Showing papers in "Powder Metallurgy in 1978"
TL;DR: In this paper, the Particle Deformation and Sliding During Compaction of Spherical Powders: A Study by Quantitative Metallography is presented. But this study is limited to the case of spherical powders.
Abstract: (1978). Particle Deformation and Sliding During Compaction of Spherical Powders: A Study by Quantitative Metallography. Powder Metallurgy: Vol. 21, No. 4, pp. 179-187.
106 citations
TL;DR: In this paper, the Fracture Toughness of Powder Metallurgy and Conventionally Produced High-Speed Steels is discussed and a discussion of the relationship between fracture toughness and high speed steels is presented.
Abstract: (1978). Fracture Toughness of Powder Metallurgy and Conventionally Produced High-Speed Steels. Powder Metallurgy: Vol. 21, No. 1, pp. 13-28.
31 citations
TL;DR: In this paper, it was shown that the compacted density was dependent on the container tube wall thickness and material, even when the ratio of the powder mass to the explosive mass was maintained constant.
Abstract: transmit a shock pulse into the powder so as to effect its compaction. The controlling parameter of the process is assumed to be the ratio of the powder mass to the explosive mass, Mp/ME, and values of this ratio necessary to fully compact various powders have been quoted· for specified explosives. Apart from an attempt by Leonard4 to relate the Mp/ME ratio for full compaction to the compressive yield strength of five powder materials, no definite relationship has been established between this ratio and any measurable. property of a metal powder. Although details of the powder container are not normally included in the literature, initial work by Ludlow,S subsequently verified by Bhalla,6 showed that compacted density was dependent on the container tube wall thickness and material, even when Mp/ME was maintained constant. Bhalla subsequently found that a rel(~tionship existed between the compacted density Dc and the kinetic energy per unit area of the tube E immediately after detonation of the explosive charge. This relationship took the form:
21 citations
18 citations
TL;DR: In this paper, the relationship between density, electrical conductivity, Young's modulus, and toughness of porous iron samples is investigated, and it is shown that these properties are related.
Abstract: (1978). Relationships Between Density, Electrical Conductivity, Young's Modulus, and Toughness of Porous Iron Samples. Powder Metallurgy: Vol. 21, No. 1, pp. 1-6.
13 citations
TL;DR: In this article, the authors discuss the aspects of fatigue of sintered iron and powder metallurgy, and propose a method to deal with it in powdermetallurgy.
Abstract: (1978). Metallographic Aspects of Fatigue of Sintered Iron. Powder Metallurgy: Vol. 21, No. 1, pp. 7-12.
12 citations
TL;DR: In this paper, a mathematical analysis of the deformation by modifying an axi-symmetric upper-bound solution and utilizing a penalty function approach to minimization to obtain the stress constants is presented.
Abstract: The mechanical properties of aluminium alloy powder compacts vary throughout the quasi-static deformation zone. Experimental evidence has suggested that the flow stress is dependent upon both strain and strain rate such that an equation of the form δ = Aeme n best describes material behaviour under deformation conditions. This paper presents a mathematical analysis of the deformation by modifying an axi-symmetric upper-bound solution and utilizing a penalty function approach to minimization to obtain the stress constants. It is shown that for a cast billet this approach predicts the specific pressure accurately and that for powder compacts the constants k, m, and n may be obtained and a satisfactory prediction of pressure facilitated.
9 citations
9 citations
TL;DR: In this article, the morphology and phase composition of products resulting from steam oxidation at 530-630°C were analyzed and the dependence of structural features on the conditions of steam oxidation and, in particular, on the cooling procedure after oxidation.
Abstract: Oxidation in superheated steam is frequently used to prevent corrosion of sintered steel parts. Corrosion resistance of oxidized sintered steel is affected by structural features of the oxidation products. The present study deals with the morphology and phase composition of products resulting from steam oxidation at 530–630°C. Data on the non-stoichio-metry of wustite are given in the cases where an appreciable amount of this phase was found in the oxidation products. The results show the dependence of structural features on the conditions of steam oxidation and, in particular, on the cooling procedure after oxidation.
8 citations
TL;DR: In this paper, the influence of surface oxide layer on the sintering process of lead was investigated and it was shown that the surface oxide layer has a strong influence on the performance of the process.
Abstract: (1978). Influence of Surface Oxide Layer on Sintering Process of Lead. Powder Metallurgy: Vol. 21, No. 4, pp. 188-194.
TL;DR: The results of tests on more than 250 separate extrusions are reported in this article, and the relationship between structure and properties is reported in some detail, and wear resistance and electrical conductivity are shown to be, respectively, superior to and equivalent to those of comparable wrought material.
Abstract: Eight differing tin bronzes have been produced by extruding atomized powders. The products have been subjected to mechanical tests and structural examination. The results of tests on more than 250 separate extrusions are reported. It is shown that the microstructure of bronzes is considerably modified if powder is utilized as stock material, and that the improvements are also a function of the processing conditions and, in the case of two-phase materials, of the original particle size. The relationship between structure and properties is reported in some detail, and wear resistance and electrical conductivity are shown to be, respectively, superior to and equivalent to those of comparable wrought material.
TL;DR: In this article, a quantitative assessment has been made of the degree of homogeneity by measuring the nickel content of a large number of small areas within a complete cross-section of the specimen and this has been compared with plated and pre-alloyed material with the same overall composition but greater homogeneity prior to sintering.
