A NiMn-based polycrystalline alloy and its preparation method and application

Abstract

The present invention provides a NiMn-based polycrystalline alloy and its preparation method and application. The preparation method comprises melting alloy raw materials to obtain a cast alloy, spray-casting the cast alloy to obtain a polycrystalline alloy ingot, and homogenizing the polycrystalline alloy ingot to obtain the NiMn-based polycrystalline alloy. The preparation process provided by the present invention is simple and controllable. The prepared NiMn-based polycrystalline alloy has few internal defects in the grains, a high degree of homogenization, and can achieve a rapid martensitic phase transformation. The magnetocaloric properties of the NiMn-based polycrystalline alloy are enhanced through the coupling of magnetic and structural phase transformations.

Description

Technical Field

[0001] The present invention belongs to the field of Heusler alloy material processing, specifically relates to a ferromagnetic shape memory alloy material, and in particular relates to a NiMn-based polycrystalline alloy and a preparation method and application thereof. Background Art

[0002] The environment and energy have always been hot topics of concern. To alleviate the environmental burden of the greenhouse effect and respond to the advocacy of energy conservation, emission reduction, and green environmental protection, the industry urgently needs to develop a new refrigeration technology that can replace traditional gas compression refrigeration technology.

[0003] Magnetic refrigeration is a refrigeration technology based on the magnetocaloric effect (MCE), offering the potential for high efficiency and environmental friendliness. MCE refers to the phenomenon in which certain materials undergo a reversible change in temperature when exposed to a magnetic field, and is particularly pronounced in rare earth elements, ferromagnetic materials, and magnetic alloys. Compared to traditional gas compression refrigeration, magnetic refrigeration eliminates greenhouse gas emissions like CFCs and theoretically offers higher energy efficiency, making it a research hotspot for next-generation green refrigeration technologies.

[0004] Currently, Ni-Mn-based Heusler alloys are attracting widespread attention due to their large MCE, tunable martensitic transition temperature, and excellent chemical stability. In particular, alloys such as Ni-Co-Mn-Ti offer broad application prospects, as their martensitic transition behavior and magnetocaloric effect can be optimized through composition and processing. During alloy preparation, microstructural properties such as grain size, interfacial properties, and defect concentration significantly influence their magnetic refrigeration performance. Studying these microstructural factors is crucial for improving the performance of magnetic refrigeration materials.

[0005] CN112760535A discloses a magnetic refrigeration material and its preparation method. Using the high-abundance rare earth element R as a substitute for Ni, Co, Mn, and Ti, the material can effectively regulate the phase transition temperature. The material preparation method is as follows: high-purity raw materials are weighed and mixed uniformly according to the stoichiometric ratio of the chemical formula; the raw materials are then prepared into a magnetic phase change material using arc melting, Czochralski method, or directional solidification method; the high-purity raw materials are arc melted under argon protection to obtain a bulk sample; and finally, a portion of the arc-melted bulk sample is vacuum melt-quenched to obtain a thin ribbon or vacuum annealed. This allows the phase transition temperature to be regulated over a wide temperature range of 100 to 350 K as the high-abundance rare earth element content increases, resulting in an enhanced magnetocaloric effect.

[0006] CN112216458A discloses a material for enhancing magnetocaloric effect and a preparation method thereof. The chemical formula of the material is Ni 35 Co 15 Mn 35-x P x Qy where \(0\leq x\leq12\), \(10\leq y\leq22\), \(P\) is one of transition elements \(Ti\), \(V\), \(Cr\), \(Mn\), \(Fe\), \(Co\), \(Ni\), \(Cu\), \(Zn\), and \(Q\) is one of \(Sc\), \(Ti\), \(Zr\), \(Hf\), \(V\), \(Nb\), \(Ta\). Weigh high-purity raw materials according to the above chemical formula ratio, and then obtain a bulk sample with the chemical formula ratio by arc melting or the pulling method or the directional solidification method under argon protection. The bulk sample is subjected to melt spinning under vacuum to obtain a thin strip material with a phase change or directly subjected to vacuum annealing treatment. Then, isostatic pressing is applied to further regulate the phase change and magnetism, so that the magnetic phase change at a lower temperature is regulated to room temperature and above, and at the same time, the magnetocaloric effect is enhanced.

