NiMnGa magnetostrictive material and preparation method thereof

Abstract

The invention relates to the technical field of magnetic functional materials, in particular to a NiMnGa magnetostrictive material and a preparation method thereof. The NiMnGa magnetostrictive material is a NiMnGa alloy prepared by adjusting the Ga content, so that the prepared NiMnGa alloy has a three-phase coexistence region in which an austenite phase, a pre-martensite phase and a martensite phase coexist; the NiMnGa alloy is subjected to directional solidification at the solidification speed of 4 m / s to 32 m / s, the NiMnGa magnetostrictive material is obtained, and the NiMnGa magnetostrictive material is of a columnar crystal structure preferentially oriented in the [110] crystal orientation. The components of the NiMnGa alloy are regulated and controlled, so that the NiMnGa alloy is close to a three-phase coexistence region of an austenite phase, a pre-martensite phase and a martensite phase, and a texture structure arranged along a specific crystal orientation is formed by adopting a directional solidification technology, so that the magnetostrictive property in a low magnetic field environment is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic functional materials, and in particular to a NiMnGa magnetostrictive material and a preparation method thereof. Background Art

[0002] Magnetostrictive materials are specialized materials that can mechanically deform in response to a magnetic field. Due to their unique physical properties, they hold great promise for applications in sensors, actuators, transducers, and intelligent structures. However, currently, widely used magnetostrictive materials fall into two main categories: one that exhibits large strain but requires a high external magnetic field strength, while the other requires a lower external magnetic field strength but exhibits relatively low strain, significantly limiting their widespread application.

[0003] In recent years, Ni-Mn-Ga Heusler alloys, as a new type of magnetostrictive material, have attracted widespread attention from researchers due to their low cost, good processability, and pronounced magnetic field-induced martensitic transformation. However, the relatively large saturation field of Ni-Mn-Ga alloys limits their application in low magnetic field environments. Therefore, developing new material design strategies and preparation methods to achieve higher magnetostriction values ​​under relatively small external magnetic field excitation has become a key issue in the current research of magnetostrictive materials. Summary of the Invention

[0004] In order to solve the technical problem that the saturation field of the existing Ni-Mn-Ga alloy is relatively large and limits the application effect in a low magnetic field environment, the present invention provides a NiMnGa magnetostrictive material and a preparation method thereof.

[0005] The present invention regulates the composition of the NiMnGa alloy to make it close to the three-phase coexistence zone of austenite phase, pre-martensite phase and martensite phase, and uses directional solidification technology to form a texture structure arranged along a specific crystal direction, thereby significantly improving the magnetostrictive performance in a low magnetic field environment.

[0006] To achieve the above objectives, the technical solutions of the present invention are as follows.

[0007] A first aspect of the present invention provides a method for preparing a NiMnGa magnetostrictive material, comprising the following steps: A NiMnGa alloy is prepared by adjusting the Ga content so that the prepared NiMnGa alloy has a three-phase coexistence zone in which an austenite phase, a pre-martensite phase, and a martensite phase coexist; the NiMnGa alloy is directionally solidified at a solidification rate of 4 m / s to 32 m / s to obtain a NiMnGa magnetostrictive material, and the NiMnGa magnetostrictive material has a columnar crystal structure preferentially oriented along the

[110] crystal direction.

[0008] Preferably, set x % represents the atomic percentage of Ga in NiMnGa alloy, the chemical formula of which is Ni 50 Mn 50x Ga x , among which, 19< x <25.

[0009] Preferably, x The value range is: 21≤ x ≤ 24.

[0010] Preferably, the NiMnGa alloy has a three-phase coexistence zone in which an austenite phase, a pre-martensite phase and a martensite phase coexist at room temperature.

[0011] Preferably, the solidification speed is 6 m / s to 12 m / s.

[0012] Preferably, the method for directional solidification of the NiMnGa alloy is as follows: The Bridgman method is used to heat the NiMnGa alloy to a molten state, and then the molten NiMnGa alloy is moved from the heating zone to the cooling zone at a solidification rate of 4m / s to 32m / s to ensure unidirectional crystallization, forming a columnar crystal structure with preferential orientation along the

[110] crystal direction, thereby obtaining a NiMnGa magnetostrictive material.

[0013] Preferably, the temperature for heating to the molten state is 1400°C to 1650°C.

[0014] A second aspect of the present invention provides a NiMnGa magnetostrictive material, which is prepared using the method for preparing the NiMnGa magnetostrictive material described in the first aspect.

