DE3015575A1 - METHOD FOR PRODUCING AN OBJECT FROM CERAMIC OR METAL MATERIAL BY ISOSTATIC PRESSING - Google Patents

Description

ASEA AB, Västeras / Sweden

Process for the production of an article from ceramic or metallic material by isostatic pressing

The invention relates to a method for producing an article from ceramic or metallic material by isostatic pressing according to the preamble of the claim

1.

Objects made of ceramic or metallic material can be made by sintering together powder from the material mentioned isostatic pressing. During isostatic pressing at sintering temperature, the powder material is used Achievement of a dense sintered product enclosed in a shell with the pressure medium, usually a gas, attached to it prevents penetration into the powder. The envelope and its contents are normally grounded during a process prior to the Sealing freed from unwanted gases. According to a known method of this type, a preformed shell is used Capsule made of homogeneous glass used, the interior of which has the same shape as the object to be manufactured, but with the dimensions are slightly larger than that of the object to be manufactured. In particular if the object to be manufactured has a

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has an intricate shape, the production of such a shape is due to the molding tools required for this and others very expensive equipment required for their manufacture.

The invention has for its object a method of the above A way to develop with which the production of a ceramic or metallic object in a much simpler way Wise and without a complicated and expensive device for the production of the shaping shell is possible.

To solve this problem, a method according to the preamble of claim 1 is proposed which, according to the invention, the in the characterizing part of claim 1 has mentioned features.

Advantageous further developments of the invention are mentioned in the subclaims.

In the method according to the invention, the shape of the to be produced Object-defining shell obtained in a simple manner. Furthermore, the invention offers other advantages from emerge from the further description. For example, the mold used to shape the object can be designed to be sucking thereby facilitating mud pouring. The invention is based on the application of a glass powder, which around a model, e.g. made of wax, the object to be manufactured is attached and bound to a shape, after which the model from the so

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obtained shape is removed and you get a mold space in the mold, which in its shape with the shape of the to be produced Object matches, with the dimensions in the form, however, larger than those of the object to be produced

Covering,'

are «This form is called gas-impermeable when isostatic Presses used.

In the description and the claims, melt is understood to be a gas-impermeable mass which is at least essentially It is thus not necessary that all parts of the embedding material are completely in the molten state are melted in order to obtain a functional gas-impermeable mass understood by the term melt.

In the practice of the present invention, the pressure means Noble gases such as argon and helium, or nitrogen, are preferred.

The ceramic material can, inter alia, consist of a nitride such as silicon nitride, a metal oxide such as aluminum oxide, or a carbide such as silicon carbide. The metallic material can consist of steel, of an iron-based alloy, such as ZoB ₀ a 3 # Cr-Mo steel "O ₉ 33 % C ₉ O ₉ 30 % Si ₅ 0.40 % Mn, 0, 01 % P, O ₉ OI % S ₈ 2 ₉ 8 % Cr, 0.6 % Mo _9, remainder Fe, or a 12% Cr = Mo ~ V ~ Nb steel "which O ₉ 18 % C ₉ 0 _s 25 % Si ₅ 0.60 % Mn, 0.01 % P, 0.01 % S ₉ 11.5 % "Cr, 0.5 % Ni ₉ 0.5 % Mo _s 0.30 % V _s 0.25 % Nb ₉ contains the remainder Fe, or an alloy that contains 1.27 % C, O ₉ 3 #Si, 0.3 % Mn ₅ 6.4 % ¥, 5 ₉ O % Mo, 3.1 % V, 4, 2 %

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Cr, the remainder Fe, or from a nickel-based alloy, such as an alloy containing 0.03 % C, 15 % Cr, 17 % Co, 5 % Mo, 3.5 % Ti, 4.4 # Al, 0.03 % B, the remainder Ni, or an alloy that contains 0.06 % C, 12? Ό Cr, 17% Co, 3% Mo, 0.06 % Zr, 4.7 Ji Ti, 5.3 % Contains Al, 0.014 90 B, 1.0 % V, the balance Ni. The percentages are percentages by weight.

