Zero hysteresis giant magnetostrictive Ni-Fe-Ga shape memory alloy micro-wire and preparation method thereof

Abstract

This invention relates to the field of shape memory alloy technology, specifically providing a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire and its preparation method. The preparation method of the alloy microwire includes: ① preparing austenitic alloy microwires using a glass coating method; ② inducing the austenite in the microwires into a full martensite structure through stress aging treatment and maintaining it at room temperature; ③ finally introducing some austenite into the martensite alloy microwires through annealing treatment, obtaining a wire material with a stable austenite / martensite coexistence structure at room temperature. The Ni-Fe-Ga ternary shape memory alloy microwires provided by this invention exhibit both zero hysteresis and giant linear elasticity characteristics under external force, with a maximum elastic strain of up to 7.7%, and the preparation method is simple, showing broad application prospects in high-precision micro-actuators and sensing fields.

Description

Technical Field

[0001] This invention relates to the field of shape memory alloy technology, specifically to a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire and its preparation method. Background Technology

[0002] Shape memory alloys can generate hyperelasticity exceeding 5% through thermoelastic martensitic phase transformation. However, since martensitic phase transformation is a first-order phase transformation, the hyperelastic curve inevitably exhibits nonlinearity and large hysteresis characteristics. Hysteresis not only wastes energy but also causes the structure and function of the material to gradually deteriorate during cycling. The nonlinearity of stress-strain can lead to functional instability of the material under critical external fields, resulting in poor control precision as a micro-actuator component. Furthermore, shape memory alloy applications are primarily based on filaments, and flexible filaments offer significant functional advantages compared to bulk materials. Under external field actuation, filaments exhibit high frequency, fast response speed, large output strain, and high flexibility, demonstrating significant functional advantages in fields such as microelectromechanical systems (MEMS), flexible electronics, and smart industry. Therefore, developing zero-hysteresis giant linear elastic shape memory alloy microfilaments is not only of significant scientific importance but also has immense practical value in the field of high-precision sensors.

[0003] While Ni-Fe-Ga shape memory alloys can produce 12% superelasticity, like traditional shape memory alloys, their superelasticity curves also exhibit large hysteresis and nonlinear characteristics. Existing technology discloses a method for preparing Ni-Fe-Ga-Co shape memory alloy microfilaments with high superelasticity, but the stress hysteresis of the prepared microfilaments reaches as high as 20 MPa, resulting in stress / strain instability during phase transformation. Other existing technologies achieve zero-hysteresis superelasticity by adding 20 at.% cobalt to ternary Ni-Fe-Ga shape memory alloy microfilaments, but the nonlinearity of the alloy's stress-strain curve cannot be eliminated. Furthermore, all of these alloys contain high amounts of cobalt. Given that China's cobalt reserves account for only 1% of the global total, and cobalt is a critical strategic resource, the high amount added significantly increases the material's manufacturing cost.

[0004] Based on this, there is an urgent need to develop a simple process for preparing zero-hysteresis giant linear elastic alloy wires in the field of shape memory alloys. At the same time, the developed material does not contain low-reserve elements, so as to meet my country's application needs in the field of precision sensing. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire and its preparation method. By stress aging, the room-temperature stable austenitic structure is transformed into a room-temperature stable martensite structure. Then, by subsequent aging, the martensite is partially transformed back into austenite. The combination of the two results in an alloy with an austenite / martensite fluctuating structure at room temperature, thereby eliminating the first-order phase transformation effect of the structural transformation under stress and helping to obtain zero-hysteresis giant linear elasticity.

[0006] According to a first aspect of the present invention, a method for preparing zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwires is provided, comprising the following steps:

[0007] Step (1): Austenitic alloy microwires were prepared using a glass coating method;

[0008] Step (2): The austenite in the austenitic alloy microwire is induced into a fully martensitic structure by stress aging treatment and retained at room temperature to form a martensitic alloy microwire;

[0009] Step (3): After annealing, some austenite is introduced into the martensitic alloy microwire to obtain zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire with a stable austenite / martensite coexistence structure at room temperature.

