Showing papers in "Powder Metallurgy in 1974"
TL;DR: In this article, the role of plastic deformation in powder compaction is reviewed, and it is suggested that the transition from Stage 1 to Stage 2 of compaction corresponds to the change from local to homogeneous plastic flow.
Abstract: Some current opinions on the role of plastic deformation in powder compaction are reviewed. The results of mechanical testing, metallographic examination, and X-ray-diffraction analyses of some atomized iron powder compacts are presented, together with those of metallographic examination of compacted spherical high-temperature, high-strength alloy powders. Extensive plastic deformation occurs even during the first stage of compaction but this is not the only cause of consolidation. A sequence of compacting mechanisms is described for the iron powder. It is suggested that the transition from Stage 1 to Stage 2 of compaction corresponds to the change from local to homogeneous plastic flow.
49 citations
TL;DR: In this article, a low-melting master-alloy powder is proposed to reduce the diffusion time of a prealloy with admixed alloying elements to the order of one particle radius.
Abstract: Prealloyed powders are dominant items in the economics of powder forgings today. Present estimates predict a maximum powder consumption that is too low to bring about essential reductions in the cost of these materials. Long homogenization discourages the use of plain iron powders with admixed alloying elements, especially where induction heating is employed, and the use of cheap alloying elements such as manganese is hampered by oxidation problems. A way of overcoming these difficulties is described. If the alloying additions needed for hardenability are made in the form of a low-melting master-alloy powder, diffusion times can be very much reduced. A condition is that the molten prealloy wets the iron particles, reducing the diffusion distance to the order of one particle radius. It is also desirable that the master alloy should penetrate quickly along the grain boundaries of the iron, further reducing the diffusion distance. Low-melting alloys of manganese with copper satisfy these conditions. ...
26 citations
TL;DR: In this article, the conditions under which electrical contacts are used differ widely and various contact phenomena must be considered and the problems that can arise under different operating conditions understood, and the final choice is frequently a material produced by powder metallurgy.
Abstract: The conditions under which electrical contacts are used differ widely. In selecting a material the various contact phenomena must be considered and the problems that can arise under different operating conditions understood. The final choice is frequently a material produced by powder metallurgy. Materials and fabrication are aimed at optimizing contact properties and method of attachment. Some contact problems and the solutions that have been developed are reviewed.
21 citations
TL;DR: In this paper, the "pin and disc" method has been used to measure the coefficient of friction for the following lubricants: aluminium, calcium, lithium, zinc stearates, and stearic acid.
Abstract: The ‘pin and disc’ method has been used to measure the coefficient of friction for the following lubricants: aluminium, calcium, lithium, zinc stearates, and stearic acid. The variation of the coefficient of friction at the surface of iron compacts has been studied with respect to metal/metal contacts exposed through the lubricant film and the behaviour of the lubricant film with variations of pressures, temperature, and speed of sliding has been related to the variation in coefficient of friction for the system.The results for a range of zinc stearates are compared with those for other stearates for reduced iron powder compacts sliding against high-chromium die-steel.
18 citations
TL;DR: In this article, the tensile properties of PM alloys were equivalent or superior to those of the conventionally cast and forged alloys, but no improvement in fatigue and fracture-toughness properties was gained Fine grain sizes (1-5 μm) were obtained by hot rolling either conventionally processed or PM bars of grade-300 maraging steel at 760, 820, and 870°C, followed by air-cooling
Abstract: Powders of 300-grade maraging steel have been produced by two different atomizing processes and consolidated by hot isostatic pressing, extrusion, hot rolling, or a combination of these methods The tensile properties of the PM alloys were equivalent or superior to those of the conventionally cast and forged alloys, but no improvement in fatigue and fracture-toughness properties was gained Fine grain sizes (1–5 μm) were obtained by hot rolling either conventionally processed or PM bars of grade-300 maraging steel at 760, 820, and 870°C, followed by air-cooling In all cases, the tensile properties and fracture toughness were improved by grain-size refinement
13 citations
TL;DR: In this article, up to 5% each of copper and nickel powders as well as 0.35 or 0.65 wt.-% graphite were added to sponge iron powder grade SC 100.
