Showing papers in "Powder Metallurgy in 1986"
TL;DR: In this paper, the properties of composites made from copper-coated titania particles were compared with those of similar composites of similar composition produced from uncoated particles, showing that the coated particles have a reduced tendency to agglomerate when present in quantities up to 5 wt-%.
Abstract: Cu–TiO2 particulate composites have been prepared from copper coated titania particles by the powder metallurgy route. The properties of composites containing 5–20 wt-%TiO2 are compared with those of composites of similar composition produced from uncoated particles. Microstructural studies showed that the coated particles have a reduced tendency to agglomerate when present in quantities up to 5 wt-%. The density of composites decreased, while their hardness and electrical resistivity increased, with increasing titania content. In all cases, composites made from coated particles possessed better properties than those produced from uncoated ones. Re-pressing and annealing of the composites resulted in an increase in properties. Cu–5TiO2 particulate composites could be suitable for use as electrical contacts in light duty applications. PM/0282
29 citations
TL;DR: In this article, a groupe de travail ISO forme pour la recherche de procedures adequates en vue de la normalisation internationale de la determination des caracteristiques de remplissage des matrices par des poudres.
Abstract: Conclusions d'un groupe de travail ISO forme pour la recherche de procedures adequates en vue de la normalisation internationale de la determination des caracteristiques de remplissage des matrices par des poudres. Expose de deux methodes fournissant des evaluations utiles, mais pour un groupe limite de poudres metalliques
28 citations
TL;DR: In this paper, a study of precipitation at the tungsten grain boundaries in the Tungsten-nickel-iron ternary alloy system has been undertaken. But the results of the study were limited to the case of ternaries with a crystal structure similar to the matrix binder phase.
Abstract: A study of precipitation at the tungsten grain boundaries in the tungsten–nickel–iron ternary alloy system has been undertaken. Scanning and transmission electron microscopy techniques have been used to study the effect of various post-sintering heat treatments on the precipitation reaction. Grain boundary precipitates with a crystal structure and lattice parameter the same as the matrix binder phase (fcc, α0 = 0·360 nm) have been shown to form at the tungsten grain boundaries during heat treatment in the 800–1300°C temperature range. A mechanism for the formation of these precipitates is proposed. It has also been found that the tungsten grain boundary precipitates consistently behave in a ductile manner upon tungsten/tungsten interfacial failure. This may give an opportunity for an improvement in ductility of the inherently brittle tungsten grain boundaries in these alloys. PM/0338
28 citations
TL;DR: Essais de frittage de poudres de molybdene a differentes teneurs en oxygene et additionnees de 0,5 a 1% en poids de nickel, montrant que l'oxygene and le nickel sont des activants du frittages de Mo, mais les echantillons frittes presentent une fragilite intergranulaire as mentioned in this paper.
Abstract: Essais de frittage de poudres de molybdene a differentes teneurs en oxygene et additionnees de 0,5 a 1% en poids de nickel, montrant que l'oxygene et le nickel sont des activants du frittage de Mo, mais les echantillons frittes presentent une fragilite intergranulaire
24 citations
TL;DR: In this article, the influence of median particle size of alloy composition and superheat is discussed and data are presented for the Cu-Sn system and zinc for the first-order linear model.
Abstract: The influence on median particle size of alloy composition and superheat is discussed and data are presented for the Cu–Sn system and zinc. The influence of atomizing water pressure on atom...
16 citations
TL;DR: In this paper, the underlying relation-ships derived from experimental sintering runs are presented and compared with practical production experience for sintered products such as cutting inserts, and it is shown that inadequate carbon control leads to incomplete densification and component distortion.
Abstract: To obtain effective sintering of high speed steel powder compacts to full density it is essential to balance the oxides present on the powder particle surface with the correct amount of added carbon, since the sintering temperature depends critically on the residual carbon content after the oxides have been reduced. In this paper the underlying relation-ships, derived from experimental sintering runs, are presented. Conclusions for the sintering of actual components are derived and compared with practical production experience. It is shown that inadequate carbon control leads to incomplete densification and to component distortion. Performance data for sintered products such as cutting inserts are presented. PM/0342
15 citations
TL;DR: In this paper, a fraction volumique de ferrite croit avec l'addition de Si and the temperature de frittage was added to AISI304L.