[0010] Preferably, step (1) specifically includes: casting the alloy ingot, which has been melted according to the component ratio, into an alloy rod, cutting it into small segments, placing it in a glass tube and heating it until the alloy and the glass tube melt, and quickly drawing the glass-coated alloy melt through cooling water to obtain austenitic alloy microwires.

[0011] Preferably, in step (1), the diameter of the alloy rod is 3-8 mm; the initial state alloy microwire has a single-phase austenitic structure.

[0012] Preferably, step (2) specifically includes:

[0013] (2.1) The austenitic alloy microwires obtained in step (1) are subjected to hyperelastic cycling at a stress aging temperature to determine the stress at which the stress-induced martensitic transformation of the microwires ends at this temperature. and the critical slip stress of martensite

[0014] (2.2) After loading the austenitic alloy microwire obtained in step (1) to a set stress σ, the temperature is increased under the stress condition to carry out stress aging. Then the alloy microwire is quickly cooled to room temperature, and finally the stress is completely unloaded at room temperature to obtain the martensitic alloy microwire.

[0015] Preferably, in step (2.2), the aging temperature is 0.1 to 0.3 times the melting point, i.e., 473 to 673 K, the heating rate is not less than 5 K / min, and the holding time is 20 to 60 min, so as to retain the martensitic structure to room temperature and obtain alloy microwires with a stable martensitic structure at room temperature.

[0016] Preferably, in step (2.2), the aging stress σ is greater than the stress at which the stress-induced martensitic transformation ends at the set aging temperature. Less than the critical slip stress of martensite satisfy Ensure that the alloy microwires have a fully martensitic structure during the aging process, and the stress loading rate is not less than 100 MPa / min.

[0017] Preferably, in step (2.2), the cooling rate is greater than 10 K / min to ensure that the martensite structure in the alloy microwires can be completely preserved to room temperature during the cooling process.

[0018] Preferably, in step (3), the wire has a single-phase martensitic structure after stress unloading.

[0019] Preferably, in step (3), the annealing temperature is greater than the critical nucleation temperature of austenite in the alloy microwire and less than the austenite transformation end temperature, that is, the selected annealing temperature is 353-473K and the annealing time is 5-30min, so as to introduce part of the austenite structure into the all-martensitic alloy microwire, and the cooling rate is greater than 10K / min to ensure that the austenite will not suddenly nucleate during the cooling process.

[0020] According to a second aspect of the present invention, a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire is provided, prepared by the preparation method according to any one of the above aspects, wherein the chemical formula of the alloy microwire is Ni. x Fe y Ga 100-x-y (at.%), where 40≤x≤50, 25≤y≤35;

[0021] Preferably, the diameter of the alloy microwires is between 10 and 900 μm, and they have a stable austenitic / martensite dual-phase structure at room temperature.

[0022] The beneficial effects of this invention are:

[0023] (1) The preparation method is simple and efficient: The Ni-Fe-Ga shape memory alloy microwires provided by this invention are prepared by a combination of glass coating technology and stress aging, which does not require complex thermomechanical processing and is suitable for industrial production.

[0024] (2) Zero hysteresis: The Ni-Fe-Ga shape memory alloy microwires provided by this invention have a single-phase martensite structure after stress aging, and then some austenite is introduced through annealing. During stress loading, the alloy has zero hysteresis linear elasticity. The zero hysteresis performance ensures that the microwires have both zero energy loss and high sensitivity when used as micro-actuators and sensors.

