EP0035601B1 - Process for making a memory alloy - Google Patents

Process for making a memory alloy Download PDF

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Publication number
EP0035601B1
EP0035601B1 EP80200184A EP80200184A EP0035601B1 EP 0035601 B1 EP0035601 B1 EP 0035601B1 EP 80200184 A EP80200184 A EP 80200184A EP 80200184 A EP80200184 A EP 80200184A EP 0035601 B1 EP0035601 B1 EP 0035601B1
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Prior art keywords
powder
temperature
process according
soft
copper
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EP80200184A
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German (de)
French (fr)
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EP0035601A1 (en
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Keith Dr. Melton
Olivier Dr. Mercier
Helmut Dr. Riegger
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BBC Brown Boveri AG Switzerland
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BBC Brown Boveri AG Switzerland
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Priority to DE8080200184T priority Critical patent/DE3065931D1/en
Priority to EP80200184A priority patent/EP0035601B1/en
Priority to US06/239,626 priority patent/US4365996A/en
Priority to JP2850481A priority patent/JPS56136942A/en
Publication of EP0035601A1 publication Critical patent/EP0035601A1/en
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/006Resulting in heat recoverable alloys with a memory effect
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C1/00Making non-ferrous alloys
    • C22C1/04Making non-ferrous alloys by powder metallurgy
    • C22C1/0425Copper-based alloys

Definitions

  • the invention is based on a method for producing a memory alloy according to the preamble of claim 1.
  • Memory alloys of the Cu / Al type or of the Cu / Al type plus at least one of the elements Ni, Fe, Mn and Co are known and have been described in various publications (for example US Pat. No. 3,783,037). Such memory alloys, which belong to the general type with the ⁇ high-temperature phase, are generally produced by melt metallurgy.
  • the invention is based on the object of specifying a production method for memory alloys of the Cu / AI type or of the Cu / AI type plus at least one of the elements Ni, Fe, Mn and Co which results in dense, compact bodies with good mechanical properties and at the same time too precisely reproducible values of the transition temperature and other quantities related to the memory effect.
  • the essence of the new process is not to start from elementary powders or from a starting powder corresponding to the final alloy, but to use a mixture of pre-alloyed powders and specially composed powder mixtures. This allows the required ductility to be optimally adapted to the processing process with extensive freedom in terms of composition.
  • the grain size of the crystallites of the finished body can largely be predetermined. Grain growth is not to be feared. Coherent oxide skins that prevent homogenization and impair mechanical properties are avoided. If a certain small percentage is present, the metal oxides are present in finely divided form as dispersoids and have a beneficial effect on the mechanical properties of the end product, preventing grain growth.
  • a round rod was made from a memory alloy with the following final composition:
  • thermomechanical processing consisted of round hammering at 950 ° C, the diameter of the rod being reduced to 18 mm in the first round hammering stitch and by 2 mm for each further stitch.
  • the procedure was such that homogenization annealing followed after 2 thermomechanical operations.
  • the rod hammered down to 8 mm in diameter was finally subjected to a final annealing in a stream of argon for 15 minutes at a temperature of 950 ° C. and immediately quenched in water.
  • the test showed a density of 99.5-99.8% of the theoretical value for the workpiece.
  • thermomechanical machining / homogenization can be continued for as long as required until the final shape of the workpiece is reached. When the theoretical density is reached, further homogenization is generally no longer necessary.
  • a round rod was made from a memory alloy with the following final composition:
  • Example I The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 15 minutes:
  • a tape was made from a memory alloy of the following final composition:
  • Example I The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 12 minutes:
  • this powder mixture were filled into a soft-annealed tombac tube with an inner diameter of 20 mm and a wall thickness of 1.6 mm and completely encapsulated by covering the ends and soldering under an argon atmosphere.
  • the tube and powder were then isostatically pressed at a pressure of 12,000 bar and the compact was reduced and presintered in a stream of hydrogen at a temperature of 850 ° C. for 11 ⁇ 2 hours and then sintered in a stream of argon at a temperature of 820 ° C. for 22 hours.
  • the workpiece was then reduced in 2 round hammer passes at a temperature of 900 ° C to 18 or 16 mm in diameter and homogenized in a stream of argon at 920 ° C for 1 h. This was followed by two round hammer passes at 900 ° C, so that the rod finally had a diameter of 13 mm.
  • the rod was rolled down in several successive hot rolling operations, each with a 20-25% reduction in cross section, to form a strip 1.5 mm thick and 20 mm wide.
  • a square bar was made from a memory alloy of the following final composition:
  • the powders given under the example were weighed out as follows and mixed in a tumble mixer for 10 min.
  • the reduction ratio (decrease in cross-section) was 11: 1.
  • the rod was then homogenized at a temperature of 920 ° C. for 30 minutes and then pulled down in 2 passes on a warming bench at a temperature of 750 ° C. to an edge length of 6 mm. After the final annealing at 900 ° C. for 15 minutes in a stream of argon, the rod was quenched in water. The density of the finished rod was 99.8% of the theoretical value.
  • a round plate was made from a memory alloy of the following final composition:
  • Example I The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 15 minutes:
  • 1000 g of this powder mixture were filled into a plastic tube with an inner diameter of 66 mm and pressed isostatically at a pressure of 12,000 bar to a cylinder with a diameter of 60 mm and a height of 80 mm.
  • the green body was reduced in a hydrogen / nitrogen stream at a temperature of 880 ° C. for 1 h and presintered and then sintered in a stream of argon at a temperature of 930 ° C. for 25 h.
  • the raw sintered body was turned to a diameter of 58 mm, introduced into a soft-annealed box made of soft iron with an outside diameter of 64 mm and completely encapsulated by putting the lid on and soldering in an argon atmosphere.
  • the workpiece produced in this way was subjected to thermomechanical processing under a hot press, interrupted by homogenization annealing.
  • the height of the cylinder was successively reduced to approx. 32 mm, whereby the material condensed to approx. 95% of the theoretical density and now had a diameter of 70 mm corresponding to the die.
  • the preformed circular plate with parallel flat end faces was inserted in a forging die with a different diameter and in several operations, which were interrupted by intermediate annealing, at temperatures between 1000 ° C and 750 ° C the finished form forged.
  • the 20 mm thick plate had a radial bead of 5 x 5 mm on the upper side and a central recess of 20 mm diameter and 5 mm axial depth on the lower side. After a final annealing at 980 ° C for 15 minutes, the plate was quenched in water. The density was 99.299.5% of the theoretical value.
  • the powder mixtures are within the following limits:
  • Isostatic pressing requires pressures of at least 8000 bar.
  • the compact is advantageously reduced and presintered in the temperature range from 700 to 1000 ° C. for at least 30 minutes in a stream of hydrogen or hydrogen / nitrogen.
  • the sintering of the compact must be above the temperature of the eutectoid transformation, i.e. H. at least 700 ° C for 10 h in a stream of argon to achieve the most homogeneous structure possible.
  • thermomechanical processing which can consist of hot pressing, hot extrusion, hot forging, hot rolling, hot drawing and / or hot round hammering, should be carried out at temperatures between 700 and 1000 ° C, as well as the intermediate homogenization in the inert gas stream (intermediate annealing) at at least 700 ° C for at least 30 min.
  • the final annealing in a stream of argon is carried out at temperatures between 700 and 1050 ° C. ( ⁇ -mixed crystal region) for 10 to 15 minutes and the workpiece is then immediately quenched in water.
  • thermomechanical processing it is expedient to encapsulate the material beforehand in a ductile metallic shell that does not react chemically with it, which is removed mechanically or chemically at the end of the shaping as a surface layer in most applications.
  • Soft-annealed metals and alloys such as copper, copper alloys and soft iron are particularly suitable as materials for the casing. Encapsulation can take place immediately before the thermomechanical processing, in that the sintered body undergoes a mechanical surface treatment beforehand by turning, milling, planing, etc., or the powder can be filled directly into a suitable tube, a can, etc., instead of into a rubber or plastic tube will.
  • the powder metallurgical method according to the invention enables the production of workpieces from a memory alloy of the Cu / Al and Cu / Al / Ni type, which compared to conventional, i.e. H. bodies produced by melt metallurgy have a fine-grained structure and optionally contain dispersoids in the form of finely divided oxide particles.
  • the mechanical properties, in particular the elongation, notch toughness and the working capacity of such workpieces are significantly better than those of cast and / or hot-kneaded bodies. This opens up a further area of application for this type of alloy.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Heat Treatment Of Nonferrous Metals Or Alloys (AREA)

