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Showing papers in "Powder Metallurgy in 1988"


Journal ArticleDOI
TL;DR: In this article, the deformation of a single sphere is measured as a direct and simple method of predicting hipping behavior for C1018 steel, copper, and API nickel superalloy and the predictions made from deformation experiments with single spheres were in good agreement with measured hipping behaviour at hipping densities <93% theoretical.
Abstract: Prediction of deformation behaviour during hipping is often difficult because data on complex material properties are required but are not usually available from the literature. From the present work, measurement of the deformation of a single sphere is proposed as a direct and simple method of predicting hipping behaviour. For C1018 steel, copper, and API nickel superalloy, the predictions made from deformation experiments with single spheres were in good agreement with measured hipping behaviour at hipping densities <93% theoretical. In addition, the creep parameters, such as the exponent n for the power law creep relation, of the powder material itself were measured during single sphere deformation. During hipping of C1018 in the density range above 90%, the use of lower pressures, which is favoured for economic reasons, showed that microstructural development and densification during the final stage of hipping are determined by relatively large pores. These large pores may result from irregul...

28 citations


Journal ArticleDOI
TL;DR: In this article, a laminated structure consisting of TiAl and Ti3AI was formed, which gave a high compressive yield strength accompanied by embrittlement of sintered TiAl compacts, no bending plastic deformation being observed at room temperature.
Abstract: Pulverised TiAl powder was cold isostatically pressed at 392 MPa and the resulting compact sintered at temperatures up to 1623 K to produce sintered TiAl with relative densities as high as 91%. This process formed a laminated structure consisting of TiAl and Ti3AI, which gave a high compressive yield strength accompanied by embrittlement of the sintered TiAl compacts, no bending plastic deformation being observed at room temperature. When centrifugally atomised powder melted in a CaO crucible was used, sintered TiAl specimens, apparently of full theoretical density, could be obtained by canned hipping at 1473 K under a pressure of 98 MPa. The hipped TiAl specimens had a grain size of ~20–30 μm, and grain coarsening was not observed, even when specimens were annealed for 720 ks at temperatures of 1273–1373 K. Hipped specimens annealed at 1273 K had a yield strength of 388 MN m −2 at room temperature, and bending ductilities > 0·4% were obtained. PM/0426

18 citations


Journal ArticleDOI
TL;DR: In this paper, a model is developed which describes the influence of size distributions of defects such as pores on the distribution of transverse rupture strength in three point bend testing of hard materials.
Abstract: A model has been developed which describes the influence of size distributions of defects such as pores on the distribution of transverse rupture strength (TRS) in three point bend testing of hard materials. The model is based on knowledge of three things: the stress distribution in the test specimen during loading; the three dimensional size distribution of the defects in the material; and the relationship between fracture toughness K IC, applied stress, and critical defect size for brittle fracture according to linear fracture mechanics. By using the fracture toughness of the material and the defect size distribution as input data the distribution of strengths of the material can be calculated. The model was tested on two WC–10%Co cemented carbides with relatively high porosity contents. The size distributions of defects such as pores and inclusions were evaluated with automatic image analysis on sections through the materials. Pores which had initiated the fracture were identified on fracture s...

15 citations


Journal ArticleDOI
TL;DR: Optimisation de l'ecoulement des poudres metalliques dans les moules par utilisation des thermoplastiques as discussed by the authors, a.k. a.
Abstract: Optimisation de l'ecoulement des poudres metalliques dans les moules par utilisation des thermoplastiques. Etude theorique et experimentale du moulage par injection

12 citations


Journal ArticleDOI
TL;DR: In this article, the surface analysis of Fe12Cr martensitic steel powder was performed using electron spectroscopy for chemical analysis and Auger electron spectrographs for surface analysis and showed that the composition and thickness of the surface oxides are independent of powder particle size.
Abstract: Surface analysis of Fe12Cr martensitic steel powder was performed using electron spectroscopy for chemical analysis and Auger electron spectroscopy. The analysed powder was produced by nitrogen gas atomisation, the average particle size being 190 μm. In the as atomised condition the powder is covered by particles of manganese, chromium, and iron oxides, as well as a thin (3 nm) layer mainly consisting of Fe2O3. The average thickness of the oxide particles is ~13 nm, whereas the total average oxide thickness is ~7 nm. The composition and thickness of the surface oxides are independent of powder particle size in spite of the difference in cooling rate between large and small metal particles. The liquid metal droplets solidify at or below 1400°C. Most of the oxide is formed during solidification. It is suggested that a mixed oxide (MnCr2O4) is produced. Above 1400°C no metallic oxide is formed due to the oxidation of carbon to carbon monoxide. At very high temperatures manganese evaporates. During c...

