Showing papers in "Powder Metallurgy in 1987"
TL;DR: In this article, a special apparatus, consisting of rectangular dies of various widths, has been utilized with copper and mixed elemental bronze powders, and the results show that filling densities decrease with decreasing die opening.
Abstract: Experiments conducted to try to establish the influence of small die openings on the actual filling density are reported. A special apparatus, consisting of rectangular dies of various widths, has been utilized with copper and mixed elemental bronze powders. The results show that filling densities decrease with decreasing die opening. The angle between sense of motion in filling and main die axis also influences the filling density, through rebounds during powder fall; these rebounds play a positive role. The changing quantity of powder entering various dies can be explained by assuming that a boundary layer is present on the die surfaces. This boundary layer, with density tending to zero when approaching the walls from the bulk of the powder, is dependent on grain shape and sieve analysis. A simple theory, including a hydraulic radius of ‘compacting’ area, has been proposed and the corresponding formulae for different die geometries derived. The theoretical lines are in good agreement with the r...
25 citations
TL;DR: In this paper, a new theoretical model for compaction of powders has been proposed based on the contribution of two different types of mechanism: rearrangement of powder particles and plastic deformation.
Abstract: A new theoretical model for compaction of powders has been proposed based on the contribution of two different types of mechanism. The first type is the rearrangement of powder particles which essentially acts at low compacting pressures. The second includes plastic deformation, fragmentation, or a combination of the two processes. The equations derived have been directly applied to the load-displacement curve obtained by pressing the powders in a die on a mechanical testing machine and recording the ram travel and the transmitted load. Tests on very different kinds of materials (organic compounds, magnesium oxide, flint clays, metallic powders) showed that the proposed theoretical model gives a very good description of the compaction process. Furthermore, the constants in the derived equations have been combined to obtain reliable parameters (maximum density attain- able, compaction ratio). PM/0447
13 citations
TL;DR: Caracterisation des proprietes physiques et mecaniques d'eprouvettes en poudre d'aluminium compactees en fonction de la temperature de frittage.
Abstract: Caracterisation des proprietes physiques et mecaniques d'eprouvettes en poudre d'aluminium compactees en fonction de la temperature de frittage
13 citations
12 citations
TL;DR: In this paper, the isochronal vacuum sintering behavior of BT42 grade high speed steel after cold compaction of annealed, water atomized powder is reported.
Abstract: The isochronal vacuum sintering behaviour of BT42 grade high speed steel after cold compaction of annealed, water atomized powder is reported. Densities of the order of 99% theoretical were readily achieved. For the as received powder the sintering temperature range was 1245–1260°C. The effect of adding nominal 0·01% elemental carbon was negligible. For 0·1%C addition densification commenced at a lower temperature and the sintering range was reduced to 1230–1250°C. The addition of carbon had no deleterious effect on the microstructure. The primary carbides present in the microstructure (compositions, excluding carbon, in weight per cent) were ∼9%M6C (4Co–4Cr–28Fe–14Mo–3V–47W), ∼13%MC (lCo–4Cr–4Fe–15Mo–41V–35W), and M3C (cemenite). When the specimens were oversintered by ∼ 20 K grain boundary eutectic carbides (4Co–14Cr–40Fe–20Mo–6V–16W) were also detected. PM/0445
12 citations
TL;DR: In this paper, the effect of secondary pore size on the formation of a transient liquid phase and thus in the creation of pores was studied by varying the alloying element powder size, and it was found that Fe-Cu can absorb small numbers of larger pores, which otherwise cause lower mechanical properties.
Abstract: Fe-Cu and Fe-Mo-C materials were sintered at temperatures resulting in the formation of a transient liquid' phase and thus in the formation of pores. By varying the alloying element powder size, the effect of secondary pore size was studied. It was found that Fe-Cu can absorb small numbers of larger pores, which otherwise cause lower mechanical properties. With Fe-Mo-C the effect of pores generated during sintering is insignificant, if the pores are not extremely large, because overall density is of markedly higher importance, the primary pores already present in the. green compact being more harmful than the secondary ones. PM/0437
12 citations
TL;DR: In this paper, the development of an automatic die wall lubrication system for use during powder compaction of ferrous-based materials is described, employing EP oil fed to the die wall interface under slight air pressure and augmented by the action of the toolset.
Abstract: The development of an automatic die wall lubrication system for use during powder compaction of ferrous based materials is described. The technique, employing EP oil fed to the die wall interface under slight air pressure and augmented by the action of the toolset, appears to work very well. Following comprehensive laboratory scale development of the technique, involving particularly lubricant selection, satisfactory works trials have been implemented. Five thousand simple preforms for subsequent powder forging and 2000 green compacts for a commercial sintered component of some geometric complexity have been produced in a modified production toolset. PM/0450
11 citations
TL;DR: In this article, the influence of processing on properties of Cemented Carbide has been investigated in the context of powder metallurgy, and it has been shown that processing has a significant influence on the properties of the powder.
