Showing papers on "Powder metallurgy published in 2008"
25 Feb 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a vapour deposited molybdenum coating on SiC powders has been used to improve the bonding strength and thermo-physical properties of the composites, using atomized Cu(X) alloys with minor additions of carbide formers.
Abstract: Thermal aspects are becoming increasingly important for the reliability of the electronic components due to the continuous progress of the electronic industries. Therefore, the effective thermal management is a key issue for packaging of high performance semiconductors. The ideal material working as heat sink and heat spreader should have a CTE of (4–8) × 10−6 K−1 and a high thermal conductivity. Metal matrix composites offer the possibility to tailor the properties of a metal by adding an appropriate reinforcement phase and to meet the demands in thermal management. Copper/SiC and copper/diamond composites have been produced by powder metallurgy. The major challenge in development of Cu/SiC is the control of the interfacial interactions. Silicon carbide is not stable in copper at the temperature needed for the fabrication of Cu/SiC. It is known that the bonding between diamond and copper is very weak in the Cu/diamond composite. Improvements in bonding strength and thermo-physical properties of the composites have been achieved by • a vapour deposited molybdenum coating on SiC powders to control interface reactions, • using atomized Cu(X) alloys with minor additions of carbide formers, e.g. X = Cr, B, to improve the interfacial bonding in Cu-diamond composites.
330 citations
TL;DR: A multi-stage rapid prototyping technique was successfully developed to produce porous titanium scaffolds with fully interconnected pore networks and reproducible porosity and pore size, which have the properties to be potentially employed in orthopaedic applications.
326 citations
TL;DR: The Fe35Mn alloy was found to be essentially austenitic with fine MnO particles aligned along the rolling direction, and it exhibits antiferromagnetic behaviour and its magnetic susceptibility is not altered by plastic deformation, providing an excellent MRI compatibility.
Abstract: An Fe–35 wt-%Mn alloy, aimed to be used as a metallic degradable biomaterial for stent applications, was prepared via a powder metallurgy route. The effects of processing conditions on the microstructure, mechanical properties, magnetic susceptibility and corrosion behaviour were investigated and the results were compared to those of the SS316L alloy, a gold standard for stent applications. The Fe35Mn alloy was found to be essentially austenitic with fine MnO particles aligned along the rolling direction. The alloy is ductile with a strength approaching that of wrought SS316L. It exhibits antiferromagnetic behaviour and its magnetic susceptibility is not altered by plastic deformation, providing an excellent MRI compatibility. Its corrosion rate was evaluated in a modified Hank's solution, and found superior to that of pure iron (slow in vivo degradation rate). In conclusion, the mechanical, magnetic and corrosion characteristics of the Fe35Mn alloy are considered suitable for further development ...
282 citations
TL;DR: In this article, the authors used atomized copper alloy with minor additions of chromium to increase the interfacial bonding in Cu/diamond composites by a thin nano-sized Cr 3 C 2 layer.
246 citations
TL;DR: In this paper, a powder can rolling technique is used to fabricate carbon nanotube-reinforced aluminium strips, which can have numerous attractive applications in the aerospace, automotive and electronics industries.
231 citations
TL;DR: In this article, the effect of the initial grain growth cannot be ignored because that it is sufficient to cause the material to lose nanocrystalline characteristics and it is generally found that the sintering temperatures of nanosized particles are dramatically lower than that of their micrometre or submicrometer sized counterparts.
Abstract: The sintering of nanosized particles is a scientific and technological topic that affects the manufacture of bulk nanocrystalline materials and the understanding of the stability of nanoparticles. Owing to their extremely small size and the high surface to volume ratio, nanoparticles during sintering exhibit a number of distinctively unique phenomena compared to the sintering of coarse powders. Particularly, it is generally found that the sintering temperatures of nanosized particles are dramatically lower than that of their micrometre or submicrometre sized counterparts. Research has also shown that the grain growth during nanosintering consists of an initial dynamic grain growth stage that occurs during heating up and the normal grain growth stage that occurs mostly during isothermal holding. For nanoparticles, the effect of the initial grain growth cannot be ignored because that it is sufficient to cause the material to lose nanocrystalline characteristics. This review aims to bring to focus th...
