Showing papers on "Powder metallurgy published in 2003"
TL;DR: Porous Ti compacts for biomedical applications are successfully fabricated in the porosity range from 50 to 371 vol% by controlling sintering conditions and Ti powder sizes as discussed by the authors, where Young's modulus and bending strength at the porosa of around 30 vol% are found to be similar to those of human cortical bone.
519 citations
TL;DR: In this article, the effects of CNTs on the tribological properties of these composites were evaluated, and the results demonstrated that the Ni-P-CNT electroless composite coating exhibited higher wear resistance and lower friction coefficient than Ni−P-SiC and Ni-p-graphite composite coatings.
448 citations
25 Oct 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effects of processing parameters such as laser power, scan rate, scan line spacing, thickness of layer, scanning geometry and sintering atmosphere were studied, and it was found that the sintered density increased sharply with increasing the specific energy input until a critical energy input had been reached.
Abstract: The densification behavior and the attendant microstructural features of iron powder processed by direct laser sintering were investigated. The effects of processing parameters such as laser power, scan rate, scan line spacing, thickness of layer, scanning geometry and sintering atmosphere were studied. A specific energy input (ψ) was defined using the “energy conservation” rule to explore the effects of the processing condition on the density and the attendant microstructure of laser sintered iron. It was found that the sintered density increased sharply with increasing the specific energy input until a critical energy input had been reached (ψ∼0.2 kJ mm−3). The microstructure consists of large pores (>0.5 mm) and elongated ferrite grains parallel to the building direction. The increase in the sintered density was followed with further increasing the specific energy, but at slower rate. Intensifying the energy input over 0.8 kJ mm−3 leads to the formation of horizontally elongated pores while the sintered density remains almost constant. The inter-agglomerates are fully dense and consist of elongated ferrite grains which are oriented parallel to the building direction. The iron powder was used as a model material so the outcomes are generic and can be applied to other material systems with congruent melting point or systems which melting/solidification approach is the mechanism feasible for the rapid bonding of metal powders in direct laser sintering.
335 citations
TL;DR: In this article, a numerical simulation of the heat flow equation has been performed and compared with experimentally obtained titanium plates, which allowed to obtain a process map of the sintering process.
332 citations
TL;DR: In this article, the most recent progress in the development of Nb-silicide-based in situ composites for potential applications in turbine engines with service temperatures of up to 1350°C is reviewed.
Abstract: This article reviews the most recent progress in the development of Nb-silicide-based in situ composites for potential applications in turbine engines with service temperatures of up to 1350°C. These composites contain high-strength Nb silicides that are toughened by a ductile Nb solid solution. Preliminary composites were derived from binary Nb-Si alloys, while more recent systems are complex and are alloyed with Ti, Hf, W, B, Ge, Cr, and Al. Alloying schemes have been developed to achieve an excellent balance of roomtemperature toughness, fatigue-crack-growth behavior, high-temperature creep performance, and oxidation resistance over a broad range of temperatures. Nb-silicide-based composites are described with emphasis on processing, microstructure, and performance. Nb silicide composites have been produced using a range of processing routes, including induction skull melting, investment casting, hot extrusion, and powder metallurgy methods. Nb silicide composite properties are also compared with those of Ni-based superalloys.
288 citations
TL;DR: In this article, a new method of blending the copper powders contained resin with chromium powders to form tool electrodes was proposed, which facilitated the formation of a modified surface layer on the work piece after EDM, with remarkable corrosion resistant properties.
