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Showing papers in "Powder Metallurgy in 1973"


Journal ArticleDOI
TL;DR: The literature concerning the wear of tungsten carbide-cobalt alloys used as tool bits in rock drilling is surveyed in this paper, where the possible mechanisms of rock breakage and of tool wear are briefly discussed.
Abstract: The literature concerning the wear of tungsten carbide-cobalt alloys used as tool bits in rock drilling is surveyed. The possible mechanisms of rock breakage and of tool wear are briefly discussed. Wear takes place as a result of shock impact or impact-fatigue spalling, by abrasion-mainly from the quartz grains in the rock, and also by thermal fatigue. The mechanism that dominates in any given conditions depends on the method of drilling and on the strength and abrasiveness of the rock. For rotary-percussive drilling, impact-fatigue wear and abrasion operate simultaneously,though essentially independently.Published data on the relations between the wear of WC-Co alloys in rock drilling and their structure and properties are critically discussed. It appears that the resistance to impact wear is a direct function of the bulk compressive or transverse rupture strength and is related to the WC grain size and the Co mean free path. It is directly proportional to the blow energy in percussion. The resul...

101 citations


Journal ArticleDOI
TL;DR: In this paper, Torre's model of a hollow sphere subjected to external pressure, developed to represent the compaction behaviour of a porous body, has been modified to cover strain-hardening of the material.
Abstract: Torre’s model of a hollow sphere subjected to external pressure, developed to represent the compaction behaviour of a porous body, has been modified to cover strain-hardening of the material. Numerical results from this model show that as the strain-hardening capacity of the material is increased, the slope of the In(1/1-D) vs. pressure plots decreases, while the linearity increases. No significant curvature is observed at high pressures.Experimental results of density for Atomet 28 iron powder are compared with theoretical predictions. There is good agreement for compacting pressures between 300 and 1000 N/mm2; outside this range the experimental results are lower than the theoretical values. Some possible reasons for the discrepancy are discussed.

29 citations


Journal ArticleDOI
Per Folke Lindskog1
TL;DR: In this article, the mechanisms operating during the sintering of iron-phosphorus PM alloys are discussed, as well as the factors contributing to the unique combination of strength, ductility, and toughness that is characteristic of these materials.
Abstract: The mechanisms operating during the sintering of iron-phosphorus PM alloys are discussed, as well as the factors contributing to the unique combination of strength, ductility, and toughness that is characteristic of these materials. Alloying methods are reviewed with special reference to powder compressibility, tool wear during compaction, and homogenization during sintering. The preferred production method is to add phosphorus in the form of a fine Fe3P powder to iron powder. The mechanical properties of a number of sintered steels made with and without Fe3P additions to sponge iron or to high-purity atomized iron powders are reported. Use of atomized powder makes it possible to reach extremely high density by single pressing and the resulting phosphorus-containing sintered steels have very high ductility and impact strength. The fatigue strength is related linearly to the tensile strength, with a correlation coefficient of 0·91. It is concluded that structural factors other than those that contr...

27 citations


Journal ArticleDOI
TL;DR: In this paper, the fracture-resistance of a range of sintered steels containing additions of copper and carbon has been measured in terms of their critical stress-intensity factor, Kc All the fractures were apparently of the flat plane-strain type, the micro cracking being a process of microvoid coalescence rather than of cleavage.
Abstract: The fracture-resistance of a range of sintered steels containing additions of copper and carbon has been measured in terms of their critical stress-intensity factor, Kc All the fractures were apparently of the flat plane-strain type, the micro cracking being a process of microvoid coalescence rather than of cleavage Toughness, in terms of Kc, is shown to depend on the percentage porosity, the level of the copper addition, and the carbon content Higher toughness is achieved with copper + carbon additions than with either independently A major feature of the results is that toughness increases with the yield stress, a trend that is contrary to the general behaviour of wrought materials

