A method for preparing a high-temperature-resistant memory metal for a temperature control device

Abstract

This invention relates to the field of metal materials technology, specifically to a method for preparing a high-temperature resistant shape memory metal for temperature control devices. The method includes S1 raw material smelting, S2 ingot pretreatment, S3 forming and processing, S4 heat treatment, and S5 surface treatment. In this invention, by adding the prepared nanorod composite material to the shape memory metal raw material, the nanorod composite material acts like a "skeleton" to anchor grain boundaries, preventing grain growth or grain boundary softening at high temperatures, enhancing the stability of the crystal structure, and preventing it from being easily "disintegrated" at high temperatures. This maintains the reversibility of phase transformation and preserves mechanical properties. Furthermore, the nanorod composite materials are interconnected through a surface-coated fibrous network structure, forming a continuous phase nanorod layer that isolates oxygen, preventing further oxidation and corrosion of the internal metal. This ensures stable performance even at high temperatures, effectively improving the high-temperature resistance of the shape memory metal.

Description

Technical Field

[0001] This invention relates to the field of metal materials technology, specifically to a method for preparing a high-temperature resistant shape memory metal for use in temperature control devices. Background Technology

[0002] Shape memory metals, as a novel functional material, possess unique shape memory effects and properties such as wear and corrosion resistance, making them promising for applications in aerospace, medical devices, and temperature control systems. Traditional shape memory metals primarily achieve their shape memory function through alloy systems like nickel-titanium, but these systems suffer from significant performance degradation at high temperatures. Current technologies improve the mechanical properties of shape memory metals by adding nanomaterials during the metal smelting process; for example, adding rod-shaped nanomaterials to iron-nickel-based alloys to construct a support structure. While this improves the material's plastic deformation capacity to some extent, it fails to fundamentally address the issue of crystal structure stability at high temperatures. Particularly in applications requiring long-term operation at high temperatures, such as temperature control devices, conventional shape memory metals are prone to lattice distortion and phase transition temperature drift, leading to shape memory failure. Furthermore, existing manufacturing processes lack sufficient control over the uniformity of nanomaterial dispersion and interfacial bonding strength, further impacting the material's performance stability under high-temperature conditions. These issues severely restrict the reliable application of shape memory metals in high-temperature environments.

[0003] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-temperature resistant shape memory metal and its nanorod composite material for temperature control devices, which has the advantages of improving the stability of crystal structure under high temperature environment, enhancing the dispersion uniformity of nanomaterials and the interfacial bonding strength.

[0005] This invention provides a method for preparing a high-temperature resistant shape memory metal for a temperature control device, specifically including the following steps: S1 Raw material smelting: Metal raw materials are added to a smelting furnace, vacuumed to 10⁻³-10⁻⁴ Pa, and the temperature is controlled at 1700-1750℃. During the smelting process, the materials are continuously turned over to promote complete melting. Then, nanorod composite materials are added, thoroughly mixed, and refined to obtain a refined solution; S2 Ingot pretreatment: The refined solution is cast into an ingot, which is then placed in an argon atmosphere annealing furnace at 900- Hold at 1000℃ for 5-8 hours, then slowly cool to room temperature; S3 Forming Processing: Heat the cooled ingot to 800-900℃ and hot forge it using a press, controlling the deformation amount at 20-30% each time, and repeatedly forge to the target size; S4 Heat Treatment: Fix the forged metal in a mold, place it in an argon atmosphere calcining furnace, hold it at 450-550℃ for 30-50 minutes, and then quickly cool it by water quenching; S5 Surface Treatment: Mechanically polish the heat-treated metal to remove scratches and oxide layers.

[0006] Furthermore, the present invention also proposes that in S1, the metal raw materials, by mass percentage, consist of Ni 29-33%, Co 7-13%, Ti 2-5%, Mn≤0.5%, Si≤0.5%, C≤0.2%, P≤0.01%, S≤0.01%, with the balance being Fe; the amount of nanorod composite material added accounts for 3.2-4.6% of the total raw materials.

[0007] Furthermore, the present invention also proposes that in S2, the cooling rate of slow cooling is 50-80℃ / h.

[0008] Furthermore, the present invention also proposes a method for preparing nanorod composite materials as follows: 1) Add isopropyl titanate and deionized water to a container at a mass ratio of 1:(10-12), stir at room temperature for 30-50 min, centrifuge for 5-10 min after stirring, wash repeatedly with deionized water, and freeze-dry to obtain titanium dioxide nanoparticles; 2) Add porous nanorod materials and titanium dioxide nanoparticles to sufficient deionized water at a mass ratio of 1:(5-8), mechanically stir for 1-2 h, and then sonicate. After processing for 1-2 hours, the product is centrifuged and dried to obtain pretreated porous nanorods; 3) The pretreated porous nanorods are added to sodium hydroxide solution, mixed and transferred to a reaction vessel, and then placed in a constant temperature oven for hydrothermal reaction at 120-125℃ for 4-6 hours. After the reaction is completed, the product is naturally cooled to room temperature, and after standing, the upper layer of sodium hydroxide solution is poured off. The residual sodium hydroxide on the surface of the product is removed with hydrochloric acid solution, and then repeatedly rinsed with deionized water until neutral. After freeze-drying, the nanorod composite material can be obtained.

[0009] Furthermore, the present invention also proposes that in step 1), the stirring speed is 500-800 r / min; and the centrifugation speed is 5000-8000 r / min.

[0010] Furthermore, the present invention also proposes that in step 2), the mechanical stirring speed is 500-800 r / min; and the ultrasonic treatment power is 500-800 W.

