Showing papers in "Powder Metallurgy in 1992"
TL;DR: In this paper, a new form of yield criterion for porous metals is proposed, which can predict experimental results of combined tension and torsion tests of sintered porous metals with a high degree of accuracy.
Abstract: A new form of yield criterion for porous metals is proposed. The equation, having a variable parameter which may be obtained from the uniaxial relative yield stress versus density data, can predict experimental results of combined tension and torsion tests of sintered porous metals with a high degree of accuracy. Other yield criteria are critically reviewed. Most of them unreasonably suggest zero yield stress only at zero relative density
103 citations
TL;DR: The success of the application is dependent on the shape and size of the part and the material properties as discussed by the authors, which is the case for all the Alloyed Soft Magnetic Materials (OFM) used for ac applications.
Abstract: Soft magnetic materials for ac applications call to mind the familiar Fe, Fe–Si, and Fe–Ni alloys commonly used for the production of components. Due to the isotropic nature of PM soft magnetic parts, design factors such as stacking and sheet thickness are not appropriate for the reduction of total losses. The success of the application is dependent on the shape and size of the part and the material properties. The production of Fe–Si and Fe– Ni alloyed PM parts is today an industrial process in which the magnetic properties are tailored by well defined process parameters such as compaction pressure, sintering time, and sintering temperature. However, the PM process permits the use of alloying elements and systems beyond the sphere of traditional soft magnetic materials. A common example is Fe–P alloyed soft magnetic materials where an addition of 0·8%P results in an isotropic part which without either shape or size adjustment is equivalent to a pure Fe stack of sheet thickness 0·65 mm. The additi...
24 citations
TL;DR: In this paper, the authors reviewed some cases where the knowledge of phase diagrams, especially calculated diagrams, plays an important role in development work, such as the accurate control of the carbon balance necessary for successful sintering of some WC-Co alloys as well as the information needed for the sintered Fe-Ni based carbides.
Abstract: Databases and programs for the calculation of phase diagrams have become valuable tools in research and development programmes for cemented carbides and steels. The number of applications of this technique for cemented carbide systems has increased lately due to the fact that some basic systems have now been analysed and entered into such databases. In the following, some cases are reviewed where the knowledge of phase diagrams, especially calculated diagrams, plays an important role in development work. These cases refer to the accurate control of the carbon balance necessary for successful sintering of some WC–Co alloys as well as the information needed for the sintering of Fe–Ni based carbides. The development work on steels within Sandvik Steel is further advanced when it comes to using phase diagrams and especially calculated diagrams as a tool for the development of new grades. This work is now facilitated by the great number of assessed systems for iron based alloys and the reliable databa...
23 citations
TL;DR: In this paper, the authors describe some high strength materials and the influence of processing parameters on their dimensional tolerances, and describe some powders such as Distaloy and Starmix.
Abstract: Development of new PM materials and processes has led to an increased use of PM machine components. Due to their good mechanical properties it is possible for them to fulfil the demand for high performance applications such as connecting rods, highly loaded gear box parts, transmission gears, etc. The competitive advantage of PM is primarily the net shape achievable with a minimum of operations. The dimensional tolerances are therefore of the greatest importance; especially for high strength materials which cannot be sized, the dimensions must be very close to those required after sintering. This has led to the development of powders such as the Distaloy grades or bonded powder mixes such as Starmix. The objective of these powder types is to reduce the range of alloying composition and thereby improve tolerances. This paper describes some high strength materials and the influence of processing parameters on their dimensional tolerances. In order to meet the demanding requirements of new applicatio...
23 citations
TL;DR: In this article, the effect of chemical composition on the sintering mechanisms and microstructure of Fe-C-P alloys was studied by metallographic and thermal analysis and by secondary ion mass spectroscopy.
Abstract: The effect of chemical composition on the sintering mechanisms and microstructure of Fe-C-P alloys was studied by metallographic and thermal analysis and by secondary ion mass spectroscopy. Pore morphology was found to tend to spheroidisation with an increase in the phosphorus and, more particularly, in the carbon content. In addition, phosphorus was found to be heterogeneously distributed in ferrite and in pearlite. These results are explained by proposing a sintering mechanism, based on two main processes. The first leads to the formation of phosphorus rich ferrite through the reaction between phosphides and low carbon austenite. The second produces transient liquid through a eutectic reaction between phosphides and carbon rich austenite
18 citations
TL;DR: The application of Shear Controlled Orientation Technology to Powder Injection Moulding is discussed in this paper, where the authors present an application of this technology to powder injection moulding.
