SE414920C - SET TO MAKE A FORM OF A MATERIAL IN THE FORM OF A POWDER THROUGH ISOSTATIC PRESSING OF A POWDER-FORMATED BODY - Google Patents

Description

15 20 25 50 55 7804992-1 the medium, normally a gas, to penetrate into the powder mop. The casing, which, like its contents, is freed from the undesirable. gesergtmder any prooessteg before sealing, must of course also have a high enough strength or viscosity during pressing so as not to penetrate into the pores of the powder body itself. If you choose as a casing a pre-shaped capsule of glass, which, then. in the case of materials with sintering temperatures above 1000 ° C, must be of the high-melting type in order not to run off or penetrate the powder body at the sintering temperature, it is not possible to prevent a wet aa from softening alone 1 pockets and other intn-yuttmae portions on. the preformed powder mop. This often leads to rupture of protruding portions of the pre-sintered object during its cooling. due to differences in the coefficient of thermal expansion of the powder material and glass. The method is therefore only suitable for the production of objects with a very simple shape. It is possible, especially in the case of the production of objects with a complicated shape, to allow cavities to form. the site by dipping the preformed powder body in a slurry of Pai-tina; of nagsmaltsnae glass (for material but ha; smtrsngttemper) or on. otherwise surround the body with a layer of particles of such glass and then heat the powder body under vacuum at such a temperature that the particles. 'forms a dense envelope around it. The latter method allows the application of a casing which can be made thin and which adheres to the shape of the powder body so. that one can avoid accumulations of glass on. the pre-sintered object and thus the disadvantages associated with it .. A tight casing is only achieved at high temperatures then. after all, the glass must be of the high-melting type in order not to run. remove or penetrate the powder body during the sintering of the powder material. It is also. edge, namely for silicon nitride, to use a porous layer of a glass of low-melting type on the outside. a porous layer of high-melting glass. In this known case, the outer porous layer is transferred to a layer impermeable to the printing medium while the powder body is being used. When a dense layer has formed, apply pressure. the enclosed powder body with a gaseous pressure medium to counteract the dissociation of the silicon nitride with continued temperature rise. With the continued rise in temperature, the glass in the outer layer reacts with the material in the inner porous layer to form an increasingly high-melting glass and while maintaining a layer impermeable to the printing medium, and finally forms a glass-impermeable glass layer of the inner part of the inner porous layer before the glass in the outer layer has time to drain. This last formed glass layer forms a tight envelope around the powder body, when the isostatic pressing of the preformed product is carried out at sintering temperature.

According to the present invention, it has been found possible to produce objects of high density pilfer material with isostatic pressing with greater reproducibility than with the previously known methods. The present invention relates to a method of producing an object of a material in the form of a powder by isostatic pressing of an Iccopp preformed with the powder with a gaseous pressure medium, the preformed body being surrounded by a gas-permeable casing which is transferred to a casing impermeable to the pressure medium and enclosing the preformed body, and the isostatic pressing during sintering of the preformed body is subsequently carried out, characterized in that the gas-permeable casing is transferred to the impermeable body for the pressure medium. the housing while being gas permeable. the housing is in contact with a pressurized gas and while a pressure of at least equal is maintained in the pressurized gas. large and simultaneously prevailing pressure in the existing gas pores of the preformed product. The preformed jump-sn is degassed, preferably only after the gas-permeable casing has been applied. the. m probable explanation to the favorable. results obtained with the method of the present invention are that the method is more effective than in the prior art. methods ensure the formation of a tight envelope around the deformed body. In the previously known methods, where the tight casing is formed on. body, the formation takes place during degassing of the body. The continuous release of gases, which occur in the powder body or which are formed in the powder body by impurities or in the powder material itself, can then first cause the formation of bubbles and later wounds or cracks in the casing which refuse to enclose the powder body tightly. that such a tight containment is not achieved. According to the present invention, on the other hand, a departure of gases from the powder body is prevented during the formation of the casing for enclosing the powder body. This is done by maintaining a pressure in the pressurized gas that is at least equal. high as the pressure in the gas present or formed in the pores of the powder body. This would lead to the formation of a casing without defects.