[0007] CN105986322A discloses a magnetic phase change material, which is prepared into a magnetic phase change material by the pulling method or the zone melting method or the directional solidification method, and its chemical formula is: Ni a-m Mn b-n Co m+n Ti c ; where \(a + b + c = 100\), \(20\lt a\leq90\), \(5\leq b\lt50\), \(5\leq c\leq30\), \(0\leq m\leq a\), \(0\leq n\leq b\), \(0\lt m + n\lt a + b\), and \(a\), \(b\), \(c\), \(m\), and \(n\) represent atomic percentage contents alone or in combination. This magnetic phase change material has high strength and toughness, high deformation rate, strong magnetism, and the characteristics of magnetic field-driven martensitic phase change.

[0008] The NiMn-based magnetic refrigeration materials disclosed in the prior art all require complex melting processes or means such as directional solidification to achieve, and the preparation process is cumbersome. Therefore, it is of great significance to provide a NiMn-based magnetic refrigeration material with a simple and controllable process and excellent magnetothermal performance. Summary of the Invention

[0009] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a NiMn-based polycrystalline alloy, its preparation method and application. The preparation process of the NiMn-based polycrystalline alloy provided by the present invention is simple and controllable. The obtained NiMn-based polycrystalline alloy has few defects inside the grains and high homogenization degree, and can realize the rapid occurrence of martensitic phase change. The magnetothermal performance of the NiMn-based polycrystalline alloy is improved by the coupling of magnetic phase change and structural phase change.

[0010] To achieve the purpose of this invention, the present invention adopts the following technical solutions:

[0011] In the first aspect, the present invention provides a preparation method of a NiMn-based polycrystalline alloy, and the preparation method includes:

[0012] Melting and casting alloy raw materials to obtain a cast alloy, spray-casting the cast alloy to obtain a polycrystalline alloy ingot, and performing homogenization annealing treatment on the polycrystalline alloy ingot to obtain the NiMn-based polycrystalline alloy.

[0013] In the present invention, "polycrystalline alloy" refers to an alloy material composed of multiple grains, each of which has a regular atomic arrangement inside and grain boundaries between different grains.

[0014] The present invention uses spray casting to achieve rapid solidification of NiMn-based polycrystalline alloys, and through homogenization annealing treatment, reduces defects inside grains, improves the degree of homogenization, and achieves a rapid occurrence of martensitic phase transformation. The magnetocaloric properties of the NiMn-based polycrystalline alloys are improved through the coupling of magnetic phase transformation and structural phase transformation.

[0015] In the present invention, the cast alloy is obtained by melting the alloy raw materials through a conventional melting and casting process, and the melting and casting method is not particularly limited.

[0016] The spray casting described in the present invention refers to the process of spraying molten metal or alloy onto a cooled substrate or mold, and forming a solid material by utilizing the spraying and rapid cooling of the liquid metal.

[0017] The present invention precisely designs the components of the NiMn-based alloy, adjusts the elemental composition, and combines the processes of spray casting and homogenization annealing to change the phase transition temperature of the NiMn-based polycrystalline alloy, thereby achieving coverage of the entire temperature range, further improving its magnetocaloric properties, and broadening the application range of the NiMn-based polycrystalline alloy.

[0018] Preferably, the alloy raw material comprises, in atomic percentage, the following components:

[0019]

[0020] X includes any one or a combination of at least two of Sc, Y, Ce, Dy, or Nd.

[0021] In the raw materials for preparing the NiMn-based polycrystalline alloy of the present invention, the Co element can increase the magnetism of the alloy and improve the saturation magnetization intensity of austenite; the Ti element can adjust the phase transition temperature of martensite and simultaneously form a stable compound to improve the thermal stability of the alloy; and the X element can form a fine precipitate phase to improve the strength and hardness of the alloy.

