EP0563140B1 - Process and device for manufacturing high-density sintered products - Google Patents

Process and device for manufacturing high-density sintered products Download PDF

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Publication number
EP0563140B1
EP0563140B1 EP92901336A EP92901336A EP0563140B1 EP 0563140 B1 EP0563140 B1 EP 0563140B1 EP 92901336 A EP92901336 A EP 92901336A EP 92901336 A EP92901336 A EP 92901336A EP 0563140 B1 EP0563140 B1 EP 0563140B1
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Prior art keywords
sintered
sintering
vacuum
pressure
gas
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Expired - Lifetime
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EP92901336A
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German (de)
French (fr)
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EP0563140A1 (en
Inventor
Hans Peter Buchkremer
Detlev STÖVER
Ludger Wenning
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Forschungszentrum Juelich GmbH
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Forschungszentrum Juelich GmbH
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    • 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
    • B22F3/10—Sintering only
    • B22F3/1003—Use of special medium during sintering, e.g. sintering aid
    • B22F3/1007—Atmosphere

Definitions

  • the invention relates to a method for producing dense sintered workpieces by sintering powdery material with subsequent hot isostatic pressing (HIP).
  • the sintering is carried out under vacuum.
  • the sintered intermediate, which is subsequently to be compressed by the HIP step, is referred to below as the "sintered intermediate".
  • Vacuum sintering followed by a HIP step is used to densify workpieces almost to their theoretically possible material density.
  • DE-A-3808123 describes a method in which two sintering steps take place before the HIP compression, the first one is sintered under a protective gas atmosphere, the second one in a high vacuum. It has been found that undesired contamination of the sintered intermediate product occurs when, during sintering under high vacuum, desorbents detach from the walls which enclose the space to be evacuated, which are deposited on the powder particles of the material to be sintered. Passive layers are formed that interfere with the sintering processes and a material structure with only a closed one Prevent porosity and affect product quality. The closed porosity is a prerequisite for an immediately subsequent HIP step with the aim of further densifying the material up to its theoretically possible density.
  • the object of the invention is to produce dense sintered workpieces by sintering green bodies made of powdery material in such a way that sintered intermediate products with porosity which are closed to the outside are formed during sintering, so that the HIP step can be connected directly. Interfering chemical reactions on the surface of the material to be sintered should be avoided.
  • a purging gas which is chemically inert to the powder material is then introduced into the pressure chamber in the vicinity of the green body to be sintered while the green body or bodies is vacuum-sintered while maintaining low pressure.
  • the pressure during vacuum sintering is set between 1 - 10 mbar.
  • Flushing with inert gas prevents chemical reactions with the material of the green body to be sintered, but essentially prevents oxidation. Intermediates with closed porosity are formed during sintering and can be hot isostatically compressed immediately after vacuum sintering.
  • the invention is explained in more detail below using an exemplary embodiment.
  • the drawing shows schematically a pressure chamber with a mold container suitable for sintering.
  • a pressure vessel 1 is shown, the pressure chamber 2 is thermally insulated from the environment.
  • Electrical heating elements 3, 4 are arranged within the pressure chamber 2.
  • the heating elements 3 heat an upper, the heating elements 4 a vertically below heating zone in the pressure chamber.
  • the heating zones are indicated in the drawing with reference numbers 5 and 6.
  • thermocouples 7 to 9 The actual temperature in the heating zones is determined by thermocouples 7 to 9.
  • a controller 10 which controls the switching on and off of the heating elements 3, 4, regulates the temperature in the pressure chamber 2 via the thermocouples 7 to 9 to a predetermined target temperature.
  • the pressure in the pressure chamber 2 is determined outside the pressure container.
  • the pressure chamber 2 is connected on the one hand to a vacuum line 11 with a vacuum valve 12, and on the other hand is connected to a pressure gas line 13 with a pressure valve 14. Vacuums of up to 10 ⁇ 3 mbar and pressures of up to 400 MPa can be set in the pressure chamber.
  • a sliding loading table 15 with a sample container 16 for receiving green bodies 17 made of powdery material to be sintered.
  • the green bodies 17 have the preform of the sintered body to be produced, they are open-pore.
  • a purge gas line 18 leads into the sample container 16 for purging the sample container with argon.
  • the purging gas flows into a purging gas chamber 19 and is guided out of this to the green bodies 17.
  • the purge gas is withdrawn from the sample container 16 again via a suction line 20.
  • the temperature of the purge gas after passage of the powdery material is measured by a thermocouple 21.
  • the purge gas drawn off flows via the suction line 20 to a gas analyzer 22 and is examined there for its impurities.
  • the pressure vessel 1 has thermal insulating plates 23 which protect the pressure chamber 2 against heat loss to the outside.
  • green bodies were produced from U 700 (UDIMET 700).
  • the powdery material for the green bodies had an average powder grain size of ⁇ 45 ⁇ m.
  • Cylindrical green bodies were used to produce ring-shaped sintered pieces.
  • the green bodies were stacked on top of one another in the sample container 16 and sintered for half an hour while introducing argon under vacuum at a pressure of 10 mbar and a temperature of 1270 ° C.
  • the sintered intermediate products were hot isostatically pressed without prior removal from the pressure chamber 2 and without intermediate cooling at a temperature of 1150 ° C. and a pressure of 150 MPa.
  • the HIP process took 3 hours.
  • the manufactured workpiece rings had a theoretical density.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Powder Metallurgy (AREA)
  • Press-Shaping Or Shaping Using Conveyers (AREA)

