Fe-doped mnco ge bulk magnetic refrigeration alloy and preparation method thereof

Abstract

The application belongs to the technical field of solid-state magnetic refrigeration materials, and particularly relates to a Fe-doped MnCoGe-based bulk magnetic refrigeration alloy and a preparation method thereof. The application solves the problems of poor room-temperature mechanical performance, easy cracking and powdering, low magnetocaloric effect, difficult phase transition temperature regulation and insufficient magnetic structure coupling of the existing MnCoGe-based magnetic refrigeration material, and cannot prepare bulk samples. The chemical general formula is (Mn 0.91 Co 1.09 Ge) 1‑x Fe x , 0<=x<=0.03. The MnCoGe-based bulk alloy is prepared by arc melting and hot-press sintering, and has excellent mechanical performance and magnetocaloric effect. After multiple cold and hot cycles, the alloy maintains good mechanical integrity, the maximum breaking strength reaches 341 MPa, the maximum magnetic entropy change reaches 36.2 J / kg K, and the alloy has a potential application prospect in the field of magnetic refrigeration.

Description

Technical Field

[0001] This invention belongs to the field of solid-state magnetic refrigeration materials technology, specifically relating to an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy and its preparation method. Background Technology

[0002] Global warming and climate change pose a fundamental threat to the sustainable development of human society, and reducing carbon emissions and promoting the low-carbon transformation of energy structure and industrial technology have become a global consensus. Against this backdrop, the elimination and upgrading of traditional high-energy-consuming and high-emission technologies are urgently needed. Refrigeration technology, as a key technology in industrial production and people's livelihoods, is particularly important for low-carbon innovation. The widely used vapor compression refrigeration technology has undergone more than 150 years of development. This technology not only has inherent drawbacks such as high energy consumption and large greenhouse gas emissions, but its energy efficiency level is also approaching its theoretical limit, making it difficult to meet the increasingly stringent requirements of low-carbon development.

[0003] Magnetic refrigeration technology, as a highly promising solid-state refrigeration technology, is widely recognized as the core development direction of next-generation low-carbon and energy-saving refrigeration technology due to its significant advantages such as being green and environmentally friendly, having high energy utilization efficiency, and eliminating refrigerant leakage pollution. The magnetocaloric effect is the core principle of magnetic refrigeration technology. Specifically, it refers to the change in magnetic entropy of a magnetic material during the application or removal of an external magnetic field, accompanied by heat absorption or release, thereby achieving a refrigeration cycle. Isothermal entropy change is the core quantitative indicator for measuring the strength of the magnetocaloric effect of a material.

[0004] Among numerous magnetic refrigeration materials, MnCoGe-based alloys have become a research hotspot in the field of room-temperature magnetic refrigeration due to their Curie temperature matching the room temperature range, their martensite-austenite first-order structural transformation temperature close to room temperature, and their excellent isothermal entropy change characteristics. However, during the austenite-martensite first-order structural phase transformation, MnCoGe-based alloys undergo severe lattice distortion and abrupt volume changes. This characteristic directly leads to the material being extremely prone to cracking and breaking into powder at room temperature, making it impossible to prepare bulk samples with intact mechanical structures, which seriously hinders its large-scale application in practical engineering.

[0005] To address the aforementioned issues, various improvement approaches have been explored in existing technologies. On the one hand, some studies have employed epoxy resin bonding to solidify and mold MnCoGe-based alloy powders. While this method can increase the compressive strength of the material from 60 MPa to 218 MPa, it significantly disrupts the magnetically ordered structure of the material, resulting in a substantial decrease in the magnetocaloric effect and making it difficult to balance mechanical and magnetocaloric properties. On the other hand, numerous studies have attempted to regulate the magnetocaloric properties of MnCoGe-based alloys through elemental doping (such as V, Fe, Ga, Cu, etc.) in an effort to optimize the coupling effect between the phase transition temperature and the magnetic structure. However, such methods can only improve the magnetocaloric effect to a certain extent, and have failed to overcome the core challenges of poor material formability and the inability to prepare high-density bulk materials. Furthermore, the introduction of some doping elements can lead to a decrease in the magnetocaloric effect due to compositional control, resulting in a predicament of "performance regulation imbalance."

