High-temperature shape-memory alloy, and shape-memory element

Abstract

The invention relates to a high-temperature shape-memory alloy which forms an austenite in a first temperature range above an austenite temperature and which forms a modulated martensite in a second temperature range below the austenite temperature. According to the invention, the high-temperature shape-memory alloy has an at least quaternary NiMnGaFe alloy system with an Mn content of more than 27.5 at.%, an Ni content of more than 49.4 at.%, and an Fe content of at least 0.1 at.%.

Description

[0001] High-temperature shape memory alloy and shape memory element

[0002] State of the art

[0003] The invention relates to a high-temperature shape memory alloy according to the preamble of claim 1, a shape memory element according to claim 13, a device according to claim 16 and a method according to claim 17.

[0004] Shape memory alloys, such as Nitinol or NiMnGa alloys, are already known. A roadblock to their broad applicability is their usable temperature range, which is limited by the transformation of the material into an austenite phase at a so-called austenite temperature. In known NiMnGa alloys, an increase in the austenite temperature is associated with the appearance of unmodulated martensite phases.

[0005] The object of the invention is, in particular, to provide an alloy with advantageous shape memory properties. This object is achieved according to the invention by the features of at least claim 1, while advantageous embodiments and further developments of the invention can be found in the subclaims.

[0006] Advantages of the invention

[0007] The invention is based on a high-temperature shape memory alloy which forms an austenite, in particular an austenite phase, in a first temperature range above an austenite temperature and which forms a modulated martensite, in particular a modulated martensite structure, in a second temperature range below the austenite temperature.

[0008] It is proposed that the high-temperature shape memory alloy be formed by an at least quaternary NiMnGaFe (nickel-manganese-gallium-iron) alloy system with a Mn (manganese) content of more than 27.5 at. %, with a Ni (nickel) content of more than 49.4 at. %, and with an Fe (iron) content of at least 0.1 at. %, and in particular with a Ga (gallium) content of at least 0.1 at. %. The alloy system according to the invention can advantageously produce a shape memory alloy, in particular a magnetic shape memory alloy, which enables the development of a wide and / or previously inaccessible range of applications, for example, certain circuit breakers, etc. Advantageously, an alloy system with previously unattained shape memory properties can be obtained. In particular, the high-temperature shape memory alloy can form a magnetic high-temperature shape memory alloy.Alternatively, however, it is also conceivable that the high-temperature shape memory alloy is advantageously provided for use free of and / or independent of magnetic fields, e.g., for superelastic use. “Provided” should be understood in particular to mean specially programmed, designed and / or equipped. The fact that an object is provided for a specific function should be understood in particular to mean that the object fulfills and / or performs this specific function in at least one application and / or operating state. In particular, the first temperature range and the second temperature range are directly adjacent to one another. The Ni content, the Mn content, the Ga content and / or the Fe content, and preferably all other contents of the alloy system, if present, are preferably determined using an X-ray fluorescence spectrometer calibrated in particular to the alloy system, e.g., the quaternary NiMnGaFe alloy system.The austenite temperatures (TA) (specified herein) are preferably determined by means of differential scanning calorimetry (DSC) or by means of temperature-dependent AC magnetometry. In particular, the austenite temperatures (specified herein) are designed as martensite-to-austenite transition temperatures. In particular, the martensite-to-austenite transition temperature is a temperature at which the alloy-internal (phase) transition from martensite to austenite occurs upon heating of the high-temperature shape memory alloy. In particular, the martensite-to-austenite transition temperature may be different from an austenite-to-martensite transition temperature, which would be measured upon cooling of the high-temperature shape memory alloy, due to possible hysteresis behavior of the high-temperature shape memory alloy.In particular, in addition to the austenite temperature, the high-temperature shape memory alloy has a phase transition temperature for a transition from a ferromagnetic phase, in particular martensite or austenite, to a paramagnetic phase, in particular martensite or austenite (Curie temperature Tc). This phase transition temperature can be above, below, or at an identical temperature to the austenite temperature. Preferably, the phase transition temperature for the transition from the ferromagnetic phase, in particular martensite or austenite, to the paramagnetic phase, in particular martensite or austenite, is above 80°C, preferably above 90°C, advantageously above 100°C, and preferably above 110°C.