The material in the powder is preferably a metallic or ceramic material, and in particular such a material having a sintering temperature exceeding 1000 ° C, such as a jambeeersa layer-mg, f; e: 3 d cr-no-stii nmerxeiimae 0.33 9% c, 0.30 9% si, 0.40 f. m, 0.01 x P, 0.01 v, s, 2.8 so cr, 0.6 n M0, against Fe enar 12 92 cr-Mo- -v-nb-stå1 containing 0.16 * A c, 0.25 in si, 0.60 ß m., O, o1 76 P, 0, 01 94 s, 11.5 70 cr, 0,5 n. Vi, 0,5 aé Mo, 0,30 nv, 0,25 så vb, me: re, en niekeibseersa alloy, te: en alloy containing 0.05 f » C, 15 9% Cr, 17 713 Co, 5 71: Mo, 3.5 7 »Ti, 4.4 73 Al, 0.05% B, residue Ni or an alloy containing 0.06 if: C, 12% cr, 17 n co, 5 s Mo, 0.06 9%. zr, 4.7 so ri, 5.3 9: 4 A1, 0.014 9% ß, 1.0 ø v, residue Ni, furthermore a metal oxide such as Al2? The levels expressed as a percentage, as well as the percentages given below, refer to a percentage by weight. Noble gases such as argon and helium as well as nitrogen are preferred as the pressure medium in the isostatic pressing. Suitable compressed gases for transferring the gas-permeable casing into the casing-impermeable casing are hydrogen, especially for sintering metallic materials, and nitrogen. However, it is possible to use other gases which do not damage the fuel plant by forming undesirable ones. reaction products or give unacceptable porosity in the powder body.

According to a suitable embodiment of the invention, the gas-permeable casing consists of an at least almost completely surrounding porous layer, which is thus transferred in a gas-tight layer around the preformed body. The porous layer, which suitably has a thickness in the range 0.05-1, mm, can be applied, inter alia, by dipping the preformed body in a slurry of a particulate material which is to form the casing, or by flame spraying or other thermal spraying. The particles may suitably have a size in the range øg1-1oolume. According to another suitable embodiment of the invention, the gas-permeable casing is derived or several. elements pre-arranged in the form of plates or the like in the form of plates or the like which soften and change shape when heated, and which are transferred in an envelope which is impermeable to the pressure medium by sintering element parts which come into contact with each other during the transformation.

If the powder has a sintering temperature in excess of 1000 ° C, the material in the casing, ie the material in the particles and the elements in the above-mentioned embodiments, can advantageously pass. of a high-melting glass such as Vycor glass containing 96.7% by weight of S102, 2.9% by weight of 3205 and 0.4% by weight of b.1203, further quartz glass and mixtures of particles (the former embodiment) such as S102 and 28205 which on heating form a gas-tight glass separator. It is also. possibly an application. a high-melting metallic material capable. to form a layer impermeable to the pressure medium, e.g. molybdenum, tungsten and other refractory metals.

When using high-melting glass in the casing, a temperature of 1200 - 1650 ° C is suitably used, as the casing is made impermeable. for the print medium.

If the powder has a sintering temperature exceeding 1000 ° 0, the material in the casing, i.e. the material in the particles and the elements in the above-mentioned embodiments, may under certain conditions also consist of a low-melting glass, namely if the preformed powder body is coated with a fine-grained layer of the powder. the body comprising the material, the fine-grained layer preventing the glass in molten form from penetrating into the powder body or if a porous layer of a high-melting material, such as a high-melting glass or high-melting metallic material, is arranged inside the casing. and transferred into a layer impermeable to the printing medium after the casing has been made impermeable to the printing medium. Even when using more than one porous layer, each porous layer can be applied to. previously described method by dipping in a slurry of the particulate material, flame spraying or other thematic spraying. Each porous layer may suitably have a thickness in the range of 0.05-1 mm and the particles a cometer size in the range of 0.1-100 .mu.m. As an example of. useful materials in casings or low-melting glass can be mentioned Pyrex glass containing 80.5 weight percent S102, 12.2 weight percent 32 3, 2.8 weight percent A120? 4.0 weight percent 111120, 0.4 weight percent E20 and 0.3 weight percent CaO, furthermore an aluminosilicate containing 56 weight percent S102, 9 weight percent 3203, 20 weight percent A120? 5% by weight of Cao and 6% by weight of MgO, as well as mixtures of particles or substances, for example: S102, 13205, Al2 O5 and alkali or alkaline earth metal oxides, which on heating form a gas-permeable glass layer.

