Effect of Sn on the Dehydrogenation Process of TiH2 in Al Foams

The study of the dehydrogenation process of TiH₂ in aluminum foams produced by the powder metallurgy technique is essential to understanding its foaming behavior. Tin was added to the Al foam to modify the dehydrogenation process and stabilize the foam. A gradual decomposition and more retention of hydrogen gas can be achieved with Sn addition resulting in a gradual and larger expansion of the foam.     

Effects of Mg addition on foam stability of Al foams made by powder metallurgy route

Abstract

Al foams were produced by applying a powder metallurgy route. Foam expansion, cell structures and foam stability of foamed samples were investigated. The results show that larger expansion and more homogeneous cell structures were achieved due to the presence of 1·0 wt-%Mg addition. Mg addition results in the formation of spinel particles through the reaction between Mg powder and alumina on Al powder. Spinel particles show good wetting with Al melt and are fully embedded into Plateau borders and cell walls. The liquid is tightly trapped within cell walls and Plateau borders in the presence of spinel particles, preventing cell walls from thinning further and improving foam stability significantly.     

Compressive Deformation Behavior of Highly Porous AA2014-Cenosphere Closed Cell Hybrid Foam Prepared Using CaH<Subscript>2</Subscript> as Foaming Agent: Comparison with Aluminum Foam and Syntactic Foam

Closed Cell AA2014-cenosphere hybrid foams have been prepared through stir-casting technique using varying amount of CaH₂ powder as foaming agent. The cenospheres in hybrid foams created micro-pores in the cell wall and in the plateau region. It reduced the requirement of CaH₂ for foaming by 30–40% by attaining equivalent level of relative density. These foams have been characterized for of microarchitechtural characteristics and mechanical properties like strength, densification strain and energy absorption. The properties of hybrid foams have been compared with those of conventional AA2014-SiC foam and Al-cenosphere syntactic foam. The closed cell AA2014-cenosphere hybrid foam exhibited comparable plateau stress, densification strain and energy absorption characteristics to those of AA2014-SiC foams with same relative density. Empirical relations to correlate plateau stress, densification strain and energy absorption for entire range of porosities have been established.     

Low Dielectric Loss Ceramics of AlN Fine and Nanopowders

The dielectric properties of ceramics pressurelessly sintered from nano (10-100 nm) and fine (0.8-1.0 μm) aluminum nitride powders have been studied. High-purity aluminum nitride sintered from nanopowder of nearly-theoretical density has been found to exhibit a low dielectric constant ε = 6.3 and low loss, tgδ = 0.011 at 3.32 GHz. Ceramics sintered from a fine aluminum nitride powder doped with yttrium oxide have revealed ε = 7.7 and tgδ = 0.021 at 3.23 GHz. The dielectric properties have allowed us to use ceramics sintered from fine aluminum nitride powder as a material for microwave windows for the diagnosis and treatment of tumors of the larynx and breast.     

Fabrication of aluminium foam through pressure assisted high frequency induction heated sintering dissolution process: an experimental observation

Abstract

A process based on powder metallurgy approach was developed to produce open celled aluminium foam. In the preparation of foam specimens, the Al powder and the NaCl (leaching agent) were dry mixed together in order to prepare a homogeneous mixture. The blended mixture was then subjected to pressure assisted sintering in which a pressure beyond atmospheric level is externally applied to the specimen during high frequency induction heated sintering. The embedded leaching agent was then dissolved in order to leave behind an open celled Al with the same chemical composition as that of the original Al powder. The final material is highly porous and has an interconnected porosity network. The structure of the resulting material has three levels of porosity (i.e. main cells, windows and microporosity). The X-ray diffraction analysis shows that, as the content of NaCl is increased to the volume fraction of 60%, no traces of NaCl presents in the foam.     

Manufacturing of copper foams through accumulative roll bonding (ARB) process: structure and damping capacity behavior

Abstract

Closed cell copper foams have been produced through accumulative roll bonding (ARB) using calcium carbonate (CaCO₃) as blowing agent. Effects of temperature, time and number of rolling passes on the final porosity of the foam have been investigated. The foam with highest porosity has been achieved at 1100°C for soaking time of 3 min. Structure of composite has also been studied by optical and electron microscopy. The result shows that increasing the number of rolling passes reduces the size of powder and homogeneously distributes the particles within the copper substrate. By reducing the size of the particles, free surfaces of particles increase and the gas releasing sites in the foams are enhanced. Consequently, the final porosity of the composite is enhanced as well. The closed-pore foams have also been examined by modal analysis. It has been found that higher porosity of the final foams results in higher natural frequency and damping index.     

