Nickel-titanium alloy with variable thermal expansion, preparation method and use method

Abstract

The invention relates to the technical field of alloys, and particularly discloses a preparation method of a thermal expansion variable nickel-titanium alloy, which comprises the following steps of: S1, preparing a NiTi alloy by taking a simple substance Ni and a simple substance Ti as raw materials according to the stoichiometric ratio of Ni to Ti being (50.3-51.7): (48.3-49.7); s2, carrying out annealing treatment on the NiTi alloy prepared in the step S1, and then carrying out solution treatment; s3, the NiTi alloy obtained in the step S2 is fixed in a mold, tensile stress or compressive stress is applied, and the strain value is 1-2%; and aging treatment is carried out under the action of keeping constant stress, and the thermal expansion variable nickel-titanium alloy is obtained. The nickel-titanium alloy prepared by adopting the method has positive thermal expansion, negative thermal expansion and zero thermal expansion properties along with the change of temperature under the action of no external force, meets diversified application scenes, and particularly has a great application prospect in the development of some temperature-sensitive precision parts.

Description

Technical Field

[0001] The present invention relates to the field of alloy technology, and in particular to a nickel-titanium alloy with variable thermal expansion, a preparation method and a use method thereof. Background Art

[0002] Thermal expansion and contraction are universal phenomena exhibited by most materials in nature. This phenomenon arises from the anharmonic vibrations of the atoms, ions, or molecules that make up the material as temperature changes. This vibration amplitude increases with increasing temperature, leading to geometric expansion of the material (a positive thermal expansion effect). However, certain material systems, such as ceramics, oxides, ferroelectric / ferromagnetic materials, and nickel-titanium alloys, may exhibit abnormally low or even negative thermal expansion due to unique physical mechanisms in their microstructures (e.g., phase transitions, magnetostriction, low-dimensional structural vibrations, or coupling effects of framework structures).

[0003] Based on the above characteristics, the existing technology usually achieves the regulation of the overall thermal expansion coefficient of the material by compounding negative thermal expansion materials with positive thermal expansion materials, and utilizing the mutual offsetting effect of the thermal expansion coefficients of the two, thereby obtaining zero thermal expansion or controllable thermal expansion materials. For example, by adjusting the composite ratio or optimizing the microstructure, the material can exhibit near-zero thermal expansion behavior within a specific temperature range. However, the performance of such composite materials is usually limited by the fixedness of their components and structures, resulting in the inability to dynamically adjust their thermal expansion characteristics under a single working condition. In other words, it is difficult for existing material systems to achieve temperature-dependent multi-mode thermal expansion responses (such as on-demand switching of positive thermal expansion, zero thermal expansion, and negative thermal expansion) in the same material, thereby limiting its application in complex environments or multifunctional devices.

[0004] With the increasing demand for material thermal stability in fields such as precision instruments, aerospace, electronic packaging, and smart devices, the development of new smart materials that can autonomously adjust their thermal expansion behavior under different temperatures or external stimuli is of great significance. Therefore, it is urgent to design materials with the ability to reversibly regulate thermal expansion properties, enabling them to dynamically switch between positive, zero, or negative thermal expansion states according to actual needs, to meet the demand for precise control of material thermal expansion properties in diverse application scenarios. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for preparing a nickel-titanium alloy with variable thermal expansion. The prepared nickel-titanium alloy has reversible thermal expansion properties to meet the requirements of the material's thermal expansion properties under different conditions.

[0006] To achieve the above objectives, the present invention provides a method for preparing a nickel-titanium alloy with variable thermal expansion, comprising the following steps: S1. Using elemental Ni and elemental Ti as raw materials, a NiTi alloy was prepared according to the stoichiometric atomic ratio of Ni:Ti of 50.3-51.7:49.7-48.3; S2, annealing the NiTi alloy prepared in step S1 and then performing a solid solution treatment; S3, fixing the NiTi alloy obtained in step S2 in a mold, applying external force, and performing aging treatment while maintaining constant stress, thereby obtaining the nickel-titanium alloy with variable thermal expansion; In step S3, the applied external force is tensile stress or compressive stress, and the strain value is 1-2%.