[0006] In summary, existing MnCoGe-based magnetic refrigeration materials generally suffer from three major technical bottlenecks: First, their room-temperature mechanical properties are extremely poor, making the materials prone to cracking and fragmentation, and preventing the preparation of mechanically intact bulk samples. Second, the magnetocaloric effect is easily affected by compositional control and bonding modification, making it difficult to maintain excellent refrigeration performance. Third, the phase transition temperature control precision is insufficient, and the coupling effect between the magnetic structure and the crystal structure is weak, limiting the practical adaptability of the materials. Therefore, how to achieve a synergistic unity of bulk, high density, high strength, and excellent magnetocaloric properties in MnCoGe-based alloys without weakening the giant magnetocaloric effect has become a key technical challenge that urgently needs to be solved in this field. Based on this, developing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy that can balance mechanical and magnetocaloric properties and its preparation method is of vital importance for promoting the engineering application of magnetic refrigeration technology. Summary of the Invention

[0007] The present invention aims to address the problems of existing MnCoGe-based magnetic refrigeration materials, such as extremely poor room temperature mechanical properties, easy cracking and pulverization making it impossible to prepare bulk samples, low magnetocaloric effect that is easily affected by composition control, difficulty in controlling phase transition temperature, and insufficient magnetic structure coupling. The invention provides an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy and its preparation method.

[0008] The present invention discloses a Fe-doped MnCoGe-based bulk magnetic refrigeration alloy with the general chemical formula (Mn 0.91 Co 1.09 Ge) 1-x Fe x , 0≤x≤0.03.

[0009] The preparation method of the Fe-doped MnCoGe-based bulk magnetic refrigeration alloy of the present invention is carried out by the following steps:

[0010] I. Material Preparation: According to the general chemical formula (Mn) 0.91 Co 1.09 Ge) 1-x Fe x Prepare the ingredients, where 0≤x≤0.03, weigh out Mn metal, Co metal, Ge metal and Fe metal as raw materials respectively, and remove the oxide scale on the surface of the metal elements;

[0011] II. Arc melting: The raw materials are placed in the copper crucible of a non-consumable high-vacuum arc melting furnace, and after gas washing, they are melted to obtain a melted alloy ingot.

[0012] 3. The smelted alloy ingot is crushed and ground into powder. The powder is then placed in a graphite mold and sintered in a hot pressing furnace to obtain sintered alloy block material.

[0013] IV. Solution Heat Treatment: The sintered bulk material is polished to remove the oxide scale, placed in a quartz tube filled with argon and sealed, and then subjected to solution heat treatment. After cooling in an ice-water mixture, a Fe-doped MnCoGe-based alloy bulk material with high mechanical properties and giant magnetocaloric effect is obtained.

[0014] Furthermore, in step one, according to the general chemical formula (Mn 0.91 Co 1.09 Ge) 1-x Fe x When preparing the ingredients, first calculate the theoretical amount of Mn metal to be added, and then adjust the actual amount added to 103% of the theoretical amount.

[0015] The gas washing process described in step two involves first evacuating the gas to below 5 MPa before alloy melting, then filling it with high-purity argon gas, and then evacuating the argon gas. This is one gas washing process, and the gas washing process is repeated more than three times.

[0016] Furthermore, the melting described in step two is completed under a working current of 50-500A, with the initial melting lasting 40 seconds, followed by 5 flips using a robotic arm.

[0017] Furthermore, the grinding described in step three is carried out in an agate mortar for 2 hours to ensure that the alloy powder reaches the micron level.

[0018] Furthermore, the argon furnace cleaning process described in step three before sintering involves first evacuating the furnace to below 1 MPa, then filling it with high-purity argon gas, and then evacuating the argon gas. This is one argon furnace cleaning process, and this process is repeated three times.

