Showing papers in "Powder Metallurgy in 1981"
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TL;DR: In this paper, the tensile strength, fatigue crack propagation behavior, and fracture toughness of a low-alloy sin tered steel were determined for the porosity range 11-17%.
Abstract: The tensile strength, fatigue crack propagation behaviour, and fracture toughness of a low-alloy sin tered steel were determined for the porosity range 11–17%. Static and cyclic strength were found to increase with density in a non-linear fashion. The pores both exerted a stress-concentrating influence and reduced the load-bearing section. The micromechanism of failure was always ductile fracture in the necks between sintered steel particles. It was concluded that the stress state at the tips of cracks subjected to static or cyclic loading was closer to plane stress than to plane strain. Retardation of fatigue crack propagation appeared to occur due to the blunting action of the pores. The presence of a wear mechanism had little influence upon fatigue crack growth rates. A companion paper (following) attempts to model the static and cyclic behaviour of the steel, based on the known micromechanisms of failure. PM/0172
94 citations
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TL;DR: In this paper, the role of surface oxide layers in the sintering of metallic powders is evaluated on the basis of thermodynamic and kinetic considerations, and the role played by surface oxide layer is evaluated.
Abstract: On the basis of thermodynamic and kinetic considerations, the role played by surface oxide layers in the sintering of metallic powders is evaluated. For metals with stable oxides, the influence of the surface layer is determined by the relative sintering and diffusional fluxes x s/x d to the interparticle neck region. When x s/x d>1 sintering is retarded by the oxide layer. Conversely, unretarded sintering occurs when x s/x d <1. For metals with oxides which are unstable with respect to dissolution in the metal at the sintering temperatures, the sintering process is preceded by an incubation period. Calculated values of the relative neck growth rates and the incubation periods provide the bases for predicting the effects of these surface layers. Predictions of the present analysis are shown to be consistent with experimental observations. PM/0174
44 citations
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TL;DR: The results of development work on a novel particle metallurgy processing technique for highly alloyed tool and high-speed steel manufacture carried out at Aurora Steels Ltd are described in this article.
Abstract: The results of development work on a novel particle metallurgy processing technique for highly alloyed tool and high-speed steel manufacture carried out at Aurora Steels Ltd are described. The technique, which employs metal splatting to achieve rapid rates of solidification, overcomes many of the problems and additional operations associated with more conventional powder routes. Conversion of the splatted deposit to finished product is achieved using conventional steelworks processing equipment. Improved hot workability increases the availability of some difficult product forms in highly alloyed high-speed steel grades. Products manufactured using this route have been submitted to extensive quality and performance testing with most encouraging results. Carbide segregation effects normally encountered during conventional high-speed steel ingot processing· are removed, and many other properties, e.g. heattreatment response, toughness, andgrindability, are all substantially improved. End user testing of highspeed steel tools in a number of product forms has demonstrated a consistent and high performance stanqard ..The process has been applied without difficulty to other steel qualities, i.e. austenitic stainless steel, and the product range currently under development includes square, round, and flat bar, forgings, sheet, and other specialist shapes. PM/OI95
42 citations
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TL;DR: A number of new powder metallurgy processes have appeared which offer con siderable promise for superior aeroengine combustor, blade, and disc alloys as mentioned in this paper, and several features of these processes can be exploited for improved material utilization such that total manufacturing costs are contained.
Abstract: Throughout the past decade a number of new powder metallurgy processes have appeared which offer con siderable promise for superior aeroengine combustor, blade, and disc alloys. Furthermore, several features of these processes can be exploited for improved material utilization such that total manufacturing costs are contained to combat steep increases in basic alloying element prices. The processes include gas atomization of superalloy powder for critical rotating parts, rotating electrode atomization for titanium powder in similar components, controlled thermomechanical processing of attrited powders to produce oxide dispersion strengthened superalloy sheet and airfoil parts, and finally plasma-sprayed gas-atomized powder for advanced hot-section overlay and thermal barrier coatings. Considerable alloy and process development work has already been undertaken on all these systems by aeroengine material suppliers and advantages accruing in terms of superior properties and/or lower processing costs ...
25 citations
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TL;DR: In this paper, two material models were developed to estimate the effect of density on the static and cyclic fracture behavior of a sintered steel, based on the known micromechanisms of failure for each type of loading.