[0025] (3) Giant linear elasticity: The Ni-Fe-Ga shape memory alloy microfilament linear elastic strain energy provided by the present invention reaches as high as 7.7%, which is comparable to the nonlinear large hysteresis hyperelastic strain of traditional Ni-Ti-based shape memory alloys. The large linear elastic strain can provide a larger driving and control stroke in engineering applications, and no functional instability will occur in the driving and control process. At the same time, it can provide a strain matrix for the regulation of material physical and chemical properties based on elastic strain engineering. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 The process flow diagrams for stress aging treatment of Ni-Fe-Ga shape memory alloy microwires in all embodiments provided by the present invention are as follows:

[0028] Figure 2 This is the XRD pattern of the initial state of Ni-Fe-Ga shape memory alloy microwires provided in Example 1 of this invention;

[0029] Figure 3 This is the XRD pattern of Ni-Fe-Ga shape memory alloy microwires provided in Embodiment 1 of the present invention after stress aging;

[0030] Figure 4 The XRD pattern of the Ni-Fe-Ga shape memory alloy microwires provided in Example 1 of this invention after annealing to introduce austenite;

[0031] Figure 5 The stress-strain curve at room temperature of the Ni-Fe-Ga shape memory alloy microwire provided in Example 1 of this invention.

[0032] Figure 6 The XRD pattern of Ni-Fe-Ga shape memory alloy microwires after annealing to introduce austenite, as provided in Example 2 of this invention;

[0033] Figure 7The stress-strain curve at room temperature of the Ni-Fe-Ga shape memory alloy microwire provided in Example 2 of this invention is shown.

[0034] Figure 8 The XRD pattern of Ni-Fe-Ga shape memory alloy microwires after annealing and austenite introduction provided in Embodiment 3 of the present invention;

[0035] Figure 9 The stress-strain curve at room temperature of the Ni-Fe-Ga shape memory alloy microwire provided in Example 3 of this invention is shown.

[0036] Figure 10 The room temperature stress-strain curves of the Ni-Fe-Ga shape memory alloy microwires provided in Comparative Example 1 of this invention are shown.

[0037] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0038] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0039] The terms "first," "second," etc., used in this disclosure are for distinguishing similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such use of terms can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0040] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0041] Multiple, including two or more.

[0042] And / or, it should be understood that, for the purposes of this disclosure, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone.

[0043] Research has shown that the avalanche-like structural transformation of the first-order phase transformation is the origin of the large hysteresis of hyperelasticity and the failure of the stress-strain curve to satisfy Hooke's law. Weakening the strong first-order phase transformation effect during the phase transformation process of shape memory alloys is key to obtaining zero-hysteresis giant linear elasticity. Based on the findings and understanding of the aforementioned problems and facts, the inventors, through extensive research and experimentation, have proposed a unique technical approach to solve the aforementioned technical challenges: stress aging transforms the room-temperature stable austenitic structure into a room-temperature stable martensite structure, and then subsequent aging partially transforms the martensite back into austenite, thereby obtaining an alloy with a room-temperature austenitic / martensite fluctuating structure. This eliminates the first-order phase transformation effect under stress, contributing to the achievement of zero-hysteresis giant linear elasticity.

[0044] Specifically, one embodiment of the technical solution of the present invention provides a method for preparing the aforementioned zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwires, comprising the following steps:

[0045] (1) The alloy ingot, which has been melted according to the component ratio, is cast into an alloy rod with a diameter of, for example, 3-8 mm. The rod is cut into small segments and placed in a glass tube and heated until the alloy and the glass tube melt. The alloy melt covered by the glass is held with tweezers and quickly pulled through cooling water to obtain the initial state alloy microwire. In a preferred embodiment, in step (1), the initial state alloy microwire has a single-phase austenitic structure.