Abstract: Electrode materials for electrical discharge machining (EDM) are usually graphite, copper and copper alloys because these materials have high melting temperature, and excellent electrical and thermal conductivity. The electrodes made by using powder metallurgy technology from special powders have been used to modify EDM surfaces in recent years, to improve wear and corrosion resistance. However, electrodes are normally fabricated at high temperatures and pressures, such that fabrication is expensive. This paper proposes a new method of blending the copper powders contained resin with chromium powders to form tool electrodes. Such electrodes are made at low pressure (20 MPa) and temperature (200 °C) in a hot mounting machine. The results showed that using such electrodes facilitated the formation of a modified surface layer on the work piece after EDM, with remarkable corrosion resistant properties. The optimal mixing ratio, appropriate pressure, and proper machining parameters (such as polarity, peak current, and pulse duration) were used to investigate the effect of the material removal rate (MRR), electrode wear rate (EWR), surface roughness, and thickness of the recast layer on the usability of these electrodes. According to the experimental results, a mixing ratio of Cu–0wt%Cr and a sinter pressure of 20 MPa obtained an excellent MRR. Moreover, this work also reveals that the composite electrodes obtained a higher MRR than Cu metal electrodes; the recast layer was thinner and fewer cracks were present on the machined surface. Furthermore, the Cr elements in the composite electrode migrated to the work piece, resulting in good corrosion resistance of the machined surface after EDM.
252 citations
TL;DR: In this paper, a cylinder-on-plate wear machine was used to evaluate the wear and friction properties of graphite and molybdenum disulfide (MoS 2 ) graphite composites.
232 citations
TL;DR: In this paper, experimental results are presented on the surface alloying of AISI H13 hot work tool steel during a die sink operation using partially sintered WC/Co electrodes operating in a hydrocarbon oil dielectric.
Abstract: Electrical discharge machining (EDM) is a widely used process in the mould / die and aerospace industries. Following a brief summary of the process, the paper reviews published work on the deliberate surface alloying of various workpiece materials using EDM. Details are given of operations involving powder metallurgy (PM) tool electrodes and the use of powders suspended in the dielectric fluid, typically aluminium, nickel, titanium, etc. Following this, experimental results are presented on the surface alloying of AISI H13 hot work tool steel during a die sink operation using partially sintered WC / Co electrodes operating in a hydrocarbon oil dielectric. An L8 fractional factorial Taguchi experiment was used to identify the effect of key operating factors on output measures (electrode wear, workpiece surface hardness, etc.). With respect to microhardness, the percentage contribution ratios (PCR) for peak current, electrode polarity and pulse on time were ~24, 20 and 19%, respectively. Typically, changes in surface metallurgy were measured up to a depth of ~30 μm (with a higher than normal voltage of ~270 V) and an increase in the surface hardness of the recast layer from ~620 HK 0.025 up to ~1350 HK 0.025 .
198 citations
TL;DR: In this paper, the die compaction of pharmaceutical powders using a variable parameter Drucker-Prager type cap model was analyzed using a die instrumented with radial pressure sensors, which was also used to measure the coefficient of friction between powder and die wall.
191 citations
TL;DR: In this paper, the results show that the densification, bulk hardness, ultimate flexural strength and ductility were improved by the electroless plating on the reinforcement, while the electrical conductivity remains at a fairly high level as the uncoated one.
136 citations
25 May 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the thermal expansion property of as-formed product was measured in the temperature range from 50 to 550 °C, which can be explained in terms of the residual stresses and the interfacial bonding between copper and silicon carbide.
Abstract: Copper/silicon carbide composites (Cu/SiC p ) were made by the powder metallurgy method. Electroless plating was employed to deposit a copper film on SiC p powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. Thermal expansion property of as-formed product was measured in the temperature range from 50 to 550 °C. The results showed that copper coating on silicon carbide particles could render uniform distribution of SiC p in the copper matrix. The composites exhibited positive thermal hysteresis behavior when cooled down from the peak temperature to room temperature, which can be explained in terms of the residual stresses and the interfacial bonding between copper and silicon carbide. The magnitude of this strain was a function of the SiC p volume fraction and the number of thermal cycles. The thermal expansion property of composites was measured and compared with those predicted from various theoretical models.
TL;DR: In this paper, the reduced W −20% Cu powder with W particle sizes of about 30-100 nm and uniform distribution of components was successfully synthesized by mechano-thermochemical process.
TL;DR: In this paper, the electrical conductivity, hardness and microstructure of Ag-W and Ag-WC refractory contact materials have been investigated and the effect of graphite addition has been evaluated.