[0007] The present invention provides a method for preparing a nickel-titanium alloy with variable thermal expansion. The nickel-titanium alloy produced using this method can exhibit positive, negative, and zero thermal expansion properties as the temperature changes without the influence of external forces, meeting diverse application scenarios and showing great potential for the development of temperature-sensitive precision parts.

[0008] Preferably, in step S1, the elemental Ni and the elemental Ti are both bulk raw materials, and the purity is not less than 99.5 wt.%.

[0009] Preferably, in step S2, the annealing treatment is performed at a temperature of 600-650° C. and for a time of 8-10 hours.

[0010] Preferably, in step S2, the temperature of the solution treatment is 850-950° C., and the time is 1-3 hours.

[0011] Preferably, in step S3, the aging treatment conditions are: When the atomic ratio of Ni:Ti is 50.3-50.8:49.7-49.2, the aging treatment temperature is 330-350°C and the time is 10-15h; Or, when the atomic ratio of Ni:Ti is 50.8-51.2:49.2-48.8, the aging treatment temperature is 310-330°C and the time is 7-12h; Alternatively, when the atomic ratio of Ni:Ti is 51.2-51.7:48.8-48.3, the aging treatment temperature is 290-310° C., and the aging treatment time is 4-9 hours.

[0012] The present invention also discloses a nickel-titanium alloy with variable thermal expansion, prepared using any of the aforementioned preparation methods. The nickel-titanium alloy of the present invention exhibits reversible thermal expansion properties. In the absence of external forces, the material exhibits positive thermal expansion, negative thermal expansion, and zero thermal expansion as the temperature changes.

[0013] The present invention also discloses a method for using the nickel-titanium alloy with variable thermal expansion in temperature-sensitive components, which further includes the following steps: first heating the nickel-titanium alloy to a fully austenitized temperature A f above, and then cooled to the first standard temperature T1.

[0014] Preferably, in the above-mentioned method of use, when the applied external force is tensile stress, when the temperature deviates from T1, the nickel-titanium alloy expands; or, when the applied external force is compressive stress, when the temperature deviates from T1, the nickel-titanium alloy contracts.

[0015] The present invention also discloses another method for using the nickel-titanium alloy with variable thermal expansion in temperature-sensitive components, comprising the following steps: first cooling the nickel-titanium alloy to a complete martensitic temperature M f Below, and then the temperature is raised to the second standard temperature T2.

[0016] Preferably, in the above-mentioned method of use, when the applied external force is tensile stress, when the temperature deviates from T2, the nickel-titanium alloy expands; or, when the applied external force is compressive stress, when the temperature deviates from T2, the nickel-titanium alloy contracts.

[0017] The reversible expansion or contraction of the nickel-titanium alloy under temperature changes can be used to prepare temperature-sensitive components, and the response accuracy can reach the micron level.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The preparation method provided by the present invention can be used to prepare a new intelligent material with the ability to control reversible thermal expansion properties. The nickel-titanium alloy can dynamically switch between positive thermal expansion, zero thermal expansion, and negative thermal expansion states as the temperature changes without external force.

[0019] (2) The nickel-titanium alloy can be used in temperature-sensitive bias temperature devices. When the nickel-titanium alloy that has been specially treated deviates from the standard temperature, it will have the same expansion or contraction state change regardless of whether the temperature is increased or decreased, and its application prospects are broad. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 is a thermal expansion cycle curve of the nickel-titanium alloy of Example 1; Figure 2 is a thermal expansion cycle curve diagram of nickel-titanium alloy in Example 2; Figure 3 is a thermal expansion cycle curve of nickel-titanium alloy of comparative example 1; Figure 4 This is the thermal expansion cycle curve of the nickel-titanium alloy of comparative example 2.

