Showing papers in "Powder Metallurgy in 1970"
TL;DR: In this paper, experimental results relating to the influence of composition, structure, and testing conditions on the hardness, compressive strength, and transverse rupture strength of sintered tungsten carbide-cobalt alloys are presented.
Abstract: The paper reviews experimental results relating to the influence of composition, structure, and testing conditions on the hardness, compressive strength, and transverse rupture strength of sintered tungsten carbide–cobalt alloys.
169 citations
TL;DR: The relationship between the mechanical properties and the structure of the sintered carbide WC-TiC-Co has been studied in this paper, where the authors showed that it is possible to sint the carbide with 7 and 15% cobalt.
Abstract: The relationship between the mechanical properties and the structure of the sintered carbide WC–TiC–Co has been studied. Specimens containing 7 and 15% cobalt were sintered at temperatures between ...
27 citations
TL;DR: The properties of a forged powder-metallurgical preform depend on all stages of manufacture from powder production to the heat-treatment of the finished forging as discussed by the authors and the effects of process variables on mechanical and metallurgical properties.
Abstract: The properties of a forged powder-metallurgical preform depend on all stages of manufacture from powder production to the heat-treatment of the finished forging. Special reference is made to the effects of process variables on mechanical and metallurgical properties.
23 citations
TL;DR: Powder forging as mentioned in this paper is a hybrid process in which preforms made by conventional PM techniques are hot forged in closed impression dies, combining many of the best features of both conventionally made PM parts and hot forgings.
Abstract: “Powder forging” is a hybrid process in which preforms made by conventional PM techniques are hot forged in closed impression dies. The process combines many of the best features of both conventionally made PM parts and hot forgings. Although the process is still in the development stages, indications are that “powder-forged” components can be produced having mechanical and physical properties equivalent to conventionally wrought steels, together with the complexity and dimensional accuracy normally associated with sintered parts. The process appears an attractive and economic manufacturing route for many components for the following reasons: Material utilization is better than in conventional forging; detail and tolerances obtainable can lead to the elimination of much, if not all, finish machining; tight weight tolerances are possible in the “as-forged” condition, which on components such as connecting rods might ultimately lead to the elimination of weight-balancing operations. The paper describes the ...
23 citations
TL;DR: In this paper, the importance of carbide particle and grain size as regards the preparation and the properties of cemented carbides, and considers the techniques of particle- and grain-size measurement.
Abstract: The paper reviews work demonstrating the importance of carbide particle and grain size as regards the preparation and the properties of cemented carbides, and considers the techniques of particle- and grain-size measurement. It is shown that the initial size of the carbide powder influences the grain size in the sintered structure. Means of size-distribution analysis are evaluated. Some problems of accurate quantitative structure analysis and its automation are discussed. The best methods at present available for routine and basic work are outlined and modern devices are described.
20 citations
TL;DR: In this paper, the authors reviewed the fatigue behavior of sintered materials and found that the total porosity content, which is mainly determined by compacting conditions, is the most important factor influencing fatigue behavior.
Abstract: Published information on the fatigue behaviour of sintered materials is reviewed.Porous sintered materials exhibit similar fatigue characteristics to cast and wrought materials, including fatigue limits in ferrous materials. Their endurance ratios are slightly lower than those of similar wrought materials and they may depend on porosity content. In some cases fatigue data for sintered materials show less scatter than those for similar wrought materials. The total porosity content, which is mainly determined by compacting conditions, is the most important factor influencing fatigue behaviour. Endurance limit decreases as the porosity content increases. In the copper- and iron-base materials investigated, fatigue behaviour is influenced only slightly by powder characteristics, sintering temperature, atmosphere, and time, and by post-sintering treatments. Environmental and surface conditions seem to influence the fatigue behaviour in the same manner as pore-free materials. However, notches have a les...
20 citations
TL;DR: In this paper, the mechanical properties and structures of both atomized and blended alloys were investigated, and a good quality atomized powder of the SAE 4600 type was used to obtain tensile and fatigue properties equivalent to those of wrought steels.