Abstract: (1987). Influence of Processing on Properties of Cemented Carbide. Powder Metallurgy: Vol. 30, No. 3, pp. 175-181.
9 citations
TL;DR: In this paper, steel tubes of varying wall thickness were compacted using trimonite explosive, and the maximum tube velocity was estimated on the basis of a relationship applicable to the acceleration of flat plates under the influence of detonating explosives.
Abstract: Powders of copper, iron, APK1 superalloy, and RSR aluminium alloy have been compacted in steel tubes of varying wall thickness using Trimonite explosive. It was assumed that compaction occurred by a rapid acceleration of the tube wall, which in turn collapsed on to the metal powder to effect compaction. The maximum tube velocity was estimated on the basis of a relationship applicable to the acceleration of flat plates under the influence of detonating explosives. Empty tubes were collapsed explosively to determine the energy absorbed during collapse to a specified strain. In compaction tests, the energy required to compact the powder was determined by subtracting the tube deformation energy from the total initial kinetic energy of the tube. The results show that definite relationships exist between the specific kinetic energy applied to the powder and the compacted density achieved. These relationships are similar to relationships established between applied pressure and compacted density in isost...
9 citations
TL;DR: In this paper, an explosive cartridge gun was used to accelerate a cylindrical impacter to a velocity of 120 m s−1 on a powder specimen contained in a thick walled cylinder die, which acted as a short circuit switch to discharge stored high voltage electrical energy through the powder during the impact.
Abstract: An explosive cartridge gun was used to accelerate a cylindrical impacter to a velocity of 120 m s−1 on to a powder specimen contained in a thick walled cylindrical die. The impacter also acted as a short circuit switch to discharge stored high voltage (up to 10 kV) electrical energy through the powder during the impact. In this way, relatively high density and tougher powder metallurgy components were obtained as compared with those from electrical discharge or impact processes applied individually. These compacts exhibited mechanical interlocking as a result of impact as well as interparticle welding due to electrical discharge. The steel impacters were partially insulated to vary the duration between the instant of electrical discharge and that of maximum compressive force. The best compact was found to be produced when the electrical energy was discharged at the instant just before maximum dynamic compaction pressure occurred. PM/0426
8 citations
TL;DR: Rotary forging of a component from powder is accomplished in a single forging operation without any cintering or other processing by firstly pressing the powder in a closed die situation to produce an initial compressed form and then subjecting this compresed form to a rotary forging process as discussed by the authors.
Abstract: Rotary forging of a component from powder is accomplished in a single forging operation without any cintering or other processing by firstly pressing the powder in a closed die situation to produce an initial compressed form and then subjecting this compresed form to a rotary forging process.
TL;DR: In this paper, the authors investigated the fundamentals of the atomization of molten metals using the Coanda effect and found that the gas flowrate from a Coanda nozzle was at least equivalent to that from a converging nozzle operating under frictionless and adiabatic conditions.
Abstract: This paper presents the results of an investigation into the fundamentals of the atomization of molten metals using the Coanda effect. Various visualization techniques were used to study the flow of the gas jet out of a Coanda nozzle, the aspiration of surrounding gas to the Coanda jet, and the atomization of molten metal. It has been shown that the Coanda gas jet is very sensitive to both nozzle surface and nozzle geometry. These design parameters control jet expansion and the efficiency of the conversion of nozzle velocity into jet momentum. The gas flowrate from a Coanda nozzle was found to be at least equivalent to that from a converging nozzle operating under frictionless and adiabatic conditions. The atomizing mechanism using the Coanda nozzle determined using high speed photography was found to follow the same sequence of events as in conventional gas atomization. However, owing to the large pressure gradient normal to the Coanda surface, the molten metal forms a semiconical sheet in the p...
TL;DR: In this article, a comparison between powder flow in quasistatic and dynamic compaction was made when both methods produce a compact of the same average density, and it was shown that compacts made using the dynamic method had a more uniform density distribution and were appreciably denser and harder near the die walls below the shoulder.
Abstract: An experimental study has been made of the flow of metal powders in an axisymmetric die incorporating a shoulder marking an abrupt reduction of diameter in the direction of compaction. A comparison has been made between powder flow in quasistatic and dynamic (shock wave) compaction when both methods produce a compact of the same average density. With the commercial grades of aluminium, iron, and copper powders studied, higher peak pressures were necessary during dynamic compaction to produce compacts with the same average density as those made quasistatically. Measurements of powder displacement and hardness distribution showed that compacts made using the dynamic compaction had a more uniform density distribution and were appreciably denser and harder near the die walls below the shoulder. With common levels of admixed lubricant, all the powders flowed smoothly around the shoulder during quasistatic compaction. For the more ductile aluminium this was also true for dynamic compaction. However, wit...