[0046] (2) The alloy microwires obtained in step (1) are subjected to hyperelastic cycling at a stress aging temperature to determine the stress at which the stress-induced martensitic transformation of the microwires ends at this temperature. and the critical slip stress of martensite

[0047] (3) After loading the alloy microwire obtained in step (1) to a set aging stress σ, the temperature is increased under the stress condition to perform stress aging. Then, the alloy microwire is rapidly cooled to room temperature, and finally the stress is completely unloaded at room temperature. In a preferred embodiment, in step (3), the aging temperature is, for example, 0.1 to 0.3 times the melting point, i.e., 473 to 673 K, the heating rate is, for example, not less than 5 K / min, and the holding time is, for example, 20 to 60 min. In a preferred embodiment, in step (3), the aging stress σ is greater than the stress at which the stress-induced martensitic transformation ends at the set aging temperature. Less than the critical slip stress of martensite satisfy To ensure that the alloy microwires have a fully martensitic structure during the aging process, the stress loading rate is not less than 100 MPa / min. In a preferred embodiment, in step (3), the cooling rate is, for example, greater than 10 K / min, to ensure that the martensitic structure in the alloy microwires is completely preserved to room temperature during the cooling process.

[0048] (4) The alloy microwires obtained in step (3) are heated to a certain temperature and annealed for a period of time, and then rapidly cooled to room temperature to obtain the zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwires. In a preferred embodiment, in step (4), the wire has a single-phase martensite structure after stress unloading. In a preferred embodiment, in step (4), the annealing temperature is greater than the critical nucleation temperature of austenite in the alloy microwires and less than the austenite transformation end temperature, i.e., the selected annealing temperature is, for example, 353-473K, and the annealing time is, for example, 5-30min, so as to introduce part of the austenite structure into the fully martensitic alloy microwires, and the cooling rate is, for example, greater than 10K / min, to ensure that austenite does not suddenly nucleate during the cooling process.

[0049] Another embodiment of the technical solution of the present invention provides a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire, wherein the chemical formula of the alloy microwire is Ni. x Fe y Ga 100-x-y (at.%), where 40≤x≤50, 25≤y≤35. In a preferred embodiment, the diameter of the aforementioned alloy microwires is, for example, between 10 and 900 μm, and they have a stable austenitic / martensite dual-phase structure at room temperature.

[0050] Example 1

[0051] This embodiment provides a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire, the chemical formula of which is Ni. 47 Fe 26 Ga 27 (at.%)

[0052] Figure 1 This is a process flow diagram of the stress aging treatment of Ni-Fe-Ga shape memory alloy microwires provided in all embodiments of the present invention. It is intended to help those skilled in the art understand the entire process of the stress aging treatment of Ni-Fe-Ga shape memory alloy microwires provided by the present invention in conjunction with the above description. Figure 1 As shown, the method for preparing Ni-Fe-Ga shape memory alloy microwires includes the following steps:

[0053] (1) Select the corresponding elemental metals nickel, iron, and gallium with a purity of 99.9% or higher according to the component ratio, and place the raw materials in a vacuum chamber with a pressure of 5×10⁻⁶.-3 In an electric arc melting furnace with a pressure below MPa, to prevent the alloy ingot from oxidizing at high temperatures during the melting process, the alloy is repeatedly turned and melted four times while continuously stirring the molten alloy using electromagnetic stirring technology to ensure uniform composition of the alloy ingot. After cooling, the alloy ingot is obtained and cast into an alloy round bar with a diameter of 5mm. The alloy bar is cut into small segments and placed in a glass tube and heated until the alloy and the glass tube melt. The glass-coated alloy melt is quickly pulled through with tweezers and cooled with cooling water to obtain an initial state alloy microwire with an austenitic structure.

[0054] (2) The alloy microwires obtained in step (1) were subjected to superelastic cycling at 473 K to obtain the stress at which the stress-induced martensitic transformation of the alloy microwires ended at this temperature. 700 MPa and the critical martensitic slip stress The pressure is 1200MPa, therefore the time-dependent stress is selected as 1000MPa.

[0055] (3) First, the initial state alloy microwires obtained in step (1) are subjected to stress at a rate of 300 MPa / min up to 1000 MPa to induce a martensitic phase transformation in the alloy. At this time, the alloy microwires have a single-phase martensitic structure, but the martensitic structure is not stable at this time and will completely revert to austenite after unloading. Then, the temperature is increased to 473 K at a rate of 20 K / min, and the microstructure inside the alloy microwires is modulated by stress aging at 473 K and 1000 MPa for 30 min. Then, the temperature is decreased to room temperature at a rate of 20 K / min while maintaining the stress to prevent the sudden nucleation and expansion of austenite in the martensitic structure during the cooling process, and to completely preserve the martensitic structure at room temperature. Finally, the stress is completely unloaded to obtain a room temperature stable state full martensitic alloy microwires.