[0015] Preferably, the NiMnGa magnetostrictive material can generate a reversible magnetostrictive strain of ≥790 ppm under a 0.15 T magnetic field.

[0016] Beneficial effects of the present invention: 1. The present invention primarily designs a Ni-Mn-Ga alloy based on the triple point principle, enabling the NiMnGa alloy to possess a three-phase coexistence zone where austenite, pre-martensite, and martensite coexist. Furthermore, by utilizing directional solidification technology and adjusting the solidification rate to form a texture aligned along a specific crystal orientation, the magnetostrictive properties of the prepared NiMnGa magnetostrictive material in a low magnetic field environment are significantly improved, thereby resolving the technical problem that the existing Ni-Mn-Ga alloy has a relatively large saturation field, which limits its application in low magnetic field environments.

[0017] 2. The NiMnGa magnetostrictive material prepared by the present invention can generate a reversible magnetostrictive strain of ≥790 ppm under a magnetic field of 0.15 T; the magnetostriction coefficient is ≥790 ppm, showing good cycle stability at a small saturation field.

[0018] 3. This invention significantly enhances the magnetic-structural coupling effect of NiMnGa magnetostrictive materials, improving magnetostrictive performance and reducing the saturation field, by utilizing a triple-point control mechanism combined with directional solidification technology while ensuring crystal orientation consistency. This method eliminates the need for rare earth elements, resulting in low cost and sustainable resources.

[0019] 4. The NiMnGa magnetostrictive material prepared by the present invention has excellent magnetostrictive performance and good stability, and is suitable for fields such as precision drives and micro-electromechanical systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 For Example 1 of the present invention x = 23 to construct a phase diagram of NiMnGa alloy with a triple point where austenite, premartensite and martensite coexist.

[0021] Figure 2 Ni prepared by directional solidification in Example 1 of the present invention 50 Mn 27 Ga 23 X-ray diffraction pattern of magnetostrictive material.

[0022] Figure 3 Ni prepared in Example 1 50 Mn 27 Ga 23 Magnetostrictive material, Ni prepared in Example 2 50 Mn 28 Ga 22 Magnetostrictive material and Ni prepared in Example 3 50 Mn 26 Ga 24 Comparison of magnetostrictive properties of magnetostrictive materials. Wherein, a represents Ni prepared in Example 3 50 Mn 26 Ga 24 Magnetostrictive performance diagram of magnetostrictive materials; b represents Ni prepared in Example 2 50 Mn 28 Ga 22 Magnetostrictive performance diagram of magnetostrictive materials; c represents Ni prepared in Example 1 50 Mn 27 Ga 23 Graph of the magnetostrictive properties of magnetostrictive materials. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0025] As a new type of magnetostrictive material, Ni-Mn-Ga Heusler alloys offer advantages such as low cost, good processability, and a pronounced magnetic field-induced martensitic transformation. However, the relatively large saturation field of Ni-Mn-Ga alloys limits their application in low magnetic field environments. Therefore, developing new material design ideas and preparation methods to achieve higher magnetostriction values ​​under relatively small external magnetic field excitation has become a key issue in the current research of magnetostrictive materials.

[0026] Prior Art 1: CN108677114A discloses a method for obtaining a recoverable large magnetostrictive effect in NiMnGa polycrystals. Prior Art 1 mainly applies stress to the pre-prepared oriented textured NiMnGa polycrystals in the austenite state along the directional solidification direction to cause the NiMnGa polycrystals to undergo a martensitic phase transformation. By applying pressure at multiple temperature points and repeating the training cycle multiple times, NiMnGa polycrystals with a recoverable large magnetostrictive effect can be obtained. However, the magnetostrictive performance of the NiMnGa polycrystals with a recoverable large magnetostrictive effect prepared by Prior Art 1 is generated in the complete martensite region, and obtaining the recoverable strain requires 50 times of superelastic training in advance. The saturation field of the obtained NiMnGa polycrystals with a recoverable large magnetostrictive effect is large, and the strain obtained under a 1T field is about 0.2%. This shows that the saturation field of NiMnGa polycrystals that can recover the large magnetostrictive effect generated in the complete martensite region by prior art 1 through 50 times of superelastic training is relatively large, which to a certain extent restricts its application effect in low magnetic field environment.