[0022] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other unless there is a conflict. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0024] A method for preparing a nickel-titanium alloy with variable thermal expansion comprises the following steps: S1. Using bulk elemental Ni and bulk elemental Ti with a purity of not less than 99.5 wt.% as raw materials, a NiTi alloy is prepared according to a stoichiometric atomic ratio of Ni:Ti of 50.3-51.7:49.7-48.3; S2, annealing the NiTi alloy prepared in step S1 at a temperature of 600-650° C. for 8-10 h; then performing a solution treatment at a temperature of 850-950° C. for 1-3 h; S3. Fixing the NiTi alloy obtained in step S2 in a mold, applying tensile stress or compressive stress with a strain value of 1-2%, and performing aging treatment while maintaining the constant stress to obtain the nickel-titanium alloy with variable thermal expansion; Aging treatment conditions are: When the atomic ratio of Ni:Ti is 50.3-50.8:49.7-49.2, the aging treatment temperature is 330-350°C and the time is 10-15h; Or, when the atomic ratio of Ni:Ti is 50.8-51.2:49.2-48.8, the aging treatment temperature is 310-330°C and the time is 7-12h; Alternatively, when the atomic ratio of Ni:Ti is 51.2-51.7:48.8-48.3, the aging treatment temperature is 290-310° C., and the aging treatment time is 4-9 hours.

[0025] In step S1, the alloy preparation process can adopt the alloy preparation method known in the art, such as arc melting, induction melting, arc fuse, etc. The quenching medium in steps S2 and S3 is water.

[0026] Through the aforementioned preparation process, the present invention allows two differently oriented Ni4Ti3 precipitated phase variants to coexist in the nickel-titanium alloy. The coherent Ni4Ti3 precipitated phase causes lattice distortion in the surrounding area, generating a directional internal stress field, which in turn induces a martensitic phase transformation with varying orientations. This structural feature allows for the relative regulation of the size and number density of the two types of Ni4Ti3 precipitated phase variants by adjusting the type of applied load and aging conditions, thereby controlling the expansion or contraction behavior of the nickel-titanium alloy during heating or cooling, and adjusting the characteristic temperature and deformation amplitude of the transition between positive and negative thermal expansion behaviors.

[0027] It should be noted that the elemental Ni and elemental Ti used in the preparation process of the present invention are both bulk raw materials and cannot be used as powdered raw materials. Alloy samples prepared using powdered materials have large pores, blurred grain boundaries that are difficult to distinguish, discontinuous structures, and low density. In addition, samples prepared using powdered Ni and Ti as raw materials exhibit brittle fracture and poor mechanical properties.

[0028] The present invention also discloses a nickel-titanium alloy prepared using the above-mentioned preparation method. The thermal expansion properties of the nickel-titanium alloy change with temperature, exhibiting positive thermal expansion, negative thermal expansion, and zero thermal expansion properties on the same material. Specifically, the following are the manifestations: When the applied external force is tensile stress, the nickel-titanium alloy first shows the characteristics of contraction and then expansion during the cooling and heating processes. Specifically, the obtained nickel-titanium alloy is first heated to above the complete austenitization temperature. In the subsequent cooling process, the nickel-titanium alloy first contracts and then expands. During this process, the nickel-titanium alloy first exhibits positive thermal expansion characteristics, and then exhibits negative thermal expansion characteristics, and has approximately zero thermal expansion characteristics near the transition point. If the obtained nickel-titanium alloy is first cooled to below the complete martensitization temperature, in the subsequent heating process, the nickel-titanium alloy still contracts and then expands. During this process, the nickel-titanium alloy first exhibits negative thermal expansion characteristics, and then exhibits positive thermal expansion characteristics, and has approximately zero thermal expansion characteristics near the transition point.

[0029] When the applied external force is compressive stress, the nickel-titanium alloy first expands and then contracts during both the cooling and heating processes. Specifically, the obtained nickel-titanium alloy is first heated to above the complete austenitizing temperature. In the subsequent cooling process, the nickel-titanium alloy first expands and then contracts. During this process, the nickel-titanium alloy first exhibits negative thermal expansion characteristics, then exhibits positive thermal expansion characteristics, and has approximately zero thermal expansion characteristics near the transition point. The obtained nickel-titanium alloy is first cooled to below the complete martensitizing temperature. In the subsequent heating process, the nickel-titanium alloy still expands and then contracts. During this process, the nickel-titanium alloy first exhibits positive thermal expansion characteristics, then exhibits negative thermal expansion characteristics, and has approximately zero thermal expansion characteristics near the transition point.

