Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
  • B22F9/22—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds using gaseous reductors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals
  • C22C1/1026—Alloys containing non-metals starting from a solution or a suspension of (a) compound(s) of at least one of the alloy constituents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

• Powder mixtures or composite powders processes for their production and their use in composite materials
• the present invention relates to powder mixtures or composite powders which consist of at least two types of powder or solid phases in disperse form and which are used as precursors for particle composites or as wettable powders for surface coatings.
• these composite powders contain refractory metals (such as W and Mo) or hard materials (such as WC, TiC, TiN, Ti (C, N) TaC, NbC and Mo 2 C) or ceramic
• Binding metals such as Fe, Ni, Co, Cu and Sn
• mixed crystals and alloys of these binding metals on the other hand.
• the invention further relates to processes for producing these composite powders and their use for particle composites and wettable powders. The most important
• particle composites are hard metals, cermets, heavy metals and functional materials with special electrical (contact and switching materials) and thermal properties (heat sinks).
• the effective properties of these particle composites e.g. Hardness, modulus of elasticity, fracture toughness, strength and wear resistance, but also electrical and thermal conductivity are determined in addition to the properties and proportions of the phases primarily by the degree of dispersion, the homogeneity and the topology of these phases as well as by structural defects (pores, impurities). These structural characteristics of the particle composites are in turn determined by the powdery raw materials and their powder metallurgical processing (pressing, sintering) into compact materials.
• Hard metals are particle composites of at least two phases, the WC hard material phase (97 - 70 m%) and the eutectic Co-WC binder metal phase (3 - 30 m%), which is formed by dissolving W and C in Co in liquid phase sintering and binds the toilet particles.
• the hard metals can carry out other phases of hard material such as the cubic (W, Ti) and (W, Ta / Nb) mixed carbides with proportions of 1 to 15 m% included. If the hard metals are particularly corrosive, the Co-based binder is completely or partially replaced by Ni, Cr (Fe) alloys. B. VC and Cr C 2 ( ⁇ 1 m%) to control grain growth and microstructure.
• the hard material particles are carriers of hardness, wear resistance and high temperature properties, while the binding metals primarily determine the fracture toughness, the thermal shock resistance and the flexural strength.
• Hard metals are characterized in particular by very favorable combinations of hardness and toughness as well as high temperature stability and wear /
• Corrosion resistance This is achieved in that either the hard material particles are fully dispersed in the binder metal or, with decreasing binder metal content, two mutually penetrating phase regions of hard material and binder are formed. During sintering, this structure runs parallel to the compaction of the compact. The compression during the
• Sintering process takes place to 70 - 85% of the density increase in the stage of solid phase sintering, ie the WC grains move under the action of the viscous flowing and wetting binder metal in energetically preferred positions, see e.g. B. GILLE, SZESNY, LEITNER; Proc. 14 l Int. Plansee Seminar, Vol. 2, Reutte 1997.
• the eutectic composition is finally achieved and the binding metal melts via the simultaneous diffusion of W and C into the co-particles.
• the remaining 15 - 30% of the compression then takes place via further particle rearrangements and pore filling with liquid binder.
• the final phase of compression and structure formation takes place through OSTWALD ripening, ie small hard material particles dissolve in the liquid binder due to the higher solution pressure and separate out from larger, adjacent hard material particles.
• the state of the art of hard metal production is shown, for example, in SCHEDLER, Hartmetall für die Praktiker, Düsseldorf 1988.
• the hard metal composition the separately produced hard material and binder metal powders are first weighed, mixed and ground.
• the WC starting powders with their grain sizes range from 0.5 ... 50 ⁇ m, are mostly slightly agglomerated and must have sufficient chemical purity.
• important properties such as hardness, toughness and wear resistance can be varied to a great extent and adapted to the specific application.
• the wet powder used today is used to transfer the various powder components into a finely divided mixture.
• Organic liquids such as z. B. hexane, heptane, gasoline, tetralin, alcohol or acetone.
• Grinding liquid and medium hard metal balls
• the powder mixture is sieved from the grinding balls and evaporated from the
• the grinding takes place mainly in attritors and ball mills, sometimes also in vibrating mills.