24 citations


Journal ArticleDOI
TL;DR: In this article, the development of a process of preparing spherical or flake powders in the size range 100-1500 μm is described, and the conditions controlling particle size and shape have been analyzed theoretically in terms of the relevant alloy, atmosphere, and m...
Abstract: The development of a process of preparing spherical or flake powders in the size range 100–1500 μm is described. The process has been applied to a wide range of materials, including iron, nickel, cobalt and titanium alloys, refractory metals, carbides, and oxides.In one mode of operation the feed material is in the form of a consumable rod electrode (cathode) and is melted by a vertical arc struck between the electrode and a rotating crucible. The melted material falls into the crucible, which may be water-cooled, and is forced up and over the walls by centrifugal action. By selecting rotation speeds in the range 500–4000 rev/min, the mean size of the particles formed as the liquid tears off the crucible lip may be varied systematically. Alternatively, granules may be fed through a hollow non-consumable electrode or the crucible may be replaced by a consumable anode.The conditions controlling particle size and shape have been analysed theoretically in terms of the relevant alloy, atmosphere, and m...

23 citations


Journal ArticleDOI
TL;DR: In this paper, the bonding strength between particle and matrix in a number of austenitic and ferritic iron alloys has been determined from electron micrographs of the solid/solid contact angle, θ, at cavities formed by cold working and annealing.
Abstract: The bonding strength, or ‘work of adhesion’, W, between particle and matrix in a number of austenitic and ferritic iron alloys has been determined from electron micrographs of the solid/solid contact angle, θ, at cavities formed by cold working and annealing. The critical strain to bring about cavitation, ec, was measured by plotting the strain corresponding to a sudden fall in rate of work-hardening. In deriving an equation to predict ec, account must be taken of the dependence of the equilibrium shape of the cavity on θ. Good correlation between experimental and predicted ec, as a function of W, was found. Brittle fracture of the matrix is likely to occur if θ is very low and the volume fraction is high. A criterion for brittle fracture, based on θ, is suggested which successfully predicts brittle fracture in one of the alloys studied.

23 citations


Journal ArticleDOI
TL;DR: In this article, a simple method of producing alloy steels by mixing, pressing, and sintering iron powder with carbides of transition metals is described, which produces steels with partly air-hardening properties.
Abstract: A simple method of producing alloy steels by mixing, pressing, and sintering iron powder with carbides of transition metals is described. The carbides must have a high carbon content and be soluble in iron. These characteristics are found in the carbides of chromium, tungsten, molybdenum, and vanadium. Tensile strengths of ∼800 N/mm2 have been achieved in annealed specimens having carbide additions of 1–12 wt.-%, depending on the carbide. The additions produce steels with partly air-hardening properties.The effects of concentration and particle size of the carbides, sintered density, sintering conditions, and cooling rate on mechanical properties have been determined. The alloys are not very sensitive to the sintering atmosphere. The effect of heat-treatment on the mechanical properties of Fe-Cr3C2 alloys is reported. A tensile strength >1300 N/mm2 was observed with 4 wt.-% Cr3C2. Dilatometric measurements were conducted with different carbide concentrations and heating conditions to study the sin...

22 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the factors governing the strength of cold-pressed metal powder compacts and concluded that the most important parameters are freedom from oxidation and the plastic properties of the powder particles.
Abstract: The factors governing the strength of cold-pressed metal powder compacts have been investigated. It is concluded that the most important parameters are freedom from oxidation and the plastic properties of the powder particles. These determine the roles played by surface energy and powder geometry in powder compaction.

18 citations


Journal ArticleDOI
TL;DR: In this article, it was demonstrated that much finer, 0·5-5μm, powders of M2 and M50 steels may be cold pressed and sintered to produce bodies with densities of 99% theoretical containing uniformly distributed 1-2μm particles of carbides.
Abstract: Various powder-metallurgy techniques have been developed during recent years to avoid segregation effects associated with the conventional methods of casting and forming high-speed steels. These techniques have generally involved the consolidation of hot working or hot pressing of 50–500μm prealloyed powders into dense billets or rods. The work described has demonstrated that much finer, 0·5–5μm, powders of M2 and M50 steels may be cold pressed and sintered to produce bodies with densities of 99% theoretical containing uniformly distributed 1–2μm particles of carbides. It is anticipated that the method will have application for the manufacture of complex-shaped parts with very small material losses and little machining. An account is given of the preparation of the fine powders by ball-milling and their subsequent compaction, sintering, and microstructure. The control of carbon and oxygen levels by carbon addition to the powders is described.