Abstract: Up to 5% each of copper and nickel powders as well as 0.35 or 0.65 wt.-% graphite were added to sponge iron powder grade SC 100.26. Tensile specimens prepared from the mixes were sintered in endogas in a belt furnace at 1120°C for 1 h. Dimensional change, hardness, and tensile properties were measured. The results show that the tensile strength increases with increasing copper and nickel additions at each carbon content level and that copper has the greatest influence. Since plain copper additions cause considerable growth during sintering, it is advantageous to combine the two elements. Conditions for ‘zero growth’ have been established. The highest strength for a ‘zero growth’ material was achieved with an alloy containing 4.0% Ni, 2·5% Cu, and 0.6% C, with a density of 7.1 g/cm3. Retention of austenite seems to limit the strengthening effect of nickel at this carbon content. Addition of molybdenum counteracts this effect and raises the strength. With a partially prealloyed powder containing 4% ...
11 citations
TL;DR: The tensile, impact, and fatigue properties of a range of powder-forged steels have been examined in this paper, where a relationship has been found between the content of non-metallic inclusions and the fatigue performance.
Abstract: The tensile, impact, and fatigue properties of a range of powder-forged steels have been examined. A relationship has been found between the content of non-metallic inclusions and the fatigue performance. The properties of powder-forged steels at 900 N/mm2 strength were compared with those of En16 wrought steel at the same level. The properties of wrought steel are demonstrably extremely variable, depending on the degree of hot work imparted during processing and on the relationship of the test-piece axis to the principal direction of working. The properties of powder-forged steel lie between the highest and lowest that can be expected in wrought steel; comparisons between the two types of material can be made only after careful consideration of their specific characteristics. Powder-forged steels were shown to be capable of developing useful properties over wide ranges of composition.
11 citations
TL;DR: In this paper, the behavior of cemented carbides subjected to pressures of 4-12 kN/mm2 in a belt-type apparatus has been investigated, and the permanent deformation characteristics as a function of composition and applied pressure were recorded, and each specimen was examined by quantitative metallography, before and after compression, to determine the relation between micro-structural changes (fractures and slips in carbide crystals) and microstructural parameters for different pressures.
Abstract: The behaviour of cemented carbides subjected to pressures of 4–12 kN/mm2 in a belt-type apparatus has been investigated. The materials studied were industrial sintered WC-Co (3–30 wt.-% Co), also TiC-Co and TiC-Ni produced in the authors’ laboratory by powder-metallurgy techniques. When necessary, the average particle size of the carbide crystals was modified by suitable annealing. The permanent deformation characteristics as a function of composition and applied pressure were recorded, and each specimen was examined by quantitative metallography, before and after compression, to determine the relation between microstructural changes (fractures and slips in carbide crystals) and microstructural parameters (grain size, contiguity, & c.) for different pressures. Fracture-path analysis was also performed on fractured compression vessels by transmission and scanning electron microscopy.
10 citations
TL;DR: In this article, a study was made of extrusion-consolidation processing variables for the production of sound material from spherical 7075 aluminium alloy powder (median particle size 132 μm) canned in evacuated cylinders at ∼60% initial density.
Abstract: A study has been made of extrusion-consolidation processing variables for the production of sound material from spherical 7075 aluminium alloy powder (median particle size 132 μm) canned in evacuated cylinders at ∼60% initial density. Maximum product integrity and tensile properties were obtained by extrusion at 644K (700°F)–700K (800°F) and 6:1–10:1 reduction ratio. At lower reduction ratios (2:1 and 3:1) the product exhibited gross cracking and was not completely dense. At a reduction ratio of 40:1, it had significantly poorer tensile properties, attributable to the formation, during extrusion and heat-treatment, of longitudinal cracks at the particle boundaries and to the microstructure produced within the particle grains by the thermomechanical conditions. In general, processing behaviour and product properties were either inferior to or, in some cases, equal to those of wrought material extruded for comparison under the same conditions. Inferior behaviour of the metal powder during processing...
