Next Issue
Previous Issue

Table of Contents

Metals, Volume 2, Issue 2 (June 2012), Pages 79-218

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-11
Export citation of selected articles as:

Research

Open AccessArticle Production and Characterization of Brass-matrix Composites Reinforced with Ni59Zr20Ti16Si2Sn3 Glassy Particles
Metals 2012, 2(2), 79-94; doi:10.3390/met2020079
Received: 12 April 2012 / Accepted: 8 May 2012 / Published: 15 May 2012
Cited by 11 | PDF Full-text (787 KB) | HTML Full-text | XML Full-text
Abstract
Brass-matrix composites reinforced with 40 and 60 vol.% of Ni59Zr20Ti16Si2Sn3 glassy particles were produced by powder metallurgy. The crystallization behavior and the temperature dependence of the viscosity of the glass reinforcement were studied [...] Read more.
Brass-matrix composites reinforced with 40 and 60 vol.% of Ni59Zr20Ti16Si2Sn3 glassy particles were produced by powder metallurgy. The crystallization behavior and the temperature dependence of the viscosity of the glass reinforcement were studied in detail to select the proper sintering parameters in order to avoid crystallization of the glassy phase during consolidation. The brass-glass powder mixtures were prepared through manual blending as well as by ball milling to analyze the effect of the matrix ligament size on the mechanical properties of the composites. The powder mixtures were then consolidated into highly-dense bulk specimens at temperatures within the supercooled liquid region by hot pressing followed by hot extrusion. The preparation of the powder mixtures has a strong influence on the mechanical behavior of the composites. The strength increases from 500 MPa for pure brass to 740 and 925 MPa for the blended composites with 40 and 60vol.% of glass reinforcement, while the strength increases to 1,240 and 1,640 MPa for the corresponding composites produced by ball milling. Modeling of the mechanical properties indicates that this behavior is related to the reduced matrix ligament size characterizing the milled composites. Full article
Open AccessArticle The Role of Foaming Agent and Processing Route in the Mechanical Performance of Fabricated Aluminum Foams
Metals 2012, 2(2), 95-112; doi:10.3390/met2020095
Received: 30 March 2012 / Revised: 30 April 2012 / Accepted: 9 May 2012 / Published: 23 May 2012
Cited by 5 | PDF Full-text (879 KB) | HTML Full-text | XML Full-text
Abstract
The results of the present study highlight the role of foaming agent and processing route in influencing the contamination of cell wall material by side products, which, in turn, affect the macroscopic mechanical response of closed-cell Al-foams. Several kinds of Al-foams have [...] Read more.
The results of the present study highlight the role of foaming agent and processing route in influencing the contamination of cell wall material by side products, which, in turn, affect the macroscopic mechanical response of closed-cell Al-foams. Several kinds of Al-foams have been produced with pure Al by the Alporas melt process and powder metallurgical technique, all performed either with conventional TiH2 foaming agent or CaCO3 as an alternative. Mechanical characteristics of contaminating products induced by processing additives, all of which were presented in one or another kind of Al-foam, have been determined in indentation experiments. Damage behavior of these contaminations affects the micro-mechanism of deformation and favors either plastic buckling or brittle failure of the cell walls. It is justified that there is no discrepancy between experimental values of compressive strengths for Al-foams comprising ductile Al + Al4Ca eutectic domains and those prescribed by theoretical models for closed-cell structure. However, the presence of low ductile Al + Al3Ti + Al4Ca eutectic domains and brittle particles/layers of Al3Ti, fine CaCO3/CaO particles, Al2O3 oxide network, and, especially, residues of partially reacted TiH2, results in reducing the compressive strength to values close to or even below those of open-cell foams of the same relative density. Full article
(This article belongs to the Special Issue Metal Foams)