When using low-melting glass in the casing and a porous layer located inside it, a temperature of 600-1000 ° C is suitably used to make the casing impermeable to the pressure medium. The inner layer is then suitably densified under isostatic pressure, which can be achieved after the outer layer has become gas-tight at temperatures of 1000-1200 ° 0. For such densification, a pressure of the order of 20-500 IIEPa is required.

The pressure and temperature at the sintering of the preformed body are of course dependent on the properties of the powder material. Normally the pressure should be at least 100 MPa, preferably at least 150 MPa. If the material consists of an iron base mixture, the temperature is via mm 1ooo ° c, fzsreeraaemv via 11oo- 420000, and if the material consists of a nickel-plated alloy at at least 1050 ° C, preferably at 1100-1250 ° C. If the material consists of alumina, the temperature should be: Via »about 12oo ° c, the frames via 15oo-15oo ° c.

The invention will be explained by description of exemplary embodiments with reference to the accompanying sohematic ones. drawing, in which Sig 1 shows a preformed body of a nickel-based alloy, the casing of which before heat treatment consists of a porous layer of high-melting glass, Fig. 2 a preformed body of true. alloy, the housing of which before heat treatment consists of elements in the form of plates of high-melting glass, Fig. 5 the same body after heat treatment, Fig. 4 a preformed body of an iron-based alloy, whose housing before heat treatment consists of a porous layer of low-melting glass, Fig. 5 shows a preformed body of a jenny-based alloy, the casing of which consists of elements in the form of plates of low-melting glass and Fig. 6. lcropp after heat treatment. 10 15 20 25 50 70804992-1 Exemæl 1 A turbine disc-shaped space in a divisible form of aluminum silicate-based material, t er of breastfeeding. type normally used in cores for investment casting of turbine blades with cooling ducts, are filled with spherical powder of a nickel-based alloy containing 0.05% c, 15 aá cr, 17 ”ß co, 5 ø mo, 3.5% mi, 4.4 7% A1, 0.05 7% B, residue Ni and with a cone size of <250 mn. The powder is vibrated together with light. encounter. the form is sintered in vacuo at 1200 ° C for 2 hours. After cooling, the mold, which is reusable, is divided and the porous turbine disk with substantially the same dimensions as the mold is removed. The porous turbine disk is then surface coated with a fine powder, grain size (1/11111, of the same alloy as the turbine disk ex consists of to a thickness of about 1 mm.

The turbixx disc 10, shown sohematically in Fig. 1, is provided with a gas-permeable cover in the form of a porous layer 11 by spraying it with a water slurry of a powder of a glass consisting of 80.5% by weight of SiO percent 13205, 2.8 weight percent A120? 4.0 weight percent Na 2 O, 0.4 weight percent K 2 O and 0.5 weight percent CaO, and dried.

It saw. treated preformed powder body is then placed in a high pressure suction which is provided with a line through which gas can be diverted for degassing of the powder body and given can be supplied to generate the required pressure for the isostatic press nizng and which is provided with heating devices.

The preformed powder body with a single housing is first degassed in the high pressure oven at room temperature for about 2 hours. Then the oven is filled with hydrogen gas at atmospheric pressure and raise the oven temperature to 750 ° C while maintaining the pressure, which can take about 5 hours. The temperature is then raised successively over the course of 2 hours from 750 ° C to 900 ° C while simultaneously introducing hydrogen to a pressure of 0.7 MPa, the pressure being maintained outside the casing of the preformed body at all times at at least the pressure prevailing in residual gas in the pores of the preformed body. When the temperature has reached 900 ° C, an envelope impermeable to the hydrogen gas is formed by the layer 11. Thereafter, additional hydrogen gas, or argon or potassium, is added to a tryol level. which gives a pressure of 160 MPa in the pressure medium at the final sintering temperature. The temperature is then raised to 1250 ° C, ie to a suitable sintering temperature for the nickel-based leg ring. Suitable time for sintering at the specified conditions is at least hours. At the end of the cycle, the oven is allowed to cool to a suitable discharge temperature and the sintered object is blasted clean from glass. In the manufacture of articles of powder with a higher sintering temperature, for example alumina, than the alloy exemplified above, a high-melting glass can be used in the porous layer 11 instead of the above-melting glass exemplified and without some fine-grained layer is applied on. the powder keg.

