Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/10—Cores; Manufacture or installation of cores
• • 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
  • C23C24/02—Coating starting from inorganic powder by application of pressure only
  • C23C24/04—Impact or kinetic deposition of particles
• • 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
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
  • C23C4/06—Metallic material
  • C23C4/08—Metallic material containing only metal elements

Definitions

• the invention relates to a method for producing a workpiece having at least one cavity, recess, notch, opening, undercut or any other portion which is not filled, and a carrier material suited for this purpose.
• Portions being not filled such as cavities, recesses, notches, undercuts, openings etc.
• Portions being not filled are generally referred to as “vacuity” in the following to simplify matters, wherein this term also includes spaces which are not completely surrounded by a wall, such as undercuts.
• a material is used which can be removed after completing the body. In order to be able to use a material for such a method, it must be removable after completion of the body for forming the vacuity, wherein the removal must be simple and cost-effective.
• a soluble material is used, which can be dissolved away after completion of the shape.
• aqueous media which are easily available and disposable, is therefore desired.
• the dissolvable material used as a “placeholder” is also referred to as “lost core” or “lost mould”.
• a material to be used for lost cores has to fulfil various requirements, i.e. it has to resist mechanical and thermal stress. These requirements are not fulfilled by the soluble salts desired to be used for the lost cores.
• salts are an interesting material in view of their solubility and availability, they cannot be used in methods with mechanical stress, such as thermal spraying, cold gas spraying or compacting, due to their brittleness. Due to their brittleness, the salts cannot resist the mechanical stress generated by those methods.
• DE 19 716 524 proposed to provide a water-soluble core made of an aluminium or magnesium alloy for producing bodies having at least one cavity. It is a subject-matter of this application to use such magnesium or aluminium alloys, the oxide content of which is adjusted such that the mechanical strength is sufficiently high on the one hand and, on the other hand, the solubility is sufficient to dissolve away the core subsequently. For solving this object, it was necessary to use alloys and to add a high proportion of oxides to the alloys.
• the material shall be removable even if very complicated or delicate shapes, e.g. narrow channels, are concerned.
• thermo spraying methods in particular kinetic spraying or cold gas spraying, i.e. which is sufficiently resistant to mechanical stress and easily available.
• a carrier material which can be used as a placeholder when structuring workpieces having at least one vacuity, which comprises a corrodible material, wherein the corrodible material is a mixture or an alloy made of magnesium and at least one additional metal component, the standard electrode potential of which is larger than that of magnesium under reaction conditions, wherein the material was compacted by a mechanically stressing method.
• a corrodible material which comprises magnesium and an additional metal component having a higher standard electrode potential under reaction conditions, loses its structure very fast when being in contact with water or an aqueous medium, wherein the magnesium dissolves and the other present metals possibly remain at least partially in the form of particles.
• the inventive material features a structure which combines interesting characteristics.
• the material offers a sufficient strength to function as a placeholder in many different methods, which placeholder can also resist mechanical or thermal stress which e.g. is generated during moulding and/or processing.
• the material dissolves very fast when in contact with a corroding liquid.
• corrosion refers to any electro-chemical reaction of magnesium with a liquid medium in the presence of an additional metal component having a higher standard electrode potential, which results in an extensive or complete dissolution of the magnesium while forming gas.
• a liquid containing ions is referred to as the corroding medium, which dissolves the magnesium based on an electro-chemical reaction in the presence of an additional metal component having a higher standard electrode potential.
• high standard electrode potential always relates to the standard electrode potential of a metal component compared to magnesium under reaction conditions (with respect to temperature, pressure, type and amount of ions in the solution etc.) and not to its position in the electrochemical series.
• metal component refers in particular to metals or metal alloys which promote the corrosion reaction of magnesium.
• the advantageous characteristics of the inventive material result from the metallic and mechanic properties of the magnesium and additional metal components and, on the other hand, from the corrosion ability of the magnesium under specific conditions.
• the carrier material is brought into contact with a corroding medium after completion of the workpiece for removing the placeholder, wherein the magnesium is dissolved and the not-dissolved carrier material together with the magnesium-containing medium is subsequently rinsed from the formed mould.
• the compacting of the metal powders produces a material, the particles of which have sufficient contact in order to promote an electro-chemical reaction.