219 citations
TL;DR: In this paper, the same graphite powder was copper-coated and used for the preparation of coated composites with 30 and 50% of graphite, and the coefficient of friction and wear rate of coated and uncoated composites at first decreases.
186 citations
TL;DR: In this paper, a closed cell composite metal foam has been produced using a powder metallurgy technique, which is processed by filling the vacancies between densely packed steel hollow spheres with steel powder and sintering them into a solid cellular structure.
174 citations
TL;DR: In this paper, the effects of reinforcement materials on tribological and mechanical properties of composite materials were investigated by wearing with 10-N load and 50-rpm on a pin-on-disc wear test rig at dry conditions.
160 citations
TL;DR: In this article, a review examines the fundamental factors underlying nanoceramic sintering and the approaches to effectively utilize these factors to improve the performance of the sintered grains.
Abstract: There are two challenges in nanoceramic sintering: fully densifying the sintered body and maintaining the sintered grains at <100 nm size. This review examines the fundamental factors underlying nanoceramic sintering and the approaches to effectively utilise the sintering factors to advantage. Nanoceramic sintering techniques are divided into four categories: pressureless sintering, pressure sintering, electrically assisted sintering, and other sintering related techniques. Pressureless sintering has mainly evolved around modifying sintering schedules, improving nanoparticle packing characteristics, and using additives to tailor the diffusion rates. Pressure sintering, which includes hot pressing, hot isostatic pressing, and sinter forging, can effectively achieve full densification for nanostructured ceramics but microstructural inhomogeneity and sintered shape limitation are difficult to overcome. For electrically assisted sintering, many nanoceramics have been sintered to full density with spar...
146 citations
TL;DR: In this article, the mechanical properties of PbTe and Pb1−xSnxTe compounds and their correlation with the respective charge carrier concentrations were investigated and it was found that although there is a similar electronic behavior (constant scattering factor of −0.5) for the various compositions examined, the mechanical property of the compounds are completely different.
TL;DR: In this paper, the magnetic entropy change for a field variation of 16 kOe and the adiabatic temperature change of 17 k Oe was measured at a temperature of 193 K and 4.2 K, respectively, at a commercial relevant range of 254 K-336 K.
Abstract: Bulk samples of La(Fe,Co,Si)13 have been prepared by powder metallurgy starting from elemental powders and cast master alloys. After sintering at about 1400 K for a few hours, the samples achieve densities of about 7.2 g/cm3. For ternary La(Fe0.893Si0.107)13 the magnetic entropy change for a field variation of 16 kOe and the adiabatic temperature change for a field variation of 17 kOe amounts to 21.9 J/kgK and 4.2 K at a temperature of 193 K, respectively. For this composition, the thermal and the field hysteresis were determined to be 2.5 K and 2.2 kOe, respectively. With increasing Si content the hysteresis as well as the entropy change decreases. By increasing the Co content from La(Fe0.865Co0.05Si0.085)13 to La(Fe0.803Co0.112Si0.085)13 the peak temperature of the magnetic entropy change was tailored to the commercial relevant range of 254 K-336 K. The Co-containing samples hardly showed any hysteresis at all. Such powders were pressed in a die and sintered to fully dense blocks of about 23times19times12 mm . The blocks can be machined by conventional techniques to the shapes required in magnetic refrigeration prototypes.
TL;DR: In this paper, the sliding wear behavior of a copper-graphite composite material (CGCM) for use in maglev vehicles and high-speed railway trains, prepared by means of the powder metallurgy method, was investigated.
TL;DR: In this paper, the morphology and structure of the carbides were evaluated by means of metallography, X-ray diffraction and electron beam backscattered diffraction, which provided new insight into how different carbide morphologies form during processing and the carbide structures that can be expected to be present in components fabricated from these steels by various types of heat treating.