Description

Die Erfindung geht aus von einem Verfahren zur Herstellung einer Gedächtnislegierung nach der Gattung des Anspruchs 1.The invention is based on a method for producing a memory alloy according to the preamble of claim 1.

Gedächtnislegierungen vom Typ Cu/AI oder vom Typ Cu/AI plus mindestens einem der Elemente Ni, Fe, Mn und Co sind bekannt und in verschiedenen Veröffentlichungen beschrieben worden (z. B. US-PS 3 783 037). Derartige Gedächtnislegierungen, die dem allgemeinen Typ mit der ß-Hochtemperaturphase angehören, werden allgemein schmelzmetallurgisch hergestellt.Memory alloys of the Cu / Al type or of the Cu / Al type plus at least one of the elements Ni, Fe, Mn and Co are known and have been described in various publications (for example US Pat. No. 3,783,037). Such memory alloys, which belong to the general type with the β high-temperature phase, are generally produced by melt metallurgy.

Beim Gießen dieser Legierungen wird in der Regel ein grobkörniges Gefüge erhalten, welches durch die anschließende Glühung im Bereich der ß-Mischkristalle durch Kornwachstum noch weiter vergröbert wird und durch thermomechanische Behandlung nicht mehr rückgängig gemacht werden kann. Dementsprechend sind die mechanischen Eigenschaften, vor allem die Dehnung und Kerbzähigkeit solcherweise hergestellter Gedächtnislegierungen verhältnismäßig schlecht und ihr Anwendungsbereich begrenzt.When these alloys are cast, a coarse-grained structure is generally obtained, which is further coarsened by grain growth due to the subsequent annealing in the region of the ß mixed crystals and cannot be reversed by thermomechanical treatment. Accordingly, the mechanical properties, especially the elongation and notch toughness of memory alloys produced in this way are relatively poor and their field of application is limited.