Abstract

The invention concerns the manufacture of dense sintered products by sintering green compacts which have been sintered from powder material in a vacuum and subsequently compressed by hot isostatic pressing (HIP). The invention calls for an inert gas to be passed round the green compacts during the vacuum-sintering stage, while still maintaining a low pressure of between (1) and (10) mbar. A suitable device for carrying out this process has inert-gas feed line (18) leading into the sample container (16). After passing round the compact(s) (17) being sintered, the gas is removed from the pressure chamber through a suction line (20).

Description

Die Erfindung bezieht sich auf ein Verfahren zum Herstellen dichter Sinterwerkstücke durch Sintern pulverförmigen Materials mit anschließendem heißisostatischen Pressen (HIP). Das Sintern wird unter Vakuum durchgeführt. Das gesinterte, nachfolgend noch durch den HIP-Schritt zu verdichtende Zwischenprodukt wird im folgenden als "Sinterzwischenprodukt" bezeichnet.The invention relates to a method for producing dense sintered workpieces by sintering powdery material with subsequent hot isostatic pressing (HIP). The sintering is carried out under vacuum. The sintered intermediate, which is subsequently to be compressed by the HIP step, is referred to below as the "sintered intermediate".

Das Vakuumsintern mit anschließendem HIP-Schritt wird angewandt, um Werkstücke annähernd bis auf ihre theoretisch mögliche Werkstoffdichte zu verdichten. In DE-A-3808123 wird ein Verfahren beschrieben, bei dem vor der HIP-Verdichtung zwei Sinterschritte erfolgen, im ersten wird unter Schutzgasatmosphäre, im zweiten in Hochvakuum gesintert. Es hat sich herausgestellt, daß unerwünschte Verunreinigungen des Sinterzwischenprodukts auftreten, wenn sich beim Sintern unter hohem Vakuum von den Wänden, die den zu evakuierenden Raum umschließen, Desorbentien lösen, die sich auf den Pulverteilchen des zu sinternden Materials niederschlagen. Es bilden sich Passivschichten aus, die die Sintervorgänge stören und eine Materialstruktur mit ausschließlich geschlossener Porosität verhindern und die Produktqualität beeinträchtigen. Die geschlossene Porosität ist Voraussetzung für einen unmittelbar nachfolgendenden HIP-Schritt mit dem Ziel einer weiteren Verdichtung des Materials bis zu dessen theoretisch möglicher Dichte.Vacuum sintering followed by a HIP step is used to densify workpieces almost to their theoretically possible material density. DE-A-3808123 describes a method in which two sintering steps take place before the HIP compression, the first one is sintered under a protective gas atmosphere, the second one in a high vacuum. It has been found that undesired contamination of the sintered intermediate product occurs when, during sintering under high vacuum, desorbents detach from the walls which enclose the space to be evacuated, which are deposited on the powder particles of the material to be sintered. Passive layers are formed that interfere with the sintering processes and a material structure with only a closed one Prevent porosity and affect product quality. The closed porosity is a prerequisite for an immediately subsequent HIP step with the aim of further densifying the material up to its theoretically possible density.