TL;DR: In this paper, the authors investigated the mechanisms of reactive sintering in a Ni + Ti powder compact using differential scanning calorimetry and microstructural analysis, and found that the amount of (β-Ti) was quantitatively determined using DSC and found to decay according to a two-stage parabolic law.
TL;DR: In this article, the hardness and fracture toughness of binderless carbides with a relative density of up to 98.5% could be obtained with simultaneous application of 60MPa pressure and induced current within 2min without significant change in grain size.
Abstract: Microstructure and mechanical properties of WC– x at.% TiC ( x = 0–50) cemented carbides fabricated by high-frequency induction heating sintering (HFIHS) method were investigated. The densification of binderless WC–TiC was accomplished using ultra fine powders of WC and TiC. Nearly fully dense hard materials with a relative density of up to 98.5% could be obtained with simultaneous application of 60 MPa pressure and induced current within 2 min without significant change in grain size. The average grain size of WC produced by HFIHS was about 200 nm. The hardness and fracture toughness of the dense WC–TiC cermets produced by rapid sintering process were investigated.
TL;DR: In this article, the production of a SiC reinforced titanium alloy using conventional powder metallurgy methods (PM) yields porosity and silicides formation, and consolidation time and temperature are considerably decreased avoiding the silicide formation, while consolidation loads were increased to obtain a denser Ti-SiC composite.
TL;DR: In this article, the effect of temperature on the density, hardness, strength, and microstructure of composite composites was investigated and detailed failure behavior was analyzed, showing that the strength tended to increase with the increasing temperature due to the formation of Al2Cu.
25 Jul 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: Two-multilayered functionally graded materials (FGMs), namely aluminium-silicon carbide (Al/SiC) and nickel-alumina (Ni/Al2O3) systems are designed, synthesized and characterized considering 10, 20, 30 and 40% ceramic concentrations as mentioned in this paper.
Abstract: Two-multilayered functionally graded materials (FGMs), namely aluminium–silicon carbide (Al/SiC) and nickel–alumina (Ni/Al2O3) systems are designed, synthesized and characterized considering 10, 20, 30 and 40 vol.% ceramic concentrations. Two, three and five-layered FGMs are fabricated into flat beam samples following powder metallurgy route for Al/SiC and thermal spraying technique for Ni/Al2O3 system. Apart from microstructural studies, porosity content and microhardness are also determined. Three bulk properties are evaluated for FGM characterizations, namely effective flexural strength, thermal fatigue behavior and thermal shock resistance. Progressive and appreciable enhancement in FGM performance is observed as the number of layers is increased from two to five keeping the extreme layers same. Microhardness variation across the interfaces is found to be consistent with the analytically obtained jump in the inplane stresses at the interfaces.
15 Sep 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a hot isostatic pressing for binary NiTi shape memory alloys is proposed to produce powder metallurgical NiTi alloys with good structural and functional properties.
Abstract: The production of high quality powder metallurgical NiTi alloys with elevated phase transformation temperatures is challenging. During processing, an unavoidable pickup of impurity elements (especially oxygen and carbon) results in a decrease of phase transition temperatures and in the formation of brittle secondary phases. We introduce a processing route including melting, gas atomization and hot isostatic pressing for binary NiTi shape memory alloys which minimizes these problems. We demonstrate that the microstructure of the Ti-rich NiTi alloy contains precipitates of Ti2Ni type which can be exploited to dissolve oxygen picked up during later process stages. In this study, three powder fractions with different grain sizes and impurity contents were subjected to hot isostatic pressing. The evolution of microstructures and material properties was studied by chemical analysis, microscopy, differential scanning calorimetry, and mechanical testing. Exploiting the solubility of oxygen in Ti2Ni, the processing route presented in the present paper succeeds in producing powder metallurgical NiTi shape memory alloys with good structural and functional properties.
TL;DR: In this article, a blended elemental press-and-inter powder metallurgy approach using hydrogenated titanium powder was used to synthesize uniform, nearly dense material with reduced grain size, at relatively low temperatures and short time.