[0019] Furthermore, the graphite mold in step three has a maximum pressure resistance of 40 MPa. When pressurizing the graphite mold, the pressure should be selected between 20-30 MPa.

[0020] Furthermore, the sintering described in step three is staged sintering, firstly holding the temperature and pressure at 700℃ and 20MPa for 30 minutes, then raising the temperature and pressure to 980℃ and 30MPa, and holding the temperature and pressure for 60 minutes.

[0021] Furthermore, the sealing described in step four is performed under conditions of argon gas.

[0022] Furthermore, the solution heat treatment in step four is performed at a temperature of 750°C for 1 hour.

[0023] Furthermore, the Fe-doped MnCoGe-based alloy bulk material with high mechanical properties and giant magnetocaloric effect obtained in step four was polished with 200-grit sandpaper to remove oxide scale and cleaned with ethanol.

[0024] This invention applies unidirectional pressure during the sintering process, causing micron-sized alloy powder particles to undergo plastic flow and close contact. This breaks down the barriers of the oxide film and adsorption layer on the particle surface, forming direct metallic bonds. Simultaneously, the pressure acts as an additional driving force, significantly reducing the porosity of the sintered powder and bringing the density close to the theoretical density, providing a structural basis for the integrity of the bulk structure. A graded process avoids the internal stress concentration caused by uneven thermal expansion under single high temperature and high pressure conditions. Pre-sintering at a low temperature stage allows the particles to initially bond and release some residual stress, while densification at a high temperature stage further strengthens the interfacial bonding, forming a bulk structure with clear phase boundaries and a uniform structure, solving the problem of cracking that easily occurs in traditional sintering. Argon gas furnace cleaning and quartz tube sealing solution treatment before sintering effectively isolate oxygen and impurities, preventing the weakening of interfacial bonding caused by powder oxidation and ensuring the mechanical integrity of the bulk material.

[0025] During the hot-pressing sintering process of this invention, the close packing of powder particles and the pressure-driven grain growth regulation form a grain structure of appropriate size. According to the Hall-Petch relationship, an appropriate grain boundary density can hinder dislocation movement and crack propagation, significantly improving the compressive strength of the material. At the same time, the local bonding adjustment and defect distribution optimization within the grains caused by Fe doping further strengthens the grain boundary strength, making the compressive strength reach a maximum of 341 MPa, far exceeding the 218 MPa of traditional resin bonding.

[0026] Fe doping increases the austenite phase content and decreases the lath martensite phase content in the alloy (consistent with DSC curves and microstructure analysis). The austenite phase is harder than the martensite phase, and its increased content alleviates lattice distortion stress during the phase transformation process, reducing microcrack initiation. Simultaneously, the introduction of Fe reduces the Mn-Mn atomic spacing, optimizes lattice matching, and reduces internal stress concentration caused by the phase transformation, thus improving the material's brittleness. Fe has a higher atomic magnetic moment than Mn, and appropriate doping (x≤0.03) can optimize the magnetically ordered structure of the alloy and enhance ferromagnetic interactions. Furthermore, Fe's smaller metallic radius than Mn, after substituting Mn sites, reduces the lattice constant, lowers the martensite transformation temperature, and shifts the phase transformation range towards room temperature (consistent with the decreasing phase transformation temperature with increasing Fe content in the DSC curve), making it more suitable for room-temperature magnetic refrigeration. Fe doping promotes the "magnetic-thermal" coupling effect in MnCoGe-based alloys, significantly increasing the magnetic field-driven martensite phase transformation. When an appropriate amount of Fe (x=0.01-0.02) is doped, the magnetization response of the alloy near the phase transformation temperature is enhanced, and the transformation from austenite to ferromagnetic martensite under a magnetic field is more complete, thus resulting in a greater maximum ΔS under a 7T magnetic field. m Reaching 36.2 J / kgK, it is at the top level among similar materials. The Fe doping amount is strictly controlled at x≤0.03, avoiding magnetic moment dilution and incomplete phase transformation caused by excessive doping (the initial slope of the MH curve decreases when x=0.03). At the same time, hot pressing sintering and solution heat treatment do not destroy the magnetically ordered structure of the alloy (consistent with the absence of magnetic domain destruction in fracture analysis), ensuring that the magnetocaloric effect is not attenuated by densification and strengthening treatment, achieving a synergistic improvement in mechanical and magnetocaloric properties.