Example 2 Same. preformed body 10 which in Example 1 is surrounded in accordance with Fig. 2 with a gas permeable housing consisting of two. elements placed perpendicularly to the axis of the turbine disc shaft in the form of plates 12 and 13 of Sami. glass as that used in the powder tube in Example 1. After the body with casing has been placed in a high-pressure furnace, it is subjected to the same treatment as the body in Example 1, ie degassed, heat-treated and isostatically pressed at the conditions indicated therein. conditions. During the temperature rise from 75 ° C # 111 in this fan 95 ° C instead of 90 ° C as 1 sample 1 and the simultaneous pressure rise, the plate 12 softens and changes shape as shown in FIG; 5 and sinter the end portions 129. and 13a together so that the casing becomes tight.

Eczema 1 Powder of 12 øá-cr-Ms-v-Nb-seal ixmchallanaa 0.18 7% c, 0.25 at si, 0.60 9% Mn, o, o1 9% P, 0.01% s, 11.5 9% cr, 0.5 9% m, o, 5 f, mo, 0.50 9% v, 0.25 9% m, m: m »and ma a grain size of (BOD / um is placed in a plastic capsule, such as plasticized polyvinyl chloride, which has a turbine disk-shaped space.After closing the capsule, it is placed in a high-pressure spreader, where the powder is compacted isostatically at room temperature at a pressure of 4OOMPa with oil as tryol medium. At the end of the compaction, the capsule is removed and the preformed powder body thus prepared is machined to the desired shape.

The pre-shaped body in the form of a turbine disk. 14 is surrounded by a gas-permeable casing in the form of a porous layer 15 of a low-melting glass and a porous layer 16 of a high-melting glass located inside it. This is accomplished by first dipping the mop into a water slurry of powder of a high melting glass consisting of 96.7 weight percent SiO 2, 2.9 weight percent 3205 and 0.4 weight percent Al 2 O; and then after drying this layer in a water slurry of a powder of a low melting glass consisting of 80.5 weight percent 85.02, 12.2 weight percent 3203, 2.8 weight percent Al 2 O? 4.0 weight percent Na2O, 0.4 weight percent KZO and 0.5 weight percent CaO followed by new drying.

The preformed body with the porous layers is placed in the high pressure furnace and heated as in Example 1 at room temperature. After filling the atmosphere with atmospheric pressure, the oven temperature is raised to 750%, which is maintained for about 5 hours. The temperature is then raised gradually over the course of 2 hours 10 15 20 25 50 7804992-1 8 m from 75o ° c now 9oo ° c mac: simultaneous ccccccciv icicaning cv mvgcc sin a pressure of 0.7 MPa, the pressure outside the preformed the casings of the body are constantly maintained at least the pressure prevailing in the remaining gas in the pores of the preformed body. When the temperature has reached 900 ° C, an OSBIIONfI-'ë-YIEP nitrogen gas shell is formed by the layer 15. Then additional nitrogen gas, or argon or helium, is added to a pressure level, which gives a pressure of 50 MPa. at 1150 ° C.

The temperature is then slowly raised to 1150 ° C. The pressure then rises, at the same time.

This temperature rise is effected slowly enough for the glass in the inner layer 16 to form. a gas impermeable layer before the glass in the casing 15 has time to drain. The pressure and temperature are then raised to 100 MPa and 1200 ° C, respectively, to sinter the preformed body.

Example 1 The same preformed body 14 as in Example 5 is surrounded in accordance with Fig. 5 by a gas permeable housing consisting of two. elements placed perpendicular to the axis of the turbine disk in the form of plates 17 and 18 of saznma. glass as that used in the layer 15 of Example 3 and with a porous layer 19 located therein of the same kind as the layer 16 of Example 5. After the body with casing is placed in a high pressure oven, the same treatment as the body of Example 3 is subjected, i.e. gasified, heat treated and * isostatically pressed under the conditions specified therein. During the pressure satisfaction from 75 ° C, in this fan 950 ° C in accordance with 90 ° C acc in Example 3 and the simultaneous pressure increase, the plate 17 molds and deforms as shown in Fig. 6 and sints the end portions 17a and 18a. together so. that the casing 'becomes tight' The elements 12, 15, 17 and 18 in Figs. 2 and 5 can of course have a shape other than plates, for example consist of more or less curved elements, or of a container or bottle provided with an opening. They should, of course, be suitably designed having regard to the shape of the deformed body.