Abstract: (1992). Application of Shear Controlled Orientation Technology to Powder Injection Moulding. Powder Metallurgy: Vol. 35, No. 2, pp. 107-112.
16 citations
TL;DR: In this article, phase relations and listed parameters in permanent magnet systems were investigated and the parameters varied were: gross composition plus additives, the liquid phase sintering process parameters, and the following heat treatment.
Abstract: Permanent magnets based on Fe–Nd–B show high magnetisation and high coercivity at room temperature but unfavourable properties at higher temperatures. This behaviour has to be improved. The hard magnetic properties are limited by nucleation of severed domains, therefore the surfaces and interfaces of the grains constituting the material are the controlling factor. For any optimisation a detailed knowledge of the phase relations and microstructure development is needed. The parameters varied were: gross composition plus additives, the liquid phase sintering process parameters, and the following heat treatment. Phase relations and listed parameters in the systems Fe–Nd–B, Fe–Dy(Tb)–B, Fe–Nd–Al, Fe–Nd–C, and Fe–Nd–Dy(Tb)–B were investigated. PM/0589
12 citations
TL;DR: In this paper, hot isostatic pressing (hipping) is an extremely efficient way of densifying ceramic and high alloy metallic powders, or for healing porosity in castings.
Abstract: Hot isostatic pressing (hipping) is an extremely efficient way of densifying ceramic and high alloy metallic powders, or for healing porosity in castings. However, depending on the parameters of pr ...
11 citations
TL;DR: In this article, a composite PM 6061 aluminium alloy based metal matrix composites were manufactured by wet blending of 6061 alloy powder and δ alumina Saffil fibres followed by hot direct extrusion of the powder-fibre blends in closed containers through a streamline die.
Abstract: Composite PM 6061 aluminium alloy based metal matrix composites were manufactured by wet blending of 6061 alloy powder and δ alumina Saffil fibres followed by hot direct extrusion of the powder-fibre blends in closed containers through a streamline die, then heat treated to T6 condition (solution treated at 540°C for 5 h and age hardened at 160°C for 16 h). Density depended on the reinforcement content: relative densities of 97.5% for composite material containing 30 vol.-% fibres to 99.3% for composite material with 10 vol.-% fibres were obtained
11 citations
TL;DR: In this article, a mixture of copper, titanium, and boron powders were mechanically alloyed for various milling periods by an attritor to produce copper composite powder with a dispersion of boride particles.
Abstract: To produce copper composite powder with a dispersion of boride particles, mixtures of copper, titanium, and boron powders were mechanically alloyed for various milling periods by an attritor. Microstructural changes of the mechanically alloyed powders with milling were examined by X-ray diffraction, SEM, and TEM. The mixed powders become finer as the milling time increases. Structures consisting of extremely fine grains, in the nanometre size range, form in the mechanically alloyed powder after prolonged milling. The refinement of the structure in the Cu-Ti powder is accelerated by additions of boron and TiB 2 powders
10 citations
TL;DR: In this paper, the energy band gap and electrical properties of polycrystalline CdS1−xTex films were investigated by measuring optical transmission spectra and Hall voltages.
Abstract: Polycrystalline CdS1−xTex films were prepared by coating (l−x) CdS +xCdTe pastes on a borosilicate glass substrate and sintering in nitrogen. The films were sintered in the temperature range 625–700°C to find the phase boundaries of the binary system in this temperature range. The energy band gap and electrical properties of these solid solution semiconductors have been investigated by measuring optical transmission spectra and Hall voltages. At 625°C, the solubility of Te in CdS is x = to 0·10 and the band gap of the S rich solid solution decreases from 2·43 eV for CdS (x=0) to 1·87 eV for CdS0·9Te0·l The solubility of S in CdTe is 0·14 and the band gap increases slightly from 1·42 eV for CdS0·14 Te0·86 to 1·46 eV for CdTe. The boundaries for the miscibility gap of the binary system at 700°C are x = 0·12 and x = 0·84. Both the carrier concentration and Hall mobility of the alloy semiconductors decreases with increasing Te content. The majority carriers were electrons in the S rich semiconductors...
TL;DR: The use of repeated solid state transformation between the grey and white allotropes of tin, which can be performed at low temperature and involves a large volume change, has been found to be an excellent means of breaking up atomised powder into fine particles of high specific surface area.