Abstract: In the present study titanium alloys were synthesized by the blended elemental press-andsinter powder metallurgy approach using hydrogenated titanium powder. Experimental investigation and modeling of the homogenization processes during synthesis were used to analyze peculiarities of mass transfer and factors affecting diffusion. Processes of alloying elements redistribution during chemical homogenization of powder blends are shown to be strongly dependent on the chemical composition of the initial powders. Optimization of the processing parameters allows to synthesize uniform, nearly-dense material with reduced grain size, at relatively low temperatures and short time. This will provide improvement of mechanical properties simultaneously with better cost-effectiveness of the process.
TL;DR: In this article, the glass reinforcement was produced by controlled milling of melt-spun Al85Y8Ni5Co2 glassy ribbons and the composite powders were consolidated into highly dense bulk specimens at temperatures within the supercooled liquid region.
Abstract: Al-based metal matrix composites were synthesized through powder metallurgy methods by hot extrusion of elemental Al powder blended with different amounts of metallic glass reinforcements. The glass reinforcement was produced by controlled milling of melt-spun Al85Y8Ni5Co2 glassy ribbons. The composite powders were consolidated into highly dense bulk specimens at temperatures within the supercooled liquid region. The mechanical properties of pure Al are improved by the addition of the glass reinforcements. The maximum stress increases from 155 MPa for pure Al to 255 and 295 MPa for the samples with 30 and 50 vol.% of glassy phase, respectively. The composites display appreciable ductility with a strain at maximum stress ranging between 7% and 10%. The mechanical properties of the glass-reinforced composites can be modeled by using the iso-stress Reuss model, which allows the prediction of the mechanical properties of a composite from the volume-weighted averages of the components properties.
TL;DR: In this paper, a mixture of Al and α-Si3N4 powders were used by milling for 5h in a ball mill with alumina balls and mechanically alloying for fiveh in high-energy attritor mill.
25 Feb 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors investigated the effect of hot pressing and spark plasma sintering shrinkage curves on the microstructures of ZrB 2 -based composite and found that no differences were observed in terms of microstructural features and mechanical properties.
Abstract: ZrB 2 + 15 vol.% MoSi 2 composites were densified by spark plasma sintering and conventional hot pressing at the same sintering conditions, i.e. maximum temperature: 1750 °C, applied pressure: 30 MPa and heating rate: 100–150 K/min. The densification behaviour was investigated through the analysis of the hot pressing and spark plasma sintering shrinkage curves. The microstructures were analyzed and compared in order to understand the influence of the two sintering techniques. The following mechanical properties were measured: Vickers hardness, fracture toughness, Young's modulus and 4-pt bending strength. The main outcome of the present work is that when the ZrB 2 -based composite was densified either by spark plasma sintering or by hot pressing using the same sintering parameters, no differences were observed in terms of microstructural features and mechanical properties.
TL;DR: How the thermal profile of electrically conductive powder metal like copper changes with particle size and also with porosity content is described, in other words, initial green density when the material is exposed to 2.45 GHz microwave radiation in a multimode microwave furnace.
Abstract: In recent years, microwave processing of metal/alloy powders have gained considerable potential in the field of material synthesis. Microwave heating is recognized for its various advantages such as: time and energy saving, rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. Microwave material interaction for materials having bound charge are well established, but for highly conductive materials like metals, there is not much information available to interpret the mechanism of microwave heating and subsequent sintering of metallic materials. The present study describes how the thermal profile of electrically conductive powder metal like copper changes with particle size and also with porosity content; in other words, initial green density when the material is exposed to 2.45 GHz microwave radiation in a multimode microwave furnace.
TL;DR: In this article, a planetary ball milling of nanostructured WC-Co powder was optimized by Taguchi method to assess the effect of the milling on the specific surface area (SSA).
