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Showing papers in "Advanced Engineering Materials in 2004"


Journal ArticleDOI
TL;DR: A new approach for the design of alloys is presented in this paper, where high-entropy alloys with multi-principal elements were synthesized using well-developed processing technologies.
Abstract: A new approach for the design of alloys is presented in this study. These high-entropy alloys with multi-principal elements were synthesized using well-developed processing technologies. Preliminary results demonstrate examples of the alloys with simple crystal structures, nanostructures, and promising mechanical properties. This approach may be opening a new era in materials science and engineering.

8,175 citations



Journal ArticleDOI
TL;DR: In this paper, multi-principal element alloy coatings of Al-Si alloys were prepared by a plasma spray method and they not only exhibited a good oxidation resistance up to 1000 °C, but also possessed an excellent abrasive wear resistance approximately two times higher than those of SUJ2 and SKD61.
Abstract: Multi-principal-element alloy coatings of Al-Si alloys were prepared by a plasma spray method They not only exhibited a good oxidation resistance up to 1000 °C, but also possessed an excellent abrasive wear resistance approximately two times higher than those of SUJ2 and SKD61 Moreover, they displayed a high temperature precipitation hardening phenomenon up to 1100 °C which is novel and seldom found in conventional alloys

573 citations


Journal ArticleDOI
TL;DR: A review of powder-metallurgy-based techniques for titanium foam processing can be found in this article, where a first group of processes is based on powder sintering with or without place-holder or scaffolds, and a second group relies on expansion of pressurized pores created during prior powder densification.
Abstract: Because of their excellent mechanical properties, low density and biocompatibility, titanium foams are attractive for structural and biomedical applications. This paper reviews current techniques for titanium foam processing, which are all based on powder-metallurgy because of the extreme reactivity of liquid titanium. A first group of processes is based on powder sintering with or without place-holder or scaffolds. A second group relies on expansion of pressurized pores created during prior powder densification.

289 citations


Journal ArticleDOI
TL;DR: In this article, the principles of the sawing process are described as far as they are understood today, as well as their application in the solar cell process and its application in solar cells.
Abstract: More than 80 % of the current solar cell production requires the cutting of large silicon crystals. While in the last years the cost of solar cell processing and module fabrication could be reduced considerably, the sawing costs remain high, about 30 % of the wafer production. At present the large crystals are cut using the multi-wire slicing technology [2] which has the advantage of a high throughput (several hundred wafers per day and machine), a small kerf loss of about 180 μm and almost no restrictions on the size of the ingots. Basic knowledge about the microscopic details of the sawing process is required in order to slice crystals in a controlled way. In the following the principles of the sawing process will be described in this review article as far as they are understood today.

201 citations


Journal ArticleDOI
TL;DR: In this article, it is shown that powder metallurgy plays an important role in research and development of γ-TiAl-based alloys and that PM is an ancient technology which has been used for the processing for almost every metal or ceramic material.
Abstract: Intermetallic γ-TiAl-based alloys represent a new class of light-weight structural materials for use at high temperatures. Because of their unique properties these alloys are considered for applications in aerospace and automotive industries. During the last decade both, alloy development and materials processing progressed significantly. New materials and powder metallurgy (PM) have formed a symbiosis since many decades. In fact, PM is an ancient technology which has been used for the processing for almost every metal or ceramic material. Therefore, it is hardly surprising that PM plays an important role in research and development of γ-TiAl-based alloys.

175 citations



Journal ArticleDOI
TL;DR: In this paper, the effect of a corrosive media and elevated temperatures on the fatigue behavior of magnesium alloys has been investigated and a very important aspect in fatigue of the material is the influence of elevated temperatures.
Abstract: Magnesium alloys show a high specific strength and are therefore increasingly used for light-weight constructions in transportation industry.[1,2] To predict the behaviour of the material under the influence of cyclic loading it is vital to understand the fatigue behaviour of magnesium alloys. Only when understood properly, it is possible to fully apply the potential weight reduction by using magnesium alloys. A very important aspect in fatigue of magnesium alloys is the influence of a corrosive media and elevated temperatures, of which both are relevant in automotive applications. These two factors tend to have deleterious effects on magnesium alloys and therefore also have to be considered in investigations on the fatigue behaviour of magnesium alloys.

165 citations


Journal ArticleDOI
TL;DR: The hydrogen-metal system can be used as a model alloy to study small size features: shifted phase boundaries and sloped isotherms are found and, also, new materials structures as mentioned in this paper.
Abstract: Systems with small sizes show significant changes compared to the bulk system. These changes are of major interest regarding the size reduction of technological applications. The hydrogen-metal system can be used as a model alloy to study small size features: shifted phase boundaries and sloped isotherms are found and, also, new materials structures. Most features can be attributed to surface- and interface contributions as well as to mechanical stress.