[0011] Furthermore, the present invention also proposes that in step 3), the ratio of the amount of pretreated porous nanorods to sodium hydroxide solution is (1-3) g: (100-300) mL; the concentration of sodium hydroxide solution is 10-13 mol / L; and the concentration of hydrochloric acid solution is 0.1-0.2 mol / L.

[0012] Furthermore, the present invention also proposes a method for preparing porous nanorod materials as follows: a) Ammonium molybdate tetrahydrate is dissolved in an acid solution, and after complete dissolution, it is transferred to a reaction vessel and reacted at a constant temperature of 200-210℃ for 20-25h. After the reaction is completed, it is naturally cooled to room temperature. The product obtained after centrifugation is repeatedly washed with deionized water and ethanol, and then vacuum dried at 70-80℃ for 12-15h to obtain a molybdenum oxide precursor; b) The molybdenum oxide precursor and glucose are placed in a mortar, ground thoroughly, and then mixed evenly. The mixture is then transferred to an alumina ceramic boat and placed in a tube furnace. Under a high-purity argon atmosphere, the temperature is raised to 800-850℃ and carbonized at a constant temperature for 2-3h. After natural cooling to room temperature, the product is thoroughly centrifuged, washed, and dried to obtain porous nanorod materials.

[0013] Furthermore, the present invention also proposes that in step a), the ratio of ammonium molybdate tetrahydrate to acid solution is (7-12) g: (200-360) mL; the acid solution is composed of 68% concentrated nitric acid and deionized water in a volume ratio of 1: (5.0-5.5).

[0014] Furthermore, the present invention also proposes that in step b), the mass ratio of molybdenum oxide precursor to glucose is 1:(2.0-2.5); and the heating rate is 5-8℃ / min.

[0015] As can be seen from the above, the high-temperature resistant shape memory metal for temperature control devices provided by the present invention effectively suppresses high-temperature lattice distortion and improves interfacial bonding strength through vacuum melting combined with nanorod composite material reinforcement, gradient heat treatment process and porous nanorod structure design. It has the advantages of improving crystal structure stability under high temperature environment, enhancing the dispersion uniformity of nanomaterials and interfacial bonding strength. Detailed Implementation

[0016] 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.

[0017] In existing technologies, shape memory materials generally suffer from crystal structure instability at high temperatures, leading to a decay of the shape memory effect. Traditional shape memory alloys, such as iron-nickel-based alloys, experience hindered reversible transformation between the austenite and martensite phases above the critical temperature, and slip deformation easily occurs at grain boundaries. This makes it difficult for temperature control devices to maintain stable shape recovery capabilities under sustained high-temperature conditions. For example, some alloy materials prepared using conventional casting processes exhibit grain coarsening during temperature cycling, causing a shift in the material's phase transformation temperature range.

[0018] To address these issues, researchers discovered a close relationship between the high-temperature stability of materials and the integrity of their crystal structure. Analysis of the high-temperature failure mechanism revealed the need to construct stable grain boundary reinforcing phases within the alloy matrix, while simultaneously optimizing the energy barrier during phase transformation. Based on this, a solution was proposed: introducing nano-reinforcing phases during the melting stage to pin grain boundaries, combined with a multi-stage thermomechanical treatment process to control crystal orientation.

[0019] Therefore, this invention proposes a preparation method including raw material smelting, ingot pretreatment, forming and processing, heat treatment, and surface treatment. Metal raw materials are melted at high temperature under vacuum and then added to a nanorod composite material. After casting and molding, the material undergoes argon-protected annealing, followed by multiple hot forging processes. Finally, phase structure regulation is achieved through short-time holding and water quenching within a specific temperature range.

[0020] Among them, tumbling melting refers to a process in which the spatial orientation of the furnace is periodically changed during the melting process to promote uniform mixing of the melt. This can be carried out using a vacuum induction melting furnace with a three-dimensional rotating mechanism, and this operation can eliminate component segregation in the molten pool. Nanorod composites refer to one-dimensional nano-reinforcements with high aspect ratios, which can be prepared by hydrothermal synthesis. They act as heterogeneous nucleation sites during alloy solidification, promoting the formation of fine grains. Argon atmosphere annealing refers to recrystallization treatment carried out in an inert gas environment. High-purity argon is introduced into a tubular annealing furnace to maintain a protective atmosphere. This process can eliminate casting stress and stabilize the austenitic matrix. Gradient hot forging refers to a plastic deformation process carried out in steps above the phase transformation temperature. A multi-directional forging press is used to apply pressure in steps according to a preset deformation amount, and dynamic recrystallization is promoted by accumulating strain energy. Water quenching refers to a process in which high-temperature workpieces are rapidly cooled to below the martensitic phase transformation temperature. A high-pressure water jet device is used to achieve rapid heat exchange. This process can fix the high-temperature phase structure and inhibit grain growth.

[0021] Specifically, in the vacuum melting stage, metallic elements achieve atomic-level mixing in a low-oxygen environment, and the addition of nanorods forms a dispersed reinforcing phase network. During ingot annealing, the slow cooling rate allows austenite grains to grow sufficiently and establish a stable crystal orientation. During hot forging, the step-by-step deformation strategy avoids overwork hardening and refines the grain size through dislocation multiplication. In the final heat treatment stage, precisely controlled holding temperatures keep the material in the austenite-martensite dual-phase region, and water quenching locks in a phase structure conducive to shape memory effects. The systematic coordination of parameters in each process, especially the synergistic effect of the nano-reinforcing phase and thermomechanical treatment, effectively improves the high-temperature phase transformation stability of the alloy.

[0022] Compared with existing technologies, traditional methods mostly employ a single heat treatment process to control phase structure, lacking in-depth application of grain boundary strengthening mechanisms. This solution introduces a nano-reinforcing phase to construct a three-dimensional strengthening network, combined with a multi-stage deformation heat treatment process, forming a systematic solution for crystal orientation optimization and grain boundary stability control. The direct quenching process commonly used in existing technologies easily induces residual stress concentration, while the gradient hot forging and step-by-step cooling strategy employed in this solution significantly improves the internal stress distribution of the material.

