A polycrystalline Co-V-Ga-Si alloy, a preparation method and application thereof

Abstract

This invention proposes a polycrystalline Co-V-Ga-Si alloy, its preparation method, and its applications, belonging to the field of shape memory alloy solid-state refrigeration technology. The general chemical formula of the polycrystalline Co-V-Ga-Si alloy is Co. 50 V 35 Ga 15‑x Si x 0X1.5, where the subscript indicates atomic percentage content. The martensitic transformation temperature range of the alloy is 220-310 K, the fracture stress is greater than 1080 MPa, and it can produce an adiabatic temperature change greater than -5.1 K under 800 MPa stress. This invention improves the elastic-thermal properties of the Co-V-Ga alloy by introducing a certain amount of semiconductor Si element, and effectively reduces the critical stress driving the martensitic transformation and the stress hysteresis during the transformation process. This invention has the advantages of simple process flow, excellent hyperelastic properties, and large elastic-thermal temperature change of the alloy, and has broad application prospects in the field of solid-state refrigeration.

Description

Technical Field

[0001] This invention relates to the field of solid-state refrigeration technology of shape memory alloys, specifically to a polycrystalline Co-V-Ga-Si alloy, its preparation method, and its applications. Background Technology

[0002] With the acceleration of global industrialization and the continuous development of the social economy, energy shortage and environmental pollution have become two core challenges restricting the sustainable development of human society. Despite the rapid development of science and technology, the widely used refrigeration technology is still vapor compression refrigeration. Although this technology has been continuously optimized, the refrigerants used are either toxic (ammonia chemicals used in industry) or deplete the ozone layer or contribute to the greenhouse effect (chlorofluorocarbons and hydrofluorocarbons used in refrigerators and other appliances). Therefore, exploring new refrigeration technologies that are efficient, environmentally friendly, low-energy, or even zero-emission is not only a hot topic in academic research but also an urgent industrial need and social responsibility to address the dual pressures of the energy crisis and environmental protection. This has prompted the scientific community to turn its attention to solid-state refrigeration technology, which does not rely on traditional gas-liquid phase change refrigerants and theoretically has higher energy conversion efficiency. Among these technologies, the elastothermal effect (eCE) has become an important direction for cutting-edge research due to its excellent performance potential.

[0003] Based on the heat absorption and release properties (i.e., thermal effect) of solid materials, novel solid-state refrigeration technology, with its energy-saving and environmentally friendly advantages, is considered a potential alternative to existing refrigeration technologies. Over the past decade, much research on eCE (excessive heat exchanger) has focused on shape memory alloys (SMAs). Researchers have been dedicated to achieving large-scale eCE in materials such as Co-based, Cu-based, Ni-Ti-based, and Ni-Mn-based alloys. Although these Heusler-type SMAs can produce a certain degree of adiabatic temperature change during unloading... However, its practical application as a solid refrigerant is still limited by significant stress hysteresis or inherent brittleness, resulting in limited ductility and insufficient fatigue resistance.

[0004] In recent years, a class of based Heusler-type shape memory alloys have attracted widespread research attention due to their diverse and multifunctional properties. Compared to Heusler alloys that have been extensively studied (such as Ni-Mn based systems), these alloys are particularly important due to their superior mechanical properties. Studies have shown that... The alloy, under a stress of 291 MPa, exhibits a yield of 5.6 × 10⁻⁶. -2 s -1 The strain rate remained at 6.2 K for 200 cycles. The alloy is at 2.7 × 10 -3 s -1At strain rates of [specific strain rate], it exhibited significantly improved cyclic stability, exceeding 4000 cycles. Despite [specific strain rate], [specific strain rate], it demonstrated significantly improved cyclic stability. The alloy exhibited significantly enhanced cycling performance, but its adiabatic temperature change was reduced to some extent. (Lower) The current value is still insufficient for practical applications. Therefore, it is necessary to study a completely new method. Shape memory alloys and their preparation methods can compensate for the shortcomings of existing solid-state elasto-thermal cooling technology. It is particularly important to improve their cycle stability while ensuring a large elasto-thermal effect. At the same time, the alloy can only have good cycle stability after it has stable superelasticity. Summary of the Invention

[0005] The present invention aims to solve the existing problems. To address the issues of high critical stress required for stress-induced martensitic phase transformation and low elasto-thermal effect in shape memory alloy elasto-thermal cooling materials, a polycrystalline alloy with a large elasto-thermal effect is proposed for solid-state cooling. Shape memory alloys and their preparation methods.