Es besteht daher ein Bedürfnis, diese Gedächtnislegierungen verfahrenstechnisch derart zu verbessern, daß für sie weitere praktische Anwendungsgebiete erschlossen werden können.There is therefore a need to improve these memory alloys in terms of process technology in such a way that further practical fields of application can be opened up for them.

Es ist bereits vorgeschiagen worden, Gedächtnislegierungen des Typs Cu/Zn/AI pulvermetallurgisch, ausgehend von tertigen, der Endzusammensetzung entsprechenden Ausgangslegierungen herzustellen (z. B. M. Follon, E. Aernoudt, Powder-metallurgically processed shape-memory alloys, 5th European Symposium on Powder Metallurgy, Stockholm 1978, S. 275-281). Dabei wird das fertige Pulver eingekapselt, kaltverdichtet, warmverdichtet und stranggepreßt.It has already been proposed to produce memory alloys of the Cu / Zn / AI type by powder metallurgy, starting from tertiary starting alloys corresponding to the final composition (e.g. BM Follon, E. Aernoudt, Powder-metallurgically processed shape-memory alloys, 5th European Symposium on Powder Metallurgy , Stockholm 1978, pp. 275-281). The finished powder is encapsulated, cold compressed, hot compressed and extruded.

Diese Methode ist jedoch zur Herstellung von kompakten und dichten Fertigkörpern aus Cu/AI/Ni ungeeignet, da sich das Pulver nicht verdichten läßt und wieder zerfällt.However, this method is unsuitable for the production of compact and dense finished parts made of Cu / Al / Ni, since the powder cannot be compacted and disintegrates again.

Der Erfindung liegt die Aufgabe zugrunde, ein Herstellungsverfahren für Gedächtnislegierungen vom Typ Cu/AI oder vom Typ Cu/AI plus mindestens einem der Elemente Ni, Fe, Mn und Co anzugeben, das zu dichten, kompakten Körpern mit guten mechanischen Eigenschaften und gleichzeitig zu genau reproduzierbaren Werten der Umwandlungstemperatur und anderen mit dem Gedächtniseffekt zusammenhängenden Größen führt.The invention is based on the object of specifying a production method for memory alloys of the Cu / AI type or of the Cu / AI type plus at least one of the elements Ni, Fe, Mn and Co which results in dense, compact bodies with good mechanical properties and at the same time too precisely reproducible values of the transition temperature and other quantities related to the memory effect.

Diese Aufgabe wird erfindungsgemäß durch die Merkmale des Anspruchs 1 gelöst.This object is achieved by the features of claim 1.

Der Kern des neuen Verfahrens besteht darin, weder von Elementarpulvern noch von einem der Endlegierung entsprechenden Ausgangspulver auszugehen, sondern eine Mischung aus vorlegierten Pulvern und speziell zusammengesetzter Pulvermischungen zu benutzen. Damit kann die erforderliche Duktilität bei weitgehender Freiheit bezüglich Zusammensetzung dem Verarbeitungsprozeß optimal angepaßt werden.The essence of the new process is not to start from elementary powders or from a starting powder corresponding to the final alloy, but to use a mixture of pre-alloyed powders and specially composed powder mixtures. This allows the required ductility to be optimally adapted to the processing process with extensive freedom in terms of composition.

Die Korngröße der Kristallite des fertigen Körpers kann weitgehend vorausbestimmt werden. Ein Kornwachstum ist nicht zu befürchten. Zusammenhängende, die Homogenisierung behindernde und die mechanischen Eigenschaften beeinträchtigende Oxydhäute werden vermieden. Falls zu einem bestimmten geringen Prozentsatz vorhanden, liegen die Metalloxyde in feiner Verteilung als Dispersoide vor und wirken kornwachstumshemmend und günstig auf die mechanischen Eigenschaften des Endproduktes ein.The grain size of the crystallites of the finished body can largely be predetermined. Grain growth is not to be feared. Coherent oxide skins that prevent homogenization and impair mechanical properties are avoided. If a certain small percentage is present, the metal oxides are present in finely divided form as dispersoids and have a beneficial effect on the mechanical properties of the end product, preventing grain growth.