• the currently dominant form of drying that has been used on an industrial scale for around 20 years is spray drying under inert gas, with simultaneous granulation of the composite powders.
• the dried and optionally granulated mixtures are pressed, extruded or injection molded (MIM) into molded parts and then sintered.
• MIM injection molded
• the actual compression process is preceded by dewaxing, ie the expulsion of pressing aids and the pre-sintering for deoxidation and pre-compression.
• Sintering takes place either under vacuum or inert gas pressures up to 100 bar at temperatures between 1350 and 1500 ° C.
• the ductility of the binding metals during grinding can lead to the powders not only being deagglomerated or dispersed more finely, but, in contrast to flat discs (flakes) or other unfavorable shapes, being plastically deformed and forged. This occurs particularly in the case of the plastically easily deformable binder metals with a motor vehicle structure and can lead to inhomogeneous binder distribution and to strength-reducing pores in the sintered hard metal.
• wet grinding can result in complete deagglomeration, a partial breakdown of primary particles and a homogeneous, finely dispersed distribution of the powder components.
• WO 95/26843 (EP-A 752 922, US-A 5 529 804) describes a process in which hard particles in polyols with reducing properties, such as, for example Ethylene glycol, with the addition of soluble cobalt or nickel salts. At the boiling point of the solvent and a 5 hour reduction time, cobalt or nickel is deposited on the hard material particles. The resulting composite powder actually results in dense microstructures in the, without costly grinding after separation of the solid material, washing, drying, pressing and sintering
• the reduction reaction in the liquid phase is terminated after a stoichiometric amount of polyol has been consumed, based on the amount of metal used, in order to suppress the formation of undesired by-products and to be able to recirculate the excess polyol.
• the intermediate product is filtered and subsequently reduced to the finished composite powder in a dry way under hydrogen at 550 ° C. and a very long reduction time of approx. 24 h.
• the hard material is suspended in an aqueous solution containing Co or Ni, and a metal compound is deposited on the surface of the hard material particles by adding ammonia or a hydroxide. After separating the solution, this intermediate product reduced at elevated temperature under hydrogen. The reduced amount of polyols used as solvents and reducing agents and the suppression of side reactions must be compensated for by a significantly longer post-reduction of the intermediate under hydrogen and at an elevated temperature.
• alcohols are also used in order to reduce metal compounds dissolved therein to the metal or alloy powder or to deposit them as a metal film on a substrate dispersed in the solvent.
• glass powder, Teflon, graphite, aluminum powder and fibers are used as substrates.
• the composite powder obtained in this way can be used to obtain sintered bodies with a pore-free structure under normal conditions.
• the disadvantages of this process are comparatively high solvent losses, corresponding safety precautions and double thermal treatment, process engineering problems due to the handling with highly viscous mixtures when evaporating the solvent and time-consuming cleaning / disposal of the decomposition products when the organic shell burns out in the first thermal process step.
• US-A 5 352 269 describes the Spray Conversion Process (NANODYNE Inc.). According to this process, aqueous solutions, e.g. B. W and Co in suitable concentrations and proportions and for example made of ammonium metatungstate and cobalt chloride, spray dried.
• the metals W and Co are mixed at the atomic level in the amorphous precursor powders formed in the process.
• finely crystalline WC particles with grain dimensions of 20-50 nm are formed, which are, however, strongly agglomerated and interspersed or bound with cobalt areas and as hollow spherical aggregates have a diameter of approx. 70 ⁇ m.
• WC and co-particles in this spray conversion process can no longer be produced separately and are already available as a mixture at the end of this process, but grinding is still necessary to improve the homogeneity of the phase distribution and above all the compression and shrinkage behavior.
• the decisive disadvantage of these composite powders is, however, that the process-related, low carburization temperature ( ⁇ 1000 ° C) leads to severely disturbed WC crystal lattices and this in turn leads to strong grain growth during sintering. An increase in the carburization temperature to form a more perfect crystal lattice is not possible due to the presence of the binding metal, since otherwise a sintering process between the toilet and the like would start.
• the mixture of W and Cu present in the oxide at the atomic level is used to achieve highly disperse W and Cu areas or particles in the metal mixture (W and Cu are in fact not soluble in one another).