[0027] Beneficial effects of this invention:

[0028] This invention enables the bulk preparation of MnCoGe-based alloys, resulting in significantly improved mechanical properties, with a compressive strength as high as 325 MPa, far exceeding the 218 MPa of traditional resin-bonded technologies. It also significantly enhances the magnetocaloric effect (MCE), with a ΔS value under a 7T magnetic field. m The maximum value reaches 36.2 J / kgK, which is one of the best values ​​reported among MnCoGe-based materials. The alloy structure after hot pressing and sintering is dense (>99.25%) with clear phase boundaries, showing potential for engineering applications. Fe doping lowers the phase transformation temperature and enhances magnetic coupling, making it more suitable for room temperature magnetic refrigeration. The material maintains mechanical integrity and does not break during multiple thermal cycles, overcoming a long-standing application bottleneck for MnCoGe-based alloys. In summary, this invention constructs a design framework for novel MnCoGe-based magnetic refrigeration materials, providing important technical support for achieving efficient room temperature magnetic refrigeration. Attached Figure Description

[0029] Figure 1DSC curves of MnCoGe-based alloys prepared for all embodiments;

[0030] Figure 2 20 μm scan and grain size diagram of MnCoGe-based alloys prepared for all embodiments;

[0031] Figure 3 Stress-strain diagrams of MnCoGe-based alloys prepared for all embodiments;

[0032] Figure 4 20 μm scanning electron microscope images of the fracture surfaces of MnCoGe-based alloys prepared for all embodiments;

[0033] Figure 5 Isothermal magnetization curves of MnCoGe-based alloys prepared for all embodiments at different temperatures;

[0034] Figure 6 Graph showing the magnetic entropy change as a function of temperature for MnCoGe-based alloys prepared in all embodiments. Detailed Implementation

[0035] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0036] Specific Implementation Method 1: A method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy is completed according to the following steps:

[0037] First, weigh the high-purity metallic elements Mn, Co, and Ge with an atomic percentage of 0.91:1.09:1. The purity of the selected metallic elements should be 99.9% or higher. Place them in sequence into the water-cooled copper crucible in the furnace chamber of the electric arc melting furnace. After shutting down the electric arc melting furnace, turn on the mechanical pump, pre-evacuation valve, combined vacuum gauge, and shut-off valve to evacuate to below 5 Pa. Then, close all the above valves in reverse order, open the charging valve to charge high-purity argon gas to -0.08 Pa, and then close the charging valve. Repeat the above steps 3 times for gas purging.

[0038] 2. After the gas washing operation is completed, perform a high vacuum operation. Open the shut-off valve, close the pre-evacuation valve, and turn on the molecular pump and main evacuation valve to evacuate to 5 × 10⁻⁶. -3 Pa, complete the vacuum operation. Prepare for melting; first, purge with high-purity argon gas to -0.03 Pa, then close the purging valve and begin melting. During melting, ensure the current does not exceed 750 A, otherwise splashing may occur, leading to inaccurate alloy composition. To ensure uniform alloy composition, after the first melting, flip the alloy and activate magnetic stirring during the subsequent four remelting processes.

[0039] 3. The sample after arc melting is crushed and ground in an agate mortar for 2 hours until the powder reaches the micron level. The powder is then placed in a graphite mold and sintered in a vacuum hot-pressing furnace. The sintering temperature is 980℃, the sintering pressure is 30MPa, and the sintering time is 1 hour. To ensure good powder flowability during sintering, the furnace temperature is held at 700℃ for 30 minutes, while maintaining a pressure of 20MPa. The temperature and pressure are then increased to the target levels.