The mold made of glass powder, into which the ceramic or metallic material is filled, is produced by surrounding a model of the object to be manufactured with the glass powder and that the glass particles are connected to form a coherent layer before the model is removed. The model is made of a material which can be removed from the continuous, unitary layer without this unit being destroyed. Wax or another low-melting material, such as an alloy of 60 % Bi and 40 % Sn or Woods metal (50 % Bi, 25 % Pb, 14% Sn and 11 % Cd), can be used as such a material, which removes this that the material can run out of the surrounding glass layer after melting, a plastic such as polystyrene, or another material that decomposes when heated and can escape in gaseous form, or a material that can be dissolved with a solvent, such as a metal that is dissolved by acid. Die.Glaspartikel can be connected to one another with an inorganic binder, for example B ₂ O, or SiO ₂ , which was formed from ethyl silicate in the mold. An organic binder such as starch or a resin binder that can be burned away can also be used.

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It is also possible to connect the glass particles to one another by sedimentation or cold compaction without application to achieve a binder.

The glass is preferably of the low-melting type. As an example of a suitable glass, a glass containing 80.3 percent by weight SiOp, 12.2 percent by weight BpO ₅ , 2.8 percent by weight AlpO, 4.0 percent by weight Na ₂ O, 0.4 Weight percent KpO and 0.3 weight percent CaO (Pyrex ^ ') also contains an aluminum silicate that contains 58 weight percent SiO ₂ »9 weight percent BpO ^, 20 weight percent AlpO, 5 weight percent CaO and 8 weight percent MgO, and mixtures of particles of substances , for example SiO ₂ , B ₂ O ₃ , Al ₂ O, as well as alkali and alkaline earth metal oxides, which form glass when heated. The term glass in the context of this description includes glass-forming material, such as, for example, the above-mentioned mixtures.

The ceramic or metallic material is, if necessary, Before it is filled into the mold space, the mold made of glass powder is given a suitable consistency by the addition an additional substance, ζ, .Β. in the form of a solvent such as methanol, Ethanol or water, a binder such as polyvinyl alcohol, a plasticizer such as polyethylene glycol, an anti-flocculant, such as benzenesulfonic acid, and / or a wetting agent, such as ethyl pentyl glycol. The introduction into the mold space can be done by mud casting or with the help of vacuum, pressure, Centrifugal force or ultrasound happen. The property of

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Shape, being porous and absorbent makes it easier especially when Mud casting the achievement of a tight filling of the mold space with the ceramic or metallic material. At the Inner wall of the mold, the pores preferably have a smaller size (diameter) than the grains of the ceramic or metallic Material.

After the mold space has been filled and its opening has been covered with glass, which together with the mold of an embedding for the Forms ceramic or metallic powder, the embedding, as already mentioned above, is converted into a melt. In order to keep the melt in place, the mold is, as mentioned, placed in a vessel that is stable at the temperature in which the isostatic pressing is carried out with sintering the powder of the ceramic or metallic powder will. Graphite is the preferred material for the vessel, but other materials such as boron nitride or molybdenum can also be used. be used.

The potting material can be made gas impermeable while it is in a vacuum. The embedding material can can also be made gas impermeable while in contact with a gas whose pressure is kept at a value which is at least as great as the gas pressure that is present in the material located in the mold space. Through this Damage to the mold caused by gas escaping from the material in the mold space can be avoided.

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The invention is intended below through the description of exemplary embodiments of the method and with reference to the figures are described in more detail «Figures 1 to 4 show various manufacturing steps in the manufacture of an object according to the method according to the invention.