Abstract: The production of fine high purity tin powders suitable for use in chemical catalysis has been investigated. Ultrasonic atomisation gave a greater fraction of fines and a more homogeneous size distribution than conventional gas atomisation. The use of repeated solid state transformation between the grey and white allotropes of tin, which can be performed at low temperature and involves a large volume change, has been found to be an excellent means of breaking up atomised powder into fine particles of high specific surface area
TL;DR: In this article, a Polypropylene based organic vehicle was used to injection mold commercial Purity aluminium powder and the test bars produced were heated, according to near optimum temperature-time schedules, in both static air and flowing nitrogen to remove the organic vehicle.
Abstract: A Polypropylene based organic vehicle was used to injection mould commercial Purity aluminium powder. The test bars produced were heated, according to near optimum temperature-time schedules, in both static air and flowing nitrogen to remove the organic vehicle. Heating was interrupted at different temperatures to measure shrinkage and strength of the test bars. Shrinkage caused by the removal of organic vehicle increases the volume percentage of aluminium in the test bars and this results in an increase in their strength but the packing efficiency attained is well below the maximum value.
TL;DR: In this article, the effect of sintering parameters on the magnetic properties of Fe-0.45P materials was investigated and it was shown that, within the range studied, magnetic properties were improved by using a high sinter temperature, long sinterding time, high heating rate, and pure hydrogen atmosphere.
Abstract: The magnetic properties of Fe-0.45P made by the powder metallurgy process are sensitive to processing parameters. This study emphasises the effect of sintering parameters on the permeability, magnetic induction, and coercive force of Fe-0.45P materials. The following sintering variables were investigated: heating rate, dew point, sintering time, sintering atmosphere, and sintering temperature. It is shown that, within the range studied, permeability and coercive force were improved by using a high sintering temperature, long sintering time, high heating rate, and pure hydrogen atmosphere
TL;DR: The metallographic development and thermal reaction of 304L stainless steel powder with silicon additions during sintering has been investigated in this paper, where a marked diffusion zone appears on the edge of silicon particles and then transforms into some kind of eutectic liquid at 950°C.
Abstract: The metallographic development and thermal reaction of 304L stainless steel powder with silicon additions during sintering has been investigated. On heating to 850°C a marked diffusion zone appears on the edge of silicon particles. This reaction zone grows inwards, and then transforms into some kind of eutectic liquid at 950°C. Upon futher sintering the silicon particles melt completely, the liquid phase dissolves and penetrates the boundaries of the 304L particles. The wettability and fluidity of the liquid phase are improved with increasing sintering temperature
TL;DR: In this paper, a powder for wear resistant materials, designed to be sintered at 1120°C for 30 min in N 2 based atmospheres, has been developed and compared to M2 high speed steel (called material B in this investigation) in certain wear situations.
Abstract: A powder for wear resistant materials, designed to be sintered at 1120°C for 30 min in N 2 based atmospheres, has been developed. After sintering it can be compared to M2 high speed steel (called material B in this investigation) in certain wear situations. The composition of the material called A in this investigation is Fe-1C-0.6P-10Mo. The influences of composition and processing parameters on the mechanical properties are shown. A comparison with sintered M2 is made showing similar hardness and wear properties
TL;DR: A prototype ion implanter equipped with a large area (40 cm 2 ), high current (20-120 mA) ion source operating at a medium acceleration voltage (5-100 kV) has been constructed for the ion beam treatment of powders as mentioned in this paper.
Abstract: A prototype ion implanter equipped with a large area (40 cm 2 ), high current (20-120 mA) ion source operating at a medium acceleration voltage (5-100 kV) has been constructed for the ion beam treatment of powders. First results obtained showed that surface cleaning, defect generation, and doping can be achieved homogeneously within the powder. The materials that were studied were mainly ceramic powders (micrometre range) such as B 4 C, SiC, TiC, and WC which are difficult to densify and thus were implanted with argon, aluminium, and silicon to create «custom tailored» powder surfaces and to enhance sinterability.
TL;DR: The consolidation of metal powders using a nutation-spin rotary forging machine is a two-stage process as discussed by the authors, where an initial, uniaxial, compaction stage is followed by a rotary stage which introduces shear deformation into the compact.