[0030] The present invention also discloses a method for using the nickel-titanium alloy in temperature-sensitive components. For example, when used in a temperature-sensitive biasing device, the method further includes heating the nickel-titanium alloy and then cooling it, or cooling it and then heating it.

[0031] The process of heating first and then cooling includes the following steps: first heating the nickel-titanium alloy to the complete austenitization temperature A f The temperature is then lowered to the first standard temperature T1. At this point, the nickel-titanium alloy may experience two conditions: If the external force applied during preparation is tensile stress, the nickel-titanium alloy will expand when the temperature deviates from the first standard temperature T1, regardless of whether the temperature is increased or decreased. If the external force applied during preparation is compressive stress, the nickel-titanium alloy will contract when the temperature deviates from the first standard temperature T1, regardless of whether the temperature is increased or decreased.

[0032] Alternatively, a process of first cooling and then heating can be used, including the following steps: first cooling the nickel-titanium alloy to the complete martensitic temperature M f The temperature is then raised to a second standard temperature T2. At this point, the nickel-titanium alloy also has two scenarios: When the external force applied during the preparation of the nickel-titanium alloy is tensile stress, the nickel-titanium alloy will expand when the temperature deviates from the second standard temperature T2, regardless of whether the temperature is increased or decreased. When the external force applied during the preparation of the nickel-titanium alloy is compressive stress, the nickel-titanium alloy will contract when the temperature deviates from the second standard temperature T2, regardless of whether the temperature is increased or decreased.

[0033] Regardless of whether the applied external force is tensile stress or compressive stress, the second standard temperature T2 is always greater than the first standard temperature T1.

[0034] The following examples are further listed to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters of the following examples are also only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not intended to be limited to the specific numerical values ​​of the examples below. For those in the examples where specific conditions are not specified, proceed according to conventional conditions or the conditions recommended by the manufacturer.

[0035] Example 1 A method for preparing a nickel-titanium alloy with variable thermal expansion comprises the following steps: S1. Using bulk elemental Ni and bulk elemental Ti with a purity of not less than 99.5 wt.% as raw materials, a nickel-titanium alloy is prepared according to a stoichiometric ratio of Ni:Ti of 51:49; S2, annealing the nickel-titanium alloy prepared in step S1 at a temperature of 600° C. for 10 h, and then performing a solution treatment at a temperature of 850° C. for 3 h; S3, fix the nickel-titanium alloy obtained in step S2 in a mold, apply compressive stress, and strain value is 2%. Under the action of constant stress, perform aging treatment at a temperature of 325°C and a time of 10 hours; thus, obtain the Ni-Ti alloy with variable thermal expansion. 51 Ti 49 alloy.

[0036] Test Ni 51 Ti 49 The alloy's thermal expansion changes during heating and cooling cycles. The test method is as follows: 1. Cyclic change of thermal expansion during heating: First, Ni 51 Ti 49 The alloy is cooled to below the complete martensitic temperature -80℃, and then the temperature is raised. The Ni 51 Ti 49 Dimensional changes in alloys.

[0037] 2. Cooling thermal expansion cycle change: First, Ni 51 Ti 49 The alloy is heated to a fully austenitized temperature of 80°C and then begins to cool down. The Ni 51 Ti 49 Dimensional changes in alloys.

[0038] The test results are as follows Figure 1 As shown. Referring to the heating curve, Ni 51 Ti49 The alloy first expands when it is heated from -80℃ to the second standard temperature of 55℃, showing positive thermal expansion characteristics. It reaches a critical point at the second standard temperature of 55℃, with approximately zero thermal expansion characteristics. Then, when the temperature continues to rise from the second standard temperature of 55℃ to 72℃, Ni 51 Ti 49 The alloy begins to shrink and exhibits negative thermal expansion characteristics. 51 Ti 49 When the alloy is in the second standard temperature of 55℃, whether it is heated or cooled, Ni 51 Ti 49 All alloys will shrink. 51 Ti 49 The alloy also expands first when it is cooled from 56℃ to the first standard temperature of 31℃, showing negative thermal expansion characteristics. It reaches the critical point at the first standard temperature of 31℃, with approximately zero thermal expansion characteristics. Then, when it continues to cool from the first standard temperature of 31℃ to -80℃, Ni 51 Ti 49 The alloy begins to shrink and exhibits positive thermal expansion characteristics. 51 Ti 49 When the alloy is in the first standard temperature of 31℃, whether it is heated or cooled, Ni 51 Ti 49 All alloys will shrink.