[0006] The technical solution of this invention is implemented as follows: This invention provides a polycrystalline Alloy, the polycrystalline The general chemical formula of the alloy is , The subscript indicates the atomic percentage content.

[0007] As a further improvement of the present invention, the martensitic phase transformation temperature range of the alloy is 220-310 K, the fracture stress is greater than 1080 MPa, and an adiabatic temperature change greater than -5.1 K can be generated under 800 MPa stress.

[0008] This invention further protects the above-mentioned polycrystalline material. The preparation method of the alloy includes the following steps: weighing according to the general chemical formula... Metallic elements, Metallic elements, Metallic elements and Using elemental metals as raw materials, alloy ingots are prepared by high-temperature melting, and then the ingots are heat-treated in an inert gas, followed by quenching to obtain the polycrystalline alloy.

[0009] As a further improvement of the present invention, the high-temperature melting is electric arc melting or induction melting.

[0010] As a further improvement of the present invention, the heat treatment is high-purity argon gas-protected tube sealing annealing, with a temperature range of 800-1100 ℃ and an annealing time of 6-120 h.

[0011] As a further improvement of the present invention, the quenching process is cooling in an ice-water mixture.

[0012] The above-mentioned polycrystalline material with large elastic-thermal effect The preparation method of shape memory alloys is completed according to the following steps: I. Material Preparation: The ingredients used are as follows The proportions, with high purity , , , The raw materials were formulated using elements (all with a purity higher than 99.9 wt.%). II. Arc Melting: Alloy button ingots are prepared by arc melting. The melting process is carried out under the protection of high-purity argon gas. The mass loss of all ingots after melting is less than 0.5%. To ensure the uniformity of the chemical composition of the alloy ingots, after each melting, the button ingots are carefully flipped over using a special flipping spoon, and the reverse side is melted again. The above process is repeated no less than three times. Throughout the entire melting process, the melting time of each session must be strictly controlled to minimize metal volatilization loss and possible oxidation. III. Homogenization heat treatment: In order to achieve uniform element distribution, the sample is sealed in a vacuum quartz tube protected by argon and placed in a muffle furnace for homogenization annealing at 800-1100 ℃ for 6-120 hours. After annealing, it is quickly quenched in cold water to retain a uniform structure.

[0013] This invention further protects the above-mentioned polycrystalline material. Application of alloys in solid-state refrigeration of shape memory alloys.

[0014] The present invention has the following beneficial effects: This invention is based on Introducing semiconductors into alloys Elements, thus significantly and effectively improving This invention improves the compressive strength and plasticity of the alloy while also giving it excellent elastic and thermal properties. The invention achieves this by introducing... This further reduced In alloys The amount of alloy used is reduced, thereby lowering the processing cost of the alloy and giving it high economic value.