After the preform is sintered as described in Examples 1-4, it is subjected to a first heat treatment in shielding gas, tea: argon, or in vacuum at 1100 ° C (mcmpcl 1 ccn 2) and via 115o ° c (mcmpfn 5 ccn 4), respectively: mac: cming 2 hours. In doing so, dissolved hydrogen gas or nitrogen gas diffuses out of the material and at the same time loosens the remnants of the glass layer that remain so that they can be easily removed completely. The pressure during this treatment should suitably not exceed 0.1 MPa.

Claims (11)

17804992-1 PATENTKIRAV A method of making an article of a material in the form of a powder by isostatic pressing of a body preformed by the powder with a gaseous pressure medium, the preformed body being surrounded by a gas permeable casing which is transferred into an impermeable to the pressure medium and the preformed body enclosing the housing by subjecting the gas-permeable housing together with the preformed body to a heating, and the isostatic pressing during sintering of the preformed body subsequently being carried out, it is known that the gas-permeable housing (11, 12-15, 15, 17-18) are transferred to the casing impermeable casing while the gas permeable casing is in contact with a compressed gas and while maintaining in the compressed gas a pressure at least equal to the prevailing pressure in the preform the product (10, 14) pores existing gas. 2. A method according to claim 1, characterized in that a pressure in the pressurized gas during the transfer of the gas-permeable into the pressure-impermeable housing is considerably lower than the pressure in the pressurized medium during the subsequent isostatic pressing during sintering of the preformed cylinder. . 3. A method according to claim 1 or 2, characterized in that a gas is used as the pressurized gas until the envelope which is impermeable to the pressure medium is used which at least mainly consists of hydrogen gas or nitrogen gas. 4. A method according to any one of claims 1-3, characterized in that the gas is permeable. the casing (11, 15) consists of a porous layer at least almost completely surrounding the preformed body (10), which is transferred into a layer which is impermeable to the pressure medium and encloses the preformed body. IN 5. A method according to any one of claims 1-3, characterized in that the gas-permeable casing consists of one or more elements (12, 15, 17, 18) arranged in the form outside the preformed body (10, 14). of plates or the like which soften and change shape on heating, and which are transferred into a housing which is impermeable to the pressure medium by sintering elements (12a, 13a, 17a, 18a) which come into contact with each other during the transformation. pp. 7804992-1 10 6. A method according to any one of the patent claims 1-5, characterized in that the sintering temperature of the powder exceeds 1000 ° C and that the material in the casing consists of a high-melting glass. 7. A method according to claim 6, characterized in that the preformed body (10, 14) is heated to a temperature of 1200-1650 ° C to form the envelope impermeable to the pressure medium. 8. A method according to any one of claims 1-5, characterized in that the sintering temperature of the powder exceeds 1000 ° C and that the material in the casing (15, 17-18) consists of a low-melting glass and that a porous layer (16, 19 ) of high-melting material are arranged inside the casing and transferred to a layer impermeable to the printing medium after the casing has been made impermeable to the printing medium. 9. The method (8, 14) is characterized in that the preformed body (10, 14) is heated to a temperature of 600-1000 ° C to form the envelope impermeable to the pressure medium and then to a temperature of 100 DEG-120 DEG C. at the same time. isesestzsk kempsxtermg. for the formation of the impermeable layer of the pressure medium of the inner porous layer (15, 17-16). the skin (16, 19). 10. A method according to any one of patent claims 1-5, characterized in that the sintering temperature of the powder exceeds 1000 ° C and that the material in the corrugated jet (11, 12-13) is constituted by a legsmanssae glass which sees: the farfemsae bopp is coated with a fine-grained layer of the material contained in the powder body. 11. A method according to any one of patents 1 to 9, characterized in that the object is heat-treated after sintering at low pressure and at such a temperature that loose pressure can diffuse out of the material. PRESENTED PUBLICATIONS: Sweden 396 371 (C045 35/58) 7894992-1 F / GJ F / a 4 78016924 Summary A body preformed from a powdery material is surrounded by a housing which is gas permeable. The keel is transferred upon heating in a layer impermeable to the pressure medium used in isostatic pressing of the preformed body, while maintaining a pressure outside the casing which is at least as high as the pressure of the pores of the preformed product. existing gas. After the casing has been made impermeable to the tryclan joint and the preformed body is enclosed therein, the isostatic pressing is performed during simultaneous sintering of the top.