9 citations
TL;DR: In this article, the hardness, tensile, and impact properties of two nickel-molybdenum powder-formed steels were determined using standard 25 mm-dia. specimens with a 25 mm gauge length.
Abstract: Hardenability, tensile, and impact properties have been determined for two nickel-molybdenum powder-formed steels. The compositions of the two steels were Fe-1·8% Ni−0·5% Mo and Fe −0·5% Ni −0·6% Mo; carbon contents studied for both materials were 0·2, 0·3, and 0·4%. Preforms (50 × 50 × 127 mm) were pressed and then sintered for 1 h in a dissociated ammonia atmosphere at 1120°C, to provide a density of 6·5 g/cm3. Preforms were hot formed to full density by upsetting (plane strain) at 980°C or by re-pressing (uniaxial strain) at 1040°C.Standard 25 mm-dia. × 100 mm-long Jominy end-quenched tests were made to determine hardenability. Room-temperature tensile properties were determined using 6·4 mm-dia. specimens with a 25 mm gauge-length. Standard Charpy V-notch specimens were used to determine the impact properties at −40, 0, 22, and 100°C. Triplicate tests were made in the as formed as well as the quenched-and-tempered conditions.The additional flow that was realized by upsetting provided higher te...
7 citations
TL;DR: In this article, a study was made of alloy systems consisting of TiC and WC in combination with ruthenium and RUThenium-palladium alloys and it was found that small amounts of the metals nickel, cobalt, or iron, which are normally picked up during milling, are necessary for the full densification of the alloys at convenient sintering temperatures.
Abstract: A study has been made of alloy systems consisting of TiC and WC in combination with ruthenium and ruthenium-palladium alloys. Particular attention was paid to alloys with high carbide contents, which have a potential application as cutting-tool materials. The alloys were successfully prepared using conventional powder-metallurgical techniques. Alloys based on the TiC-Ru system were particularly promising in preliminary machining tests. In this system, it was found that small amounts of the metals nickel, cobalt, or iron, which are normally picked up during milling, are necessary for the full densification of the alloys at convenient sintering temperatures (i.e. ∼ 1500°C). A more detailed study of TiC-(Ru,Ni) alloys showed that the small amount of nickel required for effective sintering does not seriously affect the properties of the alloy and that, with this quantity of nickel, the melting point of the binder phase is still significantly higher than that of conventional cemented carbides.
TL;DR: The radial/axial shrinkage ratio in compacts made from spherical copper powder has been investigated in this paper, also the linear dependence of R/A on compacting pressure and sintering temperature.
Abstract: The variables affecting the radial/axial (R/A) shrinkage ratio in compacts made from spherical copper powder have been investigated, also the linear dependence of R/A on compacting pressure and sintering temperature. The values of R/A for spherical powder are higher than those for irregularly shaped powder. The effect of particle shape and height/dia. ratio of the compact on R/A have been studied. The differences in green-density distributions have been determined, together with the effect on these of pressure and height/dia. ratio of the compact. The observed variation of R/A is attributed to differences in density distribution in the green compacts, resulting in anisotropic stresses during sintering.
TL;DR: In this paper, a method of measuring the interparticle friction of metal powders under conditions of applied vibrational energy has been devised, which can be expressed as an angle or as a coefficient.
Abstract: A method of measuring the interparticle friction of metal powders under conditions of applied vibrational energy has been devised. With zero vibrational energy, the friction, expressed as an angle or as a coefficient, can be correlated with the basic characteristics of a powder, provided that the conditions of settling are standardized to provide consistent density values. The effect of the variation of settled density is shown. By the application of rectilinear sinusoidal vibrational energy to the powders, it can be shown how the variation and combinations of frequency and displacement effectively reduce interparticle friction, thus enhancing flow and settling of metal powders into dies offering difficult contours and restrictive sections.