11 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of percentage content of low density polyethylene powder on the compaction of plain carbon steel powder was investigated with special emphasis on the effect on the percentage of high voltage electrical discharge compaction (EDC).
Abstract: Preforms of metal-polymer composites are produced by high voltage electrical discharge compaction (EDC). A relatively low density preform is obtained by simply connecting the powder mix, contained in a tube, across a charged capacitor bank. Above a certain voltage the oxide layers of the metal particles are broken and a heavy transient current passes through the powder column. Owing to combined electrothermal and electromagnetic effects, the powder mix consolidates into a preform in a period of ~50 μS. There is an upper level for the discharge voltage beyond which the powder column disintegrates like an exploding fuse wire. In the present paper, the EDC process is investigated with special emphasis on the effect of percentage content of low density polyethylene powder on the compaction of plain carbon steel powder. PM/0457

10 citations


Journal ArticleDOI
TL;DR: In this article, gas atomising is placed into context as a production technology by comparison with other methods of producing powder, and data obtained from the commercial production of powder in a wide range of alloys are characterised in terms of mean particle diameter and standard deviation and used to assess the efficiency of the atomiser in producing powder within the particle size distribution required for a particular end application.
Abstract: Gas atomising is placed into context as a production technology by comparison with other methods of producing powder. Data obtained from the commercial production of powder in a wide range of alloys are characterised in terms of mean particle diameter and standard deviation and used to assess the efficiency of the atomiser in producing powder within the particle size distribution required for a particular end application. PM/0484

9 citations


Journal ArticleDOI
TL;DR: The integrationrite de surface is un moyen fiable et net d'evaluation des caracteristiques geometriques, topographiques et metallurgiques de la piece usinee et de l'operation d'usinage dans le cas du percage de pieces frittees en metaux ferreux as mentioned in this paper.
Abstract: L'integrite de surface est un moyen fiable et net d'evaluation des caracteristiques geometriques, topographiques et metallurgiques de la piece usinee et de l'operation d'usinage dans le cas du percage de pieces frittees en metaux ferreux

9 citations


Journal ArticleDOI
TL;DR: In this paper, fine particles of various metals have been prepared by spark erosion in various dielectrics, and two electrodes with pieces of charge between them were employed to increase the powder production rate by at least two orders of magnitude.
Abstract: When two electrodes are immersed in close proximity in a dielectric fluid, connected to a pulsed power source, and the field strength in the gap is sufficiently high, a spark is produced as a result of the breakdown of the dielectric. In the present study, fine particles of various metals have been prepared by spark erosion in various dielectrics. Instead of the usual tool/workpiece arrangement used in electrodischarge machining, two electrodes with pieces of charge between them were employed to increase the powder production rate by at least two orders of magnitude. Powders of alloys, semiconductors, and compounds have been prepared, and it is shown that spark erosion can maintain a high production rate at low power consumption if the electrode/charge arrangement is used. PM/0479

8 citations


Journal ArticleDOI
TL;DR: In this paper, the plaquettes de coupe en acier rapide fritte revetues de TiN, TiC ou Ti(C,N) are described.
Abstract: Fabrication, caracteristiques, performances d'usinage et applications industrielles des plaquettes de coupe en acier rapide fritte revetues de TiN, TiC ou Ti(C,N)

5 citations



Journal ArticleDOI
TL;DR: In this paper, it is shown that adding more carbonate is necessary to ensure that there is a net flow of reaction products from the pores, so that furnace gases cannot enter and dilute the carburising pore gases before all the gr...
Abstract: Additions of certain alkali metal carbonates to irongraphite compacts cause the generation of a carburising gas atmosphere within the pores during sintering, and carbon alloying takes place efficiently and homogeneously at temperatures as low as 850°C if sintering is conducted in an inert gas furnace atmosphere. The process is believed to invoke the same catalytic cycle of reactions as that which is involved in pack carburising. However, in the sintering case only those carbonates which react with carbon to produce alkali metal are effective, and then only if the vapour pressure of the alkali metal is high at the sintering temperature. Both sodium and potassium carbonate are efficient catalysts at 850–950°C. It is necessary to add more carbonate than will theoretically sustain the catalytic cycle within the pores. The excess is required to ensure that there is a net flow of reaction products from the pores, so that furnace gases cannot enter and dilute the carburising pore gases before all the gr...