Die Erfindung wird anhand der nachfolgenden Ausführungsbeispiele beschrieben:The invention is described using the following exemplary embodiments:

AusführungsbeispielEmbodiment

Es wurde ein Rundstab aus einer Gedächtnislegierung folgender Endzusammensetzung hergestellt:

Figure imgb0001
A round rod was made from a memory alloy with the following final composition:
Figure imgb0001

Als Ausgangsmaterialien wurden folgende Pulver verwendet:

Figure imgb0002
The following powders were used as starting materials:
Figure imgb0002

Folgende Einwaage wurde während 10 min in einem Taumelmischer gemischt:

Figure imgb0003
The following sample was mixed in a tumble mixer for 10 min:
Figure imgb0003

240 g dieser Pulvermischung wurden in einen Gummischlauch von 20 mm Innendurchmesser abgefüllt und bei einem Druck von 8000 bar isostatisch zu einem Zylinder von 18 mm Durchmesser und 220 mm Höhe verpreßt. Der Grünling wurde im Wasserstoffstrom bei einer Temperatur von 950° C während 1 h reduziert und vorgesintert und anschließend im Argonstrom bei einer Temperatur von 950°C während 19 h fertiggesintert. Der rohe Sinterkörper wurde auf einen Durchmesser von 17 mm abgedreht, in ein weichgeglühtes Kupferrohr von 20 mm Außendurchmesser eingeführt und durch Abdecken der Enden mittels Stöpsel und Verlöten unter Argonatmosphäre vollständig eingekapselt. Das derart gebildete Werkstück wurde nun abwechslungsweise einer thermomechanischen Bearbeitung und einer Homogenisierungsglühung im Argonstrom während je 1 h bei 950°C unterworfen. Im vorliegenden Fall bestand die thermomechanische Bearbeitung in einem Rundhämmern bei 950°C, wobei im 1. Rundhämmerstich der Durchmesser des Stabes auf 18 mm und bei jedem weiteren Stich um je 2 mm reduziert wurde. Dabei wurde so vorgegangen, daß auf je 2 thermomechanischen Operationen eine Homogenisierungsglühung folgte. Der auf 8 mm Durchmesser heruntergehämmerte Stab wurde schließlich einer abschließenden Glühung im Argonstrom während 15 min bei einer Temperatur von 950°C unterworfen und unmittelbar daraufhin in Wasser abgeschreckt. Die Prüfung ergab für das Werkstück eine Dichte von 99,5-99,8% des theoretischen Wertes.240 g of this powder mixture were filled into a rubber tube with an inner diameter of 20 mm and pressed isostatically at a pressure of 8000 bar to a cylinder with a diameter of 18 mm and a height of 220 mm. The green compact was reduced and presintered in a stream of hydrogen at a temperature of 950 ° C. for 1 h and then sintered in a stream of argon at a temperature of 950 ° C. for 19 h. The raw sintered body was turned to a diameter of 17 mm, introduced into a soft annealed copper tube with an outer diameter of 20 mm and completely encapsulated by covering the ends by means of plugs and soldering under an argon atmosphere. The workpiece formed in this way was then alternately subjected to thermomechanical processing and homogenization annealing in a stream of argon for 1 h at 950 ° C. In the present case, the thermomechanical processing consisted of round hammering at 950 ° C, the diameter of the rod being reduced to 18 mm in the first round hammering stitch and by 2 mm for each further stitch. The procedure was such that homogenization annealing followed after 2 thermomechanical operations. The rod hammered down to 8 mm in diameter was finally subjected to a final annealing in a stream of argon for 15 minutes at a temperature of 950 ° C. and immediately quenched in water. The test showed a density of 99.5-99.8% of the theoretical value for the workpiece.

Selbstverständlich kann der Zyklus thermomechanische Bearbeitung/Homogenisierung beliebig lang, bis zum Erreichen der endgültigen Form des Werkstückes fortgesetzt werden. Dabei ist bei Erreichen der theoretischen Dichte eine weitere Homogenisierung in der Regel nicht mehr notwendig.Of course, the cycle of thermomechanical machining / homogenization can be continued for as long as required until the final shape of the workpiece is reached. When the theoretical density is reached, further homogenization is generally no longer necessary.

Ausführungsbeispiel II:Working example II:

Es wurde ein Rundstab aus einer Gedächtnislegierung folgender Endzusammensetzung hergestellt:

Figure imgb0004
A round rod was made from a memory alloy with the following final composition:
Figure imgb0004

Die unter dem Beispiel I angegebenen Pulver wurden wie folgt eingewogen und während 15 min in einem Taumelmischer gemischt:

Figure imgb0005
The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 15 minutes:
Figure imgb0005

240 g dieser Pulvermischung wurden in ein weichgeglühtes Kupferrohr von 18 mm Innendurchmesser und 2 mm Wandstärke abgefüllt und durch Abdecken der Enden und Verlöten unter Argonatmosphäre vollständig eingekapselt. Hierauf wurde das Rohr samt Pulver bei einem Druck von 10 000 bar isostatisch gepreßt und der Preßling im Wasserstoff/Stickstoff-Strom bei einer Temperatur von 750° C während 2 h reduziert und vorgesintert und anschließend im Argonstrom bei einer Temperatur von 800°C während 25 h fertiggesintert. Daraufhin wurde das Werkstück abwechslungsweise je 2 Rundhämmeroperationen und einer Homogenisierungsglühung bei je 900° C ähnlich Beispiel I unterworfen. Der auf 6 mm heruntergehämmerte Stab wurde einer abschließenden Glühung bei 1000°C während 10 min im Argonstrom unterzogen und in Wasser abgeschreckt. Die Dichte betrug 99,5% des theoretischen Wertes.240 g of this powder mixture were filled into a soft annealed copper tube with an inner diameter of 18 mm and a wall thickness of 2 mm and completely encapsulated by covering the ends and soldering under an argon atmosphere. The tube and powder were then isostatically pressed at a pressure of 10,000 bar and the compact was reduced and presintered in a hydrogen / nitrogen stream at a temperature of 750 ° C. for 2 h and then in a stream of argon at a temperature of 800 ° C. for 25 h sintered. The workpiece was then alternately subjected to 2 round hammer operations and a homogenization anneal at 900 ° C each, similar to Example I. The rod hammered down to 6 mm was subjected to a final annealing at 1000 ° C. for 10 minutes in a stream of argon and quenched in water. The density was 99.5% of the theoretical value.