128 citations


Journal ArticleDOI
TL;DR: In this paper, the capability of the CVD technique to produce uniform foams of different properties, with cell size ranging from ∼ 450 to ∼ 3200 μm, porosity from ∼ 70 to ∼ 98 %, and nominal thickness up to 3 mm is presented.
Abstract: In this paper, the capability of the CVD technique to produce uniform foams of different properties, with cell size ranging from ∼ 450 to ∼ 3200 μm, porosity from ∼ 70 to ∼ 98 %, and nominal thickness up to 3 mm is presented. In addition to the established application as a battery electrode material, some other potential capabilities and applications are explored.

111 citations


Journal ArticleDOI
TL;DR: In this paper, an ultra-high-temperature ceramic (UHTC) based on HfB 2 was produced, which consisted of fine and regular diboride grains with SiC particulate distributed intergranularly, not rarely in clustered formation, and low levels of secondary phases were identified.
Abstract: An ultra-high-temperature ceramic (UHTC) based on HfB 2 was produced. The microstructure consisted of fine and regular diboride grains (2 μm average size), with SiC particulate distributed intergranularly, not rarely in clustered formation, and low levels of secondary phases were identified. The resulting thermo-mechanical properties proved interesting results for microhardness and fracture toughness. The microstructural alteration experienced within the explored temperature range renders the material unsuitable for service in extreme conditions of temperature and pressure.

Journal ArticleDOI
TL;DR: In this article, the authors reported that amorphous silicoaluminum carbonitride (SiAlCN) ceramics possess anomalously high resistance to oxidation and hot-corrosion.
Abstract: In this communication we report for the first time that amorphous silicoaluminum carbonitride (SiAlCN) ceramics possess anomalously high resistance to oxidation and hot-corrosion. The materials were synthesized by thermal decomposition of polymer precursors.([18]) The oxidation kinetics of the materials was determined at 1 200 degrees C in dry air by measuring the thickness of the oxide scale as a function of annealing times up to 200 h. The hot-corrosion behavior was studied by scanning electron microscopy (SEM) observation on the surfaces of the materials that were annealed in either NaCl or water vapor environments at 1 200 degrees C for 50 h. The experiments were performed on two SiAlCN ceramics with different aluminum content (see table 1); the hot-corrosion experiments were also performed on SiCN without aluminum for comparison. A mechanism underlying the observed phenomena is discussed


Journal ArticleDOI
TL;DR: In this article, the effect of chemical composition on the structure of Cr-Al-C was studied by combinatorial thin film synthesis, and the results showed that the lattice parameters of Cr 2 AlC were independent of the chemical composition.
Abstract: The effect of the chemical composition on the structure of Cr-Al-C was studied by combinatorial thin film synthesis. By changing the Cr/C ratio from 1.72 to 3.48 and the Cr/Al ratio from 1.42 to 4.18 the formation of Cr 2 AlC, Cr 2 Al and Cr 23 C 6 phases was observed. Furthermore, based on X-ray diffraction a single phase Cr 2 AlC composition region is identified in the Cr-Al-C phase diagram. Throughout the studied composition range the lattice parameters of Cr 2 AlC were independent of the chemical composition.

Journal ArticleDOI
TL;DR: The Web of Science Record was created on 2005-01-12, modified on 2016-08-08 by as discussed by the authors, who used LTP-ARTICLE-2004-001.
Abstract: Reference LTP-ARTICLE-2004-001doi:10.1002/adem.200300574View record in Web of Science Record created on 2005-01-12, modified on 2016-08-08

Journal ArticleDOI
TL;DR: In this paper, the first attempt to fill polymers with hollow solid lubricant nanoparticles was made and it was found that application of the fullerene-like (IF) WS 2 or MoS 2 solid lubricants led to a considerable improvements in the tribological behavior of the nanocomposites.
Abstract: Recent experiments showed that the addition of inorganic fullerene-like (IF) WS 2 or MoS 2 solid lubricant nanoparticles in oil, grease or impregnated into porous matrix provides remarkable lubricating properties of friction pairs in a wide range of operating conditions. Inorganic nanoparticles filled polymer composites show low friction and high wear resistance. This work reports the first attempt to fill polymers with hollow solid lubricant nanoparticles. It was found that application of the IF solid lubricant nanoparticles leads to a considerable improvements in the tribological behavior of the nanocomposites. The morphology of the surface layers and the mechanism of the friction reduction by the IF nanoparticles are discussed.