[0056] (4) The alloy microwires obtained in step (3) are heated to 423K at a rate of 20K / min and annealed for 25min to recover some of the austenite in the alloy microwires. Then, they are cooled to room temperature at a rate of 20K / min to prevent the sudden nucleation and expansion of austenite, thereby obtaining a room temperature stable austenite / martensite dual-phase structure in the alloy microwires, that is, obtaining Ni-Fe-Ga shape memory alloy microwires with zero hysteresis giant linear elasticity.

[0057] Figure 2 The image shows the XRD pattern of the initial state alloy microwire, which has a single-phase B2 austenitic structure at room temperature. Figure 3 The image shows the XRD pattern of the initial state alloy microwire after stress aging treatment. The wire material has a stable single-phase L10 martensite structure at room temperature. Figure 4The image shows the XRD pattern of the zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire obtained in this embodiment. It can be seen that martensite and austenite peaks coexist, indicating that the alloy microwire provided in this embodiment has a room-temperature steady-state austenite and martensite dual-phase structure. Figure 5 The table shows the room temperature stress-strain curve of the zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire obtained in this embodiment. This alloy microwire with an austenitic / martensite dual-phase coupling structure exhibits excellent mechanical properties during loading and unloading, with a linear elastic strain limit of up to 7.7% and perfect zero-hysteresis characteristics.

[0058] Example 2

[0059] This embodiment provides a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire, the chemical formula of which is Ni. 46 Fe 28 Ga 26 (at.%)

[0060] The method for preparing Ni-Fe-Ga shape memory alloy microwires includes the following steps:

[0061] Step (1) in this embodiment is the same as step (1) in embodiment 1;

[0062] (2) The alloy microwires obtained in step (1) were subjected to superelastic cycling at 473 K to obtain the stress at which the stress-induced martensitic transformation of the alloy microwires ended at this temperature. 850 MPa and the critical martensitic slip stress The pressure is 1250 MPa, therefore the time-dependent stress is selected as 1000 MPa.

[0063] (3) First, the initial state alloy microwires obtained in step (1) are subjected to stress at a rate of 300 MPa / min up to 1000 MPa to induce a martensitic transformation in the alloy. At this time, the alloy microwires have a single-phase martensitic structure, but the martensitic structure is not stable at this time and will completely revert to austenite after unloading. Then, the temperature is increased to 523 K at a rate of 20 K / min, and the microstructure inside the alloy microwires is modulated by stress aging at 523 K and 1000 MPa for 20 min. Then, the temperature is decreased to room temperature at a rate of 20 K / min while maintaining the stress to prevent the sudden nucleation and expansion of austenite in the martensitic structure during the cooling process, and to completely preserve the martensitic structure at room temperature. Finally, the stress is completely unloaded to obtain a room temperature stable state full martensitic alloy microwires.

[0064] (4) The alloy microwires obtained in step (3) are heated to 373K at a rate of 20K / min and annealed for 15min to recover some of the austenite in the alloy microwires. Then, they are cooled to room temperature at a rate of 20K / min to prevent the sudden nucleation and expansion of austenite, thereby obtaining a room temperature stable austenite / martensite dual-phase structure in the alloy microwires, that is, obtaining Ni-Fe-Ga shape memory alloy microwires with zero hysteresis giant linear elasticity.

[0065] Figure 6 The image shows the XRD pattern of the zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire obtained in this embodiment. It can be seen that martensite and austenite peaks coexist, indicating that the alloy microwire provided in this embodiment has a room-temperature steady-state austenite and martensite dual-phase structure. Figure 7 The table shows the room temperature stress-strain curve of the zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire obtained in this embodiment. This alloy microwire with an austenitic / martensite dual-phase coupling structure exhibits excellent mechanical properties during loading and unloading, with a linear elastic strain limit of up to 4.2% and perfect zero-hysteresis characteristics.