• the protecting layer surrounding the particles is possibly broken by stress or deformation to an extent that the reaction can take place and is not blocked.
• the dissolution is achieved with the desired speed by means of a corroding medium, generally water or an aqueous medium.
• the inventive carrier material in particular, enables that the speed of the dissolution reaction can be adjusted selectively. In case, however, powder mixtures having a high porosity are used, which soak when water is added, this may result in a reaction which cannot be controlled.
• a material is used, the porosity of which is not higher than 20% by volume, preferably not higher than 5% by volume. In a particularly suitable embodiment, the porosity is lower than 1%.
• an inventive material i.e. a mixture or alloy containing magnesium, which was previously compacted
• a corroding medium preferably a conductive aqueous medium
• the magnesium is dissolved at least to a large extent. According to the invention, this effect is used to remove a carrier material after completion of a workpiece, by bringing the mixture into contact with a corroding material and subsequently rinsing the carrier material and the medium, which contains the magnesium in solution, from the formed mould.
• inventive carrier material is particularly suitable for the production of workpieces having cavities, recesses, notches, undercuts or openings, in particular for producing hollow bodies or workpieces with undercuts by using thermal spraying methods.
• the speed of dissolution of the magnesium depends on different parameters, such that it is possible to use standard means for finding and using the respectively optimum material or the optimum conditions.
• the parameters influencing the dissolution are i.e. the temperature, the combination of metals, the type and amount of the ions contained in the medium used for the dissolution, surface ratios and mechanical load of the surfaces as well as the hydrogen overvoltage.
• the temperature is an important parameter, since the reaction is the faster the higher the temperature.
• the electro-chemical reaction of the metals with water is exothermic.
• the speed of the dissolution may therefore be adjusted by controlling the temperature of the reaction, if required or desired. Consequently, the reaction can be adjusted by supplying heat and/or possibly by discharging heat. In the most simple case, the supplying and discharging of heat is performed by using a correspondingly tempered medium as the solvent.
• Another important parameter is the combination of the metals used in the carrier material.
• a magnesium alloy or a mixture of magnesium with at least one additional metal component is used.
• the reaction of corroding the magnesium is stronger or weaker.
• magnesium already alone tends to corrode under specific conditions, i.e. if it is exposed to an ion-containing solution.
• the corrodibility can be increased if at least one additional metal component which is more precious compared to magnesium, i.e. which has a higher standard electrode potential than magnesium, is added to the alloy or mixture.
• Each metal, which has a higher standard electrode potential than magnesium under the conditions of the corrosion reaction occurring by adding the corroding medium, is therefore suited as the inventive carrier material.
• Metals having a lower hydrogen overvoltage and in particular the metals iron, nickel and copper have a particularly strong influence on the corrodibility, which metals are therefore preferably contained in the inventive carrier material, either alone or in combination with the magnesium as a mixture or an alloy.
• a combination of magnesium and iron is particularly preferred.
• the inventive carrier material is made of magnesium and at least one additional metal component by compacting. It was found out that the corrosion advances very fast when the material and thus the individual particles are strongly stressed prior to or during the moulding. Without being bound to a theory, this may be a result of the fact that possibly existing hydroxide or oxide layers, which protect the magnesium, are disturbed or destroyed due to the stress, such that the corroding attack may then occur faster and stronger.
• Another parameter, which can accelerate the corrosion reaction is the proportion of ions and the activity of the ions which are contained in the corroding, preferably aqueous, medium which is used for the dissolution. It was found out that the corrosion and therewith the dissolution of the magnesium occurs faster when the more active anions are available.
• i.e. chloride, nitrate and sulphate ions are particularly reactive. Such ions result in a formation of easily soluble magnesium salts which accelerate the dissolution.
• the corrosion reaction is also influenced by the conductivity of the aqueous solution which in turn can be influenced by the proportion of ions.
• An aqueous medium having a high conductivity or a large proportion of ions results in a fast dissolution. Therefore, aqueous media having a large amount of ions are preferably used for the dissolution.
• a solution containing sodium chloride is used due to its availability and cost-effectiveness.
• Sea water is e.g. a very suitable medium. For economic and environmental reasons, also ion-containing wastewater from other processes is very advantageous, which can be recycled very well in this manner.