Journal ArticleDOI
TL;DR: In this article, a continuous zone melting technique was developed to fabricate long rod and plate-shape porous metals and alloys even with low thermal conductivity, and the physical properties of these materials were described together with internal friction, elasticity, thermal conductivities and sound absorption characteristics.
Abstract: Lotus-type porous metals whose long cylindrical pores are aligned in one direction were fabricated by unidirectional solidification in a pressurized gas atmosphere. The pores are formed as a result of precipitation of supersaturated gas when liquid metal is solidified. The lotus-type porous metals with homogeneous size and porosity of the evolved pores produced by a mould casting technique are limited to the metals with high thermal conductivity. On the other hand, the pores with inhomogeneous pore size and porosity are evolved for metals and alloys with low thermal conductivity such as stainless steel. In order to obtain uniform pore size and porosity, a new “continuous zone melting technique” was developed to fabricate long rod- and plate-shape porous metals and alloys even with low thermal conductivity. Mechanical properties of tensile and compressive strength of lotus-type porous metals and alloys are described together with internal friction, elasticity, thermal conductivity and sound absorption characteristics. All the physical properties exhibit significant anisotropy. Lotus-type porous iron fabricated using a pressurized nitrogen gas instead of hydrogen exhibits superior strength.

Journal ArticleDOI
TL;DR: In this paper, a measurement apparatus for observing the foaming of metals is described, consisting of a microfocus X-ray source, a small heater and a panel detector, which can be recorded in real-time with frequencies up to 9 Hz and resolutions down to 5 μm due to the small spot size.
Abstract: A measurement apparatus for observing the foaming of metals is described. It consists of a microfocus X-ray source, a small heater and a panel detector. The foaming of samples can be recorded in real-time with frequencies up to 9 Hz and resolutions down to 5 μm due to the small spot size. Magnifications up to 10x are obtained by simply changing the distance between source, sample and detector. Foaming of Al alloys and sandwiches was investigated applying different final foaming temperatures, heating rates and blowing agent pre-treatments. An image analysis program was developed to automatically recognise the foam expansion.

Journal ArticleDOI
TL;DR: In this paper, the relationship between composition, structure and properties of transition metal oxides with perovskite-type structure (AMX3-δ) is investigated.
Abstract: Transition metal oxide compounds with perovskite-type structure (AMX3-δ) show besides attractive physical properties, such as high temperature superconduction or thermoelectricity, often excellent catalytic properties for various redox reactions. The catalytic reactivity is strongly dependent on composition, structure and of course the specific surface area of the compounds. Fine-tuning of the properties can therefore be achieved by suitable cation- and anion- substitutions and by adjusting the morphology of the compounds. For systematic studies on the relationship between composition, structure and properties in these systems fine particles as well as thin films of identical compositions e.g. La1-xCaxMO3-δ (x = 0, 0.3, 0.4 , 0.5) (M = Fe, Co, Ni, Mn, Ti) are produced with diverse “chimie douce” methods. The samples are characterised concerning their chemical and physical properties. Carbon nanotube composite materials have been produced by catalytic decomposition of gaseous carbon compounds on nanometer-size transition metal clusters on top of perovskite-type metal oxides and tested for a possible application as oxygen electrodes in air based batteries.

Journal ArticleDOI
TL;DR: In this article, an overview about the preparation and characterization of asymmetric ceramic membranes that have been developed at our institute within the last few years is given, with an overview of different preparation routes.
Abstract: This article gives an overview about the preparation and characterization of asymmetric ceramic membranes that have been developed at our institute within the last years. Depending on the required pore size of the filter active layer for filtration applications ranging from microfiltration (MF) up to nanofiltration (NF) different preparation routes have to be applied.

Journal ArticleDOI
TL;DR: In this paper, carbon templates of laminar structure were manufactured from pyrolysed filter paper sheets by Laminated Object Manufacturing (LOM), and the laminates were converted into SiSiC composites by post-pressureless reactive Si-infiltration.
Abstract: Carbon templates of laminar structure were manufactured from pyrolysed filter paper sheets by Laminated Object Manufacturing (LOM). The laminates were converted into SiSiC composites by post-pressureless reactive Si-infiltration. The microstructure and mechanical properties of the fabricated materials depends on the density, porosity and pore size distribution of the biocarbon preform, which can be varied by changing the parameters of the LOM-processing.