• W and Cu are in fact not soluble in one another.
• Impregnation processes this is done with a relatively complex and expensive process, i.e. with tungsten synthesis, reduction and powder metallurgical processing.
• expensive raw materials such as the ammonium metatungstate can be used.
• composite powders with very good homogeneity, dispersity and possibly also special topology of the components / phases can be produced by the desired binder metal powder (phases) in suspensions which already contain the other components of the composite powder, such as high-melting metal or contain hard material or ceramic powder, as
• Oxalate can be felled. After the mixed precipitation, there is a multicomponent suspension with at least two different solid phases, for example the previously suspended WC particles and the precipitated Co, Fe, Ni, Cu, Sn binder metals.
• This reaction product is washed and dried, treated thermally under a reducing atmosphere and can then, if necessary after agglomeration, be pressed and sintered without further expensive grinding.
• the sintered products produced in this way are at least equivalent or superior to conventionally manufactured products with regard to porosity, microstructure and mechanical-physical properties.
• the present invention relates to a process for producing powder mixtures or composite powders from at least a first type of powder from the group of refractory metals, hard materials and ceramic powders and at least one second type of powder from the group of binder metals, binder metal mixed crystals and binder metal alloys, which is characterized in that is that the second type of powder is produced from precursor compounds in the form of aqueous salts in an aqueous suspension of the first type of powder by precipitation as oxalate, removal of the mother liquor and reduction to the metal.
• Metals with melting points above 2000 ° C. such as molybdenum, tungsten, tantalum, niobium and / or rhenium, are suitable as high-melting metals.
• molybdenum and tungsten have gained technical importance.
• TiB 2 or B 4 C are suitable as ceramic powders. Powders and mixtures of high-melting metals, hard materials and / or ceramic powders can also be used.
• the first type of powder can be used in particular in the form of finely divided powders with average particle diameters in the nanometer range up to more than 10 ⁇ m.
• Particularly suitable binding metals are cobalt, nickel, iron, copper and tin and their alloys.
• the binder metals are used as precursor compounds in the form of their water-soluble salts and their mixtures in aqueous solution.
• Suitable salts are chlorides, sulfates, nitrates or complex salts. Chlorides and sulfates are generally preferred for ease of availability.
• Oxalic acid or water-soluble oxalates such as ammonium oxalate or sodium oxalate are suitable for the precipitation as oxalate.
• the oxalic acid component can be used as an aqueous solution or suspension.
• the first type of powder can be suspended in the aqueous solution of the precursor compound of the second type of powder and an aqueous solution or suspension of the oxalic acid component can be added. It is also possible to stir the oxalic acid component in powder form into the suspension which contains the first type of powder.
• the first type of powder can also be suspended in the aqueous solution or suspension of the oxalic acid component and the aqueous solution of the precursor compound for the second type of powder can be added.
• the two suspensions or the suspension are preferably mixed with the solution with vigorous stirring.
• the precipitation can be carried out continuously by simultaneous, continuous introduction into a flow reactor with continuous withdrawal of the precipitation product. It can also be carried out discontinuously by presenting the suspension containing the first type of powder and introducing the second precipitation partner. It can ensure a uniform precipitation over the precipitation reactor volume be expedient to stir the oxalate component in the form of a solid powder into the suspension of the first type of powder and solution of the precursor compound for the second type of powder, so that the oxalate component can be distributed evenly before the precipitation occurs through its dissolution. Furthermore, the particle size for the precipitation product can be controlled via the depot effect of the use of a solid oxalate component.
• the oxalic acid component is preferably used in 1.02 to 1.2 times the stoichiometric amount, based on the precursor compound, for the second type of powder.
• the concentration of the oxalic acid component in the precipitation suspension can be 0.05 to 1.05 mol / 1, particularly preferably more than 0.6, particularly preferably more than 0.8 mol / 1.
• the solid mixture of precipitate and first type of powder is separated from the mother liquor. This can be done by filtration, centrifugation or decanting.
• the solid mixture of the first type of powder and precipitate is treated under a reducing gas atmosphere at temperatures of preferably 350 to 650 ° C.