Abstract: Obtention d'aciers biphases austeno-ferritiques par introduction de poudre de Si dans l'acier inoxydable austenitique AISI304L. La fraction volumique de ferrite croit avec l'addition de Si et la temperature de frittage. Augmentation de la durete et de la resistance a la traction, de la resistance a l'oxydation et de la resistance a la corrosion dans une solution de FeCl 3
14 citations
TL;DR: In this paper, the chill block melt spinning technique has been used to produce rapidly solidified (RS) equiatomic TI-NI nbbons, which have been consoidated by conventional powder metallurgy techniques.
Abstract: The chill block melt spinning technique has been u~ed ~o I?roduce rapidly solidified (RS) equiatomic TI-NI nbbons. The spun material has been conso!idated by conventional powder metallurgy technIques. The compaction and sintering behaviour of the prealloyed powder is compared with that of elemental blend powders. The high initial hardness of the RS powder results in lower compressibility. Sintering temperatures in excess of those used for elemental blend particles are necessary for the RS prealloyed material. This phenomenon is related to the different partial diffusion coefficients of titanium and nickel leading to vacancy generation during sintering of elemental powder compacts. The densities of elemental blend compacts decrease during sintering, unlike RS prealloyed particle specimens, which densify. RS processing causes a depression in the M s temperature of Ti- Ni. Among other reasons for the decrease in M s is the grain refinement caused by rapid solidification. PM/0373 © 1986 The Institute of Metals. Contribution to the PM Group Conference on 'The production, characterization, and handling of metal powders', held on 21-23 October 1985 at Brighton. The authors are in the Materials
14 citations
TL;DR: In this paper, the main parameters in water atomization processes for powders of high yield strength and low compressibility are discussed, together with the methods which Powdrex has developed for the production of such powders.
Abstract: The production of high alloy powders suitable for cold pressing presents certain specific technical problems. This is because, in general, to produce correct hardening response and full mechanical properties, these powders must be fully prealloyed. Fully prealloyed powders are often of high yield strength and therefore low compressibility. Further- more, powder surface oxides must be minimized so that sintering may proceed to completion and finished parts can be of minimal porosity. This paper describes the methods which Powdrex has developed for the production of such powders, together with the production and experimental atomizer facilities, and also includes a general review of the main parameters in water atomization processes for these materials. PM/0388
12 citations
TL;DR: In this article, plastisols of fine iron and hard metal powders, mixed with binder systems based upon polystyrene and polyethylene, have been formulated from which basic Theological data have been obtained.
Abstract: Plastisols of fine iron and hardmetal powders, mixed with binder systems based upon polystyrene and polyethylene, have been formulated from which basic Theological data have been obtained. These data indicate that the plastisols with powder volume loadings up to ∼80% will flow satisfactorily under injection moulding conditions. Viscosity levels were found to reduce with increasing shear rate, though a critical level of shear rate may be reached beyond which dilatant flow behaviour tends to occur. This effect is considered to be due to the dissociation of the binder system from the powder surfaces at extremes of shear rate for specific plastisol formulations. PM/0380
11 citations
TL;DR: In this article, two methods of producing PM rapidly solidified 7XXX series aluminium alloy are described: melt spinning (ribbons → flakes) and air atomization (powders).
Abstract: Two methods of producing PM rapidly solidified 7XXX series aluminium alloy are described: melt spinning (ribbons → flakes) and air atomization (powders). The microstructure and properties of particles (shape, size distribution, alloying concentration profiles) are discussed with regard to cooling rate. The reseach also emphasizes the importance of particle oxidation and its influence on their behaviour during subsequent processing. The trade-offs required between the various particle properties that are considered suggest that melt spun material should be recommended for heat treatable aluminium alloys, while powders should be used for non-heat treatable alloys. PM/0372
TL;DR: In this article, the elastic response in tension and compression was found to differ due to pore deformation, and the apparent value for G depended upon the proportions of tensile to compressive stress present in the stress system to which the material was subjected.
Abstract: Porous sintered iron powder compacts were tested in uniaxial tension and compression and values for the fundamental elastic constants E and ν determined by direct measurement. This information- was used to calculate values for G and K for wholly tensile and compressive situations. Further tests were conducted involving various combinations of tensile and compressive stress, i.e. bending and torsion tests, from which corresponding values for E and G were obtained. The study showed that the elastic response in tension differed from that in compression, due to pore deformation. Furthermore, the apparent value for G depended upon the proportions of tensile to compressive stress present in the stress system to which the material was subjected. PM/0368
TL;DR: In this article, the effect of silicon powder on the sintering behavior and microstructure of compacted 304L stainless powder has been studied, and the shrinkage ratio increases substantially with silicon content.