Ausführungsbeispiel III:Working example III:

Es wurde ein Band aus einer Gedächtnislegierung folgender Endzusammensetzung hergestellt:

Figure imgb0006
A tape was made from a memory alloy of the following final composition:
Figure imgb0006

Die unter dem Beispiel I angegebenen Pulver wurden wie folgt eingewogen und während 12 min in einem Taumelmischer gemischt:

Figure imgb0007
The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 12 minutes:
Figure imgb0007

240 g dieser Pulvermischung wurden in ein weichgeglühtes Tombakrohr von 20 mm Innendurchmesser und 1,6mm Wandstärke abgefüllt und durch Abdecken der Enden und Verlöten unter Argonatmosphäre vollständig eingekapselt. Hierauf wurde das Rohr samt Pulver bei einem Druck von 12 000 bar isostatisch gepreßt und der Preßling im Wasserstoffstrom bei einer Temperatur von 850°C während 1½ h reduziert und vorgesintert und anschließend im Argonstrom bei einer Temperatur von 820° C während 22 h fertiggesintert. Daraufhin wurde das Werkstück in 2 Rundhämmerstichen bei einer Temperatur von 900° C auf 18 bzw. 16 mm Durchmesser reduziert und während 1 h im Argonstrom bei 920° C homogenisiert. Es folgten nochmals 2 Rundhämmerstiche bei 900° C, so daß der Stab schließlich einen Durchmesser von 13 mm hatte. Nach abermaliger Homogenisierung während 1 h bei 920° C wurde der Stab in mehreren aufeinanderfolgenden Warmwalzoperationen mit jeweils 20-25% Querschnittsabnahme zu einem Band von 1,5 mm Dicke und 20 mm Breite heruntergewalzt. Nach einer abschließenden Glühung bei 950°C während 12 min wurde das Band in Wasser abgeschreckt. Die Dichte des fertigen Bandes betrug 99,7%.240 g of this powder mixture were filled into a soft-annealed tombac tube with an inner diameter of 20 mm and a wall thickness of 1.6 mm and completely encapsulated by covering the ends and soldering under an argon atmosphere. The tube and powder were then isostatically pressed at a pressure of 12,000 bar and the compact was reduced and presintered in a stream of hydrogen at a temperature of 850 ° C. for 1½ hours and then sintered in a stream of argon at a temperature of 820 ° C. for 22 hours. The workpiece was then reduced in 2 round hammer passes at a temperature of 900 ° C to 18 or 16 mm in diameter and homogenized in a stream of argon at 920 ° C for 1 h. This was followed by two round hammer passes at 900 ° C, so that the rod finally had a diameter of 13 mm. After homogenization again for 1 h at 920 ° C., the rod was rolled down in several successive hot rolling operations, each with a 20-25% reduction in cross section, to form a strip 1.5 mm thick and 20 mm wide. After a final annealing at 950 ° C for 12 minutes, the tape was quenched in water. The density of the finished tape was 99.7%.

Ausführungsbeispiel IV:Working example IV:

Es wurde ein Vierkantstab aus einer Gedächtnislegierung folgender Endzusammensetzung hergestellt:

Figure imgb0008
A square bar was made from a memory alloy of the following final composition:
Figure imgb0008

Die unter dem Beispiel angegebenen Pulver wurden wie folgt eingewogen und während 10 min in einem Taumelmischer gemischt.

Figure imgb0009
The powders given under the example were weighed out as follows and mixed in a tumble mixer for 10 min.
Figure imgb0009