[0009] In particular, the high-temperature shape memory alloy has, in addition to the austenite temperature and / or the phase transition temperature, a modulation limit temperature (TIMT) for a transition from a modulated martensite to an unmodulated martensite. In particular, the modulation limit temperature is designed as a modulated martensite-to-unmodulated martensite transition temperature. In particular, the modulated martensite-to-unmodulated martensite transition temperature is a temperature at which the alloy-internal (phase) transition from the modulated martensite to the unmodulated martensite occurs upon cooling of the high-temperature shape memory alloy.In particular, the modulated martensite-to-unmodulated martensite transition temperature may be different from an unmodulated martensite-to-modulated martensite transition temperature, which would be measured upon heating of the high-temperature shape memory alloy, due to a possible (thermal) hysteresis behavior of the high-temperature shape memory alloy. The modulation limit temperature is, in particular, below the austenite temperature. In particular, the austenite exists in a temperature range between the austenite temperature and a melting temperature. In particular, the modulated martensite exists in a temperature range between the modulation limit temperature and the austenite temperature. In particular, various modulated martensite microstructures exist, in particular with different modulation lengths.The modulation limit temperature (specified herein) is determined, in particular, by a temperature-dependent measurement of the crystal structure of the alloy system, for example, by electron or X-ray diffraction or by temperature-dependent AC magnetometry. In particular, the occurrence of a magnetic shape memory effect is linked to the presence of modulated martensite.

[0010] In particular, the alloy system of the proposed high-temperature shape memory alloy is at least quaternary. However, it is also conceivable for the alloy system of the proposed high-temperature shape memory alloy to be formed with a higher number, e.g., quinary, senary, septenary, octal, nonary, decimal, etc. In particular, the individual proportions (at. %) of the at least quaternary alloy system add up to 1 (100 at. %). In particular, elements with a proportion of less than 0.1 at. % are not assigned to the alloy system of the high-temperature shape memory alloy and are considered merely trace elements or impurities. Preferably, the high-temperature shape memory alloy, in particular the alloy system of the high-temperature shape memory alloy, is free of the metal cobalt (free of a Co content), preferably apart from impurities or trace elements.In particular, the high-temperature shape memory alloy is designed as a cobalt-free high-temperature shape memory alloy, in particular a cobalt-free magnetic high-temperature shape memory alloy.

[0011] It is further proposed that the at least quaternary NiMnGaFe alloy system has a Mn content of at least 28.3 at. % and / or a Ni content of at least 49.9 at. %. This allows the inventive advantage of the proposed NiMnGaFe alloy system to be further enhanced, particularly with regard to the temperature and / or phase transition properties of the high-temperature shape memory alloy.

[0012] If the austenite temperature, in particular the martensite-to-austenite transition temperature, is above 80°C, preferably above 90°C, advantageously above 100°C, and preferably above 110°C, a particularly wide usable temperature range of the high-temperature shape memory alloy can be advantageously achieved. This advantageously expands the application range for shape memory alloys, in particular for magnetic shape memory alloys. A particularly wide temperature range for using the shape memory alloy as a magnetic shape memory material and / or as a superelastic shape memory material can be advantageously achieved.

[0013] If, moreover, the second temperature range includes room temperature, a particularly high usability of the shape memory alloy for everyday applications can advantageously be achieved. The shape memory alloy can advantageously be intended for applications outside of temperature-controlled systems. In particular, room temperature is a commonly defined room temperature in the field of technology (e.g., physics or mechanical engineering). Preferably, the room temperature corresponds to the standardized so-called ISO 1 temperature. Preferably, the room temperature is 20°C. Preferably, the high-temperature shape memory alloy exists at room temperature as the modulated martensite.

[0014] Furthermore, it is proposed that the second temperature range extend at least over a range of values ​​between -20°C and the austenite temperature, in particular the martensite-to-austenite transition temperature, preferably at least over a range of values ​​between 0°C and the austenite temperature, in particular the martensite-to-austenite transition temperature. This advantageously allows for a particularly high usability of the shape memory alloy for everyday applications. The shape memory alloy can thus be advantageously intended for outdoor applications in a large proportion of all climate zones on Earth.