TL;DR: In this article, a self-developed Cu-based metal powder was used for direct laser sintering, which consists of two metal powders: high-purity Cu powder and pre-alloyed SCuP metal powder.
TL;DR: In this article, the effect of Mo addition on the microstructure and mechanical properties of TiC-TiN(nm) -WC-Co-Ni-C system cermets was studied.
TL;DR: In this article, the formation of nanocrystalline Mg2Si through solid-state reaction was investigated and the results indicated that mechanical milling lowers the formation temperature to ∼280 °C.
TL;DR: In this paper, the authors compared two routes for processing sintered Ti-6Al-4V products via the hydrogenation-dehydrogenation (HDH) process: single and double step.
TL;DR: In this paper, the microstructure of the bonding interfaces between particles in aluminum powder sintered specimens by the pulse electric-current sintering (PECS) process was observed, using conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscope (HRTEM).
Abstract: The microstructure of the bonding interfaces between particles in aluminum (Al) powder sintered specimens by the pulse electric-current sintering (PECS) process was observed, using conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM). The behavior of oxide film at the interface between Al particles and its effect on properties of the sintered specimens were investigated. The results showed there were two kinds of bonding interfaces in the sintered specimens, namely, the direct metal/metal bonding and the metal/oxide film layer/metal bonding interface. By increasing the fraction of the direct metal/metal bonding interfaces, the tensile strength of the sintered specimens increased, and the electrical resistivity decreased. By increasing the loading pressure at higher sintering temperatures or increasing the sintering temperature under loading pressure, the breakdown of oxide film was promoted. The broken oxide film debris was dispersed in aluminum metal near the bonding interfaces between particles.
TL;DR: The Vickers hardness varied from 150 and 180, depending on the sintering temperature as discussed by the authors, and was two to three times as high as those of conventionally cast bars of the same alloy.
TL;DR: In this paper, a study of chip formation during the machining of MMCs produced by the mechanical alloying (MA) technique is described, where the effect of Al 4 C 3 on the crack formation in shear plane, shortened the chip contact length and the chip segment thickness.
TL;DR: In this paper, a review of recent developments in modelling the sintering process of powder compacts is presented and both free sinter and pressure assisted sinterings are considered.
Abstract: Recent developments in modelling the sintering process of powder compacts are critically reviewed. Both free sintering and pressure assisted sintering are considered. The review approaches the sint...
TL;DR: In this article, the effect of porosity and cell diameter on the electrical conductivity of closed-cell aluminum alloy foams was investigated and the results were compared with a number of models.
Patent•
16 Oct 2003
TL;DR: A sintering powder containing polyamide polymer and titanium dioxide particles was used in this article for a process for laser sinter, and moldings were made from the sintered powder.
Abstract: A sintering powder containing polyamide polymer and titanium dioxide particles, a process for laser sintering, and moldings produced from the sintering powder. The moldings formed using the powder of the invention have improved surface quality due to the powders having increased yellowing resistance when exposed to thermal stress during laser sintering. Moldings produced from the sintering powder have improved mechanical properties, in particular modulus of elasticity.
TL;DR: In this article, a fully dense isotropic and anisotropic (Nd,Pr,Dy)/sub 2/Fe/sub 14/B//spl alpha/-Fe nanocomposite magnet was successfully prepared by a hot press and hot deformation technique using melt-spun precursors.
Abstract: Fully dense isotropic and anisotropic (Nd,Pr,Dy)/sub 2/Fe/sub 14/B//spl alpha/-Fe nanocomposite magnets have been successfully prepared by a hot press and hot deformation technique using melt-spun precursors. For the fully dense, hot-deformed, anisotropic nanocomposite (Nd,Pr,Dy)/sub 2/Fe/sub 14/B//spl alpha/-Fe-based magnets containing /spl sim/4 vol% and /spl sim/11 vol% /spl alpha/-Fe, the maximum energy products have reached 31 and 24 MGOe, respectively. At the time of proofreading for this paper, 42 MGOe has been reached for the nanocomposite magnets with /spl ap/4 vol% /spl alpha/-Fe.