Bisher wurde der Nachteil, daß sich nicht alle offenen Poren schließen, durch eine Kapselung des Sinterzwischenprodukts gelöst. Es bedurfte also zwischen Sintern und HIP-Schritt eines weiteren Arbeitsganges, nämlich einer Umhüllung des gesinterten Körpers mit einer gasdichten, druckfesten Kapsel.So far, the disadvantage that not all open pores close has been solved by encapsulating the sintered intermediate. A further operation was required between sintering and the HIP step, namely encasing the sintered body with a gastight, pressure-resistant capsule.

Aufgabe der Erfindung ist es, zum Herstellen dichter Sinterwerkstücke das Sintern von Grünkörpern aus pulverförmigem Material derart durchzuführen, daß beim Sintern Sinterzwischenprodukte mit nach außen geschlossener Porosität entstehen, damit der HIP-Schritt unmittelbar anschließbar ist. Störende chemische Reaktionen an der Oberfläche des zu sinternden Materials sollen vermieden werden.The object of the invention is to produce dense sintered workpieces by sintering green bodies made of powdery material in such a way that sintered intermediate products with porosity which are closed to the outside are formed during sintering, so that the HIP step can be connected directly. Interfering chemical reactions on the surface of the material to be sintered should be avoided.

Diese Aufgabe der Erfindung wird bei einem Verfahren der eingangs genannten Art durch die im Patentanspruch angegebenen Maßnahmen gelöst. Danach wird während des Vakuumsinterns des oder der Grünkörper unter Beibehaltung niedrigen Druckes in die Druckkammer in die Umgebung des zu sinternden Grünkörpers ein Spülgas eingeführt, das sich zum Pulvermaterial chemisch inert verhält. Der Druck beim Vakuumsintern wird zwischen 1 - 10 mbar eingestellt.This object of the invention is achieved in a method of the type mentioned by the measures specified in the claim. A purging gas which is chemically inert to the powder material is then introduced into the pressure chamber in the vicinity of the green body to be sintered while the green body or bodies is vacuum-sintered while maintaining low pressure. The pressure during vacuum sintering is set between 1 - 10 mbar.

Durch das Spülen mit Inertgas werden chemische Reaktionen mit dem Material des zu sinternden Grünkörpers, Oxidation im wesentlichen aber Reduktion verhindert. Es entstehen beim Sintern Zwischenprodukte mit geschlossener Porosität, die direkt im Anschluß an das Vakuumsintern heißisostatisch verdichtet werden können.Flushing with inert gas prevents chemical reactions with the material of the green body to be sintered, but essentially prevents oxidation. Intermediates with closed porosity are formed during sintering and can be hot isostatically compressed immediately after vacuum sintering.

Die Erfindung wird nachfolgend anhand eines Ausführungsbeispiels näher erläutert. Die Zeichnung zeigt schematisch eine Druckkammer mit einem zum Sintern geeigneten Formbehälter.The invention is explained in more detail below using an exemplary embodiment. The drawing shows schematically a pressure chamber with a mold container suitable for sintering.