Journal ArticleDOI
TL;DR: In this paper, the effects of dielectric type and method of incorporation in iron powder compacts on the structure and properties of DPMs are presented. And the filling factor of a dielectromagnetic in iron, being the essential material parameter used in the design of magnetic circuits, is introduced and methods of calculating it.
Abstract: The effects of dielectric type and method of incorporation in iron powder compacts on the structure and properties of dielectromagnetics are presented. The filling factor of a dielectromagnetic in iron, being the essential material parameter used in the design of magnetic circuits, is introduced and methods of calculating it are given. This enables both the establishment of a precise criterion for dividing dielectromagnetics and magnetodielectrics and the analysis of dielectric distribution inside the material, which influences dielectric and iron phase continuity. Theoretical considerations are presented concerning correlations between production and the structure and properties of dielectromagnetics, knowledge of which is essential for their wider application in magnetic cores for electrical converters. PM/0478

Journal ArticleDOI
TL;DR: In this article, models for analysing shape changes during hipping of powder compacts enclosed in preshaped containers are presented, and two limiting mechanisms are considered: homogeneous densification and the mo...
Abstract: Models for analysing shape changes during the hipping of powder compacts enclosed in preshaped containers are presented. Two limiting mechanisms are considered: homogeneous densification and the mo ...

Journal ArticleDOI
TL;DR: Developpement theorique sur le frittage des poudres dielectromagnetiques as discussed by the authors, a.k.a. poudre dielectroniques.
Abstract: Developpement theorique sur le frittage des poudres dielectromagnetiques. Modelisation des interactions

Journal ArticleDOI
TL;DR: In this paper, the effect of tin additions on metallurgical properties of hot pressed and sintered stainless steel was investigated and it was found that during hot pressing Ni-Sn intermetallic compounds were formed.
Abstract: The effect of tin additions on the metallurgical properties of hot pressed and sintered stainless steel was investigated. Samples containing 0·25–10 wt-%Sn were hot pressed at a temperature of 650°C and a pressure of 85 MPa for 5 min. After hot pressing the specimens were heat treated at a temperature of 1150°C for 10 h under vacuum conditions. It was found that during hot pressing Ni-Sn intermetallic compounds were formed. These metastable compounds subsequently dissolved in the austenitic matrix during heat treatment at 1175°C. Addition of 10 wt-%Sn resulted in a saturated matrix and residual intermetallic compounds were located along the grain boundaries. This was observed by xray diffraction and metallographic analyses of the samples after hot pressing and heat treatment at 1175°C. The tin additions enhanced grain growth during heat treatment and grain size increased from ~17 to ~ 65 μm on raising the tin content to 10 wt-%. PM/0400

Journal ArticleDOI
TL;DR: In this article, a water atomiser with a pair of main nozzles and two subnozzles was used to produce bronze powders whose median particle size ranged from 50 to 150 μm.
Abstract: Bronze powders were produced using a water atomiser possessing a pair of main nozzles and a pair of subnozzles. Process parameters were varied in the following ranges: water pressure 100–200 bar; total water flow/metal flow ratio 2·8–7·7; and primary water flow/metal flow ratio 1·2–5·2. Primary water flow from the main nozzles was directed at the molten metal stream from the tundish nozzle. These water atomisation runs produced powders whose median particle size (characterised by sieving) ranged from 50 to 150 μm. Controlling factors for powder size appeared to be water pressure and primary water flow/metal flow ratio. While it appears to be common practice to characterise water atomisation runs by total water flow/metal flow ratio and water pressure, correlation between the former and particle size was not good for the bronze powder batches produced. The present observations suggest that solidification of bronze powders atomised by the action of the primary water spray had been completed before t...

Journal ArticleDOI
TL;DR: In this paper, high speed steel powders and iron powders containing phosphorus have been pressed and sintered with and without added carbon and phosphorus to assess the potential usage of these mixes for ambient temperature wear applications.
Abstract: Mixed high speed steel powders and iron powders containing phosphorus have been pressed and sintered with and without added carbon and phosphorus. The objective was to assess the potential usage of these mixes for ambient temperature wear applications. The dimensional stability and structures have been investigated for a range of composition. It is found that a 50:50 mix of the two powders results in good compressibility, and with additions of carbon and phosphorus up to 0·8%C and 0·8%P respectively, adequate dimensional control after sintering can be achieved. As the carbon and phosphorus contents are increased there is a commensurate increase in the hardness and tensile strength of the as sintered product. However, at compositions with over 0·4%C and 0·6%P added, a transient liquid phase is formed resulting in deterioration of mechanical properties. PM/0459