[0039] Example 2 A method for preparing a nickel-titanium alloy with variable thermal expansion comprises the following steps: S1. Using bulk elemental Ni and bulk elemental Ti with a purity of not less than 99.5 wt.% as raw materials, a nickel-titanium alloy is prepared according to a stoichiometric ratio of Ni:Ti of 51:49; S2, annealing the nickel-titanium alloy prepared in step S1 at a temperature of 600° C. for 10 h, and then performing a solution treatment at a temperature of 850° C. for 3 h; S3, fix the nickel-titanium alloy obtained in step S2 in a mold, apply tensile stress, and strain value is 2%. Under the action of constant stress, perform aging treatment at 325℃ and time for 10h; thus, obtain the Ni-Ti alloy with variable thermal expansion. 51 Ti 49 alloy.

[0040] Test Ni 51 Ti 49 The alloy's thermal expansion changes during heating and cooling cycles. The test method is as follows: 1. Cyclic change of thermal expansion during heating: First, Ni 51Ti 49 The alloy is cooled to below the complete martensitic temperature -80℃, and then the temperature is raised. The Ni 51 Ti 49 Dimensional changes in alloys.

[0041] 2. Cooling thermal expansion cycle change: First, Ni 51 Ti 49 The alloy is heated to a fully austenitized temperature of 80°C and then begins to cool down. The Ni 51 Ti 49 Dimensional changes in alloys.

[0042] The test results are as follows Figure 2 As shown. Referring to the heating curve, Ni 51 Ti 49 The alloy first contracts when it is heated from -21℃ to the second standard temperature of 42℃, showing negative thermal expansion characteristics. It reaches a critical point at the second standard temperature of 42℃, with approximately zero thermal expansion characteristics. Then, when the temperature continues to rise from the second standard temperature of 42℃ to 80℃, Ni 51 Ti 49 The alloy begins to expand, showing positive thermal expansion characteristics. 51 Ti 49 When the alloy is at the second standard temperature of 42℃, whether the temperature is increased or decreased, Ni 51 Ti 49 All alloys will expand. 51 Ti 49 The alloy also contracts when it is cooled from 80℃ to the first standard temperature of 20℃, showing positive thermal expansion characteristics. It reaches the critical point at the first standard temperature of 20℃, with approximately zero thermal expansion characteristics. Then, when it continues to cool from the first standard temperature of 20℃ to -37℃, Ni 51 Ti 49 The alloy begins to expand, showing negative thermal expansion characteristics. 51 Ti 49 When the alloy is in the first standard temperature of 20℃, whether it is heated or cooled, Ni 51 Ti 49 All alloys will expand.

[0043] Comparative Example 1 A method for preparing a nickel-titanium alloy comprises the following steps: S1. Using bulk elemental Ni and bulk elemental Ti with a purity of not less than 99.5 wt.% as raw materials, a nickel-titanium alloy is prepared according to a stoichiometric ratio of Ni:Ti of 50:50; S2, annealing the nickel-titanium alloy prepared in step S1 at a temperature of 600° C. for 10 h, and then performing a solution treatment at a temperature of 850° C. for 3 h; S3, fix the nickel-titanium alloy obtained in step S2 in a mold, apply compressive stress, and strain value is 2%. Under the action of constant stress, perform aging treatment at 330℃ and time for 10h; thus, obtain Ni 50 Ti 50 alloy.

[0044] Test Ni 50 Ti 50 The alloy's thermal expansion changes during heating and cooling cycles. The test method is as follows: 1. Cyclic change of thermal expansion during heating: First, Ni 50 Ti 50 The alloy is cooled to below the complete martensitic temperature -80℃, and then the temperature is raised. The Ni 50 Ti 50 Dimensional changes in alloys.