A wax model is produced, the shape of which corresponds to the shape of an object to be produced, e.g. a turbine disk or a turbine blade, but the dimensions of which are slightly larger than the object to be produced in order to compensate for a dimensional shrinkage during the production of the object., In the middle of the A borosilicate glass tube is attached to the wax model. This tube is used, as will be described in more detail below, as an injection channel and riser pipe when pouring the mud in the finished form Parts by weight of borosilicate glass with a grain size of less than 1 / µm in 35 parts by weight of ethyl silicate until a layer 0.3-0.5 mm thick has formed on the wax model. The pore size in the layer is 0.2-0.5 μm. The mold is then further built up by dipping into a slurry of borosilicate glass particles consisting of 47 parts by weight of particles with a grain size of 45 μm, 24 parts by weight of particles with a grain size of 177 μm and 29 parts by weight of ethyl silicate. This immersion is continued until a layer of suitable thickness, ie approx. 3 = 5 mra _s , has formed around the wax model. Then the wax model with the applied layer is dried.

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The model with the surrounding glass layer is then placed in a vessel, the bottom of which has a hole corresponding to the inside diameter of the glass tube and an attachment corresponding to the outside diameter of the glass tube. The model with the glass layer is placed in the vessel in such a way that the glass tube points downwards and rests against the attachment at the bottom of the vessel. Then a slurry of borosilicate glass particles with a grain size of less than 44 Aim and water is mud-poured / sedimented in the vessel until a form with a material thickness of approx. 20 mm is obtained. After the form has been allowed to dry in the vessel, the vessel with the form is placed in an autoclave in which steam at a temperature of approx. 150 ^° C. melts the wax. The mold is then gradually heated to 550 - 600 ° C in an oven, all wax remains and the strength of the mold is increased. The shape obtained in this way is hard and porous, and there is good cohesion between the glass particles. The mold consisting of glass particles is denoted by 10, “the mold space obtained by melting out the wax is denoted by 11 and the glass tube by 12.

The mold space 11 is then filled with a silicon nitride powder 13 in the manner shown in FIG. The silicon nitride powder, which has a grain size below 5 / um and which has about 0.5 percent by weight of free silicon and about 5 percent by weight of yttrium oxide contains, is suspended with methanol to a paste-like consistency. The slurry is also made with additives added that made of polyvinyl alcohol, polyethylene glycol and benzenesulfonic acid exist, so that their contents are 2, 4 and 1

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Percent of the weight of the slurry ". Around air bubbles remove the slurry before pouring it into the mold degassed.

Because the shape is porous, the major part of methanol and additives is absorbed, so that in a successive one Filling in silicon nitride powder, the mold space is well filled with powder. When the level in pipe 12 has stopped falling, the mold space 11 can no longer hold any further material, a gas pressure of approx. 2 MPa applied. This pressure effect leads to an improved filling of the mold space and less Shrinkage while drying. Drying takes place at room temperature and atmospheric pressure and takes about 4-5 days.

The mold with its contents is then ^{heated to approximately 500 °} C. in a vacuum, the additives contained in the silicon nitride in the slurry being removed from the mold and the mold space. As can be seen from FIG. 3, the mold is then accommodated in a vessel 15 made of graphite which is internally provided with a layer of separating agent made of boron nitride. So the vessel exists

made of a material that at the sintering temperature for silicon nitride is dimensionally stable. A borosilicate glass powder 14, which covers the mold 10, is then filled into the vessel. That Powder 14 can, for example, be replaced with a sheet of glass covering the opening in glass tube 12, independently whether the glass tube has retained its original length or has been cut off level with the surface of the mold.

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All of the borosilicate mentioned in the example described is of the low-melting type and contains 80.3 percent by weight SiO ₂ , 12.2 percent by weight B ₂ O ₅ , 2.8 percent by weight Al ₂ O, 4.0 percent by weight Na ₂ O, 0.4 percent by weight K ₂ O and 0.3 percent by weight CaO. The silicon nitride has thus been provided with an embedding made of glass. One or more vessels 15 are then placed in a high pressure furnace according to FIG. For the sake of clarity, only one vessel is shown in this figure. A press frame 22, which is carried by wheels which run on rails 24 on the floor 25, belongs to the high-pressure furnace according to FIG. The press frame can be moved between the position shown in the figure and a position in which the frame surrounds the high-pressure chamber 42. The press frame consists of an upper yoke 26, a lower yoke 27 and two spacers 28 located between the yokes. The yokes and spacers are held together by a belt jacket 29 which is wound under tension. The high pressure chamber 42 is supported by a stand 49 and contains a high pressure cylinder made up of an inner tube 50, a surrounding, prestressed belt jacket 51 and end rings 52 which hold the belt jacket axially together and serve as hangers with which the high pressure chamber on Stand 49 is attached. The pressure chamber 42 has a lower end closure 53 'which protrudes into the tube 50 of the high pressure cylinder. The end closure has a groove in which a sealing ring 54 lies.