Mathematical Model to Estimate the Rate Parameters and Thermal Efficiency for the Reduction of Iron Ore–Coal Composite Pellets in Multi-layer Bed at Rotary Hearth Furnace

Aluminium foams have become popular because of their properties such as high stiffness combined with very low density. The aluminium foams are being used in many applications like automobiles, railways, aerospace, ship building, household applications etc. The development of foam with consistent quality and study of foam structure–property relation is important for both scientific and industrial applications. Metallic foams are commonly produced using hydride and carbonates foaming agents. However carbonate foaming agents are safer to handle than hydrides and produce aluminum foam with a fine, homogenous cell structure, low cost and easily available. The number of pores per inch and relative density of the foam play an important role on their physical and mechanical properties. Hence it is very important to investigate effect of grain size of calcium carbonate foaming agent on pores per inch and relative density. The present work deals with the effect of grain size of the calcium carbonate forming agent on the physical properties of an eutectic Al–Si alloy closed cell foam. The foam was produced with different grain size of calcium carbonate (150, 106, 75, 53 µm) as a foaming agent. The pores per inch and density of the foam produced with different grain size of calcium carbonates as foaming agent are determined. Relative density is in the range of 0.21–0.34, pores per inch is in the range of 11–20 for the produced eutectic Al–Si alloy closed cell foam. It is observed that as grain size of calcium carbonate used for production of aluminium foam increases, the number of pores per inch decreases, relative density decreases and porosity increases.     

Deformation and Failure of Open‐Cell Foams Made of TRIP‐Steel‐ZrO2‐Composite Materials: Experimental Observations Versus Numerical Simulations

The aim of the study is to clarify how far it is possible to describe the mechanical behavior of novel TRIP‐Steel/Mg‐PSZ composite open‐cell foam structures using beam networks generated from random tessellations. Conventional compression tests were performed with various foam samples. Furthermore, the deformation of open‐cell composite foams was observed as well by X‐ray computed tomography (XCT). Up to a compressive strain of 20% different stages of deformation could be observed. Respective bulk samples were manufactured by powder metallurgy and tested in order to determine the mechanical properties of the bulk material. Numerical simulations were employed based on the suitable modeling of foams exposed to mechanical loading. The predictions of the simulation are compared with the results of the deformation experiments.     

Fabrication of Al-3.7?Pct Si-0.18?Pct Mg Foam Strengthened by AlN Particle Dispersion and its Compressive Properties

Al-3.7 pct Si-0.18 pct Mg foams strengthened by AlN particle dispersion were prepared by a melt foaming method, and the effect of foaming temperature on the foaming behavior was investigated. Al-3.7 pct Si-0.18 pct Mg alloy containing AlN particles was prepared by noncompressive infiltration of Al powder compacts with molten Al alloy in nitrogen atmosphere, and it was foamed at different foaming temperatures ranging from 1023 to 1173 K. The porosity of prepared foam decreases and the pore structure becomes homogeneous with increasing foaming temperature. When the foaming temperature is higher than 1123 K, homogeneous pores are formed in the prepared ingot without using oxide particles and metallic calcium granules, which are usually used for stabilizing a foaming process. This stabilization of the foaming at high temperatures is possibly caused by Al₃Ti intermetallic compounds formed at high temperature and AlN particles. Compression tests for the prepared foams revealed that the absorbed energy per unit mass of prepared Al-3.7 pct Si-0.18 pct Mg foam is higher than those of aluminum foams strengthened by alloying or dispersion of reinforcements. It is remarkable that the oscillation in stress, which usually appears in strengthened aluminum foams, does not appear in the plateau stress region of the present Al-3.7 pct Si-0.18 pct Mg foam. The homogeneity in cell walls and pore morphology due to the stabilization of pore formation and growth by AlN and Al₃Ti particles is a possible cause of this smooth plateau stress region.     