[0045] 2. Cooling thermal expansion cycle change: First, Ni 50 Ti 50 The alloy is heated to a fully austenitized temperature of 80°C and then begins to cool down. The Ni 50 Ti 50 Dimensional changes in alloys.

[0046] The test results are as follows Figure 3 As shown. Referring to the heating curve, Ni 50 Ti 50 When the alloy is heated from -80℃ to 80℃, Ni 50 Ti 50 The alloy expands and always shows positive thermal expansion characteristics. 50 Ti 50 When the alloy is cooled from 80℃ to -80℃, Ni 50 Ti 50 The alloy contracts and also always exhibits positive thermal expansion characteristics.

[0047] Comparative Example 2 A method for preparing a nickel-titanium alloy comprises the following steps: S1. Using bulk elemental Ni and bulk elemental Ti with a purity of not less than 99.5 wt.% as raw materials, a nickel-titanium alloy is prepared according to a stoichiometric ratio of Ni:Ti of 51:49; S2, annealing the nickel-titanium alloy prepared in step S1 at a temperature of 600° C. for 10 h, and then performing a solution treatment at a temperature of 850° C. for 3 h; S3, fix the nickel-titanium alloy obtained in step S2 in a mold, apply tensile stress, and strain value is 2%. Under the action of constant stress, perform aging treatment at 400℃ and time for 10h; thus, obtain NiTi alloy. 51 Ti 49 alloy.

[0048] Test Ni 51 Ti 49 The alloy's thermal expansion changes during heating and cooling cycles. The test method is as follows: 1. Cyclic change of thermal expansion during heating: First, Ni 51 Ti 49 The alloy is cooled to below the complete martensitic temperature -80℃, and then the temperature is raised. The Ni 51 Ti 49 Dimensional changes in alloys.

[0049] 2. Cooling thermal expansion cycle change: First, Ni 51 Ti 49 The alloy is heated to a fully austenitized temperature of 80°C and then begins to cool down. The Ni 51 Ti 49 Dimensional changes in alloys.

[0050] The test results are as follows Figure 4 As shown. Referring to the heating curve, Ni 51 Ti 49 When the alloy is heated from -80℃ to 80℃, Ni 51 Ti 49 The alloy expands and always shows positive thermal expansion characteristics. 51 Ti 49 When the alloy is cooled from 80℃ to -80℃, Ni 51 Ti 49 The alloy contracts and also always exhibits positive thermal expansion characteristics.

[0051] It can be seen from Comparative Examples 1 and 2 that the nickel-titanium alloy with variable thermal expansion as described in the present invention cannot be obtained by changing the atomic ratio of elemental Ni and elemental Ti, or by changing the aging treatment conditions.

[0052] In summary, the nickel-titanium alloy provided by the present invention has positive thermal expansion, zero thermal expansion and negative thermal expansion properties in the same material. This property breaks through the limitation that most materials in the existing technology only have a single, fixed thermal expansion coefficient, and provides a new option for applications in precision instruments with strict requirements on dimensional stability, such as optical instruments, aerospace, and microelectronic devices. More importantly, the existing technology usually uses negative thermal expansion materials and positive thermal expansion materials to compositely control the thermal expansion coefficient to obtain materials with close to zero thermal expansion. However, due to the limitations of material properties and technical means, the temperature range applicability is extremely narrow, and it can usually only have zero thermal expansion performance at deep low temperatures (such as below -50°C or even liquid nitrogen temperature zone). It is seriously out of touch with the room temperature or near room temperature (20~40°C) use environment generally required by ground optical instruments, consumer electronics, low-Earth orbit spacecraft or human implant devices, which greatly restricts its practical application value. The data from the above embodiments show that the present invention changes the type, size, and density of precipitated phase transitions within the material, as well as the corresponding stress field distribution, phase transition distribution, and phase transition strain orientation, so that the thermal expansion behavior of the local lattice within the material at the microscopic scale can spontaneously and reversibly compensate for each other, so that the macroscopic thermal expansion coefficient at a specific transition temperature (20~55°C) can be precisely "tuned" to near zero, achieving zero thermal expansion in the room temperature range. This temperature range is highly consistent with the daily living environment of humans, the operating temperature of many precision electronic equipment, and the temperature fluctuation range of the near-Earth space environment, greatly broadening the application boundaries.