Abstract: In this paper, ball milling parameters: weight ratio of ball to powder, size of milling balls, type of medium, volume of milling medium and rotation speed in the planetary ball milling of nanostructured WC–Co powder were optimized by Taguchi method. WC grain size, median particle size (D50) and specific surface area (SSA) were used to assess the effect of the ball milling. It was found that using ethanol and a balls size combination of 12 + 18 mm could improve the reduction of WC grain size. While using distilled water and a balls size combination of 10 + 12 mm could accelerate the particle size reduction. By an analysis of variance (ANOVA) on the SSA results, it was found that except the weight ratio of ball to powder, all other factors are very significant, and the volume of ball milling medium and the rotation speed offer the largest and the second largest contributions in the SSA reduction. By 10 h of ball milling with the optimized milling parameters, D50 and WC grain size of the ball milled WC–Co powder were about 400 nm and 10 nm, respectively.
TL;DR: In this paper, a nanocomposite solders were developed using the powder metallurgy technique incorporating microwave sintering and the results of characterization studies conducted on the extruded samples revealed the presence of equiaxed grains, Cu6Sn5 phase and pores.
Abstract: Sn–0.7Cu is a low cost lead-free solder alloy that is targeted to replace the eutectic Sn–Pb solder. The main limitation of this alloy is its poor strength characteristics. Accordingly, this study aims at improving the mechanical properties of Sn–0.7Cu using Al2O3 particulates in the nanolength scale. The development of nanocomposite solders was accomplished using the powder metallurgy technique incorporating microwave sintering. Results of characterization studies conducted on the extruded samples revealed the presence of equiaxed grains, Cu6Sn5 phase and pores. The mechanical properties (microhardness, 0.2%YS and UTS) increase with the increasing presence of reinforcement with the best tensile strength realized for the composite containing 1.5% alumina that far exceeds the strength of the eutectic Sn–Pb solder.
TL;DR: In this article, the fracture toughness and behaviour of COMRAL-85 TM, a 6061 aluminium-magnesium-silicon alloy reinforced with 20vol% Al 2 O 3 -based polycrystalline ceramic microspheres, and manufactured by a liquid metallurgy route, have been investigated.
Abstract: The fracture toughness and behaviour of COMRAL-85 TM , a 6061 aluminium–magnesium–silicon alloy reinforced with 20 vol% Al 2 O 3 -based polycrystalline ceramic microspheres, and manufactured by a liquid metallurgy route, have been investigated Fracture toughness tests were performed using short rod and short bar (chevron-notch) specimens machined from extruded 19 mm diameter rod, heat treated to the T6 condition The fracture toughness in the R–L orientation was found to be lower than in the C–R or L–R orientations owing to the presence of particle-free bands in the extrusion direction Short rod tests were also conducted for the R–L orientation on six powder metallurgy composites with particle volume fractions ranging between 5% and 30% It was found that the fracture toughness decreased progressively with particle volume fraction, but at a decreasing rate A detailed examination of the fracture behaviour was made for both the liquid metallurgy and powder metallurgy processed composites
TL;DR: In this paper, high-energy milling technique was used to synthesize Al-10-wt%AlN-nanostructured composite powder in a planetary ball-mill under argon atmosphere up to 25h.
15 May 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the age-hardening kinetics of powder metallurgy processed Al-Cu-Mg alloy and composites with 5, 15 or 25vol% SiC reinforcements, subjected to solution treatment at 495°C for 05h or at 504°c for 4h followed by aging at 191°C, have been studied.
Abstract: The age-hardening kinetics of powder metallurgy processed Al–Cu–Mg alloy and composites with 5, 15 or 25 vol% SiC reinforcements, subjected to solution treatment at 495 °C for 05 h or at 504 °C for 4 h followed by aging at 191 °C, have been studied The Al–SiC interfaces in composites show undissolved, coarse intermetallic precipitates rich in Cu, Fe, and Mg, with its extent varying with processing conditions Examination of aging kinetics indicates that the peak-age hardness values are higher, and the time taken for peak aging is an hour longer on solutionizing at 504 °C for 4 h, due to greater solute dissolution Contrary to the accepted view, the composites have taken longer time to peak-age than the alloy, probably due to lower vacancy concentration, large-scale interfacial segregation of alloying elements, and inadequate density of dislocations in matrix The composite with 5 vol% SiC with the lowest inter-particle spacing has shown the highest hardness