Abstract: Two material models are developed to estimate the effect of density on the static and cyclic fracture behaviour of a sintered steel. The models are based on the known micromechanisms of failure for each type of loading. Theoretical predictions are compared with previous experimental results taken from a companion paper (preceding). The two models successfully account for the variation of yield stress, ultimate tensile stress, and fracture toughness with density. They prove less successful in predicting the effect of density on fatigue crack propagation behaviour. PM/0198
25 citations
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TL;DR: In this article, a measurement of the secondary dendrite arm spacing of gas-atomized powders indicated that S II (μm) and the powder particle diameter d (m) was described by S II = K□d where K is a constant.
Abstract: The ‘KHA process’ for producing PM high-speed steels using gas-atomizing equipment and the hot isostatic press has been developed by Kobe Steel Ltd. Measurement of the secondary dendrite arm spacing of gas-atomized powders indicated that the relation between the dendrite arm spacing S II (μm) and the powder particle diameter d (m) was described by S II= K□d where K is a constant. To establish suitable hot isostatic pressing (HIP) conditions with high productivity, density and bending strength were studied in relation to various HIP conditions. It was found that, for example, the combination of 1373K, 40MPa, 30 min was sufficient to obtain full density, but that 1473K, 40MPa, 30min was required to obtain the maximum bending strength. By studying various properties of KHA high-speed steels, it was found that they were superior to the conventional steels for toughness, grindability, and hot workability. Tools such as drills, end mills, hobs, etc. produced from KHA materials exhibited better cutting p...
19 citations
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17 citations
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TL;DR: In this article, high-temperature alloys from Powders Powder Metallurgy: Vol 24, No 1, pp 32-40 (1981) and (1982) were discussed.
Abstract: (1981) High-Temperature Alloys from Powders Powder Metallurgy: Vol 24, No 1, pp 32-40
16 citations
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14 citations
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TL;DR: In this article, the influence of phase transformation on the sintering kinetics of Ti powder has been studied comparing the behavior of Ti compacts under the effect of cyclic heating.
Abstract: The influence of phase transformation on the sintering kinetics of Ti powder has been studied comparing the behaviour of Ti compacts under the influence of cyclic heating. The results show that the effect of a~f3 transformation is to promote sintering. The reverse transformation f3~a has no effect on sintering rate. Total shrinkage of Ti compacts sintered for 5 h by cyclic heating with transformation was about twice that of compacts sintered for the same time without transformation. In the former compacts, twinlike structures were observed. PM/0163
11 citations
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TL;DR: The role of high-speed steel as a cutting tool material is described in this article, where the choice of grades for various applications is strongly influenced by economic considerations as affected by alloy availability and cost.
Abstract: The role of high-speed steel as a cutting tool material is described. The choice of grades for various applications is strongly influenced by economic considerations as affected by alloy availability and cost. While the heat treatment applied to the finished tool is critical in achieving the desired properties, many factors affecting tool manufacture and use are dependent upon proper control of steel production. The coarse structure of cast ingots necessitates heavy hot-working reductions to achieve an adequate breakdown of primary carbides. Lengthy and expensive process routes are involved. Powder metallurgy techniques can provide an ideal distribution of carbides and many potential benefits are outlined, as are some of the problems encountered. Exploitation appears to have been limited, due to the expensive plant and processes required; consequently, in many applications, use of the products cannot be justified economically. At present, the most significant benefit lies in increasing the availab...
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TL;DR: Inco has developed a very strong and corrosion re-sistant oxide dispersion strengthened superalloy, MA 6000E, by the mechanical alloying process as discussed by the authors, which exhibits a typical 100h rupture strength of 138 MN m−2 at 1093°C and 552 MN m −2 at 760°C.
Abstract: Inco has developed a very strong and corrosion re- sistant oxide dispersion strengthened superalloy, MA 6000E, by the mechanical alloying process. The alloy (15Cr–2Mo–4W–4·5Al–2·5Ti–2Ta–0·15Zr– 0·01B–1·1Y2O3–bal. Ni) exhibits a typical 100h rupture strength of 138 MN m−2 at 1093°C and 552 MN m−2 at 760°C. The oxidation and sulphidation resistances of the alloy are equal to those of IN–100 and IN–792 respectively. This paper describes how the results of laboratory research were successfully scaled-up to commercial practice. The development of a production route from mechanically alloyed powder to fully processed and heat-treated blading bar is discussed. PM/0185
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TL;DR: In this paper, an investigation was conducted to study the variation of properties of a WC-TiC-TaC-NbC-Co alloy with carbon content by adding tungsten and/or carbon black to the powder mixture.