Dureh the end closure a channel 55 is guided through which on the one hand the products to be pressed are degassed and on the other hand

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on the other hand the pressure medium, preferably argon, helium or nitrogen gas, is supplied »Furthermore, a channel 56 runs through the end closure, through which the electrical cables for the supply of the heating elements 57 by which the furnace is heated. The heating elements 57 are carried by a cylinder 58, which rests on an insulating base 59 which protrudes into an insulating jacket 60. The top end cap has a annular part 61 with a sealing ring 62 which seals against the tube 50. The jacket 60 is suspended from the part 61 and connected gas-tight to this. The end closure also includes a cover 63 for closing the opening in part 61, which is normally fixed in the high pressure cylinder. The lid has a sealing ring 64 that rests against the inner wall of the part 61 seals, and provided with a cover 65 made of insulating material, which protrudes into the cylinder 60 when the high pressure chamber is closed and forms part of the insulating envelope surrounding the furnace space 66. The cover 63 is attached to a bracket 67, which is carried by a vertically adjustable and rotatable operating rod 68. The yokes 26 and 27 take the End closure 53 and the lid 63 acting on compressive forces when Pressure is generated in the furnace chamber.

After the vessel 15 and its contents have been placed in the furnace space 66, the powder 13 with the surrounding glass 10 and 14 is degassed at room temperature for approximately two hours. The temperature is increased to approximately 1150 ^° C. with continued evacuation. The temperature increase is made so slowly that

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the pressure never exceeds 0.1 torr. At approximately 1150 ^° C., the temperature is kept constant for approximately one hour. During this time, the final degassing takes place and the glass forms a melt with low viscosity which completely surrounds the powder 13. Then argon, helium or nitrogen is fed in at the same temperature until a pressure is reached which results in a pressure of 200-300 MPa at the final sintering temperature. The temperature is then within one hour to 1700 - that is, increased 1 800 ⁰ C to a suitable sintering temperature for the silicon nitride. At the same time, the pressure increases. A suitable length of time for sintering, under the conditions mentioned, is at least 2 hours. When the cycle is complete, the oven is allowed to cool to a suitable charring temperature. The vessel 15 then contains a cake with a smooth surface in which the sintered powder body is visible through the solidified and clear glass. The powder body is completely embedded in the glass and was therefore completely below the surface of the melt during pressing. Since the high pressure required for pressing could be applied when the glass was of low viscosity and the fact that the glass has the same coefficient of thermal expansion as the silicon nitride in the solidified state, objects can be produced without errors and with good reproducibility. Due to the release agent layer, the cake comes off the jar easily. The glass can then be removed from the object by sandblasting or stripping.

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According to an alternative embodiment of the method, after the vessel 15 with the powder 13 and the surrounding glass 10 and 14 has been degassed at room temperature for about 2 hours, the furnace space 66 is filled with nitrogen under atmospheric pressure and the temperature is increased with the successive supply of nitrogen a pressure of 0.1 MPa to 1150 ⁰ C increased. When 1150 ^° C. is reached, the glass powder forms a melt with low viscosity which completely surrounds the powder body 13. Then argon, helium or nitrogen is fed in at the same temperature, and pressing and sintering are carried out under the conditions mentioned in the previous example.

The sintering of silicon nitride is advantageously carried out at a temperature of 1600 - carried out in 1900 ⁰ C, and the pressure is, when no sinterungsfordernder additive such as magnesium oxide or yttrium oxide is used, at least 100 MPa, and not less than 20 MPa in the use of such additive .