TL;DR: In this paper, the occurrence of temperature induced porosity (TIP) in hot isostatically pressed (HIP) compacts of different gamma Titanium aluminide alloys was investigated.
TL;DR: In this paper, the machinability of metal-matrix composites (MMCs) was characterized by the investigation of chip formation, cutting forces and surface roughness, and the effect of Al 4 C 3 on the crack formation in shear plane, reduced the cutting force, shortened the chip contact length and the chip segment thickness.
TL;DR: In this paper, the melting and sintering behavior of recycled high density polyethylene (rHDPE) have been analyzed through differential scanning calorimetry (DSC) and Thermomechanical Analysis (TMA).
Abstract: Sintering of polymeric powders is a peculiar characteristic of many processing technologies, including rotational moulding and selective laser sintering (SLS). During polymer sintering, viscosity reduction in the melt state promotes densification of polymer powders, through a double stage mechanism, involving powder coalescence and bubble removal. In particular, sintering of semi-crystalline polymers is strongly influenced by the melting behaviour. Nevertheless, melting itself in absence of pressure is not necessarily accompanied by powder sintering, unless low viscosities are achieved. In this work, the melting and sintering behaviour of recycled high density polyethylene (rHDPE) have been analysed through differential scanning calorimetry (DSC) and Thermomechanical Analysis (TMA). Efficient models capable of describing the melting temperature distribution and rate of sintering of rHDPE powders have been developed, highlighting the inherent differences between the two distinct processes.
15 Jun 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The behavior of spherical copper powder particles of uniform size (average diameter: 550 μm) in a powder compact was observed under an optical microscope during a single-pulse electric discharge of 500 ms duration.
Abstract: The behavior of spherical copper powder particles of uniform size (average diameter: 550 μm) in a powder compact was observed under an optical microscope during a single-pulse electric discharge of 500 ms duration. The morphologies of necks formed between powder particles were observed under a scanning electron microscope, and their diameters were measured. The results obtained are summarized as follows: pressure and pulsed current density determine whether or not a spark occurs. Spark is more likely to occur at interparticle contacts under low pressure and high current density. Where a spark occurs, particles are joined together by melting. Regardless of whether or not a spark is observed, necks are formed at points of contact between particles and neck diameter increases with pulsed current density. These results suggest that microscopic sparking, melting, and vaporization occur by means of extremely high temperature attained by local heat generation at the interparticle contacts in the initial stage of compaction.
01 Jan 2003-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the microstructural evolution of a Distaloy AE powder compact and of loose copper powder is investigated during a thermal cycle at the European Synchrotron in Grenoble (France).
Abstract: The mechanisms involved in shape changes arising during sintering of complex materials like iron-based systems are still poorly understood. New information can be obtained by use of advanced techniques such as microtomography. In this study, the microstructural evolution of a Distaloy AE powder compact and of loose copper powder is investigated during a thermal cycle at the European Synchrotron in Grenoble (France). Both materials are sintered in a furnace set in front of a high-energy X-ray source in 30–45 keV range. At various steps of sintering, hundreds of radiographs are taken with different orientations of the specimen. From these images the 3D microstructure is reconstructed. This non-destructive method provides the 3D microstructural evolution of the material during sintering. Local and statistical information can be obtained and will be used in the future for modelling the sintering process. Special attention is given to the anisotropy induced by prior compaction and to its evolution through sintering.
20 Dec 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a new type of composite material was produced from elemental Al matrix powders and 30 vol.% Al ;Cu ;Fe quasicrystal particles by a powder metallurgy technique.
Abstract: A new type of composite material was produced from elemental Al matrix powders and 30 vol.% Al ;Cu ;Fe quasicrystal particles by a powder metallurgy technique. SEM examination shows that reinforcement particle cracking perpendicular to the loading axis is the dominant failure mechanism for the composites. Because of the fine (diameter