Abstract: The effect of additions of silicon powder on the sintering behaviour and microstructure of compacted 304L stainless powder has been studied. The shrinkage ratio increases substantially with silicon content. Silicon profoundly activates the sintering process through the formation of a eutectic and/or δ ferrite, which is pseudoperitectically formed during sintering. The sintering behaviour is closely related to the microstructures, which depend upon the amount of silicon addition. Ostwald ripening is encountered in the liquid phase sintered specimens (Si≤3 wt-%). The solid phase sintered materials (Si≥ wt-%) containing δ ferrite densify more rapidly than the liquid phase sintered ones. The densification kinetics are governed by the wetting characteristics of the eutectic liquid and the formation of ferrite. As a result of the silicon addition, the austenitic stainless steel powder aggregates are sintered into duplex stainless steels with austenite-ferrite structures. PM/0395
TL;DR: In this paper, the fluidized bed granulation technology and its application to Tungsten carbide was discussed. But the application was limited to powder metallurgy and was not discussed in detail.
Abstract: (1986). Fluidized Bed Granulation Technology and Its Application to Tungsten Carbide. Powder Metallurgy: Vol. 29, No. 4, pp. 291-295.
TL;DR: Procede d'obtention d'un melange semi-solide a microstructure globulaire adequate for la coulee sous pression is described in this article.
Abstract: Procede d'obtention d'un melange semi-solide a microstructure globulaire adequate pour la coulee sous pression. De plus, des fibres discontinues ou autres dispersoides peuvent etre introduits dans le melange et conduire a des composites de composition homogene
TL;DR: In this article, the production of ultrafine aluminium alloy powder by the relatively novel route of gas atomization at high pressures (4-8 MPa) was investigated, and it was shown that such a process can be used to produce ultrafine aluminum alloy powder.
Abstract: The paper is concerned with the production of ultrafine aluminium alloy powder by the relatively novel route of gas atomization at high pressures (4–8 MPa). It is shown that such a process ...
TL;DR: In this article, a comparative study of three rapidly solidified Al-Mg powder alloys containing additions of chromium, iron, and manganese has been performed, and the results showed that the results were related to the extrusion pressure and the temperature compensated strain rate.
Abstract: A comparative study of three rapidly solidified Al–Mg powder alloys containing additions of chromium, iron, and manganese has been performed. Fine, air atomized powder of the three compositions was cold compacted and extruded after preheating, using an induction heater, to temperatures in the range 300–500°C. The Al–Mg–Cr alloy exhibited the best hot working characteristics: the iron and manganese bearing materials were less satisfactory because the extrudates exhibited surface cracking owing to hot tearing. The data from the Al–Mg–Cr alloy showed that the extrusion pressure can be related to the extrusion ratio and the temperature compensated strain rate. During extrudate tensile testing, discon-tinuous yielding was observed in the iron and manganese bearing alloys. All three alloys exhibited improved Young's modulus, but over the range of temperatures studied (20–300°C) the chromium and iron alloys displayed the best combination of strength and ductility. PM/0359
TL;DR: In this article, the authors presented a comparison of PASC45 and PASC60 contenant 0,45 and 0,6% de P fournies par Hoganos AG (Suede) avec des additions de 1 a 4% en poids de Cu, Ni ou Mo, comprimes sous une pression de 691 MPa and frittes a 1120 C pendant 30 min dans une atmosphere d'ammoniac dissocie.
Abstract: Premelanges des poudres PASC45 et PASC60 contenant 0,45 et 0,6% de P fournies par Hoganos AG (Suede) avec des additions de 1 a 4% en poids de Cu, Ni ou Mo, comprimes sous une pression de 691 MPa et frittes a 1120 C pendant 30 min dans une atmosphere d'ammoniac dissocie. Tous les elements d'addition augmentent la limite elastique et la resistance a la rupture, mais diminuent la ductilite
TL;DR: In this article, two related methods for producing rapidly solidified particulate suitable for subsequent powder metallurgical processing are described and the applicability of these processes to the manufacture of rapidly solidification particulate is described.
