Showing papers on "Powder metallurgy published in 2005"

Selective laser sintering (melting) of stainless and tool steel powders: Experiments and modelling:

Abstract: When a laser beam scans once across the surface of a metallic powder bed, the resulting track may be continuous with a crescent or an elliptic cross-section, irregularly broken, balled or only partially melted. This paper reports what laser powers and scan speeds lead to what types of track, for a CO2 laser beam focused to 0.55 mm and 1.1 mm diameters, scanning over beds made from M2 and H13 tool steel and 314S-HC stainless steel powders. Beds have been made with particle size ranges from 300 μm to 150 μm, from 150 μm to 75 μm, from 75 μm to 38 μm, and less than 38 μm. Measurements are also reported of bed physical properties that are used in a finite element model to predict melt pool dimensions and temperatures. Boundaries between regions of different track formation are explained in terms of melt surface temperature gradients, melt pool length-diameter ratio instabilities, and transitions from partial to complete melting. Implications for building metal parts in powder beds without supports are...

Improved mechanical properties and microstructural development of microwave sintered copper and nickel steel PM parts

Abstract: The application of microwave technology to a diverse range of materials and processes has resulted in a wide spectrum of materials that are commercially processed using microwaves, from the heating of food to the vulcanisation of rubber to the sintering of specialty ceramics. Microwave sintering of elemental or alloy metal powders has gained significance in recent times as a novel processing method since it offers many advantages over the conventional sintering method. Despite substantial R&D investment in this area in the past two decades, no competitive microwave technology has yet emerged for powder metallurgy (PM) sintering. In sharp contrast, because it is 'obvious' that microwaves are reflected by metals, it is not uncommon to be unable to locate many journal papers or literature, wherein metal powders have been sintered in a microwave field. This paper reports the improved mechanical properties and microstructural development of microwave sintered copper and nickel steel PM parts as compare...

Hydrodynamic bearing device

Abstract: A hydrodynamic bearing device is provided for use with a spindle motor. The hydrodynamic bearing device has a sleeve made of a sintered metal that is obtained by sintering a sintering material that is iron, an iron alloy, copper, a copper alloy or a mixture thereof. This sintered metal has independent pores, which do not communicate with each other, by selecting conditions for forming a desired sintered body within a predetermined range. The conditions includes a grain size of powdered metal of a material for the sintered metal, a molding pressure when the molded body is formed, sintering temperature and sintering period in the sintering step.

Stress–strain behavior of porous NiTi alloys prepared by powders sintering

Abstract: Porous NiTi shape memory alloys have recently attracted extensive interests for their potential use as biomedical materials. Stress–strain behaviors of porous NiTi alloy fabricated by element powder sintering in argon atmosphere were investigated in this paper by compression and flexural tests. The results indicated that the ultimate compressive strength and the flexural strength of the porous NiTi alloy depended on the densities of the porous NiTi alloy and the sintering conditions. In compression experiments, the pre-strain could completely recover while it was less than 2%. The shape recovery of porous NiTi alloy rested with the unique SME of NiTi phase and pores structure. The pores have adverse effects on the shape recovery of NiTi alloy under the experiment conditions.

An experimental study of the sintering of nanocrystalline WC-Co powders

Abstract: Since nanocrystalline WC–Co powder was produced over a decade ago, the sintering of nanocrystalline powders remains a technological challenge. The goal of sintering nanocrystalline powders is not only to achieve full densification but also to retain nanocrystalline grain sizes. This is difficult because of rapid grain growth at high temperatures. Previous studies on the sintering of nanocrystalline WC–Co have shown that grains grow rapidly during the early stage of sintering. But there are few studies on the mechanisms of grain growth and densification during this stage. This paper presents the results of an experimental investigation on grain growth and densification of nanocrystalline WC–Co powders during heat-up at equilibrium solid-state temperatures. The results have shown that nanocrystalline WC grains grow rapidly during this period concurrently with rapid densification. The rapid densification and grain growth are partially attributed to the surface energy anisotropy of tungsten carbide. The effects of vanadium carbide on grain growth at solid state during heat-up are also discussed.

Microstructure and tensile properties of bulk nanostructured Al-5083/SiCp composites prepared by cryomilling

Abstract: In order to develop high-strength and lightweight MMCs, nanostructured composite powder consisting of an Al-5083 matrix reinforced with approximately 6.5 vol.% nano-sized SiC particles (25 nm in size) was synthesized via cryomilling. Two bulk composites made from 100% of the composite powder and a blend of the composite powder with 50 wt.% conventional coarse-grained (unmilled) Al-5083 powder, respectively, were fabricated with HIP-consolidation and hot rolling processes. Microstructural investigation showed that the nano-sized SiC particles had been dispersed homogeneously in the reinforced regions in the composites and the grain size of the Al-5083 matrix in the reinforced regions ranged from 100 to 200 nm. However, coarse-grained SiC p -free regions were observed even in the composite made from 100% composite powder after HIPping. The tensile strength of the composite made from 100% composite powder was 26% higher than that of nanocrystalline Al-5083 without reinforcement. The existence of coarse-grained regions improves the ductility of the composite.