[0022] In the preparation method provided by the present invention, the alloy raw material includes 35%-37% of Ni element, for example, it can be 35%, 35.1%, 35.2%, 35.3%, 35.4%, 35.5%, 35.6%, 35.7%, 35.8%, 35.9%, 36%, 36.1%, 36.2%, 36.3%, 36.4%, 36.5%, 36.6%, 36.7%, 36.8%, 36.9% or 37%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] In the preparation method provided by the present invention, the alloy raw material includes 33%-42% of Mn element, for example, it can be 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, 36%, 36.5%, 37%, 37.5%, 38%, 38.5%, 39%, 39.5%, 40%, 40.5%, 41%, 41.5% or 42%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] In the preparation method provided by the present invention, the alloy raw material includes 13%-15% of Co element, for example, it can be 13%, 13.1%, 13.2%, 13.3%, 13.4%, 13.5%, 13.6%, 13.7%, 13.8%, 13.9%, 14%, 14.1%, 14.2%, 14.3%, 14.4%, 14.5%, 14.6%, 14.7%, 14.8%, 14.9% or 15%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] In the preparation method provided by the present invention, the alloy raw material includes 8%-17% of Ti element, for example, it can be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5% or 17%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] In the preparation method provided herein, the alloy raw material includes 0%-5% of element X, for example, 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, including but not limited to the values ​​listed above. Other values ​​not listed within the numerical range are also applicable. X includes any one or a combination of at least two of Sc, Y, Ce, Dy, or Nd. Typical but non-limiting combinations include Sc and Y, Ce and Dy, or Y and Nd.

[0027] In the present invention, the pressure of the spray casting affects the degree of supercooling during the solidification process of the NiMn-based polycrystalline alloy, thereby affecting the average grain size of the NiMn-based polycrystalline alloy. If the spray casting pressure is too low, the supercooling is too low, resulting in excessive grain growth. At the same time, the metal particles sprayed under low pressure do not have sufficient kinetic energy to complete a full cooling and solidification process, resulting in poor density of the casting and easy formation of defects such as pores and shrinkage cavities. If the spray casting pressure is too high, on the one hand, it may cause the melt to splash, affecting the homogenization of the NiMn-based polycrystalline alloy. At the same time, the metal droplets may be entrained with bubbles during flight, resulting in pores, bubbles or other defects inside the casting. On the other hand, it leads to excessive supercooling and an excessively small average grain size.

[0028] Preferably, the injection molding pressure is 0.1MPa-2MPa, for example, it can be 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1MPa, 1.1MPa, 1.2MPa, 1.3MPa, 1.4MPa, 1.5MPa, 1.6MPa, 1.7MPa, 1.8MPa., 1.9MPa or 2MPa, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 0.2MPa-1MPa.

[0029] Preferably, the spray casting is performed under a protective atmosphere.

[0030] Preferably, the protective atmosphere comprises an inert gas.

[0031] Preferably, the temperature of the homogenization annealing treatment is 600°C-1100°C, for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C or 1100°C, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the homogenization annealing treatment time is 3h-168h, for example, it can be 3h, 5h, 10h, 20h, 24h, 36h, 48h, 60h, 72h, 84h, 96h, 108h, 120h, 132h, 144h, 156h or 168h, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the cooling medium for the homogenization annealing treatment includes any one of water, ice-water mixture or liquid nitrogen, or a combination of at least two of them.

[0034] The average grain size of NiMn-based polycrystalline alloys affects the martensite phase transition temperature and the intensity of the phase transition. If the grains are too large, the number of grain boundaries will decrease and martensite nucleation will be difficult. If the grains are too small, the grain refinement can enhance the interaction between grain boundaries, and the grain boundaries will hinder the phase transition process and inhibit the occurrence of martensite phase transformation.

[0035] Preferably, after the homogenization annealing treatment, the average grain size of the NiMn-based polycrystalline alloy is 100 μm-1000 μm, for example, it can be 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm, 900 μm, 950 μm or 1000 μm, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 150 μm-500 μm.