TL;DR: The relationship between compactibility and shrinkage rate in nickel-doped tungsten compacts has been investigated in this article, where a possible explanation of the mechanism of the sintering behavior is discussed.
Abstract: The relationship between compactibility and shrinkage rate in nickel-doped tungsten compacts has been investigated. The shrinkage rate varied with the compactibility of the specimen. In the intermediate stage of sintering the shrinkage rate increased with green density. Therefore, compaction pressure must be considered as a separate parameter in any such study of sintering. A possible explanation of the mechanism of the sintering behaviour is discussed.
TL;DR: In this article, the authors discuss over-rated or under-estimated powder metallurgies in the USA and Europe, and propose a solution to the problem: over-rate or underestimate powder metals.
Abstract: (1974). PROPERTIES OF STRUCTURAL POWDER-METAL PARTS—OVER-RATED OR UNDER-ESTIMATED? Powder Metallurgy: Vol. 17, No. 33, pp. 103-125.
TL;DR: In this article, a method for the powder-metallurgy fabrication of tool-steel bar stock was developed that requires neither isostatic compaction nor low-oxygen powders.
Abstract: A method for the powder-metallurgy fabrication of tool-steel bar stock has been developed that requires neither isostatic compaction nor low-oxygen powders. The powder is heated in sealed steel tubes and directly step-forged to 99·5% density. Further reduction by rolling raises the density to 100%. A reducing agent and an oxygen getter are enclosed in the container, together with the powder for in situ reduction of particle surface oxides. This makes initial evacuation of the containers unnecessary and allows powders with high oxygen contents to be used. Mechanical properties compare well with those of material rolled from ingot.
TL;DR: In this paper, high purity beryllium powder possesses characteristics differing substantially from those of the normal powder that until recently has been the purest form available, and these characteristics are compared and discussed, together with methods for consolidating the powder and treating the compacts.
Abstract: High-purity beryllium powder possesses characteristics differing substantially from those of the normal powder that until recently has been the purest form available. These characteristics are compared and discussed, together with methods for consolidating the powder and treating the compacts. The techniques available for fabricating porous compacts and their applicability are also described.
TL;DR: In this article, the authors present results from hot-forming experiments with a variety of preform shapes and discuss possibilities of overcoming some typical preform design problems, such as cracking, overlapping or residual porosity in one or several of the sections.
Abstract: In the hot forging of powder compacts into items of complicated shape, proper preform design is critical. In particular, in cases where items having sections of different lengths in the forging direction are to be produced in tools with undivided punches, the risk of cracking, overlapping or residual porosity in one or several of the sections is great. This paper presents results from hot-forming experiments with a variety of preform shapes and discusses possibilities of overcoming some typical preform design problems.
TL;DR: In this article, the authors deal mainly with the preparation of binary Fe-Cr, Fe-Si, and also ternary Fe-cr-Si alloys obtained by the in situ decomposition of Si3N4, Cr2N, and CrSi2 in an iron matrix (WP-150).
Abstract: The techniques used in alloying in iron powder metallurgy have been extended by employing special compounds. The introduction of the alloying elements in this form and the decomposition of selected nitrides and silicides are described. Elements that oxidize readily at high temperatures (e.g. Cr, Si) can be added in a relatively pure and homogeneous state. These elements stabilize the α phase and thus improve the sintering behaviour.The paper deals mainly with the preparation of binary Fe-Cr, Fe-Si, and also ternary Fe-Cr-Si alloys obtained by ‘in situ’ decomposition of Si3N4, Cr2N, and CrSi2 in an iron matrix (WP-150).The study covers the properties of the powders and their mixtures, the pressing and sintering conditions, the sintering behaviour in the range 1000–1300°C with varying alloying additions, for different sintering times and atmospheres. The tensile strengths observed are ∼525 N/mm2 at a densityof 6·7 g/cm3, with ∼3% elongation at fracture. With respect to the low density and the carbon...
