Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C24/00—Coating starting from inorganic powder
• • 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
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B1/00—Producing shaped prefabricated articles from the material
  • B28B1/26—Producing shaped prefabricated articles from the material by slip-casting, i.e. by casting a suspension or dispersion of the material in a liquid-absorbent or porous mould, the liquid being allowed to soak into or pass through the walls of the mould; Moulds therefor ; specially for manufacturing articles starting from a ceramic slip; Moulds therefor
• • 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
• • 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

Definitions

• the invention relates to a method for producing dense sintered workpieces made of metal, a metal alloy or ceramic materials, in which a green body is first formed from a mixture of the metal in powder form, the metal alloy or the ceramic material and a binder, which removes the binder. sintered and the sintered body is compressed, if necessary, by hot isostatic pressing (HIP process).
• HIP process hot isostatic pressing
• a viscous mixture of powder and binder has previously been produced, and this mixture has been pressed into the predetermined shape under a pressure of a few hundred bars. Quite apart from the fact that with this procedure narrow cavities of the form to be filled can be inaccessible to the viscous mass, it also shows that during the subsequent binder removal or Sintering process, to which the viscous mass filled under pressure is subjected, the binder is not completely removed from the mass or. the green body escapes so that undesirable residues can remain in the workpiece.
• This object is achieved in that first the mixture of the powder, the binder, the proportion of which in the mixture is such that it is sufficient to solidify the powder-binder mixture to form the green body and thereby 2 to 5 vol %, and a solvent for the binder is formed so that it is in the form of a flowable, solid, liquid mass (casting mass), after which this mass is poured into the predetermined shape, applied or sprayed on and then dried, the solvent escaping and the remaining binder Powder-binder mixture solidified, so that the green body is formed, which is then debindered and sintered.
• the green body is removed from the mold after drying and is ready for further processing.
• the casting compound is expediently produced in a separate vessel, after which it is poured into the mold through a sprue or a funnel.
• Adequate filling of the form is achieved by gravitation and can be accompanied by targeted vibration of the form. External vibrations and / or rotations of the shape by hand or mechanically are useful for this.
• the solvent can be removed from the mass filled into the mold under normal pressure and at room temperature. However, this drying process can also take place at elevated temperature and / or under a slight negative pressure or can be accelerated thereby.
• the filling can be built up in several steps using different materials.
• a procedure which is expedient for this is that mixtures formed from different materials are poured into the mold one after the other, so that the poured-in mass and thus also the green body formed thereafter consists of layers of different composition arranged one above the other.
• a second is poured onto the first. This process is continued until the mold is completely filled, so that a layer system green body composed of different materials with a stepped structure, e.g. with regard to material, porosity, grain / particle size distribution.
• a further process variant consists in that the mixture is filled in via / or around a green body previously introduced into the mold or an already finished workpiece.
• an inner or outer coating (s) or covering of a solid part that has already been produced can be produced, the casting compound being poured into the cavities and the surface to be coated after being introduced into a suitable mold.
• the casting compound can also be applied or sprayed on with a brush and then further processed with good success.
• Composites or graded materials can be made by inserting the insert component into the premix or by inserting it into the mold prior to casting.
• the general rule is that the proportion of the binder in the mixture should be such that it is sufficient to solidify the mass to form a manageable green body.
• the amount of binder required for this can easily be determined by means of a few preliminary tests; it is in the range between 2 and 5% by volume.
• binder fraction 0.02 (2.00% by volume) with particle sizes of approximately 20 ⁇ m have considerable strength. However, when using larger particles with the same binder content, the strength is still sufficient to ensure that the green bodies are handled safely.
• the proportion of binder can be varied by controlled addition or evaporation of the liquid, volatile solvent component (carrier). In practice, the maximum volume fraction is limited by the solubility limit of the binder in the solvent or by the relative natural porosity, which is approximately 26% for ideally packed spherical particles.
• the binder condenses as a thin film on the powder particles during the removal (evaporation) of the solvent (carrier) and a rapid, continuous removal of the solvent (carrier) through the free particle spaces takes place.
• the final strength of the green body is achieved after the solvent (carrier) has been completely removed and after the binder has solidified at room temperature (possibly also at elevated temperature) as a solid network with connecting bridges between adjacent powder particles.
• the green body After the green body has been formed, it is subjected to a thermally activated debinding and sintering treatment.
• the green body is heated to remove the binder.
• This debinding process is not restricted to a specific time-temperature program (profiles, sequences, cycles), although a few partial steps are required to enable complete binder removal.
• a typical procedure is that the green body is heated at a rate of 3-10 ° C./min to a temperature in the range from 280 to 420 ° C. and, depending on the size of the body, is kept at this temperature until the binder is removed.
• the body is then heated to sintering temperature up to a rate of> 10 ° C / min.
• High temperatures promote the rapid splitting of the binder into a vapor that sublimes outside the green body either in the atmosphere or pumped out by a vacuum system. The splitting and removal takes until the binder has burned out.
• Materials such as super alloys, stainless steel, titanium alloys and aluminum alloys, iron materials, ceramic powders, for example, can be used as the material for the workpieces to be produced.
• Zirconium oxide, chromium oxide, lathan oxide, perovskite, aluminum oxide, silicon oxide can be provided.
• Wax, shellac, PMMA and alcohol, trichlorethylene, toluene (toluene) are mentioned as binders.
• the sintering of the green bodies produced by the process according to the invention was carried out using specific, known schemes for each material. Density measurements showed that the sinterability of the materials is not affected by the process itself.
• the end product can be sintered to a closed porosity. The sintered parts with closed porosity can therefore be compacted containerless up to the theoretical density by HIP.
• Chemical analyzes of end products produced by the method according to the invention showed no increase in the concentration of contaminants related to the chemical composition of the binder, such as oxygen, carbon, nitrogen and hydrogen.
• the overall composition was within the nominal concentrations of the starting products.
• the mixture was poured into a four-part stable Teflon mold, measuring 80x20x1 mm. After 2 hours of drying in air, the product achieved high strength, making handling easy.
• the total process time was 4.27 h.
• the density of the sintered part was 92.5% of the theoretical density of Ti6A14V and the chem. Analysis showed within the measurement accuracy the same composition as that of the starting powder.
• the mixture was applied to the substrate with a brush.
• the 50 ⁇ m thick layer produced in this way was then air-dried for half an hour.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Ceramic Engineering (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Dispersion Chemistry (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Ceramic Products (AREA)
• Compositions Of Oxide Ceramics (AREA)

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• 1991
  • 1991-06-22 DE DE4120706A patent/DE4120706C2/de not_active Expired - Lifetime
• 1992
  • 1992-05-26 DE DE59205549T patent/DE59205549D1/de not_active Expired - Lifetime
  • 1992-05-26 AT AT92108827T patent/ATE134922T1/de active
  • 1992-05-26 EP EP92108827A patent/EP0525325B1/fr not_active Expired - Lifetime

Patent Citations (5)

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