[0027] The magnetostrictive performance of the present invention is near the triple point where the austenite phase, pre-martensite phase and martensite phase coexist. Through the triple point control mechanism and combined with the directional solidification technology, on the basis of ensuring the consistency of the crystal orientation, the magnetic-structural coupling effect of the NiMnGa magnetostrictive material is significantly enhanced, the magnetostrictive performance is improved, and the saturation field is reduced. This is an effective means to realize the engineering application of high-performance magnetostrictive materials.

[0028] The present invention provides a method for preparing a NiMnGa magnetostrictive material, comprising the following steps: Step 1: preparing a NiMnGa alloy by adjusting the Ga content, so that the prepared NiMnGa alloy has a three-phase coexistence zone where an austenite phase, a pre-martensite phase and a martensite phase coexist.

[0029] The specific preparation method is as follows: Step 1.1, weigh Ni, Mn and Ga with purity greater than 99.9%; 50 Mn 50x Ga x The atomic ratio of the alloy is weighed for each metal; where 19< x <25.

[0030] Step 1.2: Prepare Ni by arc melting under argon protection. 50 Mn 50x Ga x The master alloy ingot is smelted 4 to 5 times repeatedly to ensure uniform composition. Specifically: the smelting is carried out in an arc melting furnace under the protection of high-purity argon with a purity of ≥99.999%. The furnace body needs to be pre-evacuated to 5×10 -3 Pa, and fill with high-purity argon gas with a purity of ≥99.999% to 0.05 MPa; turn over and re-melt after each melting, and repeat the melting at least 4 times to ensure uniform composition.

[0031] like Figure 1 As shown, by adjusting the Ga content to x = 23, a triple point where austenite, pre-martensite and martensite coexist is constructed. 50 Mn 27 Ga 23 The atomic ratio of the alloy was weighed; Ni was prepared by arc melting under argon protection. 50 Mn 27 Ga 23 The master alloy ingot is smelted 4 to 5 times repeatedly to ensure uniform composition. 50 Mn 27 Ga 23 Master alloy ingot, and the prepared Ni 50 Mn 27 Ga 23 The master alloy ingot has a three-phase coexistence zone in which an austenite phase, a pre-martensite phase, and a martensite phase coexist.

[0032] Step 2: Directionally solidify the NiMnGa alloy at a solidification rate of 4 m / s to 32 m / s to obtain a NiMnGa magnetostrictive material having a columnar crystal structure preferentially oriented along the

[110] crystal direction.

[0033] The specific preparation method is as follows: The homogenized Ni 50 Mn 27 Ga 23 The master alloy ingot was placed into an 8mm corundum tube and placed in a Bridgman furnace for directional solidification. The directional solidification parameters were set as follows: solidification speed 4m / s to 32m / s, heating temperature 1400°C to 1650°C. A GaIn alloy solution was used for cooling at the cold end to increase the interfacial cooling rate.

[0034] Ni 50 Mn 27 Ga 23 The master alloy ingot is heated until it is completely melted and kept in the melt state for 5 to 10 minutes to ensure uniform melt composition. The sample moving system is started and the crucible is controlled to descend from the heating zone to the cooling zone at a stable rate, at a solidification rate of 4 m / s to 32 m / s to ensure unidirectional crystallization. The primary crystal is formed at the bottom of the corundum tube. As the corundum tube descends, the crystal gradually grows along the temperature gradient direction, preferentially forming the

[110] crystal phase with preferential orientation. During the directional solidification process, the melt interface is slowly moved to control unidirectional growth, preferably forming columnar crystals oriented along the

[110] crystal direction, and preparing Ni 50 Mn 27 Ga 23 Magnetostrictive materials.

[0035] Magnetostrictive tests show that the maximum magnetostrictive strain coefficient is greater than 790 ppm under a magnetic field of 0.15 T. This indicates that the NiMnGa magnetostrictive material prepared by the present invention has excellent magnetostrictive performance and good stability, and is suitable for applications in precision drives, micro-electromechanical systems, and other fields.

[0036] In summary, the present invention modulates the alloy composition to approach the triple point where austenite, pre-martensite, and martensite coexist, thereby stimulating a synergistic response between the material's structure and magnetic properties. By employing a directional solidification process to achieve preferred crystal orientation and optimize the microstructure, the alloy's ability to achieve large magnetostrictive strain under low-field conditions is significantly enhanced. The resulting material is suitable for use in precision magnetostrictive devices such as microactuators and transducers, offering the advantages of high performance, low cost, and repeatability.

[0037] The technical solution of the present invention is further described below through specific embodiments.