17 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the strength of a green compact is dependent upon the interparticle metallic contacts made during compaction, probably due to the presence of broken-up oxides.
Abstract: Measurements of the tensile strength of spherical cold-pressed aluminium powder, pressed to various densities up to the theoretical maximum, have shown that compaction is a two-stage process. At some high, intermediate pressure, interparticle sliding occurs in a way that does not itself increase densification but makes it easier for further deformation to occur. It is likely that the pressure at which this sliding takes place is dependent on the work-hardening rate of the powder as well as the powder size and morphology. In any case, it is shown to be important to the densification and strength reached by the compact.It is concluded that the strength of a green compact is dependent upon the interparticle metallic contacts made during compaction. However,the green strength is well below that of wrought aluminium, probably due to the presence of broken-up oxides,which act as stress-concentrators at the interparticle boundaries.

17 citations


Journal ArticleDOI
TL;DR: In this article, a geometrical model is considered which describes the sintering kinetics between two solid, spherical particles covered by a partially wetting second phase, where conditions selected are such that the grain boundary is not penetrated by the second phase.
Abstract: A geometrical model is considered which describes the sintering kinetics between two solid, spherical particles covered by a partially wetting second phase. Conditions selected are such that the grain boundary is not penetrated by the second phase. The model is kinetically similar to the case of solid-state sintering by grain-boundary diffusion and can also be compared with Kingery’s model of liquid-phase sintering. It predicts that the sintering rate of two solid particles remains virtually unchanged when a second phase (solid or liquid) is added. An example is the sintering behaviour of SmCo5. The applicability of the model to carbide-metal and oxide-metal systems is discussed.

Journal ArticleDOI
TL;DR: In this paper, the diametral dimensional changes of the compacts during sintering below and above the melting point of copper were measured, their microstructures examined, and both related to the characteristics of the powders, particularly their specific surface.
Abstract: Three grades of iron powder-an atomized steel powder, a sponge iron powder reduced from magnetite with carbon, and a powder reduced from mill scale with hydrogen were mixed with 3% of copper powder and pressed into compacts. The diametral dimensional changes of the compacts during sintering below and above the melting point of copper were measured, their microstructures examined, and both related to the characteristics of the powders, particularly their specific surface. During sintering below the melting point of copper, compacts of all three powders shrank. Micrographic examination showed that the copper is transported by solid-state diffusion along the surfacesand grain boundaries of the iron powder particles. During sintering above the melting point of copper, compacts of the atomized and the MH-100 sponge iron powders grew while those of the hydrogen reduced mill-scale powder shrank. This phenomenon is related to the different mode of penetration of liquid copper in the compacts from the thre...

Journal ArticleDOI
TL;DR: In this article, the effect of varying the extrusion conditions on the structure and substructure development and on the mechanical properties of the final product is investigated, and the mechanism of extrusion provides an explanation for the various properties observed, and for this alloy the oxide content is not significantly property-controlling.
Abstract: Materials that are difficult to cast and work may be prepared by using powder extrusion as a primary fabricating technique. The Al-Fe system was selected for study and is examined in detail. The effect of varying the extrusion conditions on the structure and substructure development and on the mechanical properties of the final product is investigated. It is shown that the mechanism of extrusion provides an explanation for the various properties observed, and that for this alloy the oxide content is not significantly property-controlling.