[0023] Through the above technical solution, this invention effectively suppresses grain boundary slip and abnormal grain growth under high-temperature conditions, enabling shape memory alloys to maintain stable austenite-martensite reversible transformation capabilities even under continuous high-temperature conditions. Actual testing shows that the prepared alloy material exhibits a stable shape recovery rate within the set phase transformation temperature range, making it suitable for temperature control device actuators that need to operate in high-temperature environments for extended periods. This technical solution provides a reliable technical path to solve the high-temperature instability problem of shape memory alloys through a combination of material modification and process innovation.

[0024] The present invention further proposes that in the raw material smelting step, the metal raw materials are composed of nickel 29-33%, cobalt 7-13%, titanium 2-5%, manganese ≤0.5%, silicon ≤0.5%, carbon ≤0.2%, phosphorus ≤0.01%, sulfur ≤0.01%, and the balance iron by mass percentage, and the amount of nanorod composite material added accounts for 3.2-4.6% of the total raw materials.

[0025] Among these, the nickel content, controlled at 29-33%, is a key element for forming the austenitic matrix. This can be achieved by adjusting the proportion of nickel-based alloys during the smelting process. This content range ensures high-temperature phase stability while avoiding excessive brittleness. The cobalt content, 7-13%, enhances the alloy's resistance to high-temperature creep. This can be achieved by forming a solid solution with nickel, effectively suppressing lattice distortion at high temperatures. The titanium content, 2-5%, is a key element for controlling the phase transformation temperature. This can be achieved by forming intermetallic compounds with nickel, ensuring the reversibility of the phase transformation at high temperatures. The nanorod composite material addition amount, 3.2-4.6%, is a key parameter for enhancing the matrix strength through nanoparticle dispersion reinforcement. This can be achieved by adding it to the melt in batches. This proportion ensures interfacial bonding strength while avoiding excessive addition that would reduce melt fluidity.

[0026] Specifically, nickel, as the main component of the matrix phase, enhances high-temperature stability by forming a solid solution with cobalt. The addition of titanium promotes the uniform precipitation of intermetallic compounds at grain boundaries, effectively pinning grain boundary movement. Strict restrictions on impurity elements such as manganese and silicon reduce grain boundary segregation. The uniform dispersion of the nanorod composite material in the melt forms a dislocation strengthening network. The synergistic effect of these three elements allows the material to maintain a stable crystal structure even at high temperatures. By controlling the amount of nanomaterials added, both the increase in melt viscosity due to excessive addition and the sufficient dispersion of nanoparticles to form an effective reinforcing phase are avoided.

[0027] The present invention further proposes to control the cooling rate within the range of 50-80℃ / h during the cooling process after annealing in an argon atmosphere.

[0028] The slow cooling rate refers to the range of rates at which the ingot cools from a high temperature to room temperature after the annealing holding period. This can be achieved through a programmed temperature control device, such as setting a gradient cooling program in the annealing furnace to ensure the temperature decreases uniformly at a preset rate. This rate range balances grain growth and stress release, preventing microcracks at grain boundaries due to excessively rapid cooling while also preventing abnormal grain growth caused by excessively slow cooling.

[0029] Specifically, recrystallization occurs within the metal during annealing at 900-1000℃, at which point atoms possess high migration capabilities. When the temperature is lowered at a rate of 50-80℃ / h, the austenite-to-martensite phase transformation is controlled within a reasonable time window. At this rate, the lattice distortion caused by the phase transformation can be gradually released through atomic diffusion, while excessive precipitation of second-phase particles at grain boundaries is suppressed. The resulting uniform, fine-grained structure effectively resists dislocation slip under high-temperature conditions and maintains stable orientation relationships between martensite variants.

[0030] The present invention further proposes a method for preparing nanorod composite materials, comprising the following steps: mixing and stirring isopropyl titanate and deionized water in a certain proportion, centrifuging and washing to obtain titanium dioxide nanoparticles; dispersing porous nanorod materials and titanium dioxide particles in deionized water in a certain proportion, and obtaining pretreated materials by mechanical stirring and ultrasonic treatment; subjecting the pretreated materials to a hydrothermal reaction with sodium hydroxide solution, and obtaining nanorod composite materials after acid and alkali washing.

[0031] The mass ratio of isopropyl titanate to deionized water, 1:(10-12), refers to the ratio of titanium source to solvent in the hydrolysis reaction. A ratio of 1:11 can be used to control the formation rate and particle size distribution of titanium dioxide particles. The centrifugal speed of 5000-8000 r / min refers to the operating parameter for separating unreacted substances. For example, a speed of 6000 r / min can be used to achieve solid-liquid separation, ensuring effective removal of impurities from the particle surface. The hydrothermal reaction temperature of 120-125℃ refers to the constant temperature maintained in the reactor. For example, a temperature of 123℃ can be used to achieve structural reconstruction. This temperature range avoids damage to the nanorod morphology and promotes pore formation. The hydrochloric acid solution concentration of 0.1-0.2 mol / L refers to the reagent concentration for neutralizing residual alkali. A dilute hydrochloric acid solution of 0.15 mol / L can be used, which removes alkaline residues without corroding the material itself.