[0036] Preferably, the preparation method further comprises pulverizing the NiMn-based polycrystalline alloy;

[0037] Preferably, the powdering treatment method includes ball milling, impact crushing, air flow milling, spray drying, and atomization.

[0038] In a second aspect, the present invention provides a NiMn-based polycrystalline alloy, which is prepared by the preparation method described in the first aspect.

[0039] Preferably, the composition of the NiMn-based polycrystalline alloy includes Ni: 35%-37%, Mn: 33%-42%, Co: 13%-15%, Ti: 8%-17% and X: 0-5%.

[0040] The NiMn-based polycrystalline alloy provided by the present invention includes 35%-37% of Ni element, for example, 35%, 35.1%, 35.2%, 35.3%, 35.4%, 35.5%, 35.6%, 35.7%, 35.8%, 35.9%, 36%, 36.1%, 36.2%, 36.3%, 36.4%, 36.5%, 36.6%, 36.7%, 36.8%, 36.9% or 37%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] In the preparation method provided by the present invention, the alloy raw material includes 33%-42% of Mn element, for example, it can be 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, 36%, 36.5%, 37%, 37.5%, 38%, 38.5%, 39%, 39.5%, 40%, 40.5%, 41%, 41.5% or 42%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] In the preparation method provided by the present invention, the alloy raw material includes 13%-15% of Co element, for example, it can be 13%, 13.1%, 13.2%, 13.3%, 13.4%, 13.5%, 13.6%, 13.7%, 13.8%, 13.9%, 14%, 14.1%, 14.2%, 14.3%, 14.4%, 14.5%, 14.6%, 14.7%, 14.8%, 14.9% or 15%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] In the preparation method provided by the present invention, the alloy raw material includes 8%-17% of Ti element, for example, it can be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5% or 17%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] In the preparation method provided by the present invention, the alloy raw material includes 0%-5% of element X, for example, 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the average grain size of the NiMn-based polycrystalline alloy is 100-1000 μm, for example, it can be 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm, 900 μm, 950 μm or 1000 μm, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 150 μm-500 μm.

[0046] In a third aspect, the present invention provides an application of a NiMn-based polycrystalline alloy, wherein the NiMn-based polycrystalline alloy is applied in the field of magnetic refrigeration technology.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The preparation method provided by the present invention can comprehensively optimize the magnetocaloric properties of NiMn-based polycrystalline alloys. The present invention utilizes a spray-casting process combined with a homogenization annealing treatment, combining alloying, rapid solidification, and homogenization to comprehensively optimize the magnetocaloric properties of NiMn-based polycrystalline alloys. Rapid solidification reduces post-annealing internal grain defects, and by regulating the average grain size and improving homogenization, a rapid martensitic phase transformation is achieved. The magnetocaloric properties of NiMn-based polycrystalline alloys are enhanced through the coupling of magnetic and structural phase transitions. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 1 is the XRD pattern of the NiMn-based polycrystalline alloys prepared in Examples 1 to 3 and Comparative Example 1.

[0050] Figure 2 3 is a SEM image of the NiMn-based polycrystalline alloy prepared in Example 1.

[0051] Figure 3 This is a SEM image of the NiMn-based polycrystalline alloy prepared in Example 2.

[0052] Figure 4 3 is a SEM image of the NiMn-based polycrystalline alloy prepared in Example 3.

[0053] Figure 5 MT curves of NiMn-based polycrystalline alloys prepared in Examples 1 to 3 and Comparative Example 1 under a 0.2T magnetic field change.

[0054] Figure 6 MH curve of the NiMn-based polycrystalline alloy prepared in Example 1.

[0055] Figure 7 MH curve of the NiMn-based polycrystalline alloy prepared in Example 2.

[0056] Figure 8 MH curve of the NiMn-based polycrystalline alloy prepared in Example 3.

[0057] Figure 9 This is the MH curve of the NiMn-based polycrystalline alloy prepared in Comparative Example 1.

[0058] Figure 10 MH curve of the NiMn-based polycrystalline alloy prepared in Example 4.