Same procedure as above for making a turbine wheel has been described from silicon nitride, can in modified form in the production of a described below Milling cutter made of a powder of an iron-based alloy can be used, the alloy having the following composition: 1.27 percent by weight C, 0.3 percent by weight Si, 0.3 Weight percent Mn, 6.4 weight percent W, 5.0 weight percent Mo, 3-, T- weight percent V, 4.2 weight percent Cr, balance Fe. The steel powder has a grain size below 177 / µm. In this

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In this case, the wax model is coated on the inside of the 0.3-0.5 mm thick layer with a glass of high-melting type,

the end
which, for example, consists of / 96.7 percent by weight SiOp, 2.9 percent by weight BpO-2 and 0.4 percent by weight Al ₂ O, (Vycor ^ ') and has a grain size below 1 / µm. Otherwise, the same borosilicate glass as in the previous example is used for all glass materials. The high-melting glass powder sinters firmly to the glass powder in the remaining parts of the mold during sintering of the same and prevents the penetration of glass into the steel powder body during isostatic pressing, which takes place at a temperature of approx. 1100 ^° C. and a pressure of approx. 100 MPa for two hours is carried out for a long time. In order to avoid deformation of the milling cutter produced due to the different thermal expansion coefficients of glass and steel, the majority of the embedding around the milling cutter is removed as long as the glass is still at a temperature at which it has melted.

The pressure and temperature in the isostatic pressing and sintering of a ceramic or metallic material are of course dependent on the type of this material. The pressure should normally be at least 100 MPa, preferably at least 150 MPa. Were treated with regard to materials other than silicon nitride and high-speed steel, which latter in the examples is to say, the temperature for aluminum oxide is at least 1200 ° C, preferably at least 1300 to 1500 ⁰ C, for iron-based alloys at least 1000 C, preferably at -1200 ^° C., and for nickel-based alloys at

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should be 1250 ⁰ C - preferably at 1100 least 105O ⁰ C.

When producing objects made of ceramic or metallic material with a very high sintering temperature, it is conceivable to use a high-melting glass powder in the mold instead of a low-melting glass powder, such as glass made from 96.7 percent by weight SiO ₂ , 2.9 percent by weight BpO ^ and 0.4 percent by weight AlpCU (Vycor ^ '), or quartz glass and mixtures of particles, for example SiO ₂ and BgO ,, which forms a gas-tight glass layer when heated.

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Claims (5)

Patent claims: 1. A process for the production of an object made of ceramic or metallic material by isostatic pressing of a powder from said material by means of a gaseous pressure medium, the powder being placed in an embedding made of glass which is made gas impermeable before isostatic pressing under sintering conditions for the Powder takes place j, characterized in that the powder from the ceramic or metallic material is poured into the mold space of a mold made of glass powder, the mold space of which corresponds to the object to be produced, that the mold space is covered with glass ₉ which, together with the mold, is embedded for the powder of the ceramic or metallic material forms ;, that the embedding material, which is placed with the powder in a vessel which is stable at the sintering temperature is _p converted into a melt _9, which has a limited by the walls of the vessel surface, by which the material in F Ormraum lies, and that a pressure required for isostatic pressing is applied to the melt by the gaseous pressure medium. 2. The method according to claim 1 _9, characterized in ₉ since 3 the embedding material is made gas-impermeable, while the powder of the ceramic or metallic material and the embedding material are kept under vacuum. 030046/0702 > ² 9.4.1980? 0 7Ω9 P 3. The method according to claim 1, characterized in that the embedding material is made gas-impermeable while brought the powder of the ceramic or metallic material and the embedding material into contact with a gas whose pressure is kept at a value that is at least as great as the pressure that is in the respective Adjusts the temperature in the gas present in the powder from the ceramic or metallic material. 4. The method according to any one of claims 1-3, characterized in, that the ceramic material is silicon nitride. 5. The method according to any one of claims 1-3 »characterized in that that the metallic material consists of steel or an alloy based on iron or nickel. / 3 D30046 / 0702