Abstract: The consolidation of metal powders using a nutation-spin rotary forging machine is a two stage process. An initial, uniaxial, compaction stage is followed by a rotary stage which introduces shear deformation into the compact. Fundamental appreciations have been gained of the geometric, mechanical, and materials aspects of each stage and the ways which they interact. Particle geometry plays an important role: optimum geometry seems to be needles with aspect ratios close to 60:1. Enforced adoption of split die techniques to cope with local compaction pressures of several gigapascals has opened a range of possibilities for part shapes which is wider than that normally limiting PM parts. Re-entrant features, lugs, and similar features can be produced. Flow of material to replicate such features is brought about by high local pressures and shear stresses. Differing combinations of side wall segments can be used in a bolster to generate a flexible manufacturing cell. Materials successfully consolidated ...
TL;DR: In this paper, hot plane strain compression testing is shown to be more suitable than hot torsion testing in providing flow stress data for partially consolidated aluminium 2014 powder which forms the matrix of many advanced composites.
Abstract: Hot plane strain compression testing is shown to be more suitable than hot torsion testing in providing flow stress data for partially consolidated aluminium 2014 powder which forms the matrix of many advanced composites. It is demonstrated that data provided by this technique are comparable to hot torsion data by the use of a solid control alloy. Activation energies and constitutive equation constants are derived from the data for use in analytical process models. It is proposed that this method of testing provides an extremely useful way of monitoring the flow behaviour of powder based materials that are not amenable to other test methods
TL;DR: In this article, a sintered CdS/CdTe solar cell that was fabricated by using a Cd powder with an average particle size of ∼ 4 μm shows a solar efficiency of 12% when measured under a solar intensity of 80 mW cm−2.
Abstract: Transparent CdS films with low electrical resistivity have been prepared by coating a CdS slurry on a glass substrate followed by sintering in nitrogen. CdTe slurries consisting of Te powder, Cd powders of various particle sizes, and an appropriate amount of propylene glycol were coated on the sintered CdS films and were sintered in nitrogen to prepare sintered CdS/ CdTe solar cells. The efficiency of a sintered CdS/ CdTe solar cell increases with increasing Cd particle size up to 3–4 μm and then decreases with a further increase in the Cd particle size. The microstructures of the sintered CdTe layer and of the cross-section of the CdS/CdTe solar cell show that the structures are the most compact in a solar cell which started with a Cd particle size of 3–4 μm. A sintered CdS/CdTe solar cell that was fabricated by using a Cd powder with an average particle size of ∼ 4 μm shows a solar efficiency of 12% when measured under a solar intensity of 80 mW cm−2. PM/0575
Journal Article•
TL;DR: Early railway vehicles were fitted with wooden blocks which were applied to the rim of the wheel when braking was required as discussed by the authors, and this became the standard braking method and remains the most common method of stopping both rolling and traction stock around the world.
Abstract: Early railway vehicles were fitted with wooden blocks which were applied to the rim of the wheel when braking was required. In 1853, Morse filed a patent describing the use of cast iron as a friction material for railway applications and quickly this became the standard braking method. To this day, cast iron brake blocks rubbing against the tread of steel wheels remains the most common method of stopping both rolling and traction stock around the world. In the UK, however, cast iron blocks are now fitted only for the lowest speed applications.
TL;DR: A thermodynamic data set for the 11 component system C−Co−O−Ti−W−C·C cemented carbides on yttria stabilised zirconia (YSZ) in the presence of calcium alumino silicate and calcium sulphide impurities is presented in this article.
Abstract: A thermodynamic data set for the 11 component system C–Co–O–Ti–W–Y–Zr–Ca–Si–Al–S has been assembled to study the reactions and equilibria occurring during the sintering of Co–Ti–W–C cemented carbides on yttria stabilised zirconia (YSZ) in the presence of calcium alumino silicate and calcium sulphide impurities. Results are presented for the following equilibria at 1450°C: YSZ + graphite + (Co,W,Ti,C); CaO–SiO2–Al2O3 + graphite + CaS; and YSZ+(Co,W,Ti,C)+CaO–SiO2–Al2O3+CaS+ graphite. In the absence of impurities, CO(g) and Co(g) are the only gas species present with pressures greater than 1 × 10−6 bar. In the presence of impurities a liquid oxide phase can be formed, and appreciable pressures (∼3 × 10−3 bar) of SiO(g) and SiS(g) occur. These could form deposits on the cemented carbides on cooling, leading to possible contamination with Si and S. PM/0588
TL;DR: In this article, an electromagnetically levitated drop technique has been used to determine the surface tension of 316L stainless steel with impurity additions, by observing the oscillating drop from two directions.
Abstract: An electromagnetically levitated drop technique has been used to determine the surface tension of 316L stainless steel with impurity additions. By observing the oscillating drop from two directions...