for Ni2MnGa1 yCuy (0 ≤ y ≤ 0.25) alloys decreases more steeply with increasing x compared to the μs for Ni2Mn1 xCuxGa (0 ≤ x ≤ 0.40) alloys. On the basis of the experimental results, the site-occupation configurations of Ni2Mn1 xCuxGa (0 ≤ x ≤ 0.40) and Ni2MnGa1 yCuy (0 ≤ y ≤ 0.25) alloys are proposed. Full article
(This article belongs to the Special Issue Shape Memory Alloys)
Open AccessArticle Experimental Study of Helical Shape Memory Alloy Actuators: Effects of Design and Operating Parameters on Thermal Transients and Stroke
Metals 2013, 3(1), 123-149; doi:10.3390/met3010123
Received: 22 December 2012 / Revised: 3 February 2013 / Accepted: 5 February 2013 / Published: 18 February 2013
Cited by 6 | PDF Full-text (431 KB) | HTML Full-text | XML Full-text
Abstract
Shape memory alloy actuators’ strokes can be increased at the expense of recovery force via heat treatment to form compressed springs in their heat-activated, austenitic state. Although there are models to explain their behaviour, few investigations present experimental results for support or validation.
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Shape memory alloy actuators’ strokes can be increased at the expense of recovery force via heat treatment to form compressed springs in their heat-activated, austenitic state. Although there are models to explain their behaviour, few investigations present experimental results for support or validation. The aim of the present paper is to determine via experimentation how certain parameters affect a helical shape memory alloy actuator’s outputs: its transformation times and stroke. These parameters include wire diameter, spring diameter, transition temperature, number of active turns, bias force and direct current magnitude. Six investigations were performed: one for each parameter manipulation. For repeatability and to observe thermo-mechanical training effects, the springs were cyclically activated. The resultant patterns were compared with results predicted from one-dimensional models to elucidate the findings. Generally, it was observed that the transformation times and strokes converged at changing stress levels; the convergence is likely the peak where the summation of elastic stroke and transformation stroke has reached its maximum. During cyclic loading, the actuators’ strokes decreased to a converged value, particularly at larger internal stresses; training should therefore be performed prior to the actuator’s implementation for continual use applications. Full article
(This article belongs to the Special Issue Shape Memory Alloys)
Open AccessArticle Potential of Metal Fibre Felts as Passive Absorbers in Absorption Silencers
Metals 2013, 3(1), 150-158; doi:10.3390/met3010150
Received: 30 November 2012 / Revised: 19 February 2013 / Accepted: 22 February 2013 / Published: 5 March 2013
Cited by 3 | PDF Full-text (2955 KB) | HTML Full-text | XML Full-text
Abstract
The growing noise exposure of residents, due to a rising number of flights, causes significant impacts on physical health. Therefore it is necessary to reduce the noise emission of aircrafts. During take-off, the noise generated by the jet engines is dominating. One way
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The growing noise exposure of residents, due to a rising number of flights, causes significant impacts on physical health. Therefore it is necessary to reduce the noise emission of aircrafts. During take-off, the noise generated by the jet engines is dominating. One way to lower the noise emission of jet engines is to build an absorption silencer by using porous liners. Because of the high thermic and corrosive attacks as well as high fatigue loads, conventional absorbers cannot be used. A promising material is sintered metal fibre felts. This study investigates the suitability of metal fibre felts for the use as absorption material in silencers. The influences of pore morphology, absorption coefficient, determined with perpendicular sound incidence, as well as geometric parameters of the silencer to the damping are identified. To characterise the material, the parameters fibre diameter, porosity and thickness are determined using three-dimensional computer tomography images. The damping potential of absorption silencers is measured using an impedance tube, which was modified for transmission measurements. The essential parameter to describe the acoustic characteristics of porous materials is the flow resistivity. It depends on the size, shape and number of open pores in the material. Finally a connection between pore morphology, flow resistivity of the metal fibre felts and damping potential of the absorption silencer is given. Full article

Review

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Open AccessReview Mechanical Properties and Deformation Behavior of Bulk Metallic Glasses
Metals 2013, 3(1), 1-22; doi:10.3390/met3010001
Received: 2 November 2012 / Revised: 5 December 2012 / Accepted: 10 December 2012 / Published: 20 December 2012
Cited by 12 | PDF Full-text (418 KB) | HTML Full-text | XML Full-text
Abstract
Metallic glasses demonstrate unique properties, including large elastic limit and high strength, which make them attractive for practical applications. Unlike crystalline alloys, metallic glasses, in general, do not exhibit a strain hardening effect, while plastic deformation at room temperature is localized in narrow
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Metallic glasses demonstrate unique properties, including large elastic limit and high strength, which make them attractive for practical applications. Unlike crystalline alloys, metallic glasses, in general, do not exhibit a strain hardening effect, while plastic deformation at room temperature is localized in narrow shear bands. Room-temperature mechanical properties and deformation behavior of bulk metallic glassy samples and the crystal-glassy composites are reviewed in the present paper. Full article
(This article belongs to the Special Issue Amorphous Alloys)
Open AccessReview Mechanical Properties of Metallic Glasses
Metals 2013, 3(1), 77-113; doi:10.3390/met3010077
Received: 27 November 2012 / Revised: 17 January 2013 / Accepted: 28 January 2013 / Published: 31 January 2013
Cited by 24 | PDF Full-text (1838 KB) | HTML Full-text | XML Full-text
Abstract
Metallic glasses are known for their outstanding mechanical strength. However, the microscopic mechanism of failure in metallic glasses is not well-understood. In this article we discuss elastic, anelastic and plastic behaviors of metallic glasses from the atomistic point of view, based upon recent
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Metallic glasses are known for their outstanding mechanical strength. However, the microscopic mechanism of failure in metallic glasses is not well-understood. In this article we discuss elastic, anelastic and plastic behaviors of metallic glasses from the atomistic point of view, based upon recent results by simulations and experiments. Strong structural disorder affects all properties of metallic glasses, but the effects are more profound and intricate for the mechanical properties. In particular we suggest that mechanical failure is an intrinsic behavior of metallic glasses, a consequence of stress-induced glass transition, unlike crystalline solids which fail through the motion of extrinsic lattice defects such as dislocations. Full article

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