In der Zeichnung ist ein Druckbehälter 1 dargestellt, dessen Druckkammer 2 thermisch gegenüber der Umgebung isoliert ist. Innerhalb der Druckkammer 2 sind elektrische Heizelemente 3, 4 angeordnet. Die Heizelemente 3 beheizen eine obere, die Heizelemente 4 eine vertikal darunter liegende Heizzone in der Druckkammer. Die Heizzonen sind in der Zeichnung mit Bezugsziffern 5 und 6 angegeben.In the drawing, a pressure vessel 1 is shown, the pressure chamber 2 is thermally insulated from the environment. Electrical heating elements 3, 4 are arranged within the pressure chamber 2. The heating elements 3 heat an upper, the heating elements 4 a vertically below heating zone in the pressure chamber. The heating zones are indicated in the drawing with reference numbers 5 and 6.

Die Isttemperatur in den Heizzonen wird durch Thermoelemente 7 bis 9 ermittelt. Ein Regler 10 der das Ein- und Ausschalten der Heizelemte 3, 4 steuert, regelt die Temperatur in der Druckkammer 2 über die Thermoelemente 7 bis 9 auf eine vorgegebene Solltemperatur. Der Druck in der Druckkammer 2 wird außerhalb des Druckbehälters ermittelt.The actual temperature in the heating zones is determined by thermocouples 7 to 9. A controller 10, which controls the switching on and off of the heating elements 3, 4, regulates the temperature in the pressure chamber 2 via the thermocouples 7 to 9 to a predetermined target temperature. The pressure in the pressure chamber 2 is determined outside the pressure container.

Die Druckkammer 2 ist einerseits an einer Vakuumleitung 11 mit Vakuumventil 12 angeschlossen, andererseits mit einer Druckgasleitung 13 mit Druckventil 14 verbunden. Es lassen sich in der Druckkammer Vakua bis unter 10⁻³ mbar und Drücke bis zu 400 MPa einstellen.The pressure chamber 2 is connected on the one hand to a vacuum line 11 with a vacuum valve 12, and on the other hand is connected to a pressure gas line 13 with a pressure valve 14. Vacuums of up to 10⁻³ mbar and pressures of up to 400 MPa can be set in the pressure chamber.

Innerhalb der Heizzonen 5, 6 befindet sich ein verschiebbarer Ladetisch 15 mit einem Probenbehälter 16 zur Aufnahme von Grünkörpern 17 aus zu sinterndem pulverförmigen Material. Die Grünkörper 17 weisen die Vorform des zu fertigenden Sinterkörpers auf, sie sind offenporig.Within the heating zones 5, 6 there is a sliding loading table 15 with a sample container 16 for receiving green bodies 17 made of powdery material to be sintered. The green bodies 17 have the preform of the sintered body to be produced, they are open-pore.

In den Probenbehälter 16 führt eine Spülgasleitung 18 zur Spülung des Probenbehälters mit Argon. Das Spülgas strömt in eine Spülgaskammer 19 ein und wird aus dieser zu den Grünkörpern 17 geführt. Nach Umströmen der Grünkörper wird das Spülgas über eine Absaugleitung 20 aus dem Probenbehälter 16 wieder abgezogen. Die Temperatur des Spülgases nach Durchtritt des pulverförmigen Materials wird von einem Thermoelement 21 gemessen. Das abgezogene Spülgas strömt über die Absaugleitung 20 zu einem Gasanalysator 22 und wird dort auf seine Verunreinigungen hin untersucht.A purge gas line 18 leads into the sample container 16 for purging the sample container with argon. The purging gas flows into a purging gas chamber 19 and is guided out of this to the green bodies 17. After flowing around the green bodies, the purge gas is withdrawn from the sample container 16 again via a suction line 20. The temperature of the purge gas after passage of the powdery material is measured by a thermocouple 21. The purge gas drawn off flows via the suction line 20 to a gas analyzer 22 and is examined there for its impurities.

Der Druckbehälter 1 weist thermische Isolierbleche 23 auf, die die Druckkammer 2 nach außen gegen Wärmeverluste schützen.The pressure vessel 1 has thermal insulating plates 23 which protect the pressure chamber 2 against heat loss to the outside.