Journal ArticleDOI
TL;DR: In this article, the authors examined the ambient-temperature tensile fracture behavior of hot-isostatically pressed 713LC alloy compacts and found that the nature of the fracture paths varies with the thermal history of the material.
Abstract: Examination of the ambient-temperature tensile fracture behaviour of hot-isostatically pressed 713LC alloy compacts indicates that the nature of the fracture paths varies with the thermal history of the material. The fracture mode may be transgranular, interparticle, or intergranular and is apparently controlled by the structures of the grain boundaries and powder-particle boundaries. Interparticle fracture, observed after certain pressing and heat-treatment operations, can be regarded as a variant of conventional intergranular fracture. This type of fracture mode results from the formation of heavy growths of mixed MC + M23C6 carbide on powder-particle boundaries during processing.

Journal ArticleDOI
TL;DR: In this article, Ni-Mo alloy steel has been deformed at 1130°C in lubricated closed dies, the ratio D0/D, where D0 is the die diameter and D the initial preform diameter, being varied between 1·0 and 1·37.
Abstract: Preforms of Ni-Mo alloy steel have been deformed at 1130°C in lubricated closed dies, the ratio D0/D, where D0 is the die diameter and D the initial preform diameter, being varied between 1·0 and 1·37. Both the high-speed Petro-Forge and a crank press were used, and parameters such as forging load, energy, and density during the forging operation were measured.The stages by which densification proceeds are considered, together with their influence on preform design.

Journal ArticleDOI
TL;DR: In this paper, a group of specimens with nominally 4% and 12% porosity have been prepared from fine (−240 + 300), medium (−200 + 240), and coarse (−150 − 200) mesh sieve fractions of Sherritt-Gordon nickel powder by die compaction, preliminary sintering, re-pressing, and finally Sintering at 1573K (1300°C).
Abstract: Groups of specimens with nominally 4% and 12% porosity have been prepared from fine (−240 + 300), medium (−200 + 240), and coarse (−150 − 200) mesh sieve fractions of Sherritt-Gordon nickel powder by die compaction, preliminary sintering, re-pressing, and finally sintering at 1573K (1300°C). Irrespective of porosity content and the powder fraction from which they were prepared, all specimens exhibited a mixture of rounded and film-like porosity. The film-like porosity was more extensive in the more porous specimens, but in all specimens markedly influenced the fatigue behaviour. The development of persistent film-like porosity is attributed to the botryoidal form of the powder particles. The endurance limits of the less-porous specimens were almost identical, irrespective of the powder fractions from which they were prepared. However, the endurance limits of the more-porous specimens made from the coarse powder fraction were significantly lower than those made from the fine and medium powder fract...

Journal ArticleDOI
TL;DR: The fatigue properties of connecting rods made by the powder-forging process have been studied in this article, where plain iron powder was used in their production and the carbon content adjusted to ∼0·45% by adding graphite.
Abstract: The fatigue properties of connecting rods made by the powder-forging process have been studied. Plain iron powder was used in their production and the carbon content adjusted to ∼0·45% by addition of graphite. Heat-treatment raised the strength to ∼700–850 N/mm2. Fatigue performance under alternating tensile and compressive stress was investigated using a ‘push/pull’-type machine, standard drop-forged rods being tested for comparison. In addition, tests were made on parallel sided test pieces of forged iron-carbon powder and En 15 wrought bar stock.The endurance limits of the powder-forged rods were superior to those of the drop-forged rods although the results for the latter showed considerable scatter. However, the fatigue performance of polished test pieces showed wrought steel to be slightly the better. Reasons for the differences are discussed. A low-alloy steel of higher fatigue performance is under development specifically for connecting-rod application.

Journal ArticleDOI
TL;DR: In this article, the effects of the amount and method of lubrication have been investigated when compacting Hoganas sponge-iron powder, NC100-24, at both low and high speeds.
Abstract: The effects of the amount and method of lubrication have been investigated when compacting Hoganas sponge-iron powder, NC100-24, at both low and high speeds. Pressing characteristics, ejection loads, and the final properties of the sintered compacts were markedly affected by both the amount and the method of lubrication. From the results obtained, an optimum amount of admixed zinc stearate is recommended for both low and high-speed conditions.