[0015] The present invention prepared Bulk polycrystalline alloys with Elemental doping increases the valence electron concentration (e / a) in the alloy system, leading to a decrease in the martensitic phase transformation temperature. The K of the alloy was gradually increased to 235.2 K. The alloy exhibits a monotonically increasing K value towards room temperature at 302.3 K, and simultaneously achieves a large unloading adiabatic temperature change of -10.5 K under uniaxial stress of 800 MPa, which is superior to similar alloys prepared by other methods. Furthermore, the lower critical driving stress further enhances the cyclic stability of the elastothermal cooling material; after more than 6000 load-unload cycles, the adiabatic temperature change of this alloy did not show a significant decrease. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 Prepared in Examples 1-4 , DSC curve of the alloy; Figure 2 Prepared in Examples 1-4 , XRD pattern of the alloy; Figure 3 Prepared in Examples 1-4 , Alloy at strain rate Hyperelastic stress-strain response under a stress of 800 MPa; Figure 4 Prepared in Examples 1-4 , The alloy is used at room temperature. The loading strain rate and The stress-strain curve was tested by measuring the unloading strain rate. Figure 5 Prepared in Examples 1-4 , The alloy is used at room temperature. The loading strain rate and The room temperature stress-strain curves were obtained by measuring the unloading strain rate. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] A polycrystalline material with a large elastic-thermal effect Shape memory alloys and their preparation methods are as follows: Step 1: Weigh according to atomic percentage The raw materials are: 50 at% Co, 35 at% V, 13.5~15 at% Ga, and 0~1.5 at% Si. The above raw materials are placed in a vacuum arc melting furnace. Step Two: Vacuum arc melting is performed using a vacuum arc melting furnace to obtain alloy ingots. The vacuum arc melting process begins with evacuation to approximately 1 Pa. The evacuation valve is then closed, and high-purity argon gas is introduced to near atmospheric pressure. This process is repeated three times to thoroughly remove air from the furnace. A molecular pump is then activated to continue evacuating to a high vacuum (furnace pressure ≤ 1 × 10⁻⁶). -3 Finally, argon gas is introduced to approximately 0.6 atmospheres. After arc ignition, the melting current is adjusted to 200 A to melt the central zirconium ingot in the furnace to remove residual oxygen and ensure the sample is in an argon-protected environment. The current is then adjusted to 280 A, and the alloy material in each pit is melted sequentially using an electric arc. To ensure the uniformity of the alloy ingot's chemical composition, after each melting, the ingot is carefully flipped using a special sample flipping spoon, and the reverse side is melted again. This process is repeated at least three times. Throughout the melting process, the melting time for each session must be strictly controlled to minimize metal volatilization loss and potential oxidation. During each melting process, the electromagnetic stirring device at the bottom of the copper mold is activated to promote convection within the melt using electromagnetic force, thereby further improving the uniformity of the composition. It is particularly important to note that before each sample melting, the pure zirconium ingot in the central pit must first be melted completely. The strong adsorption capacity of zirconium for residual oxygen at high temperatures further purifies the furnace atmosphere, providing a clean environment for subsequent sample melting. Step 3: Cut the alloy ingot into rectangular samples of 3×3×6 mm; Step 4: Polish the cut alloy ingot to remove surface impurities, clean it, and then place it into the bottom of a pre-sealed quartz tube. Connect the quartz tube to a vacuum system and perform multiple vacuuming and argon purging cycles, following the gas washing process before melting and casting, to thoroughly remove air from the tube. During the final purging, control the argon pressure at approximately 0.7 atmospheres to ensure pressure balance inside and outside the quartz tube during high-temperature annealing and prevent bursting due to excessive internal pressure. Seal the tube opening with a solid quartz cylinder whose outer diameter is slightly smaller than the inner diameter of the quartz tube, and mark the tube wall according to the alloy composition. Finally, place the sealed quartz tube in a muffle furnace and anneal it at the target temperature and holding time. After annealing, quickly remove the quartz tube with a long-handled clamp and quench it in cold water to preserve the phase structure and atomic order at high temperatures. The treatment temperature is 1300 K, and the treatment time is 24 hours.

[0020] Example 1

[0021] The shape memory alloy of this embodiment ,for The specific preparation process of shape memory alloys is as follows: Before the melting experiment, the arc rod electrode connected to the electrode rod in the melting furnace was cleaned and sharpened. Pure zirconium was placed in the central recess of the copper mold to initiate the arc and to adsorb residual gases during the melting process. The prepared metal raw materials were placed in the melting pit, arranged in order of increasing melting point. 8.673g Co, 5.248g V, and 3.078g Ga were weighed and placed in the melting furnace. Under an argon atmosphere at 0.6 atmospheres, the pure zirconium was positioned at the bottom of the arc lance, and the distance between the arc lance and the pure zirconium was adjusted to within 1-2 mm for arc initiation. The current was slowly increased until the pure zirconium melted completely to adsorb residual gases. Magnetic stirring was applied during the melting process to ensure the homogeneity of the sample composition. After cooling, the sample was flipped with a mechanical spatula and melting continued. Each sample was melted at least three times. After all samples were melted, the ingot was allowed to cool completely. The chamber was opened, the sample was removed, and weighed to ensure a mass loss of less than 0.5%. Shape memory alloy. The molten sample was sealed in an argon-filled quartz tube, placed in a muffle furnace at 850 °C for 96 hours, and then quenched in cold water.