[0015] Furthermore, it is proposed that the modulated martensite, particularly in the second temperature range, at least to a large extent, preferably exclusively, has a modulated 10M martensite structure and / or a modulated 14M martensite structure. This advantageously makes it possible to achieve a particularly good magnetic shape memory effect, in particular one with a particularly large stroke. In this case, a "large part" is to be understood in particular as at least 80%, preferably at least 90%, more preferably at least 95%, and particularly preferably at least 99% of a total volume of a shape memory element consisting of the high-temperature shape memory alloy.It is conceivable that the modulated martensite exhibits both the modulated 10M martensite structure and the modulated 14M martensite structure simultaneously (mixed), or that the modulated martensite exhibits the modulated 10M martensite structure and the modulated 14M martensite structure at different temperatures. The modulation type of the martensite (10M, 14M, etc.) and / or the presence of non-modulated martensite is preferably determined by electron or X-ray diffraction.

[0016] If the modulated martensite exhibits either only the modulated 10M martensite structure (apart from small defects, preferably less than 1% of the total volume) or only the modulated 14M martensite structure (apart from small defects, preferably less than 1% of the total volume) over the entire second temperature range, a particularly high degree of accuracy can be achieved for applications of the high-temperature shape memory alloy. In particular, in this case, the modulated martensite in the second temperature range is free of an intermartensitic phase transition, especially between the differently modulated martensite structures.

[0017] If, in addition, the Ni content of the at least quaternary NiMnGaFe alloy system is higher than 49.4 at.% and lower than 55 at.%, preferably higher than 49.9 at.% and lower than 52 at.%, the Mn content of the at least quaternary NiMnGaFe alloy system is higher than 27.5 at.% and lower than 35 at.%, in particular higher than 27.5 at.% and lower than 32 at.% and preferably higher than 28.4 at.% and lower than 32 at.%, the Ga content of the at least quaternary NiMnGaFe alloy system is between 1 at.% and 23 at.%, preferably between 15 at.% and 22 at.%, and / or the Fe content of the at least quaternary NiMnGaFe alloy system is between 0.1 at.% and 22 at.%, preferably between 0.5 at. % and 10 At.%, the inventive advantage of the proposed NiMnGaFe alloy system can be further expanded and / or optimized, particularly with regard to the temperature and / or phase transition properties of the high-temperature shape memory alloy. In particular, the sum of the Ni, Mn, Ga, and FE components does not exceed the value of 1 (100%). In particular, the sum of the Ni, Mn, Ga, and FE components does not significantly fall below the value of 1 (100%), particularly excluding trace element components and / or impurity components.

[0018] Additionally, a shape memory element is proposed, which is formed at least partially and / or sectionally from the high-temperature shape memory alloy. The shape memory element advantageously enables novel actuator applications. The shape memory element can assume virtually any shape, for example, a cubic shape, a spherical shape, or a polygonal shape extending beyond the cubic. In particular, the shape memory element can be intended for superelastic use and / or for use as a magnetic shape memory element.

[0019] Furthermore, it is proposed that at least the modulated martensite of the high-temperature shape memory alloy be polycrystalline or monocrystalline. This advantageously enables a variety of applications for the shape memory element.

[0020] It is further proposed that the high-temperature shape memory alloy exhibit magnetic field-induced ductility in the second temperature range and a Curie temperature (Tc) above 80°C, preferably above 90°C, advantageously above 100°C, and preferably above 110°C. This advantageously allows for the creation of a magnetic high-temperature shape memory element. This advantageously enables a variety of previously unavailable applications of the magnetic shape memory effect.

[0021] Furthermore, a device, for example a circuit breaker, with an actuator unit comprising at least the shape memory element is proposed. This advantageously allows the functionality of the device, in particular of the circuit breaker, to be optimized and / or expanded. In particular, the use of the shape memory element is not limited to circuit breakers, but also encompasses a multitude of other fields of application, such as, for example, actuating and / or sensor devices for automotive engineering, industrial or medical technology, and / or measurement technology.

[0022] Furthermore, a method for producing the high-temperature shape memory alloy, in particular the shape memory element, is proposed, wherein the at least quaternary NiMnGaFe alloy system is produced in at least one alloying step. This advantageously makes it possible to obtain a shape memory alloy, in particular a magnetic shape memory alloy, which enables the development of a wide and / or previously inaccessible range of applications, for example, certain circuit breakers, etc. Advantageously, a shape memory element can be obtained from an alloy system with previously unattained shape memory properties.

[0023] The high-temperature shape memory alloy according to the invention, the shape memory element according to the invention, the device according to the invention, and the method according to the invention are not intended to be limited to the application and embodiment described above. In particular, the high-temperature shape memory alloy according to the invention, the shape memory element according to the invention, the device according to the invention, and the method according to the invention may have a number of individual elements, components, and units that differs from the number stated herein in order to fulfill a function described herein.