Journal ArticleDOI
TL;DR: Aluminium-tin powder-metallurgy alloys containing 20−40% Sn and 0−3% Cu were prepared by compaction and extrusion of prealloyed atomized powder.
Abstract: Aluminium-tin powder-metallurgy alloys containing 20–40% Sn and 0–3% Cu were prepared by compaction and extrusion of prealloyed atomized powder. The powder-metallurgy (PM) material had a fine distribution of the tin phase and was stronger, with greater fatigue strength than an Al-20% Sn-1 % Cu cast alloy but was harder and less ductile. Heat-treatment reduced the hardness of the PM alloys to values comparable with those of the cast material, whereas the strength, although also reduced, remained superior to that of the cast product.

Journal ArticleDOI
TL;DR: In this paper, two PM methods of increasing the carbide content of M2 high-speed steel have been investigated: (1) by the mechanical mixing of tool-steel powder with up to 15 wt.-% of either VC or TiC powders of two different size ranges.
Abstract: Two PM methods of increasing the carbide content of M2 high-speed steel have been investigated: (1) By the mechanical mixing of tool-steel powder with up to 15 wt.-% of either VC or TiC powders of two different size ranges. (2) By the production of fully prealloyed carbide-enriched powders by gas atomization.The mixed powders were consolidated by either cold isostatic pressing or explosive compaction, and then vacuum-sintered. Fully dense specimens, however, could be obtained only by subsequent hot working. The pre alloyed powders could not be cold compacted and were densified by hot working the canned loose powders.With the mixed powders, the carbide dispersion depended closely both on the relative sizes and amounts of the tool-steel and carbide particles and onthe total reduction during hot working. With the fully prealloyed powders a very fine uniform carbide dispersion was obtained in all samples. It was found that with proper composition control the new materials could be heat-treated in a ma...

Journal ArticleDOI
TL;DR: In this paper, the effects of post-sintering heat treatment on the properties and microstructure of a 5Ni −0·5Mo −0.5C sintered steel have been studied in detail.
Abstract: The effects of post-sintering heat-treatment on the properties and microstructure of a 5Ni–0·5Mo–0·5C sintered steel have been studied in detail. It has been demonstrated that by using a relatively high tempering temperature after oil-quenching, UTS and elongation can be simultaneously raised above their as-sintered values, while impact-resistance is at least maintained. By tempering at 650–675°C a UTS of 900 N/mm2 can thus be combined with 4% tensile elongation and with a Charpy unnotched impact value of 26 J. Properties close to these can be achieved even if oil-quenching is replaced by cooling in a furnace cold zone. Alternatively, by quenching and then tempering at 200°C the UTS can be raised to ∼1400 N/mm2 with 1 ½ elongation. The constituents of the microstructures, which are generally not homogeneous, have been identified for each heat treatment condition. It is concluded that for this steel, which is predominantly martensitic on quenching, the properties are controlled by the tempering of ...

Journal ArticleDOI
TL;DR: In this paper, the authors used gel precipitation to produce fine dispersions of thoria in iron, which raised the tensile and yield strengths by 80% compared with the iron made in the same way while retaining an acceptable level of ductility at ambient temperature and below.
Abstract: Gel precipitation has been used to produce fine dispersions of thoria in iron. The process involves coprecipitation of hydroxides followed by a hydrogen reduction. Iron containing up to 7·65 vol.-% thoria was prepared with particle sizes in two ranges averaging 6 and 110 nm in diameter. The dispersion, stable up to at least 1300°C, raised the tensile and yield strengths by 80% compared with the iron made in the same way while retaining an acceptable level of ductility at ambient temperature and below. Impact testing showed that the presence of thoria did not have an adverse effect on the ductile-brittle transition temperature for thoria contents up to 4·55 wt.-%. It was not possible to estimate the strengthening due to the dispersions from the models of Orowan bowing of dislocations between particles because of the presence of two size ranges of particles in these alloys. The thoria dispersions did not raise the primary recrystallization temperature of the iron but were extremely effective in rest...