[0040] IV. The sintered sample was sealed in an argon-filled quartz tube and then subjected to solution heat treatment. The solution heat treatment temperature was 750℃, and the holding time was 1 hour. Subsequently, the sample was cooled in an ice-water mixture, and the oxide scale was removed from the cooled sample to obtain Mn. 0.91 Co 1.09 Ge alloy sample.

[0041] Specific Implementation Method Two: In this implementation method, the magnetic refrigeration alloy material is (Mn 0.91 Co 1.09 Ge) 0.99 Fe 0.01 The mass of Fe needs to be weighed according to the atomic ratio. The remaining steps are the same as in Specific Implementation Method 1.

[0042] Specific Implementation Method 3: In this implementation method, the magnetic refrigeration alloy material is (Mn 0.91 Co 1.09 Ge) 0.98 Fe 0.02 The mass of Fe needs to be weighed according to the atomic ratio. The remaining steps are the same as in Specific Implementation Method 1.

[0043] Specific Implementation Method Four: In this implementation method, the magnetic refrigeration alloy material is (Mn 0.91 Co 1.09 Ge) 0.97 Fe 0.03 The mass of Fe needs to be weighed according to the atomic ratio. The remaining steps are the same as in Specific Implementation Method 1.

[0044] All the MnCoGe-based alloys described above were prepared using hot-pressing sintering technology. This technology applies unidirectional mechanical pressure to the powder while heating it, achieving a simultaneous heating and pressurization sintering process. The pressure provides additional driving force, enhancing the contact and plastic flow between powder particles, resulting in products with near-theoretical density (typically >99%). This high density directly contributes to the material's excellent mechanical properties. Therefore, the density of the MnCoGe-based alloys prepared using this technology was calculated to determine whether the alloy possesses good density. The density was measured using the water displacement method, with the following formula: The results are shown in Table 1. As can be seen from the table, the density of all alloys in all embodiments is above 99%, close to the theoretical density, resulting in good mechanical properties and solving the problem of difficult forming of MnCoGe-based alloys.

[0045] Table 1 Hot pressing sintering (Mn) 0.91 Co 1.09 Ge) 1-x Fe x Density of the alloy (x=0,0.01,0.02,0.03)

[0046]

[0047] The phase structure of MnCoGe-based alloys consists of austenitic and martensitic phases at room temperature, with the transformation temperatures of the two phases as follows: Figure 1 As shown in the curves, the sample size was Ф2×1mm, and the heating and cooling rates were both 40K / min. The phase transformation temperatures in the figure were obtained using the tangent method. It is evident from the figure that all alloys prepared according to the specific embodiments exhibit a pair of exothermic and endothermic peaks on the DSC curves, with a significant hysteresis, confirming the first-order martensitic transformation. The absence of a Curie temperature peak on the curves further indicates that magnetic structural coupling occurred in the alloys. Furthermore, with increasing iron content, both the austenitic and martensitic transformation temperatures shift to lower temperatures. This is because the metallic radius of Fe is smaller than that of Mn; the substitution of Fe reduces the Mn-Mn spacing, and this contraction lowers the martensitic transformation temperature.

[0048] Figure 2 The images show the scanning electron microscope (SEM) images and grain size diagrams of the MnCoGe-based alloys in Methods 1 through 4. As can be seen from the figures, all samples have clear grain boundaries, and the microstructure consists of austenite and lath martensite phases. With increasing Fe content, the lath martensite content decreases while the austenite content increases, a result consistent with DSC results. Additionally, a small number of pores are observed in the scanning images, primarily originating from hot-pressing sintering, a characteristic inherent to this technique. Table 1 also shows that the material density is 99.25% or higher, indicating it is not completely dense, hence the presence of a small number of pores. Furthermore, the addition of Fe increases the grain size of the alloy, from 26.79 μm in Method 1 to 33.53 μm in Method 4. Fe addition alters the distribution of local bonding and defects (such as vacancies and point defects) within the grains, increasing the defect density near the grain boundaries. During heating, the accelerated migration of atoms along the grain boundaries promotes the merging of adjacent grains, thereby promoting grain growth. Some microcracks can also be seen in the figure, which are mainly due to uncontrolled cooling rate during heat treatment and mechanical stress caused during polishing, further proving the inherent brittleness of the alloy system.