[0022] Example 2

[0023] The shape memory alloy of this embodiment ,for The specific preparation process of shape memory alloys is as follows: Before the melting experiment, the arc rod electrode connected to the electrode rod in the melting furnace was cleaned and sharpened. Pure zirconium was placed in the central recess of the copper mold to initiate the arc and to adsorb residual gases during the melting process. The prepared metal raw materials were placed in the melting pit, arranged in order of increasing melting point. 8.704g Co, 5.267g V, 2.986g Ga, and 0.041g Si were weighed and placed in the melting furnace. Under an argon atmosphere at 0.6 atmospheres, the pure zirconium was positioned at the bottom of the arc gun, and the distance between the arc-initiating electrode and the pure zirconium was adjusted to within 1-2mm to initiate the arc. The current was slowly increased until the pure zirconium melted completely to adsorb residual gases. Magnetic stirring was applied during the melting process to ensure the uniformity of the sample composition. After cooling, the sample was flipped with a mechanical spatula and melting continued. Each sample was melted three times. After all samples were melted, the ingot was allowed to cool completely. The chamber was opened, the sample was removed, and weighed to ensure a mass loss of less than 0.5%. Shape memory alloy. The molten sample was sealed in an argon-filled quartz tube, placed in a muffle furnace at 950 °C for 72 hours, and then quenched in cold water.

[0024] Example 3

[0025] The shape memory alloy of this embodiment ,for The specific preparation process of shape memory alloys is as follows: Before the melting experiment, the arc rod electrode connected to the electrode rod in the melting furnace was cleaned and sharpened. Pure zirconium was placed in the central recess of the copper mold to initiate the arc and to adsorb residual gases during the melting process. The prepared metal raw materials were placed in the melting pit, arranged in order of increasing melting point. 8.736g Co, 5.286g V, 2.894g Ga, and 0.083g Si were weighed and placed in the melting furnace. Under an argon atmosphere at 0.6 atmospheres, the pure zirconium was positioned at the bottom of the arc gun, and the distance between the arc gun and the pure zirconium was adjusted to within 1-2mm to initiate the arc. The current was slowly increased until the pure zirconium melted completely to adsorb residual gases. Magnetic stirring was applied during the melting process to ensure the uniformity of the sample composition. After cooling, the sample was flipped with a mechanical spatula and melting continued. Each sample was melted three times. After all samples were melted, the ingot was allowed to cool completely. The chamber was opened, the sample was removed, and weighed to ensure a mass loss of less than 0.5%, yielding Co. 50 V 35 Ga 15 Si1 shape memory alloy. The molten sample was sealed in an argon-filled quartz tube, placed in a muffle furnace at 1000 ℃ for 48 hours, and then quenched in cold water.

[0026] Example 4

[0027] The shape memory alloy of this embodiment ,for

[0028] The specific preparation process of shape memory alloys is as follows: Before the melting experiment, the arc rod electrode connected to the electrode rod in the melting furnace was cleaned and sharpened. Pure zirconium was placed in the central recess of the copper mold to initiate the arc and to adsorb residual gases during the melting process. The prepared metal raw materials were placed in the melting pit, arranged in order of increasing melting point. 8.768g Co, 5.305g V, 2.801g Ga, and 0.125g Si were weighed and placed in the melting furnace. Under an argon atmosphere at 0.6 atmospheres, the pure zirconium was positioned at the bottom of the arc gun, and the distance between the arc gun and the pure zirconium was adjusted to within 1-2mm to initiate the arc. The current was slowly increased until the pure zirconium melted completely to adsorb residual gases. Magnetic stirring was applied during the melting process to ensure the uniformity of the sample composition. After cooling, the sample was flipped with a mechanical spatula and melting continued. Each sample was melted repeatedly three times. After all samples were melted, the ingot was allowed to cool completely. The chamber was opened, the sample was removed, and weighed to ensure a mass loss of less than 0.5%. Shape memory alloy. The molten sample was sealed in an argon-filled quartz tube, placed in a muffle furnace at 1050 °C for 24 hours, and then quenched in cold water.