[0024] Drawings

[0025] Further advantages are shown in the following drawing description.

[0026] An embodiment of the invention is shown in the drawings.

[0027] The drawings, the description, and the claims contain numerous features in combination. A person skilled in the art will also conveniently consider the features individually and combine them into further meaningful combinations.

[0028] They show:

[0029] Fig. 1 is a schematic perspective view of a shape memory element formed from a high-temperature shape memory alloy according to the invention,

[0030] Fig. 2 is a schematic representation of a device with an actuator unit which comprises the shape memory element and Fig. 3 is a schematic flow diagram of a method for producing the high-temperature shape memory alloy.

[0031] Description of the embodiment

[0032] Fig. 1 shows a schematic perspective view of a shape memory element 10. The shape memory element 10 is designed as a magnetic shape memory element. The shape memory element 10 is made of a high-temperature shape memory alloy. The shape memory element 10 is made of a magnetic high-temperature shape memory alloy. The high-temperature shape memory alloy of the shape memory element 10 forms an austenite in a first temperature range above an austenite temperature. The austenite temperature of the high-temperature shape memory alloy of the shape memory element 10 is above 80°C. The austenite temperature of the high-temperature shape memory alloy of the shape memory element 10 is above 110°C. The high-temperature shape memory alloy of the shape memory element 10 forms a modulated martensite in a second temperature range below the austenite temperature.The modulated martensite of the high-temperature shape memory alloy of the shape memory element 10 has, at least for the most part, a modulated 10M martensite structure and / or a modulated 14M martensite structure. The modulated martensite of the high-temperature shape memory alloy of the shape memory element 10 shown as an example in Fig. 1 is monocrystalline. Alternatively, a polycrystalline formation of the modulated martensite is also conceivable. The second temperature range of the high-temperature shape memory alloy of the shape memory element 10 comprises room temperature. The second temperature range of the high-temperature shape memory alloy of the shape memory element 10 extends at least over a value range between -20°C and the austenite temperature. The high-temperature shape memory alloy of the shape memory element 10 has magnetic field-induced extensibility in the second temperature range.The high-temperature shape memory alloy of the shape memory element 10 has a Curie temperature above 80°C in the second temperature range. The high-temperature shape memory alloy of the shape memory element 10 has a Curie temperature above 110°C in the second temperature range.

[0033] The high-temperature shape memory alloy of the shape memory element 10 is formed by a quaternary NiMnGaFe alloy system. The Ni content of the quaternary NiMnGaFe alloy system of the high-temperature shape memory alloy of the shape memory element 10 illustrated by way of example in Fig. 1 is between 49.9 at.% and 52 at.%. The Mn content of the quaternary NiMnGaFe alloy system of the high-temperature shape memory alloy of the shape memory element 10 illustrated by way of example in Fig. 1 is between 28.4 at.% and 32 at.%. The Ga content of the quaternary NiMnGaFe alloy system of the high-temperature shape memory alloy of the shape memory element 10 illustrated by way of example in Fig. 1 is between 15 at.% and 22 at.%. An Fe content of the quaternary NiMnGaFe alloy system of the high-temperature shape memory alloy of the shape memory element 10 shown as an example in Fig. 1 is between 0.5 at. % and 10 at. %.The quaternary NiMnGaFe alloy system of the high-temperature shape memory alloy of the shape memory element 10 shown as an example in Fig. 1 is cobalt-free.

[0034] The alloy system according to the invention preferably exhibits the advantageous properties over the entire specified variation range, particularly with regard to the Curie temperature, the austenite temperature, and / or the modulation limit temperature. Tests have shown that particularly good results can be achieved with, among others, the parameters / compositions listed in the following table.

[0035] The respective proportions of the composition of the high-temperature shape memory alloy, in particular of the shape memory element 10, can of course also be in the intermediate ranges between the proportions mentioned in the table above or outside the mentioned proportions, but within the claimed limits.