[0049] Figure 3 Stress-strain diagrams of MnCoGe-based alloys prepared for all embodiments are shown, with a compression rate of 0.01 mm / min and sample size of 2 × 2 × 4 mm, until fracture. The diagrams show that the maximum compressive stress of the alloy in Embodiment 1 is 341 MPa, while that of the alloy in Embodiment 2 is 325 MPa, slightly lower than that of Embodiment 1. The compressive stresses of the alloys in Embodiments 3 and 4 also decrease monotonically, indicating a decrease in load-bearing capacity at high iron content. The stress-strain response is approximately linear, with no obvious yield plateau. The grain size of the alloys increases with increasing iron content. According to the Hall-Petch relationship, larger grains generally lead to poorer mechanical properties. In fine-grained samples, higher grain boundary density hinders the movement of dislocations and cracks under applied stress, requiring greater external force to propagate defects. Furthermore, from... Figure 2 As can be seen, with the addition of Fe, porosity and microcracks become more pronounced. These can act as stress concentration zones, promoting local instability and premature fracture in the alloy, thereby reducing its compressive strength. However, the compressive stress of the alloys prepared in all embodiments is currently the highest among MnCoGe-based alloys, which also indicates that the alloy prepared in this embodiment has excellent mechanical properties.

[0050] Figure 4 The compressive fracture morphology of the MnCoGe-based alloys prepared in all embodiments is shown at a magnification of 20 μm. The fracture morphology in the figure shows that the alloys obtained in all embodiments exhibit predominantly planar fracture surfaces with distinct cleavage patterns and river patterns, indicating brittle fracture. Figure 4 Some defects such as pores and microcracks can also be observed. These defects act as stress concentration points under load and are the sites of crack initiation. Once a microcrack is initiated, it preferentially propagates rapidly along the transgranular cleavage planes within the martensite laths or grains, resulting in a river-like fracture surface, i.e., transgranular cleavage fracture. Figure 4 The fracture surface also shows that some cracks propagate along grain boundaries, indicating that intergranular fracture also exists in the alloy. In general, the fracture mechanism of the alloy can be determined to be a combination of transgranular and intergranular fracture. The most cracks were observed in the fracture surface when the Fe content increased to 0.03%, which also reflects the reason why the mechanical properties of the alloy decrease with increasing Fe content. Figure 3 They corroborate each other.

[0051] Figure 5 Isothermal magnetization curves (MH curves) of MnCoGe-based alloys prepared for all embodiments are shown at different temperatures. MH curves are collected in small temperature increments within the martensite-to-austenite transformation region. The alloys maintained good mechanical integrity after multiple thermal cycles. fThe following describes the martensitic magnetization process. The magnetization curve shows an instantaneous increase in response to the applied magnetic field, followed by saturation, at which point the alloy exhibits ferromagnetic properties. In A... f The magnetization intensity changes almost linearly with the magnetic field, indicating that the austenite exhibits weak magnetism at this point. Within the phase transformation region, a magnetic field-driven martensitic transformation occurs, accompanied by hysteresis, indicating the transformation of weakly magnetic austenite into ferromagnetic martensite. This phenomenon is attributed to the Zeeman energy introduced by the magnetic field during the martensitic phase transformation. Alloys with an appropriate amount of Fe (Examples 2 and 3) show a greater increase in the MH curve near the phase transformation temperature, indicating enhanced magnetic coupling and increased sensitivity to field-induced phase transformation. Excess Fe (Example 4) reduces the initial slope and slightly decreases the saturation magnetization, indicating that the austenite-to-martensite transformation under the magnetic field is incomplete.