Abstract: This paper describes two related methods for producing rapidly solidified particulate suitable for subsequent powder metallurgical processing. The first, melt extraction, is a commercial process used for a range of steel compositions but is limited in the cooling rates and structures that can be achieved. The second, melt overflow, is a developmental process capable of making extremely fine particulate at cooling rates in excess of 106K s−1. The applicability of these processes to the manufacture of rapidly solidified particulate is described and the potential for fine melt overflow products out-lined. PM/0374
TL;DR: In this article, the advantages and disadvantages of various techniques are discussed including the Fisher sub-sieve sizer, the Coulter counter, gas adsorption (BET), laser, sedimentation, and new experimental methods which are based on image analysis and on the oxidation of WC powders.
Abstract: There is an increasing need for size measurement of particles of submicrometre diameter in the hard-metal and ceramic industries, and in associated technologies such as wear evaluation by wear debris sizing. Specific studies of the problem have been made on fine grained WC powders by comparing the results from conventional instrumental techniques with those obtained by two new methods. The advantages and disadvantages of the various techniques are discussed including the Fisher sub-sieve sizer, the Coulter counter, gas adsorption (BET), laser, sedimentation, and new experimental methods which are based on image analysis and on the oxidation of WC powders. All the different measurement procedures gave useful information although some, such as the laser and Coulter counter, were thought to be more limited than, for example, the BET and oxidation techniques. The most informative and accurate results were probably those obtained from semi-automatic image analysis of scanning electron micrographs, and ...
TL;DR: In this article, experiences and conclusions in the development of iron powder manufacturing at Hoganas AB, Sweden, from what today would be called a pilot scale operation are presented, with a focus on developing suitable equipment and methods for powder processing and handling, and also effective systems for process and quality control.
Abstract: For the iron powder producers the development in the iron powder consuming industries has been a matter not only of meeting demands for greater volumes but also of supplying a variety of powder grades with properties adapted to an increasing number of new applications in various fields, each application requiring specific combinations of the physical and chemical powder properties. A factor of great importance for the growth of iron powder consuming processes has been the ability of the powder producers to meet the increasing demands for consistent properties, i.e. narrow powder specifications, on a high quality level. In large volume powder production this has required specific attention to the development of suitable equipment and methods for powder processing and handling, and also of effective systems for process and quality control. In this paper, experiences and conclusions in the development of iron powder manufacturing at Hoganas AB, Sweden, from what today would be called a pilot scale op...
TL;DR: In this article, a pusher furnace was used for the reduction of fine haematite powders under varying reduction conditions and it was shown that during the reduction process the fine particles coalesce and form agglomerates, the internal porosity of which decreases with increasing reduction temperature.
Abstract: Reduction of fine haematite powders was carried out in a pusher furnace in flowing hydrogen under varying reduction conditions. It was shown that during the reduction process the fine particles coalesce and form agglomerates, the internal porosity of which decreases with increasing reduction temperature. The very high overall porosity of the powder compact is not, however, actually lowered, the coalesced particles being surrounded by large pores, and the compact can be easily milled. Loose iron powders sintered under the same conditions, in contrast, result in massive blocks of comparatively high overall density. PM/0383
TL;DR: In this paper, cold compacts have been prepared from Al-Mg-Mn rapidly solidified powders containing 7, 12, and 15 wt-%Mg and were subsequently extruded using a wide range of temperature compensated strain rates.
Abstract: Cold compacts have been prepared from Al–Mg–Mn rapidly solidified powders containing 7, 12, and 15 wt-%Mg The compacts were subsequently extruded using a wide range of temperature compensated strain rates Despite their high alloy content, each of these powder alloys could be extruded with relative ease It is the fine nature of the powder state which assists the extrusion of these alloys which are inherently difficult to fabricate in the cast state The mode of deformation is shown to occur by dynamic recrystallization The subsequent microstructure is of a fine grain size and is shown to be related to the processing conditions A relation-ship between the high temperature flow stress and the extruded structure is also indicated Observations of the powder microstructure are reported It is shown that the original powder structure is completely transformed during the extrusion process PM/0364
TL;DR: In this article, the microstructure of rapidly solidified powders of compositions corresponding to X7090 and X7091 have been characterized by the use of optical, scanning, and transmission microscopy.