Open AccessArticle Thermal Conductivity Computations of Sintered Hollow Sphere Structures
Metals 2012, 2(2), 113-121; doi:10.3390/met2020113
Received: 17 April 2012 / Revised: 10 May 2012 / Accepted: 14 May 2012 / Published: 30 May 2012
Cited by 2 | PDF Full-text (339 KB) | HTML Full-text | XML Full-text
Abstract
The thermal conductivity of sintered hollow sphere structures (HSS) is investigated within the scope of this paper. For this purpose, finite element analyses based on micro-computed tomography images are performed on HSS structures. The complex geometry of the real sintered HSS sample [...] Read more.
The thermal conductivity of sintered hollow sphere structures (HSS) is investigated within the scope of this paper. For this purpose, finite element analyses based on micro-computed tomography images are performed on HSS structures. The complex geometry of the real sintered HSS sample is accurately captured with this new hybrid method. The numerical computations are investigated in three perpendicular directions (i.e., x, y and z) in order to examine the anisotropic material behaviour. The results indicate that sintered HSS reveals quasi-isotropic behaviour in terms of effective thermal conductivity. For the first time, the influence of the sphere wall thickness of real HSS is investigated. To this end, the computed tomography data is carefully manipulated by changing the thickness of the hollow sphere wall. The variation of the wall thickness alters the relative density and has a significant influence on the thermal conductivity. The influence of the relative density on the thermal conductivity reveals a linear dependency. Full article
Open AccessArticle Characterisation and Mechanical Testing of Open Cell Al Foams Manufactured by Molten Metal Infiltration of Porous Salt Bead Preforms: Effect of Bead Size
Metals 2012, 2(2), 122-135; doi:10.3390/met2020122
Received: 16 April 2012 / Revised: 17 May 2012 / Accepted: 28 May 2012 / Published: 1 June 2012
Cited by 3 | PDF Full-text (2828 KB) | HTML Full-text | XML Full-text
Abstract
Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration [...] Read more.
Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration of molten Al occurred into beads of all sizes and was predicted using a simple model. The yield strength of the porous structures increased with increasing density and decreasing pore (bead) size. Despite the non-optimum distribution of metal in the porous structure, due to partial infiltration within the beads, the magnitude and density dependence of the yield stress were comparable with those for pure Al foams reported in similar studies. The structural efficiency was improved for structures produced at lower infiltration pressure, where the metal is predominantly distributed in the cell walls. The rate of salt dissolution from the preforms was high, in particular for high density preforms, large beads and preforms infiltrated at low pressures, owing to the ability of the porous beads to collapse as well as dissolve. Full article
Open AccessArticle Molding of Aluminum Foams by Using Hot Powder Extrusion
Metals 2012, 2(2), 136-142; doi:10.3390/met2020136
Received: 29 March 2012 / Revised: 9 May 2012 / Accepted: 25 May 2012 / Published: 5 June 2012
Cited by 4 | PDF Full-text (281 KB) | HTML Full-text | XML Full-text
Abstract
In order to form aluminum foams directly from powder, a combined process of hot powder extrusion and molding is proposed. Aluminum powder mixed with a foaming agent is extruded into the mold through the die heated to a temperature higher than the [...] Read more.
In order to form aluminum foams directly from powder, a combined process of hot powder extrusion and molding is proposed. Aluminum powder mixed with a foaming agent is extruded into the mold through the die heated to a temperature higher than the melting point, and the mold is filled with the aluminum foam. When a stainless steel pipe is used for a simple mold, an aluminum foam bar is obtained of which the relative density varies between 0.2 and 0.3. The molding of aluminum foam by using three types of mold shape shows the influence of gravity and friction. The effect of gravity is significant when a large step exists at the connection between the mold inlet and the die outlet, and friction is dominant in cases where foam is mold in a narrow space. Full article