[0052] Figure 6 The magnetic entropy change of MnCoGe-based alloys prepared for all embodiments is shown as a function of temperature. Figure 6 As shown, the magnetization of the alloys in all embodiments changed drastically near the phase transition, indicating a significant change in the isothermal entropy change (ΔS). m Using Maxwell's relation: ,in accordance with Figure 5 The MH data in the calculation of ΔS for all alloys in all implementation methods m Value, result as Figure 6 As shown. |ΔS m The value increases approximately linearly with the applied magnetic field. Under conditions of 7T and 5T, the maximum |ΔS|... m The values ​​reached 36.2 J / kgK and 26.6 J / kgK, respectively. These values ​​are among the highest in existing magnetic refrigeration materials, indicating that the alloys prepared through all embodiments possess excellent magnetocaloric effects. Furthermore, with increasing iron content, |ΔS m The peak temperature of | gradually shifts to lower values, which is related to Figure 1 The measurement results are consistent.

Claims

1. A Fe-doped MnCoGe-based bulk magnetic refrigeration alloy, characterized in that... The general chemical formula of Fe-doped MnCoGe-based bulk magnetic refrigeration alloys is (Mn 0.91 Co 1.09 Ge) 1-x Fe x , 0≤x≤0.

03.

2. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy as described in claim 1, characterized in that... The preparation method of Fe-doped MnCoGe-based bulk magnetic refrigeration alloy is completed according to the following steps: I. Material Preparation: According to the general chemical formula (Mn) 0.91 Co 1.09 Ge) 1-x Fe x Prepare the ingredients, where 0≤x≤0.03, weigh out Mn metal, Co metal, Ge metal and Fe metal as raw materials respectively, and remove the oxide scale on the surface of the metal elements; II. Arc melting: The raw materials are placed in the copper crucible of a non-consumable high-vacuum arc melting furnace, and after gas washing, they are melted to obtain a melted alloy ingot.

3. The smelted alloy ingot is crushed and ground into powder. The powder is then placed in a graphite mold and sintered in a hot pressing furnace to obtain sintered alloy block material. IV. Solution Heat Treatment: The sintered bulk material is polished to remove the oxide scale, placed in a quartz tube filled with argon and sealed, and then subjected to solution heat treatment. After cooling in an ice-water mixture, a Fe-doped MnCoGe-based alloy bulk material with high mechanical properties and giant magnetocaloric effect is obtained.

3. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The gas washing process described in step two involves first evacuating the gas to below 5 MPa before alloy melting, then filling it with high-purity argon gas, and then evacuating the argon gas. This is one gas washing process, and the gas washing process is repeated more than three times.

4. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The melting process described in step two is completed under a working current of 50-500A, with the initial melting lasting 40 seconds, followed by 5 flips using a robotic arm.

5. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The grinding described in step three is carried out in an agate mortar for 2 hours to ensure that the alloy powder reaches the micron level.

6. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The argon furnace cleaning process described in step three before sintering involves first evacuating the furnace to below 1 MPa, then filling it with high-purity argon gas, and then evacuating the argon gas. This is one argon furnace cleaning process, and this process is repeated three times.

7. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The sintering described in step three is a staged sintering process. First, the temperature and pressure are maintained at 700℃ and 20MPa for 30 minutes, and then the temperature and pressure are increased to 980℃ and 30MPa, and maintained at 70℃ and 20MPa for 60 minutes.

8. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The sealing process described in step four is carried out under conditions of argon gas.

9. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The solution heat treatment in step four is performed at a temperature of 750°C for 1 hour.

10. The method for preparing an Fe-doped MnCoGe-based bulk magnetic refrigeration alloy according to claim 2, characterized in that... The Fe-doped MnCoGe-based alloy bulk material with high mechanical properties and giant magnetocaloric effect obtained in step four was polished with 200-grit sandpaper to remove oxide scale and cleaned with ethanol.

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