Abstract: The microstructure of rapidly solidified powders of compositions corresponding to X7090 and X7091 have been characterized by the use of optical, scanning, and transmission microscopy. The powders were then cold compacted, heated, and extruded by a conventional route. It is shown that extrudates exhibiting excellent surface characteristics can be produced and that the pressure may be predicted from data obtained from torsion testing. The extrusion process can be performed utilizing greater ram speeds than are possible when processing IM (ingot metallurgy) material. The extrudate properties were investigated in the heat treated condition for both press quenched and aged and solution soaked and aged treatments. For both treatments the properties were similar and compared well with published data concerning these alloys. PM/0329
TL;DR: In this paper, the maintien dans la vapeur d'eau a 500 C donne a ces produits une couche dure et adherente d'oxyde.
Abstract: Premelanges de poudres de fer contenant 0,4 a 0,6% de phosphore avec 1 a 4% de cuivre, frittes a 1120 C pendant 30 min dans l'hydrogene sec. Un maintien dans la vapeur d'eau a 500 C donne a ces produits une couche dure et adherente d'oxyde. Les additions de Cu augmentent l'epaisseur de la couche d'oxyde
TL;DR: The constructive application of explosives in the Department of Mechanical and Industrial Engineering at Queen's began in the early 1960s when Professor B. Crossland, FRS entered the then relatively new field of explosive welding as discussed by the authors.
Abstract: The constructive application of explosives in the Department of Mechanical and Industrial Engineering at Queen's began in the early 1960s when Professor B. Crossland, FRS entered the then relatively new field of explosive welding. In the following years, a considerable amount of work was done on the application of explosive welding to the cladding of plate metals and to the welding of tubes into tube plates. In 1970, work began on the use of explosives in the compaction of powders.
TL;DR: In this paper, the physicochemical and physical properties of tungsten carbide and cobalt powders have been investigated in relation to their advantages and disadvantages, and it has been shown that the very important characteristic of particle shape and particle agglomeration is the particle aggregation.
Abstract: Although hardmetal has been manufactured, by the powder metallurgy route for well over 55 years, the characterization of the starting powders, basically tungsten carbide and cobalt, still commands the attention of powder metallurgists. Three fine cobalt powders and two 1·2 μm (FSSS) tungsten carbide powders, freely available, have been both chemically and physically characterized. Various techniques of measuring physical characteristics, such as FSSS, BET gas adsorption, pore volume and area, sedimentation, SEM powder, and SEM polished and etched sections of copper impregnated powders, have been studied. The techniques have been discussed in relation to their advantages and disadvantages. The measurement by FSSS and BET gas adsorption give fairly reproducible results, as does the sedimentation technique. However, by reference to the two SEM techniques it has been shown that the very important characteristic of particle shape and, more importantly for tungsten carbide powder, particle agglomeration...
TL;DR: In this paper, the determination of particle size distribution is a probabilistic process which produces practical and theoretical problems, depending as it does on shape, size range, and operating conditions.
Abstract: The determination of particle size distribution is a probabilistic process which produces practical and theoretical problems, depending as it does on shape, size range, and operating conditions. The author's Group produces metal powders of many different compositions, size ranges, and shapes. From initial hand sieving, several methods of measurement, mechanical, air jet, sedimentation, and counter based, have been developed. Thousands of results are stored in the companies' files. This paper does not attempt a systematic examination of these results, but rather deals with some difficult cases that have been encountered in practice. PM/0385
TL;DR: In this paper, two measuring techniques are described, as well as the outcome of actual measurements performed on four forged PM materials with varying inclusion contents, and the results are correlated with the mechanical properties of these materials.
Abstract: The non-metallic inclusions in fully dense PM products are supposed to affect the mechanical properties, but it is difficult to know to what extent. General investigations concerning the mechanical properties of inclusion containing materials, especially the dynamic properties, should take account of the influence of non-metallic inclusions; their size and number may also be important. Measuring techniques are relevant in this connection, because the results will vary considerably, depending on the method of defining the extent of inclusions composed of more or less dispersed minute subparticles. Such inclusions will be referred to as ‘spotty’ in this paper. Two measuring techniques are described, as well as the outcome of actual measurements performed on four forged PM materials with varying inclusion contents. The results are correlated with the mechanical properties of these materials. The conclusions drawn from these experiments stress the need to specify the measuring technique when reporting...
TL;DR: The potential of ceramics for the Aero Gas Turbine Engine Powder Metallurgy: Vol 29, No 3, pp 169-169 as mentioned in this paper, was discussed in detail.
Abstract: (1986) The Potential of Ceramics for the Aero Gas Turbine Engine Powder Metallurgy: Vol 29, No 3, pp 169-169