EP0086011A2 - Process for generating a reversible two-way memory effect in a component made from an alloy showing a one-way effect - Google Patents

Abstract

A notable two-way effect can be induced in components made of a memory alloy exhibiting only a one-way effect by applying an external force which gives rise to an internal stress opposing the one-way effect. Component made of a memory alloy in the form of a tension, compression bending, or torsion rod (helical spring 2). External force by weight or spring (counter-spring 3).

Description

The invention is based on a method for generating a two-way memory effect according to the preamble of claim 1.

In the case of memory alloys, a so-called two-way effect can generally be distinguished from a one-way effect. While the latter is generally more pronounced and well-known (Ni / Ti alloys, β-brasses) and has also led to numerous applications, the two-way effect is more problematic and difficult to master. However, there is a general need in technology for components which have a sufficiently large two-way effect in terms of quantity in order to open up another interesting area of application. Most of the time, however, the point of the martensitic transformation of the classic two-way effect alloys lies in an unfavorable temperature range. However, there are a number of memory alloys, in particular the classic Cu / Al / Ni and Cu / Al alloys belonging to the β-brass type, whose transformation point is favorable, which may have a clear one-way but hardly a well-known two-way effect.

• R. Haynes, Some Observations on Isothermal Transformations of Eutectoid Aluminium Bronzes Below Their M_S Temperatures, Journal of the Institute of Metals 1954-55, Vol. 83, Seiten 357-358; W.A. Rachinger, A "super-elastic" single Crystal calibration bar, British Journal of Applied Physics, Vol. 9, Juni 1958, Seiten 250-252; R.P. Jewett, D.J. Mack. Further Investigation of Copper-Aluminium Alloys in the Temperature Range below the β
  
  α+γ₂ Eutectoid, Journal of the Institute of Metals 1963-64, Vol. 92, Seiten 59-61; K.Otsuka and K. Shimizu, Memory Effect and Thermoelastic Martensite Transformation in Cu-Al-Ni Alloy, Scripta Metallurgia, Vol. 4, 1970 Pergamon Press Inc., Seiten 469-472; Kazuhiro Otsuka, Origin of Memory Effect in Cu-Al-Ni Alloy, Japanese Journal of Applied Physics, Vol. 10, No. 5, May 1971, Seiten 571-579.

The following documents can be cited as state of the art:

• R. Haynes, Some Observations on Isothermal Transformations of Eutectoid Aluminum Bronzes Below Their M _S Temperatures, Journal of the Institute of Metals 1954-55, Vol. 83, pages 357-358; WA Rachinger, A "super-elastic" single crystal calibration bar, British Journal of Applied Physics, Vol. 9, June 1958, pages 250-252; RP Jewett, DJ Mack. Further Investigation of Copper-Aluminum Alloys in the Temperature Range below the β
  
  α + γ ₂ Eutectoid, Journal of the Institute of Metals 1963-64, Vol. 92, pages 59-61; K.Otsuka and K. Shimizu, Memory Effect and Thermoelastic Martensite Transformation in Cu-Al-Ni Alloy, Scripta Metallurgia, Vol. 4, 1970 Pergamon Press Inc., pages 469-472; Kazuhiro Otsuka, Origin of Memory Effect in Cu-Al-Ni Alloy, Japanese Journal of Applied Physics, Vol. 10, No. 5, May 1971, pages 571-579.

There is therefore a need for components made of memory alloys of the β-brass type which have a well-known two-way effect at a transformation temperature which is favorable for certain applications.

The invention is based on the object of specifying a method for components made of an alloy which normally only shows a one-way effect in order to induce a considerable reversible two-way memory effect in these components, at least in the operating state.

This object is achieved by the features specified in the characterizing part of claim 1.

The invention is described on the basis of the following exemplary embodiments explained by a figure.

The figure shows

a component working according to the method using the example of a spring combination.

1 is a frame (or yoke), between the parallel legs of which a helical spring 2 made of a memory alloy showing only a one-way effect and a conventional spring 3 is installed. The springs 2 and 3 are connected to each other by a movable element 4 (armature), the function of which is to transmit its movement to a display device, a trigger mechanism or a force transmission element. The springs 2 and 3 and element 4 are in the basic position, i.e. drawn in a completely relaxed state. When heated, the movable element assumes position 5, in order to return to position 4 with subsequent cooling. This is indicated by the corresponding arrows.