TL;DR: In this paper, the lateral flow of metal was observed and investigations undertaken as to how density variations across the preform might assist the consolidation process, and some guidelines to assist in designing preforms for sinter forging and to attempt to minimize the "trial and error" approach.
Abstract: An important difference between sinter forging and conventional forging is that of consolidation of the PM preform. It therefore follows that sinter forging would seem to be a hot-compaction process with some bulk metal plastic flow. The permitted amount of plastic flow is considerably less for a PM preform than for a preform produced from wrought material of equivalent composition, since PM preforms exhibit poor ductility and are therefore more prone to cracking. The purpose of this study is to produce some guidelines to assist in designing preforms for sinter forging and to attempt to minimize the ‘trial and error’ approach. This has been undertaken by the production and study of a component suitable for PM forging, which at present is produced by conventional forging.The lateral flow of metal was observed and investigations undertaken as to how density variations across the preform might assist the consolidation process. An iron powder containing 1% graphite and 1% zinc stearate was used in the...
TL;DR: In this paper, the feasibility of glass-ceramic as a die material for the die-compaction of lubricated and unlubricated iron powder has been evaluated and the results indicate that possibilities may lie in the further development of ceramics as inexpensive die materials for powder compaction in which die-wall friction could be significantly reduced.
Abstract: Glass-ceramic inserts have been made and shrink-fitted into steel bolsters to assess the feasibility of glass-ceramic as a die material for the die-compaction of lubricated and unlubricated iron powder. Measurements of compacting pressures and ejection stresses were lower for the glass-ceramic die compared with those for a standard tool-steel die in lubricated conditions, while in unlubricated conditions ejection stresses were appreciably higher, with scoring and brittle fracture of the insert. The results indicate that possibilities may lie in the further development of ceramics as inexpensive die materials for powder compaction in which die-wall friction could be significantly reduced.
TL;DR: In this paper, an extruded nickel-chromium-cobalt alloy of the Nimonic 90 type, using powders, wires, and conventional cast billets as starting materials, resulted in a wide variety of grain sizes and structures and the performance of the materials, as assessed by stress-rupture, fatigue, and impact data, also differed considerably.
Abstract: Preparation of an extruded nickel-chromium-cobalt alloy of the Nimonic 90 type, using powders, wires, and conventional cast billets as starting materials, resulted in a wide variety of grain sizes and structures. The form of the oxide/carbide and its distribution varied with the production route. The performance of the materials, as assessed by stress-rupture, fatigue, and impact data, also differed considerably. The stability of the grains was directly related to the distribution of the oxides/carbides and was therefore interrelated to the stress-rupture properties. Fatigue properties were sensitive to a fine general distribution of oxides/carbides and impact properties were sensitive to an intergranular distribution. With the best structure, of a fibrous nature, it was possible to achieve an attractive combination of stress-rupture, fatigue, and impact properties—the last being unusually high.
TL;DR: In this article, an investigation has been conducted into the effectiveness of two post-sinter surface treatments, namely steam treatment and oil impregnation, as methods of improving the corrosion-resistance of ferrous powder-metallurgy parts.
Abstract: An investigation has been conducted into the effectiveness of two ‘production-line’ post-sinter surface treatments, namely steam treatment and oil impregnation, as methods of improving the corrosion-resistance of ferrous powder-metallurgy parts. Electrochemical techniques and simple immersion tests followed by transverse rupture strength determination were used to evaluate corrosion behaviour in aqueous chloride and dilute sulphuric acid solutions. ‘As-sintered’ and wrought and machined parts were tested for comparison purposes.In the chloride solution the corrosion-resistance of the treated parts was higher than that of either the as-sintered or machined parts, the steam treatment being particularly effective. In the acid solution, steam-treated parts showed the lowest corrosion-resistance of the four, with oil impregnation giving the highest resistance.