[0032] Specifically, a multi-level composite structure is constructed through a stepwise preparation process. Titanium dioxide nanoparticles generated from the hydrolysis of isopropyl titanate possess high melting points, providing a heat-resistant framework for the composite material. The synergistic effect of mechanical stirring and ultrasonic treatment ensures a uniform dispersion of porous nanorods and titanium dioxide particles, enhancing interfacial bonding strength. The hydrothermal reaction in an alkaline environment promotes etching and reorganization on the nanorod surface, forming a stable three-dimensional porous network structure. Acid-base cleaning effectively removes reaction byproducts and impurities, ensuring the material's chemical stability. This composite structure can suppress grain boundary migration at high temperatures, buffering thermal stress through pores, thereby maintaining the crystal structure stability of the shape memory metal.

[0033] The present invention further proposes that, in the process of preparing titanium dioxide nanoparticles, the stirring speed should be controlled at 500-800 rpm and the centrifugation speed should be controlled at 5000-8000 rpm.

[0034] The stirring speed refers to the mechanical stirring rate when mixing isopropyl titanate and deionized water. This can be achieved using a variable frequency speed-controlled stirrer. By controlling the speed range, the hydrolysis reaction can be fully completed while preventing particle agglomeration. The centrifugal speed refers to the rotational speed used to separate the reaction products. This can be achieved using a high-speed centrifuge. By controlling the centrifugal force range, impurities can be effectively separated while maintaining the integrity of the particle structure.

[0035] Specifically, the selection of the stirring speed range balances the mixing efficiency and the influence of shear force. Within the range of 500-800 rpm, it can promote the uniform hydrolysis of isopropyl titanate to form titanium dioxide nanoparticles, while avoiding particle aggregation due to excessive shear force caused by excessive speed. The selection of the centrifugation speed range takes into account both separation effect and particle protection. Within the range of 5000-8000 rpm, it can effectively remove unreacted substances and byproducts, while avoiding damage to the crystal morphology of titanium dioxide nanoparticles by excessive speed, thereby ensuring the surface activity and size uniformity of the particles.

[0036] The present invention further proposes that in step 2), the rotation speed of mechanical stirring is controlled within the range of 500-800 r / min, and the power of ultrasonic treatment is controlled within the range of 500-800 W.

[0037] The mechanical stirring speed refers to the number of revolutions per unit time of the stirrer, which can be achieved by using a variable frequency speed-regulating motor in conjunction with the stirring paddle. This speed range can generate appropriate shear force during the mixing process. The ultrasonic treatment power refers to the energy intensity output by the ultrasonic generator, which can be achieved by using an amplitude-modulated ultrasonic processor. This power range can produce an effective cavitation effect.

[0038] Specifically, at a mechanical stirring speed of 500-800 r / min, the fluid shear force generated by the stirring paddle can both break the van der Waals forces between the porous nanorods and titanium dioxide particles and avoid nanostructure breakage caused by excessively high speed. When combined with ultrasonic treatment at 500-800 W, the microjets generated by the collapse of cavitation bubbles can penetrate the adsorption layer on the surface of the nanoparticles, allowing the titanium dioxide nanoparticles to be fully embedded in the pore structure of the porous nanorods. The synergistic effect of these two parameters achieves uniform dispersion of the nanomaterials in the liquid phase system while maintaining the original morphology of the nanostructure.

[0039] The present invention further proposes that in step 3), the ratio of pretreated porous nanorods to sodium hydroxide solution be controlled within the range of 1-3 grams corresponding to 100-300 ml, the concentration of sodium hydroxide solution be controlled within the range of 10-13 mol / L, and the concentration of hydrochloric acid solution be controlled within the range of 0.1-0.2 mol / L.

[0040] The pretreated porous nanorods refer to porous nanorod materials loaded with titanium dioxide nanoparticles. Specifically, this can be achieved by combining mechanical stirring and ultrasonic treatment to ensure uniform adhesion of titanium dioxide particles to the porous structure surface. The concentration range of the sodium hydroxide solution refers to the molar concentration of the strong alkali in the reaction system. This can be achieved by mixing analytical grade sodium hydroxide reagent with deionized water in a specific ratio. This concentration range effectively dissolves surface impurities while avoiding excessive corrosion of the framework structure. The concentration range of the hydrochloric acid solution refers to the acidic environment used to neutralize residual alkali. This can be achieved by diluting concentrated hydrochloric acid. This concentration range neutralizes alkaline residues while avoiding excessive acidity that could damage the nanorod materials.

[0041] Specifically, during the sodium hydroxide solution treatment, by limiting the solid-liquid ratio of the nanorods to the solution, each nanorod surface can be fully contacted with the strong alkaline medium, effectively removing residual titanium dioxide particles and organic impurities from the preparation process. High-concentration sodium hydroxide solution can accelerate impurity dissolution under high-temperature hydrothermal conditions, but excessively high concentrations can cause the hydroxylation degree of the nanorod framework to exceed a critical value, leading to structural collapse. Subsequent neutralization with dilute hydrochloric acid solution creates a weakly acidic environment that eliminates the influence of alkaline residues on material properties while avoiding damage to the active sites on the nanorod surface by strong acid, thus maintaining the integrity of the porous structure and surface chemical stability.

[0042] This invention further proposes a method for preparing porous nanorod materials, which includes dissolving ammonium molybdate tetrahydrate in an acid solution, obtaining a molybdenum oxide precursor through a hydrothermal reaction, and then mixing it with glucose and performing high-temperature carbonization treatment.

[0043] The acid solution is a mixture of concentrated nitric acid and deionized water in a specific volume ratio. Adjusting the acid concentration controls the growth direction of the precursor crystals, promoting the formation of the nanorod morphology. The mass ratio of molybdenum oxide precursor to glucose is set within a specific range, ensuring that the carbon layer generated during carbonization uniformly coats the nanorod surface, forming a stable porous framework. The high-temperature carbonization process is carried out under argon protection to prevent material oxidation and maintain the integrity of the nanorod morphology.