'250 g dieser Pulvermischung wurden in einen Gummischlauch von 35 mm Innendurchmesser abgefüllt und bei einem Druck von 12000 bar isostatisch zu einem Zylinder von 31 mm Durchmesser und 80 mm Höhe verpreßt. Der Grünling wurde im Wasserstoffstrom bei einer Temperatur von 920°C während 1 h reduziert und vorgesintert und anschließend im Argonstrom bei einer Temperatur von 950°C während 20 h fertiggesintert. Der rohe Sinterkörper wurde auf einen Durchmesser von 30 mm abgedreht, in den Rezipienten einer Strangpresse eingesetzt und bei einer Temperatur von 780° C zu einem Vierkantstab quadratischen Querschnitts von 8 mm Kantenlänge verpreßt. Das Reduktionsverhältnis (Querschnittsabnahme) betrug dabei 11 : 1. Daraufhin wurde der Stab bei einer Temperaturvon 920° C während 30 min homogenisiert und anschließend in 2 Stichen auf einer Warmziehbank bei einer Temperatur von 750°C auf eine Kantenlänge von 6 mm heruntergezogen. Nach der abschließenden Glühung bei 900° C während 15 min im Argonstrom wurde der Stab in Wasser abgeschreckt. Die Dichte des fertigen Stabes betrug 99,8% des theoretischen Wertes.250 g of this powder mixture were filled into a rubber tube with an inner diameter of 35 mm and pressed isostatically at a pressure of 12,000 bar to a cylinder with a diameter of 31 mm and a height of 80 mm. The green compact was reduced and presintered in a stream of hydrogen at a temperature of 920 ° C. for 1 h and then sintered in a stream of argon at a temperature of 950 ° C. for 20 h. The raw sintered body was turned to a diameter of 30 mm, inserted in the recipient of an extrusion press and pressed at a temperature of 780 ° C. to form a square rod with a square cross section and an edge length of 8 mm. The reduction ratio (decrease in cross-section) was 11: 1. The rod was then homogenized at a temperature of 920 ° C. for 30 minutes and then pulled down in 2 passes on a warming bench at a temperature of 750 ° C. to an edge length of 6 mm. After the final annealing at 900 ° C. for 15 minutes in a stream of argon, the rod was quenched in water. The density of the finished rod was 99.8% of the theoretical value.

Ausführungsbeispiel V:Embodiment V:

Es wurde eine runde Platte aus einer Gedächtnislegierung folgender Endzusammensetzung hergestellt:

Figure imgb0010
A round plate was made from a memory alloy of the following final composition:
Figure imgb0010

Die unter dem Beispiel I angegebenen Pulver wurden wie folgt eingewogen und während 15 min in einem Taumelmischer gemischt:

Figure imgb0011
The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 15 minutes:
Figure imgb0011

1000 g dieser Pulvermischung wurden in einen Kunststoffschlauch von 66 mm Innendurchmesser abgefüllt und bei einem Druck von 12 000 bar isostatisch zu einem Zylinder von 60 mm Durchmesser und 80 mm Höhe zusammengepreßt. Der Grünling wurde im Wasserstoff/Stickstoff-Strom bei einer Temperatur von 880°C während 1 h reduziert und vorgesintert und anschließend im Argonstrom bei einer Temperatur von 930° C während 25 h fertiggesintert. Der rohe Sinterkörper wurde auf einen Durchmesser von 58 mm abgedreht, in eine weichgeglühte Dose aus Weicheisen von 64 mm Außendurchmesser eingeführt und durch Aufsetzen des Deckels und Verlöten in Argonatmosphäre vollständig eingekapselt. Das derart hergestellte Werkstück wurde einer thermomechanischen Bearbeitung unter einer Warmpresse, unterbrochen von Homogenisierungsglühungen, unterzogen. Durch abwechslungsweises Stauchen und Glühen bei 900° C wurde die Höhe des Zylinders sukzessive auf ca. 32 mm reduziert, wobei sich das Material bis auf ca. 95% der theoretischen Dichte verdichtete und nun einen dem Gesenk entsprechenden Durchmesser von 70 mm aufwies. Nach einer zusätzlichen Homogenisierungsglühung bei 950° C während 1 h wurde die vorgeformte kreisrunde Platte mit parallelen ebenen Stirnflächen in ein in ihren Durchmessern abgesetztes Schmiedegesenk eingesetzt und in mehreren Arbeitsgängen, welche durch Zwischenglühungen unterbrochen waren, bei Temperaturen zwischen 1000° C und 750° C auf die fertige Form heruntergeschmiedet. Die 20 mm dicke Platte wies bei einem maximalen Außendurchmesser von 90 mm auf der oberen Seite einen radialen Wulst von 5 x 5 mm und auf der unteren Seite eine zentrale Ausnehmung von 20 mm Durchmesser und 5 mm axialer Tiefe auf. Nach einer abschließenden Glühung bei 980°C während 15 min wurde die Platte in Wasser abgeschreckt. Die Dichte betrug 99,2­99,5% des theoretischen Wertes.1000 g of this powder mixture were filled into a plastic tube with an inner diameter of 66 mm and pressed isostatically at a pressure of 12,000 bar to a cylinder with a diameter of 60 mm and a height of 80 mm. The green body was reduced in a hydrogen / nitrogen stream at a temperature of 880 ° C. for 1 h and presintered and then sintered in a stream of argon at a temperature of 930 ° C. for 25 h. The raw sintered body was turned to a diameter of 58 mm, introduced into a soft-annealed box made of soft iron with an outside diameter of 64 mm and completely encapsulated by putting the lid on and soldering in an argon atmosphere. The workpiece produced in this way was subjected to thermomechanical processing under a hot press, interrupted by homogenization annealing. By alternately upsetting and annealing at 900 ° C, the height of the cylinder was successively reduced to approx. 32 mm, whereby the material condensed to approx. 95% of the theoretical density and now had a diameter of 70 mm corresponding to the die. After an additional homogenization annealing at 950 ° C for 1 h, the preformed circular plate with parallel flat end faces was inserted in a forging die with a different diameter and in several operations, which were interrupted by intermediate annealing, at temperatures between 1000 ° C and 750 ° C the finished form forged. With a maximum outer diameter of 90 mm, the 20 mm thick plate had a radial bead of 5 x 5 mm on the upper side and a central recess of 20 mm diameter and 5 mm axial depth on the lower side. After a final annealing at 980 ° C for 15 minutes, the plate was quenched in water. The density was 99.299.5% of the theoretical value.