• Hydrogen or a hydrogen / inert gas mixture is preferably used as the reducing gas, more preferably a nitrogen / hydrogen mixture.
• the oxalate is completely broken down into gaseous components, some of which promote the reduction (H 2 O, CO 2 , CO), and the second type of powder is produced by reduction to metal.
• the oxalate decomposition and reduction can be carried out continuously or batchwise in a moving or static bed, for example in tube furnaces or rotary tube furnaces or push-through furnaces, and under flowing, reducing gases. Any reactor suitable for carrying out solid-gas reactions, such as fluidized bed furnaces, is also suitable.
• the powders of the first and second types are present partly as separate (“powder mixture”) and partly as mutually adhering (“composite powder”) components in an extremely uniform distribution, essentially without the formation of agglomerates. They can be processed without any further treatment.
• the powders are suitable for the production of hard metals, cermets, heavy metals, metal-bound diamond tools or electrotechnical functional materials by sintering, optionally using organic binders for producing sinterable green bodies. They are also suitable for the surface coating of parts and tools, for example by thermal or plasma spraying or for processing by extrusion or metal injection molding (MIM).
• a hard metal test was carried out with this powder according to the following procedure without any other treatment: producing a green body with a pressure of 150 MPa, heating the green body in vacuo at a rate of 20 K / min to 1 100 ° C., holding for 60 minutes at this temperature , further heating at a rate of 20 K / min to 1400 ° C., holding for 45 minutes at this temperature, cooling to 1100 ° C., holding for 60 minutes at this temperature and then cooling to room temperature.
• tungsten carbide of the DS 80 grade (supplier HCStarck) and 1 g of carbon black were homogeneously dispersed in a suspension of 465.4 g of oxalic acid dihydrate in 1.6 l of deionized water over a period of 60 minutes. Then 2 l of Co solution with 893.4 g of CoCl 2 * 6H 2 O were added quickly and the mixture was stirred for a further 10 min to complete the precipitation. After filtration and washing of the precipitate with deionized water (until chloride was no longer detectable in the drain), the mixture was spray-dried and then in a tubular oven for 90 minutes at 420 ° C. in an atmosphere of 4% by volume hydrogen and 96% by volume. % Nitrogen reduced. The resulting composite powder contained 8.24% Co, 5.63% total carbon, 0.06% carbon free (according to DIN ISO 3908), 0.395% oxygen and
• a hard metal test was carried out with this powder under conditions similar to those in Example 1 and the following properties were measured on the resulting sintered body: density 14.71 g / cm 3 , coercive force 19.1 kA / m or 240 Oe, hardness HV30 1626 kg / mm 2 or HRA 92.0, magnetic saturation 157.8 G cm 3 / g or 15.8 ⁇ TmVkg, low porosity A00 B02 COO and a homogeneous, microdisperse structure.
• the resulting composite powder contained 3.60% Co, 2.50% Ni, 2.56% Fe, 5.53% total carbon, 0.07% carbon free, 0.596% oxygen and 0.0176% nitrogen.
• the SEM analysis shows a well deagglomerated
• the resulting composite powder had the following chemical composition: 4.46% Ni, 4.26% Fe, 5.52% total carbon, 0.08% carbon free, 0.653% oxygen, 0.0196% nitrogen, the rest tungsten.
• the SEM analysis shows a well deagglomerated powder (FIG. 9) with a uniform Fe and Ni distribution (FIGS. 10 and 11).
• tungsten metal powder grade HC 100, supplier HCStarck
• tungsten metal powder grade HC 100, supplier HCStarck
• a solution of 1.592 kg of CuSO 4 * 5H 2 O in 6 l of deionized water was added, and the resulting precipitation suspension was stirred for a further 30 minutes to complete the precipitation and homogenize the suspension.
• the precipitate was subsequently filtered, washed free of anions with deionized water, then spray-dried and reduced in a tubular oven at 500 ° C. for 120 minutes under hydrogen.
• the resulting composite powder contained 80.78% W and 18.86% Cu in addition to a residual oxygen content of 0.37%.
• the SEM analysis shows a very fine-grained powder (FIG. 12) and, in the case of energy-dispersive evaluation, a uniform distribution of the copper in the tungsten powder matrix (FIG. 13).

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