• Als Ausgangsmaterial wurde eine kommerziell hergestellte β -Titanlegierung der folgenden Zusammensetzung im gekneteten Zustand verwendet:
  
  Ein geeignetes Werkstück in Stabform wurde zunächst einer Lösungsglühung im β-Mischkristallgebiet bei einer Temperatur von 850°C während 15 min unterworfen und anschliessend in Wasser abgeschreckt. Aus dem Werkstück wurde durch spanabhebende Bearbeitung ein zylindrischer Probestab von 7 mm

Example 1:

• A commercially produced β-titanium alloy of the following composition in the kneaded state was used as the starting material:
  
  A suitable workpiece in the form of a rod was first subjected to solution annealing in the β mixed-crystal region at a temperature of 850 ° C. for 15 minutes and then quenched in water. The workpiece was machined into a cylindrical test bar of 7 mm

Diameter and 25 mm measuring length worked out. This test bar was subjected to a tensile stress in the longitudinal direction and stretched such that it had a total elongation of 3%. The load required for this expansion was then reduced to a level that only a tensile stress of 200 MPa was effective on the cross-section of the rod. In this state, the test bar was heated to a temperature of 250 ° C. A contraction in the longitudinal direction of 0.7% was observed, which corresponded to the one-way memory effect. After the subsequent cooling to room temperature, an extension of the test rod in the longitudinal direction by 0.3% was determined, that is to say a two-way memory effect. Further temperature cycles between room temperature and 250 ° C showed the effects to be completely repeatable, which proved that there was a reversible two-way effect.

In a comparative test, a rod of the same dimensions and the same heat treatment was subjected to an identical temperature cycle but without a simultaneous static load. In this case, no two-way effect could be observed. This proved that in a material that only shows a one-way effect after appropriate thermal and mechanical pretreatment, an additional superimposed static load can produce a remarkable two-way memory effect, measured in terms of the elasticity range of an ordinary steel.

• Das Ausgangsmaterial bestand aus einer dem_/3 -Messingtyp angehörenden, nach herkömmlichen pulvermetallurgischen Methoden hergestellter Gedächtnislegierung. Die Zusammensetzung der Legierung war wie folgt:
  

Working example II:

• The starting material consisted of a memory alloy belonging to the _{/ 3} brass type and manufactured according to conventional powder metallurgical methods. The composition of the alloy was as follows:
  

The alloy was transferred to a band 2.5 mm thick by hot rolling. Then test strips of square cross section 2.5 x 2.5 mm and 35 mm long were cut out of this strip and solution-annealed at 950 ° C. for 15 minutes and quenched in water. The test bars were then subjected to a bending stress such that the outer fiber suffered an elongation of 5%. Then a test bar was clamped into a measuring device determining the deflection (deflection) and subjected to a temperature cycle between 20 ° C and 250 ° C under various mechanical loads exerting a transverse force in a positive or negative direction. It was found that practically no two-way effect could be found under zero load. If a load that inhibited or supported the free movement of the test rod was applied, a well-known two-way effect could be determined in both cases. The effect reached a maximum when the transverse force was applied against the direction of movement of the rod and was chosen so large that it corresponded to a tension in the outermost fiber of 200 MPa. The maximum achievable deflection corresponded to a reversible expansion (= two-way memory effect) of approx. 1.8%. If the load was further increased, the two-way effect decreased again.

• Probestäbe der gleichen Zusammensetzung und Abmessungen wie in Beispiel II wurden in der gleichen Weise lösungsge- glüht_Jabgeschreckt und um 5 % verformt. Zusätzlich wurden sie nach der Verformung einer Formstabilisierungsbehandlung bei 300°C während 30 min unter statischer Last und einer Martensitstabilisierungsbehandlung bei 300°C während 30 min ohne Last unterworfen. Die nachherige Prüfung gemäss Beispiel II zeigte bereits bei der Belastung Null einen namhaften Zweiwegeffekt von ca. 1,5 % (Dehnung), der aber bei einer Spannung von 100 MPa entsprechenden, gegen die Bewegungsrichtung des Stabes gerichteten Belastung auf ca. 2 % gesteigert werden konnte. Wurde das Vorziehen der Belastung umgekehrt, nahm der Zweiwegeffekt beträchtlich ab und betrug bei einer Spannung von -100 MPa weniger als 0,8 %.