TL;DR: In this article, the dependence of some sintered properties on the initial packing density of copper sphere compacts was investigated in order to explain the relationship between sinterability and initial packing densities.
Abstract: The dependence of some sintered properties on the initial packing density of copper sphere compacts was investigated in order to explain the relationship between sinterability and initial packing density for the loosely sintered product. Spherical copper powders with various initial packing densities were pressureless formed in a cylindrical quartz tube and sintered at the appropriate temperature. Sintered properties, shrinkage, electrical resistivity, and breaking strength, were measured and examined on the basis of simple geometrical model. These properties were found to be dependent on the initial packing density of the green compact. Sintering shrinkage and breaking strength increased with increasing initial packing density, whereas electrical resistivity decreased. The activation energy of the sintering process for the copper spheres was determined as 172·6 kJ mol−1 and volume diffusion from the grain boundaries appeared to be the most plausible mechanism for sintering of the copper sphere co...
TL;DR: Caracterisation des microstructures par microscopie electronique a balayage d'un acier maraging compacte a chaud. Influence de la taille des particules sur les proprietes mecaniques de ces aciers.
Abstract: Caracterisation des microstructures par microscopie electronique a balayage d'un acier maraging compacte a chaud. Influence de la taille des particules sur les proprietes mecaniques de ces aciers
TL;DR: In this article, a finite element method was used in the dimensioning of prestrained die tools for powder compaction, and the die geometry has been varied and also the die has also been subject to different types of stresses and strains.
Abstract: Stress and strain are studied using the finite element method in the dimensioning of prestrained die tools for powder compaction. The die geometry has been varied and the die has also been subjecte ...
TL;DR: In this paper, some developments in simplifying the procedures for determining fracture toughness parameters and for measuring properties of edges are described using the example of applications where fracture is a dominant failure mechanism.
Abstract: The different objectives of scientists and industry in testing hard materials create conditions where laboratory tests are developed which are unrealistic because they are too sophisticated for general use by industry or they are irrelevant to properties required in service. Using the example of applications where fracture is a dominant failure mechanism, some developments in simplifying the procedures for determining fracture toughness parameters and for measuring properties of edges are described. PM/0413
TL;DR: In this paper, the compaction and green strength of Ferrite Powders were investigated and the results showed that Ferrite powders have a green strength and compressive properties.
Abstract: (1987). Compaction and Green Strength of Ferrite Powders. Powder Metallurgy: Vol. 30, No. 4, pp. 267-271.
TL;DR: Melt extraction and melt overflow rapid solidification processes provide excellent production routes for the manufacture of fine metallic particulate as mentioned in this paper, which offers exact control over particulate dimension and composition, and flexibility in the use of standard or non-standard alloys.
Abstract: Melt extraction and melt overflow rapid solidification processes provide excellent production routes for the manufacture of fine metallic particulate. The processes offer exact control over particulate dimension and composition, and flexibility in the use of standard or non-standard alloys. Material produced in this way can be either directly compacted or chopped and milled to a desired sieve size. The structure and properties of typical materials produced by these methods are described. PM/0422
TL;DR: In this article, a detailed study of the induction heating of a range of preform shapes applicable to the production of low alloy steel engineering components was planned, and the experimental techniques used to determine electrical resistivity, thermal conductivity, and magnetic permeability over the temperature range 20-1000°C, for sintered preforms made from two commercially available, low-alloy steel powders.
Abstract: Induction heating is a convenient and efficient method of preparing slugs of simple shape, for closed die forging. The main requirement of the sinter forging process is to provide a sintered preform of shape and dimensions close to those of the finished component. A detailed study, including modelling, of the induction heating of a range of preform shapes applicable to the production of low alloy steel engineering components was planned. An immediate problem was the lack of physical property data for sintered steel, so that an initial requirement of the experimental programme described in this paper was to determine relevant physical properties. Subsequent objectives were to investigate the effect of electromagnetic variables on preform heating characteristics and to establish quantitative relationships which would be useful in induction coil design. The first part of the paper is a discussion of the relative, basic scientific principles, in the light of published information. This is followed by a description of the experimental techniques used to determine electrical resistivity, thermal conductivity, and magnetic permeability over the temperature range 20-1000°C, for sintered preforms made from two commercially available, low alloy steel powders. Analysis of the results confirmed the reliability of the test procedures, and the behaviour observed was shown to be similar to that reported for the 'corresponding' wrought steels. Simple numerical relationships between compact density and a physical property were proved to be applicable. It is concluded that the information presented in the paper forms a sound basis for the design of coils suitable for induction heating low alloy steel sintered preforms. PM/0438
Journal Article•
TL;DR: Mise en place des controles de qualite for l'obtention de metaux frittes ayant de tres bonnes caracteristiques mecaniques as mentioned in this paper.
Abstract: Mise en place des controles de qualite pour l'obtention de metaux frittes ayant de tres bonnes caracteristiques mecaniques
Journal Article•