Journal ArticleDOI
TL;DR: In this article, a system of equations is established describing how variations in powder characteristics and process parameters are related to the quality of the sintered product, and the basic assumption is that a cylindrical body is to be fabricated by cold pressing and sintering.
Abstract: A system of equations is established describing how variations in powder characteristics and process parameters are related to the quality of the sintered product.The basic assumption is that a cylindrical body is to be fabricated by cold pressing and sintering. It is also assumed that the allowable variations in the diameter, the bulk density, and/or the linear density of this sintered body are specified.The powder material is characterized by the slope, K, of the curve of green density vs. sintered dem,ity. Values near unity give least variation in sintered diameter. An important parameter of the process is the variation, Bg, of the green density.Variation of the parameters, B of bulk density, L of linear density, and D of sintered diameter are dependent on two groups of variables. The total variation may be composed of variations in the powder quality and the sintering conditions (group 1) or of variations in the green density (group 2).Taking a practical example, equations are derived for the ...

Journal ArticleDOI
TL;DR: In this paper, the shrinkage of powder compacts during heat-treatment was recorded dilatometrically and the major effects of milling seem to be to alter the grain size and morphology of the powder and to form a fine dispersion of small particles of Co3O4.
Abstract: Cemented carbide powders milled for various times have been studied with respect to the shape and internal structure of the grains. The shrinkage of powder compacts during heat-treatment was recorded dilatometrically. The major effects of milling seem to be to alter the grain size and morphology of the powder and to form a fine dispersion of small particles of Co3O4.

Journal ArticleDOI
TL;DR: In this article, a gel precipitation method was used to produce metastable iron oxide particles containing calcium, magnesium, or zirconium in solid solution, which were reduced to metal with hydrogen/nitrogen mixtures in a fluidized-bed furnace.
Abstract: Metastable iron oxide particles containing calcium, magnesium, or zirconium in solid solution were produced by the gel precipitation method. These were reduced to metal with hydrogen/nitrogen mixtures in a fluidized-bed furnace at 800°C to yield iron powders containing dispersed oxide phases within each iron particle. The oxide phases were either 2CaO.Fe2O3, a solid solution of MgO and FeO, or ZrO2, which appeared to be free from iron. Consolidation by compacting the powders into cans, sealing under vacuum, and hot extrusion yielded bars in which the oxide particles were dispersed. Hardness and tensile-test data for material heated to 1000°C for up to 100 h suggest that the oxides containing iron coarsen rapidly and contribute to strengthening only by maintaining a small matrix grain size. The iron-free ZrO2 appears to be a true dispersion hardener and to restrain grain growth more than do the other oxides investigated.

Journal ArticleDOI
TL;DR: In this paper, a wide range of copper and tin powder additions to iron powder sintered compacts has been studied and it has been shown that when using sinteririg temperatures of 900-1100°C in nitrogen/10% hydrogen atmospheres there is an optimum copper: tin ratio of 15:2.
Abstract: A wide range of copper and tin powder additions to iron powder sintered compacts hasbeen studied. From mechanical-property tests it has been shown that when using sinteririg temperatures of 900–1100°C in nitrogen/10% hydrogen atmospheres there is an optimum copper: tin ratio of 15:2. The mechanical properties obtained from compacts pressed from iron mixed with 4% copper+tin in this ratio and sintered at 900°C were similar to those obtained from iron −l0% copper powder compacts sintered at 1100°C. Moreover, the iron-copper-tin components showed improved dimensional accuracy.In a further series of experiments, it was shown that tin additions to iron-copper alloy compacts increased the solubility of iron in the liquid phase at the sintering temperature and simultaneously decreased the rate of diffusion of copper into the iron particles. At the same time, tin improved the wettability of the liquid, reducing its surface tension and allowing it to disperse more completely throughout the matrix. The mech...