[0044] Specifically, ammonium molybdate tetrahydrate undergoes hydrolysis in an acidic environment, forming molybdenum oxide nanostructures with specific crystal forms by controlling the hydrothermal temperature and time. Vacuum drying eliminates internal stress and maintains the stability of the precursor structure. During the carbonization stage, the carbon source generated from glucose decomposition reacts with molybdenum oxide to form a composite structure with interconnected channels. The chosen carbonization temperature ensures a moderate reduction reaction within the material while retaining sufficient molybdenum oxide framework for support. This porous structure, when subsequently combined with a metal matrix, enhances grain boundary stability through interfacial bonding, thereby suppressing abnormal grain growth at high temperatures.

[0045] The present invention further proposes that in step a), the ratio of ammonium molybdate tetrahydrate to acid solution is 7-12g corresponding to 200-360mL, and the acid solution is composed of 68% concentrated nitric acid and deionized water in a volume ratio of 1:5.0-5.5.

[0046] The ratio of ammonium molybdate tetrahydrate to acid refers to the mass-to-volume ratio of the precursor to the acidic reaction medium. This can be achieved by dissolving 7-12g of the solid powder in 200-360mL of acid. This ratio ensures that the reactant concentration is at the critical state of dissolution equilibrium and crystallization nucleation. The acid composition refers to adjusting the acidity of the solution by adjusting the volume ratio of concentrated nitric acid to deionized water. This can be achieved by measuring 68% concentrated nitric acid with a pipette and then diluting it proportionally. This ratio maintains the nitric acid concentration within a range that dissolves ammonium molybdate ions without damaging their molecular structure.

[0047] Specifically, when the amount of ammonium molybdate tetrahydrate added is less than 7g, the acid volume is too large, resulting in an overly dilute reaction system and an insufficient concentration of molybdate ions. When the amount added exceeds 12g, the acid volume is insufficient, preventing the solid particles from completely dissolving. By limiting the ratio of 7-12g of ammonium molybdate tetrahydrate to 200-360mL of acid, the reactants are saturated and dissolved in the liquid phase, providing a stable ion concentration environment for the subsequent hydrothermal reaction. Simultaneously, a concentrated nitric acid solution with a volume ratio of 1:5.0-5.5 is used to control the pH of the solution between 1.2 and 1.8, satisfying the dissociation requirements of ammonium molybdate tetrahydrate while avoiding excessive acidity that could break molybdenum-oxygen bonds. This precise ratio control results in a uniform colloidal dispersion of the precursor solution, laying the foundation for the subsequent formation of porous nanorods with a regular pore structure.

[0048] The present invention further proposes that, in the preparation of porous nanorod materials, the mass ratio of molybdenum oxide precursor to glucose be controlled at 1:2.0-2.5, and high-temperature carbonization treatment be carried out at a heating rate of 5-8℃ / min.

[0049] The mass ratio of molybdenum oxide precursor to glucose refers to the mass ratio of the two substances when mixed. This ratio can be achieved by weighing them proportionally using a precision electronic balance. This ratio ensures that glucose, as a carbon source, fully coats the surface of the molybdenum oxide precursor, providing a uniform carbon layer coverage for the subsequent carbonization reaction. The heating rate refers to the rate of temperature change in the tube furnace as it rises from room temperature to the target temperature. This rate can be achieved by adjusting the heating power in stages using a programmed temperature control system. This rate balances the thermodynamic conditions of the carbonization reaction with the stability of the material structure, avoiding crystal defects caused by sudden temperature changes.

[0050] Specifically, during the high-temperature carbonization process, after the molybdenum oxide precursor is mixed with glucose in a certain proportion, the glucose decomposes upon heating to form a carbon layer, which is then uniformly deposited on the surface of the molybdenum oxide. When the mass ratio is less than 1:2.0, the carbon source is insufficient to completely cover the precursor, resulting in uneven carbon layer distribution; when the mass ratio is greater than 1:2.5, excess carbon source forms a dense structure that hinders gas diffusion. By limiting this ratio range, a sufficient supply of carbon source can be ensured while avoiding an excessively thick carbon layer that could affect the pore structure. Simultaneously, controlling the heating rate within the range of 5-8℃ / min allows the carbonization reaction to proceed under controllable kinetic conditions. This prevents excessively rapid heating from causing localized thermal stress and lattice distortion, while also avoiding excessively slow heating that could lead to prolonged reaction time and particle agglomeration. Example

[0051] A method for preparing a high-temperature resistant shape memory metal for a temperature control device specifically includes the following steps:

[0052] S1 raw material smelting

[0053] According to mass percentage, a metallic raw material composed of Ni 29%, Co 7%, Ti 2%, Mn≤0.5%, Si≤0.5%, C≤0.2%, P≤0.01%, S≤0.01%, with the balance being Fe, is added to a smelting furnace and evacuated to 10... -3 Pa, with the temperature controlled at 1700℃, is continuously turned over during the melting process to promote full melting of the raw materials. Then, nanorod composite material is added, with the amount of nanorod composite material added accounting for 3.2% of the total amount of raw materials. After thorough mixing, it is refined to obtain a refined solution.

[0054] The refining process utilizes VOD technology for ladle refining, employs vacuum oxygen blowing technology for decarburization and desulfurization to achieve S≤0.001%, and then proceeds with tundish casting.

[0055] S2 Ingot Pretreatment

[0056] The refined solution is cast into an ingot, which is then placed in an annealing furnace under an argon atmosphere and held at 900°C for 5 hours. The cooling rate is then controlled at 50°C / hour to slowly cool the ingot to room temperature.

[0057] S3 molding process

[0058] The cooled ingot is heated to 800℃ and hot forged using a press, with each deformation controlled at 20%, and the forging is repeated until the target size is reached.