Im Ausführungsbeispiel wurden Grünkörper aus U 700 (UDIMET 700) hergestellt. Das pulverförmige Material für die Grünkörper wies eine mittleren Pulverkorngroße von < 45 µm auf. Es wurden zylindrisch geformte Grünkörper zur Herstellung von ringförmigen Sinterstücken eingesetzt. Die Grünkörper wurden im Probenbehälter 16 aufeinandergeschichtet und unter Einleitung von Argon unter Vakuum bei einem Druck von 10 mbar und einer Temperatur von 1270°C eine halbe Stunde gesintert.In the exemplary embodiment, green bodies were produced from U 700 (UDIMET 700). The powdery material for the green bodies had an average powder grain size of <45 µm. Cylindrical green bodies were used to produce ring-shaped sintered pieces. The green bodies were stacked on top of one another in the sample container 16 and sintered for half an hour while introducing argon under vacuum at a pressure of 10 mbar and a temperature of 1270 ° C.

Nach Beendigung des Sintervorgangs wurden die Sinterzwischenprodukte ohne vorhergehende Entnahme aus der Druckkammer 2 und ohne Zwischenkühlung bei einer Temperatur von 1150°C und einem Druck von 150 MPa heißisostatisch gepreßt. Der HIP-Vorgang dauerte 3 Stunden.After the sintering process had ended, the sintered intermediate products were hot isostatically pressed without prior removal from the pressure chamber 2 and without intermediate cooling at a temperature of 1150 ° C. and a pressure of 150 MPa. The HIP process took 3 hours.

Die gefertigten Werkstückringe wiesen theoretische Dichte auf.The manufactured workpiece rings had a theoretical density.

Claims (1)

  1. Process for producing dense sintered workpieces by sintering green bodies produced from pulverulent material in vacuo and subsequently densifying the sintered intermediates by hot isostatic pressing (HIP), characterized in that an inert gas is passed around the green body/bodies during the vacuum sintering while maintaining a low pressure, the pressure being 1 - 10 mbar.
EP92901336A 1990-12-22 1991-12-17 Process and device for manufacturing high-density sintered products Expired - Lifetime EP0563140B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE4041514 1990-12-22
DE4041514A DE4041514C2 (en) 1990-12-22 1990-12-22 Process for producing dense sintered workpieces
PCT/DE1991/000983 WO1992011106A1 (en) 1990-12-22 1991-12-17 Process and device for manufacturing high-density sintered products

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EP0563140A1 EP0563140A1 (en) 1993-10-06
EP0563140B1 true EP0563140B1 (en) 1996-02-07

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EP92901336A Expired - Lifetime EP0563140B1 (en) 1990-12-22 1991-12-17 Process and device for manufacturing high-density sintered products

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DE (2) DE4041514C2 (en)
WO (1) WO1992011106A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013167289A1 (en) * 2012-05-05 2013-11-14 Wdt-Wolz-Dental-Technik Gmbh Sintered insert for a sintering furnace for the oxygen-free sintering of metal or ceramic material
DE202013104916U1 (en) * 2013-11-04 2013-11-11 Thermo-Star GmbH sintering apparatus

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS526716A (en) * 1975-06-30 1977-01-19 Gen Electric Silicon carbide sintered articles
GB1590953A (en) * 1977-10-04 1981-06-10 Powdrex Ltd Making articles from metallic powder
SE447610B (en) * 1985-04-02 1986-11-24 Asea Atom Ab SET TO MANUFACTURE SINTERED NUCLEAR FUEL BODIES
DE3808123A1 (en) * 1988-03-11 1988-07-07 Krupp Gmbh Process for producing sintered parts of finely particulate metal or ceramic powders

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Publication number Publication date
DE59107394D1 (en) 1996-03-21
WO1992011106A1 (en) 1992-07-09
DE4041514C2 (en) 1995-05-24
DE4041514A1 (en) 1992-07-02
EP0563140A1 (en) 1993-10-06

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