Open AccessArticle Influence of Nickel Particle Reinforcement on Cyclic Fatigue and Final Fracture Behavior of a Magnesium Alloy Composite
Metals 2012, 2(2), 143-169; doi:10.3390/met2020143
Received: 12 April 2012 / Revised: 25 May 2012 / Accepted: 29 May 2012 / Published: 7 June 2012
Cited by 2 | PDF Full-text (8203 KB) | HTML Full-text | XML Full-text
Abstract
The microstructure, tensile properties, cyclic stress amplitude fatigue response and final fracture behavior of a magnesium alloy, denoted as AZ31, discontinuously reinforced with nano-particulates of aluminum oxide and micron size nickel particles is presented and discussed. The tensile properties, high cycle fatigue [...] Read more.
The microstructure, tensile properties, cyclic stress amplitude fatigue response and final fracture behavior of a magnesium alloy, denoted as AZ31, discontinuously reinforced with nano-particulates of aluminum oxide and micron size nickel particles is presented and discussed. The tensile properties, high cycle fatigue and final fracture behavior of the discontinuously reinforced magnesium alloy are compared with the unreinforced counterpart (AZ31). The elastic modulus and yield strength of the dual particle reinforced magnesium alloy is marginally higher than of the unreinforced counterpart. However, the tensile strength of the composite is lower than the monolithic counterpart. The ductility quantified by elongation to failure over 0.5 inch (12.7 mm) gage length of the test specimen showed minimal difference while the reduction in specimen cross-section area of the composite is higher than that of the monolithic counterpart. At the microscopic level, cyclic fatigue fractures of both the composite and the monolithic alloy clearly revealed features indicative of the occurrence of locally ductile and brittle mechanisms. Over the range of maximum stress and at two different load ratios the cyclic fatigue resistance of the magnesium alloy composite is superior to the monolithic counterpart. The mechanisms responsible for improved cyclic fatigue life and resultant fracture behavior of the composite microstructure are highlighted. Full article
(This article belongs to the Special Issue Magnesium Technology)
Open AccessArticle Mitigation of Blast Effects on Protective Structures by Aluminum Foam Panels
Metals 2012, 2(2), 170-177; doi:10.3390/met2020170
Received: 13 April 2012 / Revised: 16 May 2012 / Accepted: 1 June 2012 / Published: 11 June 2012
Cited by 4 | PDF Full-text (824 KB) | HTML Full-text | XML Full-text
Abstract
Aluminum foams have low density and are attractive materials to mitigate high-speed pressure by blast loads due to high-energy absorption capabilities. In order to develop nonlinear material models for the aluminum foam with different density, mechanical properties of the foam and foam [...] Read more.
Aluminum foams have low density and are attractive materials to mitigate high-speed pressure by blast loads due to high-energy absorption capabilities. In order to develop nonlinear material models for the aluminum foam with different density, mechanical properties of the foam and foam panels under compression, tension, shear and bending moment were obtained by numerous tests. Through the explicit analyses of the foam panels by LS-DYNA, the derived models were verified. Performance of the foam panels with different scaled distances was evaluated by blast tests. Thickness, density and skin plate properties of the panel are the most important parameters to estimate the transmitted pressure to protective structures. Because the pressure of close range blast loading is not uniform, the skin plays an important role in the behavior of the foam. Numerical simulations considering the parameters provided basic design guidelines for the protective structures with sacrificial foam panels. Properly designed panels for the required blast loads can control the transmitted pressure to the target structure under a certain pressure on the yield strength of the foam. Full article
Figures