Abstract: The paper describes preliminary work on sinter/forged low-alloy steels. The mechanical properties and structures of both atomized and blended alloys were investigated. By using a good-quality atomized powder of the SAE 4600 type, tensile and fatigue properties equivalent to those of wrought steels could be obtained. Atomized alloy powders with higher oxygen contents had poor ductility and impact values because of surface oxides on the powder particles.Blended iron alloys gave tensile strengths up to 72 tonf/in2 (1112 MN/m2) with much higher ductility and impact-resistance than would be obtained with conventionally pressed and sintered alloys.
16 citations
TL;DR: In sintered hard-metals grain-size control is of exceptional importance because the basic properties of wear-resistance and strength are critically dependent upon it as discussed by the authors In some applications a change in average grain size from 5·0 to 1·0 μm can increase wear resistance by as much as twenty times, while the same change can halve the transverse rupture strength.
Abstract: In sintered hard-metals grain-size control is of exceptional importance because the basic properties of wear-resistance and strength are critically dependent upon it In some applications a change in average grain size from 5·0 to 1·0 μm can increase wear-resistance by as much as twenty times, while the same change can halve the transverse rupture strengthEach step in manufacture, from the chemical processing of the ore to the final sintering operation, can influence the final grain size The factors operating at each stage are not yet completely understood However, the most important processes of tungsten reduction and carburizing have been closely studied and these are chosen to control and monitor grain size during manufacture The factors influencing grain size during these operations are discussed in some detail The difficulty of relating powder-particle size and sintered-product grain size is mentioned This is largely due to the weaknesses of conventional methods of measurement Size cha
14 citations
TL;DR: In this article, a test piece with enlarged ends has been developed for the assessment of the very high static and fatigue compressive strength of hard-metals and the results can be rationalized by being plotted against the mean free path in the binder metal.
Abstract: Procedures for the assessment of the very high static and fatigue compressive strength of hard-metals are briefly reviewed. A test-piece with enlarged ends has been developed. Using this, stress/strain curves and fatigue–strength data have been obtained on WC–Co hard-metals with various cobalt contents and carbide grain sizes. The results can be rationalized by being plotted against the mean free path in the binder metal.
13 citations
TL;DR: In this paper, the philosophy of total quality control is introduced by describing the special problems associated with the applications of hard-metals, and the manufacturing process should be capable of yielding the required quality under simply maintained operating conditions.
Abstract: The philosophy of “Total Quality Control” is introduced by describing the special problems associated with the applications of hard-metals. There are no simple direct tests to measure the important parameters. These have to be assessed and controlled in an indirect way; nevertheless, experience has shown that the system of quality control described is most effective.Hard-metal is very expensive and this factor alone provides a special incentive for manufacturers to supervise quality, not only to satisfy customers but also to reduce their own scrap costs. The manufacturing process should be capable of yielding the required quality under simply maintained operating conditions. A high degree of involvement on the part of operating and supervising personnel is required. The manufacturing method is illustrated with flow sheets and described only in sufficient detail to indicate the significance and relevance of the quality-control tests. Emphasis is placed on chemical purity, precise carbon control, an...
13 citations
TL;DR: In this paper, the furnace atmospheres used in the manufacture of hard-metal from the pressed compact to the sintered component are discussed, and the removal of pressing lubricant, presintering and final sintering all involve heating the components to temperatures at which reactions with the furnace atmosphere can occur.
Abstract: The furnace atmospheres used in the manufacture of hard-metal from the pressed compact to the sintered component are discussed.The very fine size (0·5–8·0 μm) of the powder particles makes the compacts particularly prone to react with furnace atmospheres. All these reactions affect the carbon content of the alloys, which must be controlled within extremely close limits to ensure good quality.The removal of pressing lubricant, presintering, and final sintering all involve heating the components to temperatures at which reactions with the furnace atmosphere can occur. Both hydrogen and vacuum furnaces are used and care is required to maintain a quality of atmosphere that will not lead to a deleterious change in carbon content.