Die Erfindung ist nicht auf die in den Beispielen beschriebenen Größen und Werte beschränkt. Ganz allgemein können die Pulverzusammensetzungen und die Partikelgrößen in folgenden Grenzen variiert und substituiert werden:

Figure imgb0012
The invention is not restricted to the sizes and values described in the examples. In general, the powder compositions and particle sizes can be varied and substituted within the following limits:
Figure imgb0012

Die Pulvermischungen bewegen sich in folgenden Grenzen:

Figure imgb0013
The powder mixtures are within the following limits:
Figure imgb0013

Das isostatische Pressen erfordert Drücke von mind. 8000 bar. Das Reduzieren und Vorsintern des Preßlings erfolgt zweckmäßigerweise im-Temperaturbereich von 700 bis 1000° C während mindestens 30 min im Wasserstoff- oder Wasserstoff/Stickstoff-Strom. Das Sintern des Preßlings muß oberhalb der Temperatur der eutektoiden Umwandlung, d. h. bei mindestens 700°C während 10 h im Argonstrom durchgeführt werden, um ein möglichst homogenes Gefüge zu erzielen. Die thermomechanische Bearbeitung, welche in einem Warmpressen, Warmstrangpressen, Warmschmieden, Warmwalzen, Warmziehen und/oder Warm-Rundhämmern bestehen kann, soll bei Temperaturen zwischen 700 und 1000°C bewerkstelligt werden, desgleichen das dazwischengeschaltete Homogenisieren im Inertgasstrom (Zwischenglühen) bei mindestens 700°C während mindestens 30 min. Das abschließende Glühen im Argonstrom wird bei Temperaturen zwischen 700 und 1050°C (ß-Mischkristallgebiet) während 10 bis 15 min durchgeführt und das Werkstück sofort danach in Wasser abgeschreckt.Isostatic pressing requires pressures of at least 8000 bar. The compact is advantageously reduced and presintered in the temperature range from 700 to 1000 ° C. for at least 30 minutes in a stream of hydrogen or hydrogen / nitrogen. The sintering of the compact must be above the temperature of the eutectoid transformation, i.e. H. at least 700 ° C for 10 h in a stream of argon to achieve the most homogeneous structure possible. The thermomechanical processing, which can consist of hot pressing, hot extrusion, hot forging, hot rolling, hot drawing and / or hot round hammering, should be carried out at temperatures between 700 and 1000 ° C, as well as the intermediate homogenization in the inert gas stream (intermediate annealing) at at least 700 ° C for at least 30 min. The final annealing in a stream of argon is carried out at temperatures between 700 and 1050 ° C. (β-mixed crystal region) for 10 to 15 minutes and the workpiece is then immediately quenched in water.

Für die meisten thermomechanischen Bearbeitungsarten ist es zweckmäßig, das Material zuvor in eine duktile, mit ihm chemisch nicht reagierende metallische Hülle einzukapseln, die am Schluß der Formgebung als Oberflächenschicht in den meisten Anwendungsfällen mechanisch oder chemisch entfernt wird. Als Werkstoffe für die Hülle bieten sich vor allem weichgeglühte Metalle und Legierungen wie Kupfer, Kupferlegierungen und Weicheisen an. Das Einkapseln kann unmittelbar vor der thermomechanischen Bearbeitung erfolgen, indem der Sinterkörper zuvor eine mechanische Oberflächenbehandlung durch Abdrehen, Fräsen, Hobeln etc. erfährt, oder es kann das Pulver direkt statt in einen Gummi- oder Kunststoffschlauch in ein entsprechendes Rohr, eine Dose etc. eingefüllt werden.For most types of thermomechanical processing, it is expedient to encapsulate the material beforehand in a ductile metallic shell that does not react chemically with it, which is removed mechanically or chemically at the end of the shaping as a surface layer in most applications. Soft-annealed metals and alloys such as copper, copper alloys and soft iron are particularly suitable as materials for the casing. Encapsulation can take place immediately before the thermomechanical processing, in that the sintered body undergoes a mechanical surface treatment beforehand by turning, milling, planing, etc., or the powder can be filled directly into a suitable tube, a can, etc., instead of into a rubber or plastic tube will.