[0053] On the other hand, by utilizing the dynamic characteristics of the temperature curve of the nickel-titanium alloy described in the present invention, when its temperature deviates from the transition temperature, the material contracts or expands, realizing efficient conversion of temperature to mechanical displacement, and its response accuracy can reach the micron level. This makes it an ideal core material for temperature-sensitive bias temperature devices (such as precision temperature control actuators, safety valves, micro-drivers, etc.). In practical applications, the transition temperature and bias temperature action state can be adjusted by adjusting the alloy composition, aging temperature and time parameters, selecting tensile stress or compressive stress, performing austenite initialization or martensite initialization, and adjusting the transition temperature. This allows engineers to "customize" the response characteristics of the material, thereby perfectly adapting to different application scenarios.

[0054] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention specification under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a nickel-titanium alloy with variable thermal expansion, characterized in that: The steps include: S1. Using elemental Ni and elemental Ti as raw materials, a NiTi alloy was prepared according to the stoichiometric atomic ratio of Ni:Ti of 50.3-51.7:49.7-48.3; S2, annealing the NiTi alloy prepared in step S1 and then performing a solid solution treatment; S3, fixing the NiTi alloy obtained in step S2 in a mold, applying external force, and performing aging treatment while maintaining constant stress, thereby obtaining the nickel-titanium alloy with variable thermal expansion; In step S3, the applied external force is tensile stress or compressive stress, and the strain value is 1-2%.

2. The method for preparing a nickel-titanium alloy with variable thermal expansion according to claim 1, wherein: In step S1, the elemental Ni and the elemental Ti are both bulk raw materials, and the purity is not less than 99.5 wt.%.

3. The method for preparing a nickel-titanium alloy with variable thermal expansion according to claim 1, wherein: In step S2, the annealing treatment is performed at a temperature of 600-650° C. for 8-10 hours.

4. The method for preparing a nickel-titanium alloy with variable thermal expansion according to claim 1, wherein: In step S2, the temperature of the solution treatment is 850-950° C., and the time is 1-3 hours.

5. The method for preparing a nickel-titanium alloy with variable thermal expansion according to claim 1, wherein: In step S3, the aging treatment conditions are: When the atomic ratio of Ni:Ti is 50.3-50.8:49.7-49.2, the aging treatment temperature is 330-350°C and the time is 10-15h; Or, when the atomic ratio of Ni:Ti is 50.8-51.2:49.2-48.8, the aging treatment temperature is 310-330°C and the time is 7-12h; Alternatively, when the atomic ratio of Ni:Ti is 51.2-51.7:48.8-48.3, the aging treatment temperature is 290-310° C., and the aging treatment time is 4-9 hours.

6. A nickel-titanium alloy with variable thermal expansion, characterized in that: The product is prepared by the preparation method described in any one of claims 1 to 5.

7. A method for using the nickel-titanium alloy with variable thermal expansion according to claim 6 in temperature-sensitive components, characterized in that: The method further comprises the following steps: heating the nickel-titanium alloy to a completely austenitizing temperature A f above, and then cooled to the first standard temperature T1.

8. A method of use according to claim 7, characterized in that: When the applied external force is tensile stress, when the temperature deviates from T1, the nickel-titanium alloy expands; Alternatively, when the applied external force is compressive stress, when the temperature deviates from T1, the nickel-titanium alloy contracts.

9. A method for using the nickel-titanium alloy with variable thermal expansion according to claim 6 in temperature-sensitive components, characterized in that: The nickel-titanium alloy is first cooled to a complete martensitic temperature M f Below, and then the temperature is raised to the second standard temperature T2.

10. A method of use according to claim 9, characterized in that: When the applied external force is tensile stress, when the temperature deviates from T2, the nickel-titanium alloy expands; Alternatively, when the applied external force is compressive stress, when the temperature deviates from T2, the nickel-titanium alloy contracts.

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