[0059] Figure 11 This is the MH curve of the NiMn-based polycrystalline alloy prepared in Comparative Example 2.

[0060] Figure 12 This is the magnetic entropy change ΔSM diagram of the NiMn-based polycrystalline alloy prepared in Example 1.

[0061] Figure 13 This is the magnetic entropy change ΔSM diagram of the NiMn-based polycrystalline alloy prepared in Example 2.

[0062] Figure 14 This is the magnetic entropy change ΔSM diagram of the NiMn-based polycrystalline alloy prepared in Example 3.

[0063] Figure 15 This is a magnetic entropy change ΔSM diagram of the NiMn-based polycrystalline alloy prepared in Comparative Example 1.

[0064] Figure 16 This is the magnetic entropy change ΔSM diagram of the NiMn-based polycrystalline alloy prepared in Example 4.

[0065] Figure 17 This is the magnetic entropy change ΔSM diagram of the NiMn-based polycrystalline alloy prepared in Comparative Example 2.

[0066] Figure 18 It is a comparison diagram of the magnetic entropy change ΔSM of the NiMn-based polycrystalline alloys prepared in Examples 1 to 3 and Comparative Example 1. DETAILED DESCRIPTION

[0067] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0068] Example 1

[0069] This embodiment provides a method for preparing a NiMn-based polycrystalline alloy, the preparation method comprising:

[0070] Configuration composition is Ni 36 Co 13 Mn 35 Ti 16 The alloy raw material (at.%) is smelted into a cast alloy in an arc melting furnace. The cast alloy is spray-casted under Ar protection at a pressure of 0.3 MPa. The spray-cast ingot is subjected to a homogenization annealing treatment at a temperature of 1050°C for 96 hours and a cooling method of water quenching to obtain the Ni 36 Co 13 Mn 35 Ti 16 Polycrystalline alloy.

[0071] The Ni prepared in this example 36 Co 13Mn 35 Ti 16 The polycrystalline alloy is in austenite phase at room temperature, as shown in the SEM image. Figure 2 As shown, the average grain size is 157 μm, and the XRD diffraction pattern is as follows Figure 1 shown.

[0072] Example 2

[0073] This embodiment provides a method for preparing a NiMn-based polycrystalline alloy, the preparation method comprising:

[0074] Configuration composition is Ni 35 Co 15 Mn 42 The alloy raw material of Ti8 (at.%) is smelted into a cast alloy by an arc melting furnace. The cast alloy is spray-casted under Ar protection with a spray-casting pressure of 0.1 MPa. The spray-cast ingot is subjected to a homogenization annealing treatment at a temperature of 700°C for 120 hours and quenched with an ice-water mixture to obtain the Ni 35 Co 15 Mn 42 Ti8 polycrystalline alloy.

[0075] The Ni prepared in this example 35 Co 15 Mn 42 Ti8 polycrystalline alloy is austenite at room temperature, SEM image is as follows Figure 3 As shown, the average grain size is 249.2 μm, and the XRD diffraction pattern is as follows Figure 1 shown.

[0076] Example 3

[0077] This embodiment provides a method for preparing a NiMn-based polycrystalline alloy, the preparation method comprising:

[0078] Configuration composition is Ni 36 Co 14 Mn 40 Ti 12 The alloy raw material (at.%) is smelted into a cast alloy by an arc melting furnace. The cast alloy is spray-casted under Ar protection at a pressure of 1 MPa. The spray-cast ingot is subjected to a homogenization annealing treatment at a temperature of 900°C for 108 hours and cooled with liquid nitrogen to obtain the Ni 36 Co 14 Mn 40 Ti 12 Polycrystalline alloy.

[0079] The Ni prepared in this example 36 Co 14 Mn40 Ti 12 The polycrystalline alloy is in austenite phase at room temperature, as shown in the SEM image. Figure 4 As shown, the average grain size is 461.2 μm, and the XRD diffraction pattern is as follows Figure 1 shown.