Microstructural evolution of injection molded gas- and water-atomized 316L stainless steel powder during sintering

Abstract: The present study investigates the microstructural evolution and densification behavior of water- and gas-atomized 316L stainless steel powder. Dilatometry and quenching studies were conducted to determine the extent of densification and corresponding microstructural changes. Results indicate that water-atomized powder could be sintered to 97% of theoretical density, while gas-atomized powders could be sintered to near-full density. The difference in the densification behavior is examined in terms of the particle morphology, initial green density and the particle chemistry.

Liquid phase sintering of functionally graded WC–Co composites

Abstract: Functionally graded cemented tungsten carbide (WC–Co) is an example of functionally graded materials (FGM) in which mechanical properties are optimized by the presence of microstructural gradients such as cobalt gradient and grain size differences within the microstructure. In particular, a cobalt gradient is preferred. However, the manufacture of FGM WC–Co with a cobalt gradient is difficult because the flow of the liquid phase during liquid phase sintering (LPS) would eliminate any initial cobalt gradient built into the powder compacts. In this paper, different factors, which can be used to influence the migration of liquid during sintering, are investigated. These factors include gradients in grain size, carbon and cobalt content, and sintering time. It is shown that a difference in particle size may induce a step-wise profile of cobalt concentration. Initial carbon content differences, however, can be used to obtain a gradient of cobalt during sintering. The effects of these factors are explained based on the roles of capillary force and phase reactions.

Mechanical properties, phases and microstructure of ultrafine hardmetals prepared by WC–6.29Co nanocrystalline composite powder

Abstract: WC–629Co nanocrystalline composite powder prepared by spray thermal decomposition–continuous reduction and carburization technology was consolidated by spark plasma sintering (SPS), spark plasma sintering with hot isostatic pressing (HIP), vacuum sintering and vacuum sintering with hot isostatic pressing (HIP) The mechanical properties, phases and microstructure of WC–629Co hardmetals prepared by different processes were researched The results show that WC–629Co ultrafine cemented carbide consolidated by spark plasma sintering with hot isostatic pressing can reach 990% relative density, and transverse rupture strength (TRS) is more than 2740 MPa, Rockwell A hardness (HRA) is more than 938, the average grain size is less than 400 nm, and WC–629Co ultrafine cemented carbide with excellent properties is achieved Although specimens consolidated by spark plasma sintering can reach 991% relative density, Rockwell A hardness is more than 94, but transverse rupture strength (TRS) is very low Compared with specimens prepared by spark plasma sintering, there are no eta phases in specimens consolidated by spark plasma sintering with hot isostatic pressing Furthermore the average grains size of specimens prepared by vacuum sintering or vacuum sintering with hot isostatic pressing is coarser than that of specimens prepared by spark plasma sintering with hot isostatic pressing, but mechanical properties are lower than that of specimens prepared by spark plasma sintering with hot isostatic pressing Spark plasma sintering with hot isostatic pressing can not only decrease the average grain size of sintered specimens, but also increase mechanical properties of WC–629Co ultrafine cemented carbide The specimens prepared by spark plasma sintering with hot isostatic pressing have better properties than those prepared by spark plasma sintering, vacuum sintering or vacuum sintering with hot isostatic pressing

Production of titanium alloys for advanced aerospace systems by powder metallurgy

Abstract: Titanium alloys parts are ideally suited for advanced aerospace systems because of their unique combination of high specific strength at both room temperature and moderately elevated temperature, in addition to excellent corrosion resistance. Despite these features, use of titanium alloys in engines and airframes is limited by cost. The alloys processing by powder metallurgy eases the obtainment of parts with complex geometry. In this work, results of the Ti-6Al-4V and Ti-13Nb-13Zr alloys production are presented. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 up to 1500 °C, in vacuum. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. It was shown that the samples were sintered to high densities and presented homogeneous microstructure from the elements dissolution with low interstitial pick-up.

Titanium tungsten alloys produced by additions of tungsten nanopowder

Abstract: Disclosed herein are titanium-tungsten alloys and composites wherein the tungsten comprises 0.5% to 40% by weight of the alloy. Also disclosed is a method of making such alloys and composites using powders of tungsten less then 3 μm in size, such as 1 μm or less. Also disclosed is a method of making the titanium alloy by powder metallurgy, and products made from such alloys or billets that may be cast, forged, or extruded. These methods of production can be used to make titanium alloys comprising other slow-diffusing beta stabilizers, such as but not limited to V, Nb, Mo, and Ta.