[0059] S4 heat treatment

[0060] The forged metal is fixed in a mold and placed in a calcining furnace under an argon atmosphere. It is held at 450°C for 30 minutes and then rapidly cooled by water quenching.

[0061] S5 Surface Treatment

[0062] The heat-treated metal can be mechanically polished to remove scratches and oxide layers.

[0063] The preparation method of the nanorod composite material is as follows:

[0064] 1) Dissolve 7g of ammonium molybdate tetrahydrate in 200mL of acid solution, which is composed of 68% concentrated nitric acid and deionized water in a volume ratio of 1:5. After complete dissolution, transfer the solution to a reaction vessel and react at 200℃ for 20h. After the reaction is completed, allow it to cool to room temperature naturally. Wash the product obtained by centrifugation repeatedly with deionized water and ethanol, and dry it under vacuum at 70℃ for 12h to obtain the molybdenum oxide precursor.

[0065] 2) The molybdenum oxide precursor and glucose were placed in a mortar and ground thoroughly and mixed evenly. The mixture was then transferred to an alumina ceramic boat and placed in a tube furnace. Under a high-purity argon atmosphere, the temperature was increased to 800℃ at 5℃ / min and carbonized at a constant temperature for 2 hours. After natural cooling to room temperature, the product was thoroughly centrifuged, washed, and dried to obtain porous nanorod materials.

[0066] 3) Add isopropyl titanate and deionized water to a container at a mass ratio of 1:10, stir at 500 r / min for 30 min at room temperature, centrifuge at 5000 r / min for 5 min after stirring, wash repeatedly with deionized water and freeze dry to obtain titanium dioxide nanoparticles.

[0067] 4) The porous nanorod material and titanium dioxide nanoparticles were added to a sufficient amount of deionized water at a mass ratio of 1:5. The mixture was mechanically stirred at 500 r / min for 1 h, and then ultrasonically treated at 500 W for 1 h. After the treatment was completed, the product was centrifuged and dried to obtain the pretreated porous nanorods.

[0068] 5) Add 1g of pretreated porous nanorods to 100mL of 10mol / L sodium hydroxide solution, mix and transfer to a reaction vessel, then place in a constant temperature oven and hydrothermally react at 120℃ for 4h. After the reaction is complete, allow it to cool naturally to room temperature, let it stand, pour off the upper layer of sodium hydroxide solution, remove the residual sodium hydroxide on the surface of the product with 0.1mol / L hydrochloric acid solution, and then rinse repeatedly with deionized water until neutral. After freeze-drying, the nanorod composite material can be obtained. Example

[0069] A method for preparing a high-temperature resistant shape memory metal for a temperature control device specifically includes the following steps:

[0070] S1 raw material smelting

[0071] According to mass percentage, a metallic raw material consisting of Ni 31%, Co 10%, Ti 3%, Mn≤0.5%, Si≤0.5%, C≤0.2%, P≤0.01%, S≤0.01%, with the balance being Fe, is added to a smelting furnace and evacuated to 10... -4 Pa, with the temperature controlled at 1720℃, is continuously turned over during the melting process to promote full melting of the raw materials. Then, nanorod composite material is added, with the amount of nanorod composite material added accounting for 3.7% of the total amount of raw materials. After thorough mixing, it is refined to obtain a refined solution.

[0072] The refining process utilizes VOD technology for ladle refining, employs vacuum oxygen blowing technology for decarburization and desulfurization to achieve S≤0.001%, and then proceeds with tundish casting.

[0073] S2 Ingot Pretreatment

[0074] The refined solution is cast into an ingot, which is then placed in an annealing furnace under an argon atmosphere and held at 950°C for 7 hours. The cooling rate is then controlled at 60°C / h to slowly cool it to room temperature.

[0075] S3 molding process

[0076] The cooled ingot is heated to 850°C and hot-forged using a press, with each deformation controlled at 25%, and the forging is repeated until the target size is reached.

[0077] S4 heat treatment

[0078] The forged metal is fixed in a mold and placed in a calcining furnace under an argon atmosphere. It is held at 500°C for 40 minutes and then rapidly cooled by water quenching.

[0079] S5 Surface Treatment

[0080] The heat-treated metal can be mechanically polished to remove scratches and oxide layers.

[0081] The preparation method of the nanorod composite material is as follows:

[0082] 1) Dissolve 10g of ammonium molybdate tetrahydrate in 300mL of acid solution, which is composed of 68% concentrated nitric acid and deionized water in a volume ratio of 1:5.2. After complete dissolution, transfer the solution to a reaction vessel and react at 205℃ for 24h. After the reaction is completed, allow it to cool to room temperature naturally. Wash the product obtained by centrifugation repeatedly with deionized water and ethanol, and dry it under vacuum at 75℃ for 13h to obtain the molybdenum oxide precursor.

[0083] 2) The molybdenum oxide precursor and glucose were placed in a mortar and ground thoroughly and mixed evenly. The mixture was then transferred to an alumina ceramic boat and placed in a tube furnace. Under a high-purity argon atmosphere, the temperature was increased to 820℃ at 6℃ / min and carbonized at a constant temperature for 2.5h. After natural cooling to room temperature, the product was thoroughly centrifuged, washed, and dried to obtain porous nanorod materials.

[0084] 3) Add isopropyl titanate and deionized water to a container at a mass ratio of 1:11, stir at 700 r / min for 40 min at room temperature, centrifuge at 7000 r / min for 7 min after stirring, wash repeatedly with deionized water and freeze dry to obtain titanium dioxide nanoparticles.

[0085] 4) The porous nanorod material and titanium dioxide nanoparticles were added to a sufficient amount of deionized water at a mass ratio of 1:6. The mixture was mechanically stirred at 600 r / min for 1.5 h, and then ultrasonically treated at 600 W for 1.5 h. After the treatment was completed, the product was centrifuged and dried to obtain the pretreated porous nanorods.