[0036] The proposed high-temperature shape memory alloys are located in a new composition range of the quaternary alloy system NiMnGaFe. Despite the diverse efforts that the international research community has made over many years to develop magnetic high-temperature shape memory alloys, it has not yet been possible to stabilize the modulated martensites at comparably high temperatures. Figure 2 schematically shows a device 12 with an actuator unit 14. The actuator unit 14 has the shape memory element 10. The device is designed as a circuit breaker. Depending on a magnetic field of a conductor 18 through which current flows, the shape memory element 10 of the device 12 contracts or not. Upon contraction of the shape memory element 10, a contact switch 16 of the device 12 opens, thereby interrupting the current flow through the conductor 18.

[0037] Fig. 3 shows a schematic flow diagram of a method for producing the high-temperature shape memory alloy, in particular the shape memory element 10. In at least one alloying step 20, the quaternary NiMnGaFe alloy system of the high-temperature shape memory alloy, in particular the shape memory element 10, is produced by alloying at least the metals nickel, manganese, gallium and iron in appropriate proportions.

[0038] Reference symbol

[0039] 10 Shape memory element

[0040] 12 Device

[0041] 14 Actuator unit

[0042] 16 contact switches

[0043] 18 conductors

[0044] 20 alloying step

Claims

Claims High-temperature shape memory alloy which forms an austenite in a first temperature range above an austenite temperature and which forms a modulated martensite in a second temperature range below the austenite temperature, characterized by an at least quaternary NiMnGaFe alloy system with a Mn content of more than 27.5 at. %, with a Ni content of more than 49.4 at. % and with an Fe content of at least 0.1 at. %. High-temperature shape memory alloy according to claim 1, characterized in that the at least quaternary NiMnGaFe alloy system has a Mn content of at least 28.3 at. %. High-temperature shape memory alloy according to claim 1 or 2, characterized in that the at least quaternary NiMnGaFe alloy system has a Ni content of at least 49.9 at. %.High-temperature shape memory alloy according to one of the preceding claims, characterized in that the austenite temperature is above 80°C, preferably above 90°C, advantageously above 100°C and preferably above 110°C. High-temperature shape memory alloy according to one of the preceding claims, characterized in that the second temperature range comprises room temperature. High-temperature shape memory alloy according to one of the preceding claims, characterized in that the second temperature range extends at least over a value range between -20°C and the austenite temperature. High-temperature shape memory alloy according to one of the preceding claims, characterized in that the modulated martensite has at least a modulated 10M martensite structure and / or a modulated 14M martensite structure, at least to a large extent. High-temperature shape memory alloy according to claim 7, characterized in that the modulated martensite has either only the modulated 10M martensite structure or only the modulated 14M martensite structure over the entire second temperature range.High-temperature shape memory alloy according to one of the preceding claims, characterized in that the Ni content of the at least quaternary NiMnGaFe alloy system is higher than 49.4 at.% and lower than 55 at.%, preferably higher than. 49.9 At.% and lower than 52 At.%.

10. High-temperature shape memory alloy according to one of the preceding claims, characterized in that the Mn content of the at least quaternary NiMnGaFe alloy system is higher than 27.5 at.% and lower than 35 at.%, in particular higher than 27.5 at.% and lower than 32 at.% and preferably higher than 28.4 at.% and lower than 32 at.%.

11. High-temperature shape memory alloy according to one of the preceding claims, characterized in that a Ga content of the at least quaternary NiMnGaFe alloy system is between 1 at.% and 23 at.%, preferably between 15 at.% and 22 at.%.

12. High-temperature shape memory alloy according to one of the preceding claims, characterized in that the Fe content of the at least quaternary NiMnGaFe alloy system is between 0.1 at.% and 22 at.%, preferably between 0.5 at.% and 10 at.%.

13. Shape memory element (10) which is formed at least partially and / or sectionally from a high-temperature shape memory alloy according to one of the preceding claims.

14. Shape memory element (10) according to claim 13, characterized in that at least the modulated martensite of the high-temperature shape memory alloy is polycrystalline or monocrystalline. Shape memory element (10) according to claim 13 or 14, characterized in that the high-temperature shape memory alloy in the second temperature range has a magnetic field-induced extensibility and a Curie temperature above 80°C, preferably above 90°C, advantageously above 100°C and preferably above 110°C. Device (12), for example a circuit breaker, characterized by an actuator unit (14) which comprises at least one shape memory element (10) according to one of claims 13 to 15. Method for producing a high-temperature shape memory alloy according to one of claims 1 to 12, in particular a shape memory element (10) according to one of claims 13 to 15, characterized in that in at least one alloying step (20) the at least quaternary NiMnGaFe- alloy system is produced.

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