Computational Plasticity in Powder Forming Processes

Abstract: The powder forming process is an extremely effective method of manufacturing structural metal components with high-dimensional accuracy on a mass production basis. The process is applicable to nearly all industry sectors. It offers competitive engineering solutions in terms of technical performance and manufacturing costs. For these reasons, powder metallurgy is developing faster than other metal forming technology. "Computational Plasticity in Powder Forming Processes" takes a specific look at the application of computer-aided engineering in modern powder forming technologies, with particular attention given to the Finite Element Method (FEM). FEM analysis provides detailed information on conditions within the processed material, which is often more complete than can be obtained even from elaborate physical experiments, and the numerical simulation makes it possible to examine a range of designs, or operating conditions economically. It describes the mechanical behavior of powder materials using classical and modern constitutive theories. It is devoted to the application of adaptive FEM strategy in the analysis of powder forming processes. 2D and 3D numerical modeling of powder forming processes are presented, using advanced plasticity models.

Mechanochemical synthesis of Cu-Al2O3 nanocomposites

Abstract: Nanocomposite powders of Cu–Al 2 O 3 were produced by simple milling at room temperature in high-energy attritor mill using mixtures of Cu, Cu 2 O and Al powder ingredients. The milled powders were then consolidated by hot pressing (HP) in high-density graphite die at 800, 850 and 900 °C under 50 MPa. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that the consolidated materials were comprised of a mixture of nanocrystalline fcc-Cu and α-Al 2 O 3 phase. The results of microstructural analysis also showed that Cu grains were of order of 20–30 nm with a bimodal size distribution of Al 2 O 3 dispersoids: the coarse dispersoids are about 50–100 nm and fine ones about 10–20 nm. Average hardness number of the hot pressed materials consolidated at 850 °C increases from 70 to 103 HR B (Rockwell hardness number) with increasing vol.% of Al 2 O 3 .

Assessment of a powder metallurgical processing route for refractory metal silicide alloys

Abstract: A powder metallurgical (PM) processing route for the manufacturing of two different refractory metal silicide alloys comprising inert gas atomization of presintered bars, hot isostatic pressing, and hot extrusion (reduction in cross section of 6:1) was established. The mechanical properties between room temperature and 1200 °C of the PM-processed Mo-3Si-1B and Nb-24Ti-20Si-5Cr-3Hf-2Al alloys (in wt pct) were assessed with tensile tests vs a state-of-the-art Ni-base single crystalline alloy (CMSX 4) and a directionally solidified (MASC) niobium-base silicide alloy, respectively. The microstructural characterization of both the hot-isostatically pressed and extruded materials was carried out applying scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) analysis. The Mo-Si-B alloy is characterized by an intermetallic matrix surrounding globular Mo particles in the hot isostatic press and a nearly continuous molybdenum solid solution matrix with dispersed intermetallic particles in the hot-extruded condition. Hot extrusion results in a substantial reduction of the DBTT of about 200 °C and tensile strengths superior to CMSX 4 at temperatures above 1000 °C. In the case of the Nb-base silicide alloy, a niobium solid solution surrounding intermetallic particles with Nb5Si3-type structure characterizes the final alloy. In the intermediate temperature range of 500 °C to 816 °C, a strength level equivalent to the directionally solidified MASC alloy was observed.

TEM study of PM 2000 steel

Abstract: Transmission electron microscopy (TEM) as well as corresponding analytical techniques, such as high resolution TEM (HRTEM), energy dispersive X-ray (EDX) analysis, electron energy loss spectroscopy...

Some aspects on workability of aluminium–iron powder metallurgy composite during cold upsetting

Abstract: Workability is a measure of the extent of deformation that a powder metallurgy materials can withstand prior to fracture occurred in the forming or upsetting processes Ductile fracture is the most common mode of failure in bulk forming process The formability is a complicated phenomenon, dependent upon the process as well as the material parameters A complete experimental investigation on the workability behaviour of Al–Fe composite was performed under the triaxial stress state Upsetting of Al–Fe composite having different iron contents with different aspect ratios and iron particle sizes were carried out and the formability behaviour of the compacts at triaxial stress condition was determined A new true strain considering the effect of the bulging was taken in to account The curves plotted for different compacts were analyzed and concluded that there is a drastic changes in the formability behaviour of compacts because of different content of iron and its particle sizes and aspect ratios

Thermal conductivity and phase stability of plasma sprayed ZrO2–Y2O3–La2O3 coatings

Abstract: Thermal conductivity and phase stability of La 2 O 3 ,Y 2 O 3 stabilized ZrO 2 plasma sprayed coatings were investigated. La 2 O 3 was selected as a stabilizer because it had a significant effect on reducing densification of Y 2 O 3 stabilized ZrO 2 (YSZ). The developed coating showed low thermal conductivity even after high temperature exposure due to its high resistance to sintering. However, phase stability and thermal cycle life of the coating decreased as the amount of La 2 O 3 was increased. It was concluded that optimum amount of La 2 O 3 addition was about 1 mol% to suppress sintering with little degradation of other properties.