Open AccessArticle Microstructure and Mechanical Properties of Mg-5Nb Metal-Metal Composite Reinforced with Nano SiC Ceramic Particles
Metals 2012, 2(2), 178-194; doi:10.3390/met2020178
Received: 14 May 2012 / Revised: 4 June 2012 / Accepted: 6 June 2012 / Published: 11 June 2012
Cited by 2 | PDF Full-text (4887 KB) | HTML Full-text | XML Full-text
Abstract
In this work, a Mg-5Nb metal–metal composite was reinforced with nano SiC (SiCn) ceramic reinforcement of varying volume fractions, using the disintegrated melt deposition technique. The extruded Mg-5Nb-SiCn composites were characterized for their microstructure and mechanical properties. Based on [...] Read more.
In this work, a Mg-5Nb metal–metal composite was reinforced with nano SiC (SiCn) ceramic reinforcement of varying volume fractions, using the disintegrated melt deposition technique. The extruded Mg-5Nb-SiCn composites were characterized for their microstructure and mechanical properties. Based on the results obtained, it was observed that the volume fraction of nano-SiC reinforcement played an important role in determining the grain size and improving the mechanical properties. A comparison of properties with those of pure Mg and Mg-5Nb composite showed that while the improvement in hardness occurred at all volume fractions, a minimum volume fraction of ~0.27% SiCn was required to increase the tensile and compressive strengths. The observed mechanical response of the composites were investigated in terms of the effect of SiCn volume fraction, processing, distribution of metallic and ceramic reinforcements and the inherent properties of the matrix and reinforcements. The influences of these factors on the mechanical behavior of the composites are understood based on the structure–property relationship. Full article
(This article belongs to the Special Issue Magnesium Technology)
Open AccessArticle Noise Reduction Potential of Cellular Metals
Metals 2012, 2(2), 195-201; doi:10.3390/met2020195
Received: 15 April 2012 / Revised: 29 May 2012 / Accepted: 7 June 2012 / Published: 12 June 2012
Cited by 4 | PDF Full-text (317 KB) | HTML Full-text | XML Full-text
Abstract
Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 [...] Read more.
Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C only metallic or ceramic structures can be used. Due to fatigue loading and the notch effect of the pores, mechanical properties of porous metals are superior to the ones of ceramic structures. Consequently, cellular metals like metallic foams, sintered metals, or sintered metal felts are most promising materials. However, acoustic absorption depends highly on pore morphology and porosity. Therefore, both parameters must be characterized precisely to analyze the correlation between morphology and noise reduction performance. The objective of this study is to analyze the relationship between pore morphology and acoustic absorption performance. The absorber materials are characterized using image processing based on two dimensional microscopy images. The sound absorption properties are measured using an impedance tube. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined. Full article
Open AccessArticle Gas Atomization of Aluminium Melts: Comparison of Analytical Models
Metals 2012, 2(2), 202-210; doi:10.3390/met2020202
Received: 31 March 2012 / Revised: 28 May 2012 / Accepted: 6 June 2012 / Published: 18 June 2012
Cited by 3 | PDF Full-text (221 KB) | HTML Full-text | XML Full-text
Abstract
A number of analytical models predicting the size distribution of particles during atomization of Al-based alloys by N2, He and Ar gases were compared. Simulations of liquid break up in a close coupled atomizer revealed that the finer particles are [...] Read more.
A number of analytical models predicting the size distribution of particles during atomization of Al-based alloys by N2, He and Ar gases were compared. Simulations of liquid break up in a close coupled atomizer revealed that the finer particles are located near the center of the spray cone. Increasing gas injection pressures led to an overall reduction of particle diameters and caused a migration of the larger powder particles towards the outer boundary of the flow. At sufficiently high gas pressures the spray became monodisperse. The models also indicated that there is a minimum achievable mean diameter for any melt/gas system. Full article
Open AccessArticle Dynamic Behavior of Hybrid APM (Advanced Pore Morphology Foam) and Aluminum Foam Filled Structures
Metals 2012, 2(2), 211-218; doi:10.3390/met2020211
Received: 3 May 2012 / Revised: 29 May 2012 / Accepted: 11 June 2012 / Published: 20 June 2012
Cited by 5 | PDF Full-text (1433 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this work is to evaluate the effect of different densities of hybrid aluminum polymer foam on the frequency behavior of a foam filled steel structure with different ratios between steel and foam masses. The foam filled structure is composed [...] Read more.
The aim of this work is to evaluate the effect of different densities of hybrid aluminum polymer foam on the frequency behavior of a foam filled steel structure with different ratios between steel and foam masses. The foam filled structure is composed of three steel tubes with a welded flange at both ends bolted together to form a portal grounded by its free ends. Structure, internal and ground constraints have been designed and manufactured in order to minimize nonlinear effects and to guarantee optimal constraint conditions. Mode shapes and frequencies were verified with finite elements models (FEM) to be in the range of experimental modal analysis, considering the frequency measurement range limits for instrumented hammer and accelerometer. Selected modes have been identified with suitable modal parameters extraction techniques. Each structure has been tested before and after filling, in order to compute the percentage variation of modal parameters. Two different densities of hybrid aluminum polymer foam have been tested and compared with structures filled with aluminum foams produced using the powder compact melting technique. All the foam fillings were able to suppress high frequency membrane modes which results in a reduction of environmental noise and an increase in performance of the components. Low frequency modes show an increase in damping ratio only when small thickness steel frames are filled with either Hybrid APM or Alulight foam. Full article

Journal Contact

MDPI AG
Metals Editorial Office
St. Alban-Anlage 66, 4052 Basel, Switzerland
metals@mdpi.com
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
Editorial Board
Contact Details Submit to Metals
Back to Top