[0038] In the following examples, the methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0039] In the following embodiments, the purity of the three metal powders, Ni, Mn, and Ga, is greater than 99.9%.

[0040] Example 1 A method for preparing a NiMnGa magnetostrictive material comprises the following steps: Step 1, follow Ni 50 Mn 27 Ga 23 The atomic ratio of the alloy is to weigh the metal powders; the purity of Ni, Mn and Ga is greater than 99.9%. Ni is prepared by arc melting under argon protection. 50 Mn 27 Ga 23 The master alloy ingot is smelted 4 to 5 times repeatedly to ensure uniform composition; the homogenized Ni 50 Mn 27 Ga 23 Master alloy ingot.

[0041] Step 2: homogenize the Ni 50 Mn 27 Ga 23 The master alloy ingot was placed into an 8mm corundum tube and placed in a Bridgman furnace for directional solidification. The directional solidification parameters were set to: solidification speed 8m / s, heating temperature 1600°C. A GaIn alloy solution was used for cooling at the cold end to increase the interfacial cooling rate.

[0042] Ni 50 Mn 27 Ga 23 The master alloy ingot is heated until it is completely melted and kept in the melt state for 5 to 10 minutes to ensure uniform melt composition. The sample moving system is started and the crucible is controlled to descend from the heating zone to the cooling zone at a stable rate, at a solidification rate of 8 m / s to ensure unidirectional crystallization. The primary crystal is formed at the bottom of the corundum tube. As the corundum tube descends, the crystal gradually grows along the temperature gradient direction, preferentially forming the

[110] crystal phase with preferential orientation. During the directional solidification process, the melt interface is slowly moved to control unidirectional growth, preferably forming columnar crystals oriented along the

[110] crystal direction, and preparing Ni 50 Mn 27 Ga 23 Magnetostrictive materials.

[0043] The Ni prepared in Example 1 50 Mn 27 Ga 23 The magnetostrictive material was analyzed by X-ray diffraction using an X-ray diffractometer. The results are as follows: Figure 2 shown.

[0044] like Figure 2 The X-ray diffraction pattern can confirm that the Ni prepared in Example 1 50 Mn 27 Ga 23The microstructure of magnetostrictive materials is a

[110] crystal phase preferential orientation.

[0045] Example 2 A method for preparing a NiMnGa magnetostrictive material comprises the following steps: Step 1, follow Ni 50 Mn 28 Ga 22 The atomic ratio of the alloy is to weigh the metal powders; the purity of Ni, Mn and Ga is greater than 99.9%. Ni is prepared by arc melting under argon protection. 50 Mn 28 Ga 22 The master alloy ingot is smelted 4 to 5 times repeatedly to ensure uniform composition; the homogenized Ni 50 Mn 28 Ga 22 Master alloy ingot.

[0046] Step 2: homogenize the Ni 50 Mn 28 Ga 22 The master alloy ingot was placed into an 8mm corundum tube and placed in a Bridgman furnace for directional solidification. The directional solidification parameters were set to a solidification speed of 12 m / s and a heating temperature of 1600°C. A GaIn alloy solution was used for cooling the cold end to increase the interfacial cooling rate.

[0047] Ni 50 Mn 28 Ga 22 The master alloy ingot is heated until it is completely melted and kept in the melt state for 5 to 10 minutes to ensure uniform melt composition. The sample moving system is started and the crucible is controlled to descend from the heating zone to the cooling zone at a stable rate, at a solidification rate of 12 m / s to ensure unidirectional crystallization. The primary crystal is formed at the bottom of the corundum tube. As the corundum tube descends, the crystal gradually grows along the temperature gradient direction, preferentially forming the

[110] crystal phase with preferential orientation. During the directional solidification process, the melt interface is slowly moved to control unidirectional growth, preferably forming columnar crystals oriented along the

[110] crystal direction, and Ni is prepared. 50 Mn 28 Ga 22 Magnetostrictive materials.

[0048] Example 3 A method for preparing a NiMnGa magnetostrictive material comprises the following steps: Step 1, follow Ni 50 Mn 26 Ga 24The atomic ratio of the alloy is to weigh the metal powders; the purity of Ni, Mn and Ga is greater than 99.9%. Ni is prepared by arc melting under argon protection. 50 Mn 26 Ga 24 The master alloy ingot is smelted 4 to 5 times repeatedly to ensure uniform composition; the homogenized Ni 50 Mn 26 Ga 24 Master alloy ingot.