[0086] 5) Add 2g of pretreated porous nanorods to 200mL of 12mol / L sodium hydroxide solution, mix and transfer to a reaction vessel, then place in a constant temperature oven and hydrothermally react at 123℃ for 5h. After the reaction is complete, allow it to cool naturally to room temperature, let it stand, pour off the upper layer of sodium hydroxide solution, remove the residual sodium hydroxide on the surface of the product with 0.2mol / L hydrochloric acid solution, and then rinse repeatedly with deionized water until neutral. After freeze-drying, the nanorod composite material can be obtained. Example

[0087] A method for preparing a high-temperature resistant shape memory metal for a temperature control device specifically includes the following steps:

[0088] S1 raw material smelting

[0089] Metal raw materials, composed of Ni 33%, Co 13%, Ti 5%, Mn ≤ 0.5%, Si ≤ 0.5%, C ≤ 0.2%, P ≤ 0.01%, S ≤ 0.01%, and the balance being Fe, are added to a smelting furnace and evacuated to 100°C. -4 Pa, with the temperature controlled at 1750℃, is continuously turned over during the melting process to promote full melting of the raw materials. Then, nanorod composite material is added, with the amount of nanorod composite material added accounting for 4.6% of the total amount of raw materials. After thorough mixing, it is refined to obtain a refined solution.

[0090] The refining process utilizes VOD technology for ladle refining, employs vacuum oxygen blowing technology for decarburization and desulfurization to achieve S≤0.001%, and then proceeds with tundish casting.

[0091] S2 Ingot Pretreatment

[0092] The refined solution is cast into an ingot, which is then placed in an annealing furnace under an argon atmosphere and held at 1000℃ for 8 hours. The cooling rate is then controlled at 80℃ / h to slowly cool it to room temperature.

[0093] S3 molding process

[0094] The cooled ingot is heated to 900℃ and hot forged using a press. The deformation amount is controlled at 30% each time, and the forging is repeated until the target size is reached.

[0095] S4 heat treatment

[0096] The forged metal is fixed in a mold and placed in a calcining furnace under an argon atmosphere. It is held at 550°C for 50 minutes and then rapidly cooled by water quenching.

[0097] S5 Surface Treatment

[0098] The heat-treated metal can be mechanically polished to remove scratches and oxide layers.

[0099] The preparation method of the nanorod composite material is as follows:

[0100] 1) Dissolve 12g of ammonium molybdate tetrahydrate in 360mL of acid solution, which is composed of 68% concentrated nitric acid and deionized water in a volume ratio of 1:5.5. After complete dissolution, transfer the solution to a reaction vessel and react at 210℃ for 25h. After the reaction is completed, allow it to cool to room temperature naturally. Wash the product obtained by centrifugation repeatedly with deionized water and ethanol, and dry it under vacuum at 80℃ for 15h to obtain the molybdenum oxide precursor.

[0101] 2) The molybdenum oxide precursor and glucose were placed in a mortar at a mass ratio of 1:2.5, ground thoroughly and mixed evenly. The mixture was then transferred to an alumina ceramic boat and placed in a tube furnace. Under a high-purity argon atmosphere, the temperature was increased to 850℃ at 8℃ / min and carbonized at a constant temperature for 3 hours. After natural cooling to room temperature, the product was thoroughly centrifuged, washed, and dried to obtain porous nanorod materials.

[0102] 3) Add isopropyl titanate and deionized water to a container at a mass ratio of 1:12, stir at 800 r / min for 50 min at room temperature, centrifuge at 8000 r / min for 10 min after stirring, wash repeatedly with deionized water and freeze dry to obtain titanium dioxide nanoparticles.

[0103] 4) The porous nanorod material and titanium dioxide nanoparticles were added to a sufficient amount of deionized water at a mass ratio of 1:8. The mixture was mechanically stirred at 800 r / min for 2 h, and then ultrasonically treated at 800 W for 2 h. After the treatment was completed, the product was centrifuged and dried to obtain the pretreated porous nanorods.

[0104] 5) Add 3g of pretreated porous nanorods to 300mL of 13mol / L sodium hydroxide solution, mix and transfer to a reaction vessel, then place in a constant temperature oven and hydrothermally react at 125℃ for 6h. After the reaction is complete, allow to cool naturally to room temperature, let stand and then pour off the upper layer of sodium hydroxide solution. Remove the residual sodium hydroxide on the surface of the product with 0.2mol / L hydrochloric acid solution, and then rinse repeatedly with deionized water until neutral. After freeze-drying, the nanorod composite material can be obtained.

[0105] Comparative Example 1: This comparative example is basically the same as Example 1, except that glucose in step 2) is omitted in the preparation of the nanorod composite material.

[0106] Comparative Example 2: This comparative example is basically the same as Example 1, except that steps 3)-5) are omitted in the preparation of the nanorod composite material.

[0107] Comparative Example 3: This comparative example is basically the same as Example 1, except that step 4 is omitted in the preparation of the nanorod composite material.

[0108] Comparative Example 4: This comparative example is basically the same as Example 1, except that step 5 is omitted in the preparation of the nanorod composite material.

[0109] Comparative Example 5: This comparative example is basically the same as Example 1, except that it does not contain nanorod composite material.