Abstract: An investigation was conducted to study the variation of properties of a WC–TiC–TaC–NbC–Co alloy with carbon content. Carbon content was varied by adding tungsten and/or carbon black to the powder mixture. Lattice parameter measurements by X-ray diffraction showed the maximum solubility of tungsten in cobalt to be ∼10%. Besides α-cobalt, the presence of e-cobalt was also observed. There is little change in cobalt lattice parameters, hardness, and coercive force outside the region where three phases are present. Although toughness reaches a maximum above the stoichiometric carbon content, optimum machining performance is obtained at a rather lower carbon content. With 5–8% tungsten in solution in the binder, the binder strength is improved, which explains the satisfactory machining results. PM/0193
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TL;DR: In this article, a sintering equation based on generalized geometric and structural conceptions is derived from the known characteristics of Sintering real systems which enables the authors to describe geometric changes in the particle contact region.
Abstract: A sintering equation based on generalized geometric and structural conceptions is derived from the known characteristics of sintering real systems which enables the authors to describe geometric and structural state changes in the particle contact region. Information is given on the influence of sintering time, heating rate, and pressure on the structural activity and densification kinetics during isothermal sintering. The known model theoretical sintering equations are incorporated as special cases in the present theoretical statements. PM/0130
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TL;DR: In this article, the influence of inclusion content on the mechanical properties of two powder-forged low-alloy steels was investigated and an improvement in the fatigue endurance limit was achieved in the ATST-D material following a 60% reduction in the percentage area of inclusions.
Abstract: This paper gives an indication of the influence of inclusion content on the mechanical properties of two powder-forged low-alloy steels. The powders used were Hoganas ATST–D (0·3–0·4Mn–0·1–0·25Cr–0·2–0·3Ni–0·25–0·35Mo) and Hoganas ATST–A (0·25–0·35Mn–0·1 max. Cr–1·8–2·2Ni–0·45–0·55Mo). The inclusion content and distribution were modified by subjecting the powder preforms to different preforging treatments. Different matrices were produced for the ATST–D material by tempering at different temperatures after quench-hardening in oil. A number of fatigue samples were nitrocarburized to examine the effect of surface treatment on fatigue behaviour. An improvement in the fatigue endurance limit of 14% was achieved in the ATST–D material following a 60% reduction in the percentage area of inclusions. In comparison, nitrocarburizing improved the endurance limit of the higher inclusion content material by 43%. A combination of reduced inclusion content and nitrocarburizing produced an increase of 50% in en...
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TL;DR: In this article, a rotating electrode process was used to combine hot isostatic pressing (HIP), hot explosive compaction (HEC), and hot rolling (HR) to optimize the processing parameters in order to obtain fully dense compacts and desired microstructures and mechanical properties.
Abstract: Prealloyed Ti–6Al–2Sn–4Zr–2Mo titanium alloy powders made by a rotating electrode process were consolidated by three techniques: hot isostatic pressing (HIP), hot explosive compaction (HEC), and hot rolling (HR), to optimize the processing parameters in order to obtain fully dense compacts and the desired microstructures and mechanical properties. Room-temperature tensile properties show that all three techniques are capable of giving full density and mechanical properties equivalent to or better than wrought properties. Control of processing parameters which may require another step of deformation such as rolling gives more reliability for HIP and HEC compacts. Metallography and scanning electron microscopic studies on fractured tensile specimens revealed the presence of both metallic and non-metallic inclusions in the compacts. The control of such contaminations during manufacturing as well as processing is necessary for good mechanical properties. PM/0181
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TL;DR: In this article, a recently developed square indentation test, used for comparing strength proved to be superior to bend tests in flexibility and in discriminating between the various steels, mainly M2 grades.
Abstract: Mechanical tests and micro structural examinations have been performed on various tool steels, mainly M2 grades, manufactured by conventional cast and wrought processes and by powder metallurgy routes. A recently developed square indentation test, used for comparing strength proved to be superior to bend tests in flexibility and in discriminating between the various steels. Most of the powder metallurgy products were as strong as the conventional steels but they displayed more variability, partly because pores and inclusions behaved as incipient cracks. Oxygen in amounts as high as 0·054% did not affect the strength of the hot-extruded powder steels significantly, except when it was combined with other impurities to form coarse inclusions. Generally, it appears that the strength of M2 grades is probably determined by a microstructural feature such as a weakness at grain boundaries or carbide/matrix interfaces, which is also related to the aspect ratio of the prior austenite grain structure. Furthe...