THE EFFECT OF PHOSPHORUS ADDITIONS ON THE TENSILE,FATIGUE, AND IMPACT STRENGTH OF SINTERED STEELS BASED ON SPONGE IRON POWDER AND HIGH-PURITY ATOMIZED IRON POWDER

Abstract

The mechanisms operating during the sintering of iron-phosphorus PM alloys are discussed, as well as the factors contributing to the unique combination of strength, ductility, and toughness that is characteristic of these materials. Alloying methods are reviewed with special reference to powder compressibility, tool wear during compaction, and homogenization during sintering. The preferred production method is to add phosphorus in the form of a fine Fe₃P powder to iron powder. The mechanical properties of a number of sintered steels made with and without Fe₃P additions to sponge iron or to high-purity atomized iron powders are reported. Use of atomized powder makes it possible to reach extremely high density by single pressing and the resulting phosphorus-containing sintered steels have very high ductility and impact strength. The fatigue strength is related linearly to the tensile strength, with a correlation coefficient of 0·91. It is concluded that structural factors other than those that control ductility and toughness are responsible for the fatigue resistance of sintered steels.     

The role of particle size on the laser sintering of iron powder

The effects of powder particle size on the densification and microstructure of iron powder in the direct laser sintering process were investigated. Iron powders with particle sizes ranging from 10 to 200 μm were used. It was found that the sintered density increases as the laser energy input is increased. There is, however, a saturation level at which higher density cannot be obtained even at very intensive energy input. This saturation density increases as the size of the iron particles decreases. Meanwhile fine powders with narrow particle size distributions have a tendency toward agglomeration, and coarse powders with broad particle size distributions have a tendency toward segregation, both of them resulting in lower attainable density. In order to investigate the role of particle size, a “densification coefficient (K)” was defined and used. This coefficient depends on the particle size and the oxygen content of iron powder. The results of this investigation demonstrate that the presence of oxygen significantly influences the densification and pore morphology of laser-sintered iron. At higher oxygen concentrations, the iron melt pool is solidified to agglomerates, and formation of pores with orientation toward the building direction is more likely to occur. When the oxygen concentration is kept constant, the densification coefficient decreases with decreasing the particle size, meaning the densification kinetics enhances. This article presents the role of powder characteristics and the processing parameters in the laser sintering of iron powder as a model material. The mechanism of particle bonding and microstructural features of laser-sintered parts are addressed.     

多孔钛的粉末冶金法制备及其力学性能

采用粉末冶金法成功制备出力学性能与骨匹配的开孔型多孔钛,其孔隙率分布在8.6%～35.4%之间,平均孔径随孔隙率增加而增加;抗压强度随孔隙率的增加而降低,分布在252～848 MPa之间;通过应力-应变曲线计算得到其弹性模量在7.2～9.9 GPa之间,接近人骨弹性模量。此多孔钛有望成为理想的人工骨修复材料。     

Analysis of liquid flow through ceramic porous media used for molten metal filtration

A two-dimensional mathematical model has been developed to study fluid flow inside ceramic foam filters, used for molten metal filtration, as a function of their structural characteristics. The model is based on the selection of a unit cell, geometric model, formed by two interconnected half-pores. The good agreement between experimental and computed permeabilities showed that the unit cell model approximates very well the effect of filter structure on the flow conditions inside the filter. The validity of the model is supported by the fact that permeabilities are calculated from directly measured structural parameters,i.e., without the introduction of any fitting variable, such as tortuosity. The laminar flow solutions for the Navier-Stokes equation, in steady state, were obtained numerically using the control-volume method. The boundary of the unit cell was represented through axisymmetrical, body-fitted coordinates to obtain a better representation of the complex pore shape. The generality of the model, to study fluid flow in reticulated media, was tested by comparing the computed specific permeabilities with values measured for ceramic foam filters and for the new ceramic filter of lost packed bed (CEFILPB). Such a comparison shows good agreement and discloses a fundamental property of the last kind of porous medium: the critical porosity. The model indicates how porosity and pore dimensions of reticulated filters may be tailored to meet specific fluid flow requirements.     

造孔剂法制备泡沫钛的研究现状与进展

泡沫钛融合了泡沫结构与金属钛的双重属性,具有出色的力学性能、优异的耐腐蚀性和良好的生物相容性等优点,在航空、航天、海洋工程、生物医学、能源与环保等领域应用前景广阔。基于粉末冶金技术的造孔剂法是目前制备泡沫钛的主流方法,不仅具有操作简单、设备要求低的优点,而且能通过调整造孔剂参数来控制最终制品的结构与性能。本文综述了造孔剂法制备泡沫钛领域的研究现状与进展,通过分析文献、整理数据,讨论了高孔隙率泡沫钛的研究历程和瓶颈问题,指出了泡沫钛孔隙率研究的发展趋势。     