TL;DR: In this article, a dilatometric method is described by which the transformation characteristics of sintered steel may be determined using continuous cooling diagrams on typical sinted steels.
Abstract: The factors influencing the hardenability of sintered steels are discussed. Special problems are encountered in establishing hardenability tests suitable for porous materials. A dilatometric method is described by which the transformation characteristics of sintered steel may be determined. Such data can be used directly as a hardenability criterion. Data are given in the form of continuous cooling diagrams on some typical sintered steels.
TL;DR: In this article, the mechanical properties of sintered iron-nickel alloys produced by hot compacting in six stages were investigated, and the dependence of tensile strength, elongation at fracture, and Brinell hardness of alloys with Ni contents of 1-10% on the sintering temperature and time, on the furnace conditions, and on raw-material variables.
Abstract: Powder-metallurgy components which are to withstand high dynamic stress are frequently required to possess both high strength and great toughness. This combination of properties can best be achieved by increasing the density of the sintered component and one method of doing so is bot pressing.This paper deals with the mechanical properties of sintered iron–nickel alloys produced by hot compacting in six stages, as follows:(1) Preparation of the powder mix.(2) Production of compacts under a pressure of 8 Mp/cm2(3) Heating the compacts to 1000°C (1275 K).(4) Re-pressing the hot compacts in a die heated to 300°C (575 K).(5) Cooling in air.(6) Sintering at optimum temperature and time under optimum furnace conditions.The investigation covered the dependence of tensile strength, elongation at fracture, and Brinell hardness of alloys with Ni contents of 1–10% on the sintering temperature and time, on the furnace conditions, and on raw-material variables.It was found that Fe–Ni powder-metallurgy parts wi...
TL;DR: In this article, it is shown that the liquid permeability in porous metal is not independent of time and pressure as is the gas permeability, and that the influence of surface active additives in the mineral oil on the liquid and gas percolation coefficients of porous metal bearing is studied.
Abstract: Previous work on the determination of the fluid permeability of porous materials is reviewed, and methods for the measurement of the gas and liquid permeability coefficients of porous metal bearings are described. It is shown that the liquid permeability in porous metal is not independent of time and pressure as is the gas permeability. By the use of relatively simple experimental methods, the influence of surface-active additives in the mineral oil on the liquid permeability can be studied. By a complete understanding of the interactions between the lubricating oil and the metal surfaces of the porosity, an improvement in the performance prediction of porous metal bearings is to be expected.
TL;DR: In this article, a preliminary examination has been made of some factors likely to affect the isostatic pressing of ferrous powders and where possible the influence of such factors upon the application of isostatically pressing to mass production is discussed.
Abstract: A preliminary examination has been made of some factors likely to affect the isostatic pressing of ferrous powders. Where possible the influence of such factors upon the application of isostatic pressing to mass production is discussed.
TL;DR: In this article, the processes used in the production of friction materials for aircraft brakes are outlined and stringent quality control procedures adopted at all stages of raw-material testing, mixing, pressing, and sintering are discussed and examples given that show the necessity for these procedures.
Abstract: The processes used in the production of friction materials for aircraft brakes are outlined. The stringent quality-control procedures adopted at all stages of raw-material testing, mixing, pressing, and sintering are discussed and examples given that show the necessity for these procedures. The control system results in an end product that gives reproducible friction properties and wear rates and can fulfil the requirements of an emergency stop.
TL;DR: In this article, an original method of activating the sintering of copper powder is discussed, which is based on the interaction of formic or acetic acid vapour with copper powder, which results in adsorption of one or more of the decomposition products.
Abstract: The paper discusses an original method of activating the sintering of copper powder. The technique is based on the interaction of formic or acetic acid vapour with copper powder, which results in adsorption of one or more of the decomposition products. It is shown that the adsorbed layers enhance densification, hardness, and tensile strength. The study includes observations on the effect of activator content, sintering atmosphere, temperature, time, and powder particle size.
TL;DR: In this article, a range of densities from 5·6 to 7·2 g/cm3 was produced from sponge-iron powder using a single-end-pressing technique.