• Another parameter influencing the corrosion reaction is the surface ratio of anodic particles to cathodic particles and the distance between anodic and cathodic particles.
• the small distance between the anode and cathode can be obtained by the compacting processing which generates the structure of the inventive carrier material. Also the proportion of the individual components has an influence on this parameter.
• the corrosion is also influenced by the hydrogen overvoltage. It was found out that metals having a lower hydrogen overvoltage are effective cathodes when combined with magnesium and therefore promote the reaction. Metals having a lower hydrogen overvoltage include nickel, copper and iron, which are therefore preferred.
• Another parameter, which influences the dissolution speed and the progress of the reaction, is the motion of the medium. If the medium is moved after starting of the reaction, the formation of a continuous coating layer made of magnesium hydroxide above the magnesium particles is hindered, such that the corrosion is again further promoted.
• the speed can be adapted to the process, wherein one or more of the aforementioned parameters can be adjusted.
• the inventive carrier material is applicable for moulding methods of any kind.
• the inventive material in particular stands out due to its mouldability, machinability, formation of layers with true contours, imaging properties and compatibility with other materials. It can be used in particular when moulds are formed by structuring layers which are then mechanically post-processed for forming simple and complicated, and also delicate bodies which function as placeholders for any kind of vacuity, including undercuts, in materials of any kind. Complicated or delicate moulds can be formed from the material by mechanical processing, normally machining.
• the layers formed by the inventive carrier material maintain the contours of the substrate onto which they are applied and adhere thereto. Therefore, the inventive material can be used in many ways.
• the body When workpieces having a vacuity are produced by spraying, the body is structured by layers and the inventive material is applied in regions which are intended to form the vacuity or the undercut later on, which material can be rinsed away after completion of the workpiece.
• the mixture or alloy forming the carrier material is processed such that a compacted material results from the metal powders or the alloy, which material may also be present in sintered form. It is important that the metal particles of the at least two metals have a tight contact.
• Alloys are materials made of at least two components and including at least one metal, wherein the second component of the alloy is either dissolved in the metal or homogeneously distributed in the metal, or is only dissolved to a limited extent such that an alloy enriched second phase is obtained.
• inter-metallic compounds are concerned if the second or further components of the alloy are also metals, i.e. atoms of the one metal are included into the matrix of the other metal.
• the macroscopic properties of the alloy differ from those of the individual metal powders. According to the invention, it is essential that a compacted material is used, since this offers the reactivity and close contact which are required for the corrosion reaction.
• the inventive carrier material contains magnesium powder and at least one additional powder of a more precious metal or metal compound compared to magnesium; preferably, it substantially comprises only of magnesium and metal or metal powder. Due to the potential difference between these two components, the addition of a corroding medium, in particular of water or an aqueous medium, results in a redox reaction which has the effect that the magnesium, as the less precious metal, is dissolved.
• a further component can be present which adds a further desired property.
• Said component can be selected from many different materials, with the reservation that it neither disturbs the formation of the structure nor the electro-chemical corrosion.
• an additional material being inert with respect to the electro-chemical reaction can be added, which influences the mechanical properties; for example, a harder material can be added as a third component to enhance the adhesion during the kinetic compacting.
• a material catalysing the electro-chemical reaction as a further component, in order to influence the beginning and/or progress of the reaction. This may be a substance stabilizing the powders during storage, e.g. lime, with the reservation that it does not affect the electro-chemical reaction.
• an additional component is used for the inventive carrier material, its content should not exceed 25% by volume.
• the respectively best suitable amount can be determined by the skilled person by routine experiments. The content must not be so large that it disturbs the formation of the structure and the progress of the reaction. On the other hand, the amount must be sufficient to obtain the desired effect.
• the metal powders forming the inventive material are variable in view of their grain size and grain shape.
• the shape of the particles is uncritical, spherical as well as flake shapes or other forms can be considered.
• the particle size is uncritical, with the reservation that the particles must not be larger than the vacuity to be filled. With thermal spraying, particles having a size up to 0.5 mm can be processed. Preferably, particles up to 0.25 mm are used.
• the dissolution behaviour can also be influenced by the particle size of the powder, such that the optimum material for each application can be chosen by routine experiments. Further, the compacting behaviour and the structure can be influenced by the selection of the particle sizes of both powders and their ratio. Therefore, the particle size can be chosen selectively for one powder or both of them such that the desired characteristics in view of structure and dissolution are obtained.