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TL;DR: In this article, the current status of PM stainless steel parts production in the USA and developments likely to influence the future are discussed, and the potential market segments and marketing requirements are discussed.
Abstract: The author diseusses the current status of PM stainless steel parts production in the USA and developments likely to influence the future. Processing parameters and market-segment analysis are presented to show progress over nearly two decades. Application limitations to mildly corrosive environments are recognized. Recent studies of powder particle surface chemistry explain some of the historical performance limitations. Alloy composition and processing methods, applicable to the existing PM industry, offer substantially improved corrosion resistance. Potential market segments and marketing requirements are discussed. PM/0178
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TL;DR: In this paper, the influence of additions of Ti and TiO2 to a ferritic matrix (Fe-13Cr-1·5 Mo) has been investigated, and the room-temperature tensile properties of these alloys were determined as a function of O2 content at fixed free Ti content and as a functional function of Ti content at a fixed O2 level.
Abstract: The influence of additions of Ti and TiO2 to a ferritic matrix (Fe–13Cr–1·5 Mo) has been investigated. The alloys were prepared by beating together the TiO2 and the powders of the different elements constituting the alloy. The beaten powders were then consolidated by hot compaction and hot extrusion in the form of bars which were further hot and cold worked by swaging. The particle size distribution of the beaten powders was determined by dry sieving. The microhardness and oxygen content were also measured. The mean size has been found to decrease with the amount of oxide. The room-temperature tensile properties of these alloys were determined as a function of O2 content at fixed free Ti content and as a function of Ti content at a fixed O2 level. It was found that after addition of more than O·25%O2 (as TiO2) the strength properties almost reach saturation while the ductility continues to decrease. Addition of Ti at a fixed O2 level increases the strength continuously and leaves the ductility alm...
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TL;DR: In this paper, the authors derived compatibility equations which take into account the combined effects of ν and C and the relative proportions of solid metal to porosity, and combined these equations to provide a general equation connecting apparent plastic Poisson's ratio.
Abstract: PM preform material is regarded as two-phase, consisting of a mixture of matrix metal and pores. During the upsetting stage of the powder-forging process, the metallic portion deforms in accordance with the ideal plastic Poisson's ratio (ν=0·5) while previously published experimental observations suggest that the porosity diminishes at a decreasing rate. This gives rise to the assumption that the total volume of the porosity decreases exponentially in the longitudinal direction for corresponding increases in radial strain, which leads to the concept of a ‘coefficient of consolidation’ C. The actual value of this coefficient varies between 0 and 0·5 depending upon the initial preform density, mode of deformation, and prevailing frictional conditions. Compatibility equations are derived which take into account the combined effects of ν and C and the relative proportions of solid metal to porosity. These equations are combined to provide a general equation connecting apparent plastic Poisson's ratio ...
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TL;DR: In this article, the authors investigated the operating conditions in a furnace with a good production rate and suggested a means by which the sintering atmosphere may be controlled, as well as suggesting possible explanations for this.
Abstract: The difficulties in the production of steel parts, with a uniform carbon content from the surface to the centre and a constant carbon content from one part to another, are well known Recent progress on sintering atmospheres with regard to carbon content is assessed and found lacking, especially when compared with the current demands of the automotive industry The author investigates the operating conditions in a furnace with a good production rate and submits possible explanations for this, as well as suggesting a means by which the sintering atmosphere may be controlled PM/0142
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TL;DR: In this paper, the effect of compacting pressure, in the range 150-600 MPa, and the addition of 0·5%Mo on the properties of sintered Hametag iron powder and manganese steels was investigated.
Abstract: An investigation has been carried out on the effect of compacting pressure, in the range 150–600 MPa, and of the addition of 0·5%Mo on the properties of sintered Hametag iron powder and manganese steels. Higher sintering activity compared with standard iron resulted in higher density and higher mechanical properties in the presence of manganese vapour. The addition of 0·5%Mo in the form of ferromolyb-denum caused an increase in density and strength properties in the Fe–C and Fe–Mn–C steels. PM/0157