[0066] Example 3

[0067] This embodiment provides a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire, the chemical formula of which is Ni. 48 Fe 28 Ga 24 (at.%)

[0068] The method for preparing Ni-Fe-Ga shape memory alloy microwires includes the following steps:

[0069] Step (1) in this embodiment is the same as step (1) in embodiment 1;

[0070] (2) The alloy microwires obtained in step (1) were subjected to superelastic cycling at 473 K to obtain the stress at which the stress-induced martensitic transformation of the alloy microwires ended at this temperature. For 600 MPa and the critical martensitic slip stress The pressure is 1150 MPa, therefore the time-dependent stress is selected as 900 MPa.

[0071] (3) First, the initial state alloy microwires obtained in step (1) are subjected to stress at a rate of 300 MPa / min up to 900 MPa to induce a martensitic transformation in the alloy. At this time, the alloy microwires have a single-phase martensitic structure, but the martensitic structure is not stable at this time and will completely revert to austenite after unloading. Then, the temperature is increased to 573 K at a rate of 20 K / min, and the microstructure inside the alloy microwires is modulated by stress aging at 573 K and 900 MPa for 35 min. Then, the temperature is decreased to room temperature at a rate of 20 K / min while maintaining the stress to prevent the sudden nucleation and expansion of austenite in the martensitic structure during the cooling process, and to completely preserve the martensitic structure at room temperature. Finally, the stress is completely unloaded to obtain a room temperature stable state full martensitic alloy microwires.

[0072] (4) The alloy microwires obtained in step (3) are heated to 423K at a rate of 20K / min and annealed for 10min to recover some of the austenite in the alloy microwires. Then, they are cooled to room temperature at a rate of 20K / min to prevent the sudden nucleation and expansion of austenite, thereby obtaining a room temperature stable austenite / martensite dual-phase structure in the alloy microwires, that is, obtaining Ni-Fe-Ga shape memory alloy microwires with zero hysteresis giant linear elasticity.

[0073] Figure 8 The image shows the XRD pattern of the zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire obtained in this embodiment. It can be seen that martensite and austenite peaks coexist, indicating that the alloy microwire provided in this embodiment has a room-temperature steady-state austenite and martensite dual-phase structure. Figure 9 The table shows the room temperature stress-strain curve of the zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire obtained in this embodiment. This alloy microwire with an austenitic / martensite dual-phase coupling structure exhibits excellent mechanical properties during loading and unloading, with a linear elastic strain limit of up to 4% and perfect zero-hysteresis characteristics.

[0074] Comparative Example 1

[0075] Comparative Example 1 provides a Ni-Fe-Ga shape memory alloy microwire, the chemical formula of which is Ni. 47 Fe 26 Ga 27 (at.%)

[0076] Select the corresponding elemental metals nickel, iron, and gallium with a purity of 99.9% or higher according to the component ratio, and place the raw materials into a vacuum chamber at 5×10⁻⁶. -3In an electric arc melting furnace with a pressure below MPa, to prevent the alloy ingot from oxidizing at high temperatures during the melting process, the alloy is repeatedly turned and melted four times while continuously stirring the molten alloy using electromagnetic stirring technology to ensure uniform composition of the alloy ingot. After cooling, the alloy ingot is obtained and then cast into an alloy round bar with a diameter of 5 mm. The alloy bar is cut into small segments and placed in a glass tube and heated until the alloy and the glass tube melt. The glass-coated alloy melt is then quickly pulled through with tweezers and cooled with cooling water to obtain alloy microwires with an austenitic structure.