[0080] Example 4

[0081] This embodiment provides a method for preparing a NiMn-based polycrystalline alloy, the preparation method comprising:

[0082] Configuration composition is Ni 37 Co 13 Mn 34 Ti 15.75 Sc 0.25 The alloy raw material (at.%) is smelted into a cast alloy in an arc melting furnace. The cast alloy is spray-casted under Ar protection at a pressure of 1.5 MPa. The spray-cast ingot is subjected to a homogenization annealing treatment at a temperature of 1050°C for 96 hours and a cooling method of water quenching to obtain the Ni 37 Co 13 Mn 34 Ti 15.75 Sc 0.25 Polycrystalline alloy.

[0083] Example 5

[0084] This embodiment provides a method for preparing a NiMn-based polycrystalline alloy. The preparation method is the same as that of Example 1 except that the spray casting pressure is 0.05 MPa.

[0085] Example 6

[0086] This embodiment provides a method for preparing a NiMn-based polycrystalline alloy. The preparation method is the same as that of Example 1 except that the spray casting pressure is 3 MPa.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing a NiMn-based polycrystalline alloy, comprising:

[0089] Configuration composition is Ni 37 Co 13 Mn 34 Ti 15.75 Sc 0.25 The alloy raw material with a content of (at.%) is smelted into cast titanium alloy by an arc melting furnace. The cast alloy is subjected to homogenization annealing treatment at a temperature of 1050° C. for 96 h, and the cooling method is water quenching.

[0090] The Ni prepared in this comparative example 37 Co13 Mn 34 Ti 15.75 Sc 0.25 The polycrystalline alloy is in austenite phase at room temperature, and the XRD diffraction pattern is as follows Figure 1 shown.

[0091] Comparative Example 2

[0092] This comparative example provides a method for preparing a NiMn-based polycrystalline alloy, comprising:

[0093] Configuration composition is Ni 36 Co 13 Mn 35 Ti 16 The alloy raw material with a content of (at.%) is smelted into cast titanium alloy by an arc melting furnace. The cast alloy is subjected to homogenization annealing treatment at a temperature of 1050° C. for 96 h, and the cooling method is water quenching.

[0094] Performance testing:

[0095] The magnetocaloric properties of the NiMn-based polycrystalline alloys prepared in all the above examples and comparative examples were tested. The test method was as follows: when measuring the MT curve, the test range was selected to be 50-390K, and the heating rate and cooling rate were both 3K·min -1 , a constant magnetic field of 0.2 T was applied; during the measurement of the MH curve, the rate of magnetic field reduction was 200 Oe·s -1 In the process of testing the MH curve, the MH near the phase transition temperature (±20K) is tested using the loop method, that is, recording two cycles of increasing magnetic field-decreasing magnetic field-increasing magnetic field-decreasing magnetic field.

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098] <![CDATA[Magnetic entropy / J·kg -1 ·K -1 > Martensitic transformation temperature / K Example 1 35.2 189.1 Example 2 45.2 180.15 Example 3 49.4 169.9 Example 4 24.11 283 Example 5 22.7 197.9 Example 6 20.8 183.7 Comparative Example 1 18.1 211 Comparative Example 2 17.83 230

[0099] According to the data results of Examples 1 to 3 and Comparative Example 1, the present invention comprehensively optimizes the magnetocaloric properties of the NiMn-based polycrystalline alloy by first spray-casting the cast alloy and then performing homogenization annealing through three mechanisms: alloying, rapid solidification, and homogenization. The internal defects of the grains after annealing are reduced by rapid solidification. The average size of the grains is controlled to improve the degree of homogenization and achieve a rapid occurrence of martensitic phase transformation. The magnetocaloric properties of the NiMn-based polycrystalline alloy are improved through the coupling of magnetic phase transformation and structural phase transformation.