Durch das erfindungsgemäße pulvermetallurgische Verfahren wird die Herstellung von Werkstücken aus einer Gedächtnislegierung des Cu/Al- und Cu/AI/Ni-Typs ermöglicht, welche gegenüber herkömmlich, d. h. schmelzmetallurgisch erzeugten Körpern ein feinkörniges Gefüge aufweisen und gegebenenfalls Dispersoide in Form von fein verteilten Oxydpartikeln enthalten. Die mechanischen Eigenschaften, insbesondere die Dehnung, Kerbzähigkeit und das Arbeitsvermögen derartiger Werkstücke sind bedeutend besser als diejenigen gegossener und/oder weiterhin warmgekneteter Körper. Damit wird diesem Legierungstyp ein weiteres Anwendungsgebiet erschlossen.The powder metallurgical method according to the invention enables the production of workpieces from a memory alloy of the Cu / Al and Cu / Al / Ni type, which compared to conventional, i.e. H. bodies produced by melt metallurgy have a fine-grained structure and optionally contain dispersoids in the form of finely divided oxide particles. The mechanical properties, in particular the elongation, notch toughness and the working capacity of such workpieces are significantly better than those of cast and / or hot-kneaded bodies. This opens up a further area of application for this type of alloy.

Eine Gegenüberstellung für die Legierung mit 13 Gew.-% Aluminium, 3 Gew.-% Nickel und 84 Gew.-% Kupfer dient zur Illustration der oben erwähnten Unterschiede:

Figure imgb0014
A comparison for the alloy with 13% by weight aluminum, 3% by weight nickel and 84% by weight copper serves to illustrate the differences mentioned above:
Figure imgb0014

Claims (8)

1. Process for making a memory alloy of the Cu/Al type or of the type Cu/Al plus at least one of the elements Ni, Fe, Mn and Co, characterised by the following steps:
a) Preparation of a powder A having a particle size from 10 to 200 µm from a copper-rich master alloy with 84 to 99% by weight of Cu, the remainder being Al, making a powder B having a particle size from 5 to 100 µm by mixing and/or alloying 95 to 99.5% by weight of aluminium powder with 0.5 to 5% by weight of copper powder, and making a powder C having a particle size from 10 to 100 gm from at least one of the elements nickel, iron, manganese and cobalt;
b) Mixing of 0.5 to 10% by weight of powder B and 0 to 6% by weight of powder C, the remainder being powder A, in a tumbler mixer for at least 10 minutes;
c) Isostatic pressing of the powder mixture in a plastic or rubber hose or in a tube of soft-annealed copper, iron or a soft copper alloy under a pressure of at least 8.000 bar;
d) Reducing and presintering the compact produced under c) in a hydrogen stream or hydrogen/nitrogen stream at a temperature between 700 and 1,000° C for at least 30 minutes;
e) Sintering-of the reduced and presintered compact in an argon stream at a temperature of at least 700° C for at least 10 hours;
f) Alternating thermo-mechanical working at a temperature between 700 and 1,000°C and homogenising in an inert gas stream at a temperature of at least 700° C for at least 30 minutes; and
g) Final annealing in an argon stream at a temperature between 700 and 1,050°C for 10 to 15 minutes and immediately subsequent quenching in water.
2. Process according to Claim 1, characterised in that the isostatic pressing is carried out in a plastic or rubber hose and that the sintered workpiece is subjected to a mechanical surface treatment before the process step f) and is then encapsulated in a shell of soft-annealed copper, iron or a soft copper alloy.
3. Process according to Claim 2, characterised in that the mechanical surface treatment consists in ,turning off, and the workpiece thus machined is introduced into a softannealed copper tube and the latter is completely sealed by covering the ends with a plug and soldering under an argon atmosphere.
4. Process according to Claim 1, characterised in that the isostatic pressing under c) is carried out in a tube of soft-annealed copper, iron or a soft copper alloy, and that the shell thus formed is removed, mechanically or chemically, only after the process step g).
5. Process according to Claim 1, characterised in that the thermo-mechanical working of process step f) consists in warm-pressing, warm-extrusion, warm-forging, warm-rolling or warm-drawing.
6. Process according to Claim 1, characterised in that the thermo-mechanical working of process step f) consists in swaging.
7. Process according to Claim 6, characterised in that the workpiece has the shape of a rod and that, in alternation during process step f) two swage passes at 950° C are followed by homogenisation annealing at 950° C, in such a way that in total 6 swage passes and 2 to 3 homogenisation annealings are carried out.
8. Process according to Claim 1, characterised in that the cycle indicated under process step f) is continued any number of times, until the final shape of the workpiece has been reached.
EP80200184A 1980-03-03 1980-03-03 Process for making a memory alloy Expired EP0035601B1 (en)

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DE8080200184T DE3065931D1 (en) 1980-03-03 1980-03-03 Process for making a memory alloy
EP80200184A EP0035601B1 (en) 1980-03-03 1980-03-03 Process for making a memory alloy
US06/239,626 US4365996A (en) 1980-03-03 1981-03-02 Method of producing a memory alloy
JP2850481A JPS56136942A (en) 1980-03-03 1981-03-02 Production of copper - aluminum - nickel memory alloy

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