[0110] Test experiment:

[0111] The shape memory metals provided in Examples 1-3 and Comparative Examples 1-5 were processed into rectangular strips with a width of 8 mm and a thickness of 1 mm. These strips were mounted on a fixed support, and the length L0 of the strips was measured. An external force was applied at -20°C to deform the strips, and the length after deformation was measured as L1. The strips were then cyclically heated between -20°C and 100°C. Each cycle consisted of holding at low temperature for 10 min, heating to high temperature, holding at high temperature for 10 min, and cooling down to low temperature. The number of cycles was set to 100. After the cycle was completed, the deformed sample was heated to 120°C, and the length L2 after recovery was measured. The recovery rate η was calculated as η = (L1-L2) / (L1-L0) × 100%. The results are shown in Table 1.

[0112] Table 1

[0113]

[0114] As shown in Table 1, the shape memory metal in this invention still has excellent shape recovery rate in environments higher than the austenite transformation end temperature, indicating that it has good temperature resistance. In high-temperature environments, the performance degradation is not obvious and it can still be used normally.

[0115] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a high-temperature resistant shape memory metal for a temperature control device, characterized in that, Specifically, the steps include the following: S1 raw material smelting The metal raw materials are fed into the smelting furnace, and a vacuum of 10 is drawn. -3 -10 -4 Pa, with the temperature controlled at 1700-1750℃, is continuously turned and melted during the smelting process to promote the full melting of the raw materials. Then, nanorod composite materials are added, and after thorough mixing, the mixture is refined to obtain a refined solution. S2 Ingot Pretreatment The refined solution is cast into an ingot, which is then placed in an annealing furnace under an argon atmosphere and held at 900-1000℃ for 5-8 hours, and then slowly cooled to room temperature. S3 molding process The cooled ingot is heated to 800-900℃ and hot forged using a press. The deformation amount is controlled at 20-30% each time, and the forging is repeated until the target size is reached. S4 heat treatment The forged metal is fixed in a mold and placed in a calcining furnace under an argon atmosphere. It is held at 450-550℃ for 30-50 minutes and then rapidly cooled by water quenching. S5 Surface Treatment The heat-treated metal can be mechanically polished to remove scratches and oxide layers. In S1, the metal raw material, by mass percentage, consists of Ni 29-33%, Co 7-13%, Ti 2-5%, Mn≤0.5%, Si≤0.5%, C≤0.2%, P≤0.01%, S≤0.01%, with the balance being Fe; The amount of the nanorod composite material added accounts for 3.2-4.6% of the total raw materials; The preparation method of the nanorod composite material is as follows: 1) Add isopropyl titanate and deionized water to a container at a mass ratio of 1:(10-12), stir at room temperature for 30-50 min, centrifuge for 5-10 min after stirring, wash repeatedly with deionized water and freeze dry to obtain titanium dioxide nanoparticles. 2) Add porous nanorods and titanium dioxide nanoparticles to sufficient deionized water at a mass ratio of 1:(5-8), stir mechanically for 1-2 hours, and then sonicate for 1-2 hours. After treatment, centrifuge the product and dry it to obtain pretreated porous nanorods. 3) Add the pretreated porous nanorods to the sodium hydroxide solution, mix and transfer to the reaction vessel, then place in a constant temperature oven and hydrothermally react at 120-125℃ for 4-6 hours. After the reaction is completed, allow it to cool naturally to room temperature, let it stand, pour off the upper sodium hydroxide solution, remove the residual sodium hydroxide on the surface of the product with hydrochloric acid solution, rinse repeatedly with deionized water until neutral, and freeze-dry to obtain the nanorod composite material. The preparation method of the porous nanorod material is as follows: a) Dissolve ammonium molybdate tetrahydrate in acid solution. After complete dissolution, transfer it to a reaction vessel and react at a constant temperature of 200-210℃ for 20-25h. After the reaction is completed, cool naturally to room temperature. Wash the product obtained by centrifugation repeatedly with deionized water and ethanol, and dry it under vacuum at 70-80℃ for 12-15h to obtain the molybdenum oxide precursor. b) The molybdenum oxide precursor and glucose were placed in a mortar and ground thoroughly and mixed evenly. Then, the mixture was transferred to an alumina ceramic boat and placed in a tube furnace. Under a high-purity argon atmosphere, the temperature was raised to 800-850℃ and carbonized at a constant temperature for 2-3 hours. After naturally cooling to room temperature, the product was thoroughly centrifuged, washed, and dried to obtain porous nanorod materials.

2. The method for preparing a high-temperature resistant shape memory metal for a temperature control device according to claim 1, characterized in that, In S2, the cooling rate of the slow cooling is 50-80℃ / h.

3. The method for preparing a high-temperature resistant shape memory metal for a temperature control device according to claim 1, characterized in that, In step 1), the stirring speed is 500-800 r / min; The centrifuge speed is 5000-8000 r / min.

4. The method for preparing a high-temperature resistant shape memory metal for a temperature control device according to claim 1, characterized in that, In step 2), the mechanical stirring speed is 500-800 r / min; The power of the ultrasonic treatment is 500-800W.

5. The method for preparing a high-temperature resistant shape memory metal for a temperature control device according to claim 1, characterized in that, In step 3), the ratio of the amount of pretreated porous nanorods to sodium hydroxide solution is (1-3) g: (100-300) mL; The concentration of the sodium hydroxide solution is 10-13 mol / L; The concentration of the hydrochloric acid solution is 0.1-0.2 mol / L.

6. The method for preparing a high-temperature resistant shape memory metal for a temperature control device according to claim 1, characterized in that, In step a), the ratio of the amount of ammonium molybdate tetrahydrate to the acid solution is (7-12) g : (200-360) mL; The acid solution is composed of 68% concentrated nitric acid and deionized water in a volume ratio of 1:(5.0-5.5).

7. The method for preparing a high-temperature resistant shape memory metal for a temperature control device according to claim 1, characterized in that, In step b), the mass ratio of the molybdenum oxide precursor to glucose is 1:(2.0-2.5). The heating rate is 5-8℃ / min.

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