Influence of Powder Morphology and Chemical Composition on Metallic Foams produced by SlipReactionFoamSintering (SRFS)‐ Process

The SlipReactionFoamSintering (SRFS)‐ process is a metallurgical method to produce open‐cell metallic foams of iron based materials, steels and nickel based materials. In this process several chemical reactions take place. Through the most influential parameter, the morphology of the metallic powder, different properties of the foam can be adjusted, such as the viscosity of the slip, the cell structure and the mechanical properties. Several examples are presented in this paper. Moreover, the thermal conductivity of three foams is measured with the transient‐heat‐source‐technique.     

泡沫铝及其三明治结构累积叠轧制备

通过累积叠轧法制备泡沫铝.采用称重法研究泡沫铝孔隙结构,利用光学显微镜观察泡沫铝孔隙形貌.发现以TiH₂为发泡介质,当发泡温度660~680℃和发泡时间6~10 min时,利用累积叠轧法制备泡沫铝的孔隙结构特性最好.发泡温度和发泡时间的最佳值与发泡剂用量有关,TiH₂质量分数为1.5%,在670℃发泡8 min,泡沫铝的孔隙率可达到42%,孔径为0.43 mm.以制备的泡沫铝为夹芯,通过轧制复合制备了TC4钛合金/泡沫铝芯和1Cr18Ni9Ti不锈钢/泡沫铝芯三明治板.利用光学显微镜和能谱仪研究了三明治板的界面.面板与芯板间的化合反应形成了界面的反应层,界面实现了冶金结合.      

Diary

Abstract

The addition of amorphous Fe–Si–B particles to Fe powder increases the shrinkage of sintered components resulting in higher densification rates. Consequently, several research groups worldwide have studied the properties of such systems in an attempt to produce superior structural alloys. In the present work, Fe₇₅Si₁₀B₁₅ ribbons obtained by melt spinning were milled in a high energy Spex mill for times varying from 2 to 32 h. The resulting powders were characterised by differential thermal analysis and X-ray diffraction. The results showed that the amorphous characteristics of the ribbons persisted after the milling process. Next, samples consisting of a mixture of Fe powder and 4 wt-% milled amorphous phase were uniaxially pressed and sintered following a series of thermal cycles. High temperature microstructures were obtained for compacts subjected to rapid cooling from the sintering temperature. The results of scanning electron microscopy and energy dispersive spectroscopy revealed substantial precipitation of fine Fe₂B particles before α → γ allotropic transformation. In addition, an oxide phase was observed in the interface between Fe and the additive particles. Preliminary analysis suggested that the oxide particles can be easily reduced by adding small amounts of carbon to the system. PM/0765     

Evaluation of mechanical properties of porous 6061 alloys fabricated by the powder compression and induction heating process

The purpose of this study is to evaluate the mechanical properties of 6061 Al foam products, which were fabricated by the powder compression and multistep induction heating method, and to build the database necessary for computer-aided modeling or foam components design. In this study, 6061 Al foams with various porosity fractions were fabricated according to the porosity fractions-final heating temperature curve. The relationships between porosity fraction and morphological properties (porosity diameter, number per unit area of porosities, and surface skin thickness) were investigated. Mechanical properties such as compressive strength, energy absorption capacity, and efficiency were investigated to evaluate the feasibility of foams as crash-energy-absorbing components. Furthermore, the effect of the surface skin thickness on the plateau stress and strain sensitivity of the 6061 Al foam with low porosities (pct) was studied.     

Effect of sintering parameters (time and temperature) upon the fabrication process of organic binder-based metallic hollow sphere

Metallic hollow spheres (MHSs) are developed to be used in structural applications in syntactic and metal foams. These foams are lightweight and energy-absorbing structures which also can be used for acoustic insulation. In this study, the fabrication process of MHSs with optimum mechanical properties has been investigated. To achieve this goal, polystyrene spheres were coated with iron powder and an organic binder. During the multi-stage heat treatment, the green spheres were sintered into MHSs. Sintering was done at various temperatures (1125, 1150, 1175 and 1200°C) at different durations (3:30, 4:30 and 5:30?h). The influence of the different sintering durations and temperatures on mechanical features, microstructure and density was studied as well. The obtained results indicate that samples that were sintered at the temperature of 1175°C for 4:30?h resulted in superior mechanical and physical properties.