[0100] like Figure 2As shown, by combining the process of spray casting and homogenization annealing, the phase transition temperature of the Ni-Co-Mn-Ti based polycrystalline alloy prepared by the present invention is reduced from 211K to 169.9K, realizing controllable adjustment in the low temperature zone. The phase transition temperature of the Ni-Co-Mn-Ti-X based polycrystalline alloy prepared in the present invention is increased from 230K to 283K, realizing controllable adjustment in the higher temperature zone, that is, the present invention realizes full temperature range controllable adjustment of the phase temperature of the NiMn based polycrystalline alloy by designing the components of the NiMn based polycrystalline alloy and combining the spray casting and homogenization annealing process. The magnetic entropy of the NiMn based polycrystalline alloy prepared by the present invention can reach 49.54J·kg -1 ·K -1 .

[0101] like Figure 6-Figure 9 Compared with the NiMn-based polycrystalline alloy prepared in Comparative Example 1, the phase transition temperature of the NiMn-based polycrystalline alloy prepared in Example 1 decreased from 211K to 189.1K under a 5T magnetic field. The phase transition temperatures of the NiMn-based polycrystalline alloys prepared in Example 2 and Example 3 decreased to 180.15K and 169.9K, respectively.

[0102] like Figure 10-11 Compared with the NiMn-based polycrystalline alloy prepared in Comparative Example 2, the phase transition temperature of the NiMn-based polycrystalline alloy prepared in Example 4 is increased from 230K to 283K under a 5T magnetic field change.

[0103] like Figure 12-15 Compared with the NiMn-based polycrystalline alloy prepared in Comparative Example 1, the magnetic entropy of the NiMn-based polycrystalline alloy prepared in Example 1 is 18.1 J·kg -1 ·K -1 Increased to 35.2 J·kg -1 ·K -1 The magnetic entropy of the NiMn-based polycrystalline alloy prepared in Example 2 and Example 3 was increased to 45.2 J·kg -1 ·K -1 and 49.4 J·kg -1 ·K -1 .

[0104] like Figure 16-17 Compared with the NiMn-based polycrystalline alloy prepared in Comparative Example 2, the magnetic entropy of the NiMn-based polycrystalline alloy prepared in Example 4 is 17.83 J·kg -1 ·K -1 Increased to 24.11 J·kg -1 ·K -1 .

[0105] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a NiMn-based polycrystalline alloy, characterized in that: The preparation method comprises: Melting alloy raw materials to obtain a cast alloy, spray-casting the cast alloy to obtain a polycrystalline alloy ingot, and performing homogenization annealing on the polycrystalline alloy ingot to obtain the NiMn-based polycrystalline alloy; In terms of atomic percentage, the composition of the alloy raw material includes: Ni 35%-37%; Mn 33%-42%; Co 13%-15%; Ti 8%-17%; X 0-5%； X includes any one or a combination of at least two of Sc, Y, Ce, Dy or Nd; The pressure of the spray casting is 0.1MPa-2MPa; the spray casting is carried out under a protective atmosphere; the protective atmosphere includes an inert gas; The temperature of the homogenization annealing treatment is 600° C.-1100° C.; the time of the homogenization annealing treatment is 3 hours-168 hours; After the homogenization annealing treatment, the average grain size of the NiMn-based polycrystalline alloy is 100 μm-1000 μm.

2. The preparation method according to claim 1, wherein The pressure of the injection casting is 0.2MPa-1MPa.

3. The preparation method according to claim 1, wherein The cooling medium for the homogenization annealing treatment includes any one of water, ice-water mixture or liquid nitrogen, or a combination of at least two of them.

4. The preparation method according to claim 1, wherein After the homogenization annealing treatment, the average grain size of the NiMn-based polycrystalline alloy is 150 μm-500 μm.

5. The preparation method according to claim 1, wherein The preparation method further comprises pulverizing the NiMn-based polycrystalline alloy.

6. The preparation method according to claim 5, wherein The powdering treatment methods include ball milling, impact crushing, air flow milling, spray drying and atomization.

7. A NiMn-based polycrystalline alloy, characterized in that: The NiMn-based polycrystalline alloy is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the NiMn-based polycrystalline alloy according to claim 7, characterized in that: The NiMn-based polycrystalline alloy is used in the field of magnetic refrigeration.

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