[0049] Step 2: homogenize the Ni 50 Mn 26 Ga 24 The master alloy ingot was placed into an 8mm corundum tube and placed in a Bridgman furnace for directional solidification. The directional solidification parameters were set to a solidification speed of 6 m / s and a heating temperature of 1600°C. A GaIn alloy solution was used for cooling the cold end to increase the interfacial cooling rate.

[0050] Ni 50 Mn 26 Ga 24 The master alloy ingot is heated until it is completely melted and kept in the melt state for 5 to 10 minutes to ensure uniform melt composition. The sample moving system is started and the crucible is controlled to descend from the heating zone to the cooling zone at a stable rate, at a solidification rate of 6 m / s to ensure unidirectional crystallization. The primary crystal is formed at the bottom of the corundum tube. As the corundum tube descends, the crystal gradually grows along the temperature gradient direction, preferentially forming the

[110] crystal phase with preferential orientation. During the directional solidification process, the melt interface is slowly moved to control unidirectional growth, preferably forming columnar crystals oriented along the

[110] crystal direction, and preparing Ni 50 Mn 26 Ga 24 Magnetostrictive materials.

[0051] The Ni prepared in Example 1 50 Mn 27 Ga 23 Magnetostrictive material, Ni prepared in Example 2 50 Mn 28 Ga 22 Magnetostrictive material and Ni prepared in Example 3 50 Mn 26 Ga 24 The magnetostrictive material is tested for magnetostrictive performance, and the results are as follows Figure 3 shown.

[0052] Table 1 Magnetostrictive properties of NiMnGa magnetostrictive materials with different Ga contents, 0.1 T magnetic field Note: The magnetostrictive value is the magnetostrictive coefficient.

[0053] Depend on Figure 3 It can be seen that compared with Examples 2 and 3, the Ni 50 Mn 27 Ga 23 The magnetostrictive strain of magnetostrictive material is the largest, the magnetostrictive coefficient is greater than 790ppm, and the saturation field is also small, which is 0.1T. This shows that x =23, the magnetostrictive strain is the largest and the saturation field is also the smallest, indicating that the triple point control mechanism is the most effective.

[0054] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a NiMnGa magnetostrictive material, characterized in that: The following steps are involved: A NiMnGa alloy is prepared by adjusting the Ga content, so that the prepared NiMnGa alloy has a three-phase coexistence zone in which an austenite phase, a pre-martensite phase and a martensite phase coexist; The NiMnGa alloy is directionally solidified at a solidification rate of 4 m / s to 32 m / s to obtain a NiMnGa magnetostrictive material, wherein the NiMnGa magnetostrictive material has a columnar crystal structure preferentially oriented along a [110] crystal direction.

2. The method for preparing the NiMnGa magnetostrictive material according to claim 1, wherein: set up x % represents the atomic percentage of Ga in NiMnGa alloy, the chemical formula of which is Ni 50 Mn 50x Ga x , among which 19 < x < 25.

3. The method for preparing the NiMnGa magnetostrictive material according to claim 2, wherein: x The value range is: 21≤ x ≤ 24.

4. The method for preparing the NiMnGa magnetostrictive material according to claim 1, wherein: The NiMnGa alloy has a three-phase coexistence zone in which an austenite phase, a pre-martensite phase and a martensite phase coexist at room temperature.

5. The method for preparing the NiMnGa magnetostrictive material according to claim 1, characterized in that: The solidification speed is 6m / s to 12m / s.

6. The method for preparing the NiMnGa magnetostrictive material according to claim 1, wherein: The method for directional solidification of the NiMnGa alloy is as follows: The Bridgman method is used to heat the NiMnGa alloy to a molten state, and then the molten NiMnGa alloy is moved from the heating zone to the cooling zone at a solidification rate of 4m / s to 32m / s to ensure unidirectional crystallization, forming a columnar crystal structure with preferential orientation along the [110] crystal direction, thereby obtaining a NiMnGa magnetostrictive material.

7. The method for preparing the NiMnGa magnetostrictive material according to claim 6, characterized in that: The temperature for heating to a molten state is 1400°C to 1650°C.

8. A NiMnGa magnetostrictive material, characterized in that: The magnetostrictive material is prepared by the method for preparing the NiMnGa magnetostrictive material according to any one of claims 1 to 7.

9. The NiMnGa magnetostrictive material according to claim 8, characterized in that The NiMnGa magnetostrictive material can generate a reversible magnetostrictive strain of ≥790 ppm under a 0.15 T magnetic field.

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