[0029] Performance testing Figure 1 Prepared in Examples 1-4 , The DSC curve of the alloy. As shown in the figure, the exothermic and endothermic peaks observed in the 220–300 K temperature range correspond to the temperature-driven martensitic phase transformation and its reverse phase transformation, respectively. Moreover, the endothermic and exothermic peaks of each sample show a certain thermal hysteresis, indicating that the phase transformation is a first-order phase transformation. The martensitic transformation temperature of the alloy increases with increasing Si doping content. , , , The martensitic transformation temperatures of the alloys are approximately 235.2 K, 247.3 K, 259.0 K, and 302.3 K, respectively.

[0030] Figure 2 Prepared in Examples 1-4 , The XRD curve of the alloy shows that the alloy exhibits characteristic peaks of typical (220) and (400) L21 austenitic structures.

[0031] Figure 3 Prepared in Examples 1-4 , Alloy at strain rate Hyperelastic stress-strain response under a stress of 800 MPa; as shown in the figure, with With increasing doping content, the critical stress required for the alloy to induce martensitic phase transformation gradually decreases. , , , The critical stresses for martensitic transformation of the alloys are 261 MPa, 229 MPa, 134 MPa, and 72 MPa, respectively.

[0032] Figure 4 Prepared in Examples 1-4 , The alloy is used at room temperature. The loading strain rate and Stress-strain curves were tested using the unloaded strain rate. As shown in the figure, the undoped Si alloy maintained extremely low residual strain throughout the progressively increasing loading-unloading cycles, with each cycle curve exhibiting good closure and typical reversible hyperelastic behavior. With increasing doping content, the superelastic behavior of the alloy changes significantly. and The alloy maintains low residual strain under various stress levels, exhibits good curve closure, and demonstrates excellent hyperelastic properties. However, when Doping level increased to At that time, the superelastic behavior of the alloy degrades to some extent.

[0033] Figure 5 Prepared in Examples 1-4 , The alloy is used at room temperature. The loading strain rate and The room temperature stress-strain curves obtained from the unloading strain rate show that the adiabatic temperature change of all alloys exhibits a significant dependence on the applied stress. As the maximum applied stress gradually increases from 300 MPa to 800 MPa, both the exothermic peak generated during loading and the endothermic peak generated during unloading show a gradually increasing trend. The alloy achieved the best temperature change of 10.5 K in the series; when the Si doping content was further increased to 1.5%, the elastothermal effect decreased slightly to 9.7 K.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polycrystalline Alloy, characterized in that, The polycrystalline The general chemical formula of the alloy is , The subscript indicates the atomic percentage content.

2. The polycrystalline material according to claim 1 Alloy, characterized in that, The alloy has a martensitic transformation temperature range of 220-310 K, a fracture stress greater than 1080 MPa, and can produce an adiabatic temperature change greater than -5.1 K under a stress of 800 MPa.

3. A polycrystalline material as described in claim 1 or 2 The method for preparing the alloy is characterized in that, The steps include: weighing out the following substances according to their general chemical formulas. Metallic elements, Metallic elements, Metallic elements and Using elemental metals as raw materials, alloy ingots are prepared by high-temperature melting, and then the ingots are heat-treated in an inert gas, followed by quenching to obtain the polycrystalline alloy.

4. The preparation method according to claim 3, characterized in that, The high-temperature melting is either electric arc melting or induction melting.

5. The preparation method according to claim 3, characterized in that, The heat treatment is a high-purity argon-protected tube sealing annealing, with a temperature range of 800-1100 ℃ and an annealing time of 6-120 h.

6. The preparation method according to claim 3, characterized in that, The quenching process involves cooling in an ice-water mixture.

7. A polycrystalline material as described in claim 1 or 2 Application of alloys in solid-state refrigeration of shape memory alloys.

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