• the corroding medium can be any liquid which supports the corrosion reaction. Normally, it is ion-containing water or an aqueous solution which initiates and promotes the redox reaction with which the magnesium is oxidized, and hydroxide ions and simultaneously hydrogen is generated. Therewith, a part of the carrier material is dissolved, its structure is destroyed and the not-dissolved particles are released. These particles are then rinsed away together with the solution which contains the magnesium in a dissolved state. Due to the formation of gas, a sufficient motion is generated to keep the reaction going, even if narrow channels or delicate cavities are concerned.
• the pH-value may be shifted to the acidic or basic range, depending on the material and medium used.
• a material being corrodible upon acidic or basic pH-values is used for producing the workpiece, same can be protected by selecting the carrier material and/or the corroding medium correspondingly such that the corrosion of the material of the workpiece is prevented.
• the generation of a basic solution is advantageous if the material forming the mould is steel, since the basic solution in this case quasi acts as a rust protection.
• a slightly acidic pH-value which can be obtained by the used medium, may be preferable.
• a carrier material is thus provided which is not completely dissolved, but the structure of which is destroyed when being in contact with water, since only a portion is dissolved, which, however, is sufficient to rinse the complete material.
• at least magnesium and an additional metal component is required, which are preferably used in a possibly pure form. Pure in the context of the present invention means that the powder contains at most small portions of impurities of disturbing elements.
• Such a structure is preferably generated by thermal spraying, cold gas spraying and/or kinetic spraying.
• a structure is obtained in which the particles form a densified matrix.
• the material applied by such a method has a porosity less than 20%, particularly preferred less than 5% and more preferred less than 1%. If the porosity of the material and therewith the proportion of open pores becomes too large, the carrier material might soak with the aqueous medium and, dependent on the reaction conditions and reactants, dissolve so fast that an uncontrolled reaction with a high gas pressure would result, which is not desired. Besides, the removal of the not-dissolved particles may be disturbed due to an increase of volume by formation of hydroxide.
• the matrix made of the metals is so dense that the surfaces of the particles have sufficient contact to promote the electro-chemical reaction when water is added.
• the metal powders are used in amounts which ensure that the electro-chemical reaction proceeds in the desired scope.
• the magnesium is dissolved at least partially, while the additional component(s) remain(s) as powder. Therefore, the magnesium must be present to such an extent that its dissolution dissolves or destroys the structure formed previously by compacting to such an extent that the generated material, i.e. substantially metal particles, can be rinsed away.
• the proportion of other metals is too large, it is difficult to remove the carrier material.
• the proportion of the more precious metal(s) should not be too less, such that the electro-chemical reaction may proceed sufficiently fast.
• the volume ratio of magnesium vis-à-vis the further components ranges between 250:1 and 1:10.
• the metal powders are combined in a volume ratio of magnesium vis-à-vis the more precious metal from 5:1 to 1:10, preferably 3:1 to 1:3.
• the magnesium powder and the “more precious” components are combined in approximately equal volume proportions.
• any liquid corroding magnesium can be used, as explained above.
• the corroding, preferably aqueous medium is uncritical and any medium comprising mainly of water is suited for this purpose. It has to be taken care that no substances affecting the electro-chemical reaction are contained in the water.
• an aqueous medium is used which promotes the electro-chemical reaction, in particular a solution containing ions. Suited are acidic, neutral and basic solutions containing ions, e.g. salt solutions. Diluted acids or bases may also be used. Also media containing ions, which are obtained as wastewater, are suitable. These are preferred for environmental and economic reasons. Therefore, tap water as well as wastewater from other processes, which is preferably containing salt, can be used, as long as the redox reaction is not affected.
• Another subject-matter of the invention is a method for producing a workpiece having at least one vacuity, i.e. inter alia an undercut, a cavity, a recess or a notch, in which the space forming the vacuity is filled with a carrier material which is rinsed away after completion, wherein the carrier material is a material as defined in claim 1 .
• inventive carrier material is very well suited to form a lost core for a moulding method, with which the workpieces having cavities or undercuts are formed.
• inventive carrier material stands out by its mechanical load capacity, such that it can be used at any place where a material having a mechanical load capacity is required.