Working example III:

• Test bars of the same composition and dimensions as in Example II were quenched in the same way as solution-annealed _J and deformed by 5%. In addition, they were subjected to a shape stabilization treatment at 300 ° C for 30 minutes under static load and one after the deformation Subjected to martensite stabilization treatment at 300 ° C for 30 min without load. The subsequent test according to Example II already showed a well-known two-way effect of approx. 1.5% (elongation) at zero load, but this was increased to approx. 2% at a stress of 100 MPa corresponding to the direction of movement of the rod could. When the advance of the stress was reversed, the two-way effect decreased significantly and was less than 0.8% at a stress of -100 MPa.

• Siehe Figur.

Working example IV:

• See figure.

A wire with a diameter of 1 mm was produced from the material according to Example II using conventional methods and wound into a coil spring with a coil diameter of 14 mm. This spring was solution annealed at 900 ° C for 10 minutes and quenched in water. The coil spring was deformed by a critical amount in order to bring it into the condition necessary for the memory effect. In the frame 1, the coil spring 2 made of memory alloy and an ordinary spring 3 were installed coaxially and without pretension. The movable element 4, which can be used to transmit a measured value or a force, served as the connection between 2 and 3. The individual parts 2, 3 and 4 are drawn in the basic position. When heated to approximately 200 ° C, the spring 2 expanded and compressed the spring 3, which thus exerted a variable counterforce on 2. The movable element 5 is drawn in the deflected position after heating (direction of movement: dashed arrow). When it cooled down, 2 contracted again and the movable element returned to the basic position corresponding to 4 (direction of movement: solid arrow). This cycle could be repeated any number of times, what that Proven presence of a reversible two-way effect in the whole of the assembled component.

The invention is not restricted to the exemplary embodiments. To generate a reversible two-way memory effect in a composite component, in principle a component made of any memory alloy can be used which, under normal conditions, i.e. only shows a one-way effect with free, unimpeded movement. In the operating state, care must be taken that a force is exerted on the component which results in an internal tension which counteracts the one-way effect. This can be done by applying an external load in the form of a counterweight, a spring, etc. The memory alloy component can have the shape of a tension, compression, bending or torsion bar (also in the form of a helical spring). The preload impressed on the outside can be constant or variable depending on the purpose of the use of the component.

The main alloys are Cu / Al / Ni, Cu / Al, Cu / Zn / Al, Ti / V, Ti / Nb, Ni / Ti and Ni / Ti / Cu memory alloys.

The method according to the invention makes it possible to induce a well-known two-way effect in a component that normally has no or only an insignificant two-way memory effect. This opens up a further, practically important area of use in relay, switch and temperature release construction for an important alloy class.

Claims (5)

1. A method for producing a reversible two-way memory effect in a component consisting of a memory alloy which, under normal conditions, shows only a one-way effect, the component being first subjected to solution annealing in the temperature region of the β mixed crystal with subsequent quenching in water and deformation that the component in the operating state is subjected to an inner load, which counteracts the one-way effect and generates an additional tension, in the form of an additional weight, a spring or a blocking additional component which inhibits the free movement of the component and is firmly connected to it. 2. The method according to claim 1, characterized in that the memory alloy is a Cu / Al / Ni, Cu / Al, Cu / Zn / A1, Ti / V, Ti / Nb, Ni / Ti or Ni / Is Ti / Cu alloy. 3. The method according to claim 1, characterized in that the component is a tension rod, which an axial static preload is pressed on in the form of a weight. 4. The method according to claim 1, characterized in that the component is a bending rod, to which a static preload acting transversely to the longitudinal axis is pressed in the form of a weight or by means of a spring. 5. The method according to claim 1, characterized in that the component is a helical spring which is counteracted by a counter-spring which counteracts the same axis but counteracts the one-way effect and thereby a variable preload is pressed onto the component.

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