Abstract: Billets 25 mm in dia. and weighing ∼135 g have been compacted from sponge-iron powder using a single-end-pressing technique. A range of densities from 5·6 to 7·2 g/cm3 was produced. The billets were then hot extrusion forged, at high speed, into tensile specimens of gauge-dia. 10 mm, gauge-length 28 mm, and head dimensions of 13 mm dia. × 12·5 mm long. About half the billets were pre-sintered before heating to forging temperature, while others were hot-forged without a pre-sintering stage. The tensile specimens were then tested and selected ones examined metallographically.The work was extended to investigate the extrusion forging of alloy steel powder.
TL;DR: In this article, a comprehensive quality control procedure for ferrous structural sintered parts production has been formulated and a set of practical parameters within which these variables should be controlled are suggested.
Abstract: Although recognized quality-control procedures are used in ferrous structural sintered parts production, there are areas where the controls must be tailored to accommodate the special techniques used in the process. This paper sets out to define the variables that can occur at all stages of production and suggests the practical parameters within which these variables should be controlled. From this information a comprehensive quality-control procedure has been formulated.
TL;DR: In this paper, the authors describe a set of bearers designed by Sintering METAL POWDERS with solided lubricants for powder metallurgy.
Abstract: (1970). BEARINGS PRODUCED BY SINTERING METAL POWDERS WITH SOLID LUBRICANTS. Powder Metallurgy: Vol. 13, No. 25, pp. 67-70.
TL;DR: In this article, an appreciation of the reactions occurring between the metal-powder compacts and the surrounding atmosphere is an essential basis for the choice of atmosphere composition for sintering atmospheres.
Abstract: Sintering atmospheres play an important part in the production of high-quality sintered-metal components. The type of atmosphere required and the accuracy of control are dependent upon the materials being processed and the customer’s specification.This paper, dealing with the application of reformed hydrocarbon gases, demonstrates how an appreciation of the reactions occurring between the metal-powder compacts and the surrounding atmosphere is an essential basis for the choice of atmosphere composition. The techniques of atmosphere control are discussed and recommendations given for reliable gas analysis on which to base this control.
TL;DR: In this paper, Ormerly et al. compared the hot pressibility of a beryllium powder with and without the addition of 500 ppm silicon as an activator.
Abstract: SMALL additions of activating elements to beryllium powder have been shown to improve the vacuum hot-pressing characteristics of the metal at 1100°C (1375 K). Compared with the behaviour of non-activated powder, the improvement is most clearly evidenced as an increase in density throughout the compact, and is particularly marked as the distance from the platen exceeds a length: dia. ratio of 1. Fig. l(d) of Ref. (1) contrasts the hot pressibility of a beryllium powder with and without the addition of 500 ppm silicon as an activator. It is apparent from these densification curves that in the absence of an activator the particles have been tightly compacted together only in the region close to the moving platen. As the distance from the platen becomes greater, the transmission of load via the consolidated powder particles to the lower, loosely packed, region has been impeded by particle welding at points of contact. This causes high interparticle friction, thereby enhancing densification in the uppermost parts by plastic deformation of the particles and leading to non-uniform compaction. An important consequence, therefore, of adding an activator, is to promote bulk:flow of particles and facilitate their arrangement into more closely packed positions, to give the excellent uniform densification observed in the figure. Under these easy :flowconditions, the transmission of load from the moving platen through the powder is improved, since the particles are able to slide past one another without adhering appreciably at points of contact as is usual in a sintering process. Further work has established that this lack of adhesion between particles results from the existence of the intervening oxide layer * Manuscript received 1 January 1970. Oral contribution to a Symposium on "Lubrication, Friction, and Wear (Tribology) in Powder Metallurgy," held in Eastbourne on 24-26 November 1969. These notes are complementary to an earlier paper, identified by Ref. (1). t International Nickel Limited, forIl!erly at A.W.R.E., Aldermaston. t Bath University of Technology, fOrmerly at A.W.R.E., Aldermaston.