• it can be processed by a shaping process, in particular a machining process, to form complex shapes.
• the inventive carrier material is particularly suited for a processing by means of thermal spraying, kinetic compacting or cold gas spraying.
• the inventive material is used for a method for producing workpieces, in which a layer-wise structure is formed by thermal spraying, wherein the layers are then post-processed by machining.
• a method for producing a workpiece in which a structure is generated by thermal spraying, kinetic compacting or cold gas spraying, wherein portions which are intended to form a vacuity in the final body are formed by the inventive carrier material, wherein the carrier material is removed upon contact with a corroding medium after completion of the workpiece.
• the inventive carrier material may also be used for other methods in which a placeholder is required, but it is particularly preferred for methods using thermal spraying.
• the thermal spraying is performed by kinetic spraying.
• the inventive carrier material is very well suited to form lost cores. It can be processed to form various shapes.
• the matrix generated upon application of the material is destroyed by an electro-chemical reaction upon contact with a corroding medium, and due to the motion resulting from the gas formation during the electro-chemical reaction, a sufficient water replacement occurs, in order to promote the electro-chemical reaction in an appropriate manner.
• the metal powder remaining after destruction of the matrix may then be rinsed away easily together with the resulting solution and may possibly be recycled.
• the electro-chemical reaction and thus the dissolution of the magnesium and the destruction of the structure can be promoted in a preferred embodiment by generating a motion of the medium during and after adding the aqueous medium. This may e.g. be performed by rinsing, moving the workpiece or by an ultrasound treatment.
• a carrier material which offers an ideal combination of properties due to its mechanical load capacity as well as ductility and its electro-chemical reactivity.
• a method is provided with which also very complicated shapes can be produced, since it is possible to build-up the workpieces in layers by spraying methods and to subsequently form even complicated recesses, cavities, notches, openings, undercuts or other unfilled portions by rinsing away the carrier material.
• the aforementioned inventive material is very well suited for any kind of placeholder. Due to the advantageous mechanical and electro-chemical properties, the inventive carrier material can be used in case it is required to keep free a space for a certain period of time and to remove the placeholder material subsequently. In particular, the inventive carrier material is suited if the placeholder is mechanically stressed in its function, e.g. is exposed to stress. Except for the aforementioned use for producing a workpiece having cavities, the inventive carrier material may therefore also be used as a lug, spacer, placeholder and lost core in any form.
• a combination of magnesium and at least one of metals iron, nickel or copper are particularly preferred.
• metals iron, nickel or copper are particularly preferred.
• the combination of magnesium and iron is particularly preferred, since an aqueous suspension is obtained upon dissolving the carrier material, which comprises only magnesium or its decomposition product obtained by corrosion and iron as metals.
• This combination is non-polluting and can be either disposed easily as wastewater without damaging the environment or be recycled. In case other metals are used in addition to iron or instead of iron, it may be required to recycle the resulting solution before disposing.
• the mechanical properties and the environmental acceptability of the product generated after dissolution contribute to the fact that the inventive carrier material is particularly advantageous.
• the inventive carrier material which comprises magnesium and at least one additional metal component which is selected from iron, nickel and copper, is compacted by a mechanically stressing method.
• the same methods as explained above and the same proportions of the components as explained above are also applicable for the use of the carrier material in general as a placeholder.
• the dissolution of the placeholder is performed in the same way as explained above, i.e. with an aqueous solution containing ions, in particular an aqueous medium containing active anions.
• aqueous media including chloride, nitrate and/or sulphate ions. Due to its good availability, e.g. seawater is a very suitable medium.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Powder Metallurgy (AREA)
• Coating By Spraying Or Casting (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Mold Materials And Core Materials (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)

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• 2007
  • 2007-04-16 DE DE102007017762.5A patent/DE102007017762B4/de active Active
• 2008
  • 2008-04-16 EP EP08735289.4A patent/EP2136942B1/de active Active
  • 2008-04-16 JP JP2010503405A patent/JP5143891B2/ja active Active
  • 2008-04-16 WO PCT/EP2008/003049 patent/WO2008125351A1/de active Application Filing
  • 2008-04-16 US US12/596,134 patent/US20110091660A1/en not_active Abandoned
  • 2008-04-16 ES ES08735289.4T patent/ES2687269T3/es active Active

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