Abstract: Commercial production of low-alloy steel components from blended mixtures of the constituents in powder form involves the use of sintering times which are too short to allow the production of a chemically homogeneous material. This has prompted an investigation into the relationships between the degree of homogeneity, microstructure, and mechanical properties in a sintered and heat-treated low-alloy steel, prepared in this way. A quantitative assessment has been made of the degree of homogeneity by measuring the nickel content of a large number of small areas within a complete cross-section of the specimen and this has been compared with plated and pre-alloyed material with the same overall composition but greater homogeneity prior to sintering. Provided the degree of homogenization was greater than a certain critical value the relationship between tensile strength and porosity fitted well with previously published work. The production of small quantities of non-martensitic phases from austenite ...
Abstract: Electrical conductivities of pure iron powders have been measured during compaction. Measured conductivities are at least two orders of magnitude less than expected from the volume fraction of metal. They decrease on re-pressing and on decreasing the compaction rate. These phenomena are attributed to the effects of included thin oxide films on the particle surfaces. All observations can be interpreted consistently by the competition between mechanical film disruption and the growth of new oxide on freshly exposed metal surfaces.
TL;DR: In this article, the fracture characteristics of three different steels produced by the process of powder-forging have been evaluated by the crack opening displacement (COD) testing method on fatigue pre-cracked specimens.
Abstract: The fracture characteristics of three different steels produced by the process of powder-forging have been evaluated by the crack opening displacement (COD) testing method on fatigue pre-cracked specimens. It is shown that the COD at initiation and at maximum load, as well as the fracture mode, are dependent on the oxygen content of the steels that result from differing deoxidation treatments during sintering. For the same oxygen level the COD values are dictated by the metallic matrix properties, showing an inverse proportionality· to the matrix hardness for various tempering conditions. The results are interpreted as a function of the distribution of non-metallic inclusions and the work-hardening characteristics of the different structures.
TL;DR: In this article, bearing materials by powder metallurgy are discussed and the authors propose a bearing material by powdermetallurgy (BME) method. pp. 80-85.
Abstract: (1978). Bearing Materials by Powder Metallurgy. Powder Metallurgy: Vol. 21, No. 2, pp. 80-85.
TL;DR: In this article, it was found that a reduction of about 11% was the most effective for extrusion and a reduction about 0.2 mm, by a small reduction per pass with a small diameter roll, was more effective for rolling, which may be attributed mainly to an appropriate density gradient which is given by the small cold-reduction in forming.
Abstract: The mechanical properties, particularly strength and toughness, of sintered steels are improved considerably by surface densifying treatments consisting of small reduction extrusion and rolling and subsequent full annealing. It has been found that a reduction of about 11% is most effective for extrusion and a reduction of about 0·2 mm, by a small reduction per pass with a small diameter roll, is most effective for rolling. The toughening mechanism may be ascribed mainly to an appropriate density gradient which is given by the small cold-reduction in forming. Also the collapsed pores in the surface layers are reduced in size and spheroidized, and the interparticle bonding is increased by the subsequent full annealing.
TL;DR: In this article, the conductivity of copper-base sintered alloys is investigated and it is shown that the conductivities above 8·6Mg m3 are easy to produce.
Abstract: 2 As Fig. 1 for copper-base sintered alloys. carbon is not soluble in copper. The tensile strength and elongation are often very poor. One solution, which was patented some time ago,3 is to press at a density between 6·5and 7·0Mg m3, oxidize the parts at 380°C for 20 min, and then sinter. Shrinkage is of the order of 5% and the tolerances of the tools must be calculated to allow for this. The parts are coined afterwards in a die into which they enter freely with a clearance which varies with the shape and height. Densities above 8·6Mg m3 are easy to produce. Electrical conductivity is then given by the formula:
TL;DR: In this article, the authors conjured up pictures of their meetings in 25 years' time being held on an offshore rig in the Atlantic rather than inland England, and their feelings about the stability and multiple sources are exactly yours.
Abstract: THE CHAIRMAN: Thank you for conjuring up pictures of our meetings in 25 years' time being held on an offshore rig in the Atlantic rather than inland England. It was interesting to hear your comments on the iron powder supply situation in America because I think we have a similar sort of situation in England,.and our feelings about the stability and multiple sources are exactly yours. It was very encouraging to hear that your thoughts were exactly the same. We are not alone in our problem. Professor H. F. FISCHMEISTER (Chalmers University): What happened to the Loose~Pack Powder process?
TL;DR: In this article, a hot-swaging method was used to determine the processing parameters for producing fully consolidated products from ingot Beta III titanium alloy spherical powders, which were obtained by 54·2 and 65·2% reductions at all four temperatures and by 37·5% reduction at 1227 K.
Abstract: A hot-swaging method was used to determine the processing parameters for producing fully consolidated products from Beta III titanium alloy spherical powders. Four temperatures (1005 K, 1033 K, 1144 K, and 1227 K) and four percentage reductions (25·1, 37·5, 54·2, and 65·2) of the can outside diameter were selected for study. Fully consolidated powder products were obtained by 54·2 and 65·2% reductions at all four temperatures and by 37·5% reduction at 1227 K. The other processing conditions did not give fully dense products.Room-temperature tensile and fracture toughness properties of the swaged powder products in the heat-treated condition were determined. The fully consolidated swaged powder products had tensile and fracture toughness properties equal to or better than reported properties of wrought products made from ingot Beta III titanium alloy. The properties of the other swaged powder products (not fully dense) reflected lower mechanical properties because of poor consolidation.
TL;DR: In this article, the authors investigated the properties of some ferrous sintered alloys and showed that adding H2S to the γ-nitriding atmosphere may improve machinability.
Abstract: The heat-treatment and properties of some ferrous sintered alloys are investigated. The approach has been to introduce nitrogen to enhance the heat-treatment response during the heat-treatment cycle. The process is known as γ-nitriding to distinguish it from the ferritic nitriding process which is a surface-hardening treatment. Addition of H2S to the γ-nitriding atmosphere may be used to improve machinability. It is suggested that the economics of the process may be favourable enough for the process to be commercially viable.