Journal ArticleDOI
TL;DR: In this article, a design support tool, the exchange constant chart, has been developed in order to assist designers selecting materials in such multi-criteria situations, and two case studies are presented to illustrate the use of this tool.
Abstract: Material selection in real-world problems normally entails considering several, usually conflicting, design criteria/objectives. Thus, a designer has to strike a balance between these objectives to find the best compromise solution for the particular application. A novel design support tool, the exchange constant chart, has been developed in order to assist designers selecting materials in such multi-criteria situations. Two case studies are presented to illustrate the use of this tool.

Journal ArticleDOI
TL;DR: In this article, the authors assume an equi-incremental mechanical work in each constituent in stress-strain mixture law and compare this approach with other modelling methods such as Taylor, Sachs, self-consistent or 3D finite element modelling.
Abstract: Assuming an equi-incremental mechanical work in each constituent in stress-strain mixture law, this article focuses on the interest of this approach through comparison with miscellaneous experimental results and with other modelling methods as Taylor, Sachs, self-consistent or 3D finite element modelling.

Journal ArticleDOI
TL;DR: In this article, the effect of oxygen content of the blowing gas on composition and structure of the inner surface of the foam cells is studied by varying gas composition from argon, nitrogen and air to pure oxygen.
Abstract: Metal foams were produced by blowing gas into aluminium alloy melts. The effect of oxygen content of the blowing gas on composition and structure of the inner surface of the foam cells is studied by varying gas composition from argon, nitrogen and air to pure oxygen. Scanning Electron Microscopy, Auger Electron Spectroscopy and Transmission Electron Microscopy are used to analyse the surfaces. Initially particle-free melts are pre-treated by bubbling air through them after which a certain degree of foam stability is achieved. The oxidation products are characterised by microscopy on such foams.

Journal ArticleDOI
TL;DR: In this article, the fabrication of nanotubes polymer/nanocomposites tailored to fit aerospace needs has been discussed and further insight is given on developments in nanofibers and nanotube production for good load transfer on the composite systems.
Abstract: Nanocomposite polymers have tremendous potential to enhance the performance of macromolecular materials used for composite matrices. Effective utilization of carbon nanotubes in composite applications depends strongly on the ability to homogeneously disperse them throughout the matrix without destroying their integrity. This work looks at the fabrication for montmorillonite, fullerenes and nanotubes polymer/nanocomposites tailored to fit aerospace needs. Further insight is also given on developments in nanofibers and nanotubes production for good load transfer on the composite systems.


Journal ArticleDOI
TL;DR: In this article, percolation and conductivity of photoresist polymers were investigated using LMIS4-ARTICLE-2004-011, which is the Web of Science Record created on 2005-09-13.
Abstract: Keywords: percolation ; conductivity ; photoresist ; polymer ; mems Reference LMIS4-ARTICLE-2004-011doi:10.1002/adem.200400068View record in Web of Science Record created on 2005-09-13, modified on 2017-05-10

Journal ArticleDOI
TL;DR: In this article, the preparation and characterization of the powder suspension using silicon carbide powders has been discussed, which has been recognized as a high performance material and has been shown to be mechanically stronger than polyurethane replica methods.
Abstract: SiC foams were fabricated by gelcasting with a commercially available powder and agar as gelling agent. Ceramic foams processed by gel casting have dense struts and are therefore mechanically stronger than foams produced by the conventional poly-urethane replica method. First, special attention was given to the preparation and characterization of the powder suspension using silicon carbide powders which has been recognized as a high performance material.

Journal ArticleDOI
TL;DR: In this article, the authors summarized published data and also dealt with technology, structure, applications, and properties of gasars -new porous materials based on original findings obtained by authors.
Abstract: The paper summarizes published data and also deals with technology, structure, applications, and properties of gasars - new porous materials based on original findings obtained by authors. The method consists of melting a material in a gas atmosphere to saturate it with hydrogen and directional solidifying under strictly controlled thermodynamic and kinetic conditions. The materials produced by this method, have a monolithic matrix and pores of proper geometric shapes, providing to gasars higher strength, plasticity, thermal and electrical conductivities as compared with those of other porous materials. Gasar is recommended for prospective application as filters, bearings, metal-matrix composites.

Journal ArticleDOI
TL;DR: In this paper, structural properties of AlSi7 foams using TiH 2 variants as foaming agent are evaluated, and the effects induced by treatment time, temperature and atmosphere variation are compared.
Abstract: With series production of aluminium foams according to the Fraunhofer process a reality, further improvement of structural homogeneity has gained interest. Since this characteristic is strongly influenced by blowing agent decomposition, means to adapt the latter have been investigated: The paper concentrates on thermal treatment of TiH 2 , comparing effects induced by treatment time, temperature and atmosphere variation. Structural characteristics of AlSi7 foams using TiH 2 variants as foaming agent are evaluated.