[0077] Figure 10 The table shows the room temperature stress-strain curves of the initial austenitic Ni-Fe-Ga shape memory alloy microwires obtained in Comparative Example 1. Clearly, compared to the extreme zero hysteresis and excellent linear elasticity exhibited by the stress-strain curves of the zero-hysteresis giant linear elastic alloy microwires provided in Examples 1, 2, and 3, the initial austenitic alloy microwires provided in Comparative Example 1 undergo a first-order phase transformation under stress, and their hyperelastic curves exhibit significant stress hysteresis and nonlinear characteristics. This nonlinear hyperelasticity severely limits the application of alloy microwires in high-precision micro-actuators, while the large stress hysteresis significantly increases driving energy consumption and reduces response sensitivity.

[0078] In summary, this invention provides a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire and its preparation method. The chemical formula of the alloy microwire is Ni. x Fe y Ga 100-x-y (at.%), where 40≤x≤50, 25≤y≤35. The preparation method of this alloy microwire includes: ① preparing austenitic alloy microwires using a glass coating method; ② inducing the austenite in the microwires into a full martensitic structure through stress aging treatment and retaining it to room temperature; ③ finally introducing some austenite into the martensitic alloy microwires through annealing treatment, obtaining a wire with a stable austenite / martensite coexistence structure at room temperature. The Ni-Fe-Ga ternary shape memory alloy microwires provided by this invention exhibit both zero hysteresis and giant linear elasticity characteristics under external force, with a maximum elastic strain of up to 7.7%, and the preparation method is simple, showing broad application prospects in high-precision micro-actuators and sensing fields.

[0079] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0080] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0081] Through the above description of the embodiments, those skilled in the art can clearly understand that the above implementation methods can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0082] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for preparing zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwires, characterized in that, Includes the following steps: Step (1): Austenitic alloy microwires are prepared by glass coating method; specifically, the alloy ingots that have been melted according to the composition ratio are cast into alloy rods, cut into small segments and placed in a glass tube and heated until the alloy and the glass tube melt. The glass-coated alloy melt is quickly drawn and passed through cooling water to obtain austenitic alloy microwires. Step (2): The austenite in the austenitic alloy microwires is induced to transform into a fully martensitic structure through stress aging treatment and maintained at room temperature to obtain martensitic alloy microwires; specifically including: (2.1) The austenitic alloy microwires obtained in step (1) are subjected to superelastic cycling at a stress aging temperature to determine the stress at which the stress-induced martensitic transformation of the microwires ends at this temperature. ; (2.2) The austenitic alloy microwires obtained in step (1) are loaded to a set time-dependent stress. Then, under sustained stress conditions, the temperature was increased to induce stress aging, followed by rapid cooling of the alloy microwire to room temperature. Finally, the stress was completely unloaded at room temperature to obtain martensitic alloy microwires. The aging temperature was 473–673 K, the heating rate was not less than 5 K / min, and the holding time was 20–60 min. The stress at which the martensitic transformation ends is greater than the stress induced at the set aging temperature. Less than the critical slip stress of martensite ,satisfy The stress loading rate is not less than 100 MPa / min; the cooling rate is greater than 10 K / min; Step (3): After annealing, some austenite is introduced into the martensitic alloy microwire to obtain zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire with a stable austenite / martensite coexistence structure at room temperature; wherein, the annealing temperature is 353~473 K, the annealing time is 5~30 min, and the cooling rate is greater than 10 K / min.

2. The preparation method according to claim 1, characterized in that, In step (1), the diameter of the alloy rod is 3~8 mm; the initial state alloy microwire has a single-phase austenitic structure.

3. The preparation method according to claim 1, characterized in that, In step (3), the wire material has a single-phase martensitic structure after stress unloading.

4. A zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire prepared by the preparation method according to any one of claims 1 to 3, characterized in that, The chemical formula of the alloy microwire is Ni. x Fe y Ga 100-x-y (at.%), where 40 ≤ x ≤ 50, 25 ≤ y ≤ 35; The alloy microwires have a diameter between 10 and 900 μm and exhibit a stable austenitic / martensite dual-phase structure at room temperature.

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