Journal ArticleDOI
TL;DR: In this paper, Martensitic steel powder (Fe12Cr) was consolidated using hot isostatic pressing (hipping) at three combinations of temperature, pressure, and time: 770°C/150 MPa/8 h, 1000°C /50 MPa /2 h, and 1150°C + 150 MPa 2 h. The two lower hipping temperatures were chosen to obtain fracture along the prior particle boundaries.
Abstract: Martensitic steel powder (Fe12Cr) was consolidated using hot isostatic pressing (hipping) at three combinations of temperature, pressure, and time: 770°C/150 MPa/8 h; 1000°C/50 MPa/2 h; 1150°C/ 150 MPa/2 h. The two lower hipping temperatures were chosen to obtain fracture along the prior particle boundaries (PPBs). Thereby, it was possible to study the reaction products formed on the PPBs during consolidation using Auger electron spectroscopy. During consolidation at 770°C the manganese and chromium oxides formed on the surface of the powder during atomisation are coarsened. At 770 and 1000°C silicon, vanadium, and nitrogen diffuse to the PPBs and form compounds. After compaction at 1000°C no MnO was detected on the fracture surface, which indicates that MnO is reduced at higher temperatures. Raising the hipping temperature to 1150°C enhances densification, thus no PPB failure is observed. PM/0440B

Journal ArticleDOI
TL;DR: In this paper, a comparison of various types of lubricant on the basis of their molecular structures and how these affect the properties of the test specimens obtained was made, and the tested lubricants provided green and sintered density results and sINTered hardness values that were higher than those obtained with zinc stearate.
Abstract: A comparison is made of various types of lubricant on the basis of their molecular structures and how these affect the properties of the test specimens obtained. The substances considered possess long hydrocarbon chains, with amide or hydroxyl functional groups at one end of the molecule. The variation in density and hardness of compacted and sintered iron parts with type of lubricant used is reported. The present lubricants, being fully organic, provide certain advantages with respect to traditional lubricants, since their combustion is complete, leaving no residues in the metal part and producing no toxic fumes. The tested lubricants provided green and sintered density results and sintered hardness values that are higher than those obtained with zinc stearate. PM/0429

Journal ArticleDOI
TL;DR: In this paper, Fourier analysis has been used for morphological analysis of copper powders, which can be represented in terms of a large number of harmonic amplitudes and associated phase angles.
Abstract: Powder particle shape, which has been selected as the attribute for classifying copper powders of different origins by Fourier analysis, can be represented in terms of a large number of harmonic amplitudes and associated phase angles. Compared with conventional methods of powder classification where the particle shape is lost, this method can be used to regenerate the particle profile closely by successive addition of harmonics. Harmonic amplitudes for large numbers of particles from various copper powder batches are presented in the form of mean harmonic amplitude spectra and frequency distribution histogra~s to illustrate shape variations and the presence of morphological relationships between powder particles from particular batches. Similarities and differences between powder batches have been elucidated using X2 tests, which compare two or more frequency histograms interval by interval. The effectiveness of Fourier analysis for morphological classification of these powders is clearly demonstrated. PM/0445

Journal ArticleDOI
TL;DR: In this article, the chemistry of a high performance cast superalloy, ZhS6-K, was modified by slight reductions in carbon, titanium, and aluminium content and minor additions of niobium and hafnium, and two variants of the modified alloy chemistry with different boron contents were prepared by vacuum induction melting, argon atomization, and consolidation by hot isostatic pressing at three temperatures.
Abstract: The chemistry of a high performance cast superalloy, ZhS6–K (Ni–10Cr–5Co–5W–5Al–3·5Mo–3Ti–0·2C–0·02B), was modified by slight reductions in carbon, titanium, and aluminium content and minor additions of niobium and hafnium. Two variants of the modified alloy chemistry with different boron contents (0·02 and 0·08 wt–%) were prepared by vacuum induction melting, argon atomization, and consolidation by hot isostatic pressing at three temperatures. It was observed that, unlike carbon, an increase in boron content did not promote the formation of continuous precipitates at the prior powder particle boundaries. Increased boron content narrowed down the consolidation temperature range and changed the morphology of γ′ particles from cuboidal to dendritic. Precipitation of an eutectic γ + γ′ structure and formation of continuous boride films at the grain boundaries severely degraded the mechanical properties of the high boron PM superalloy that was consolidated at a temperature marginally above the γ′ solv...