Application of metastable beta titanium alloy in wide-temperature-range solid-state refrigeration

Abstract

The invention discloses application of a metastable beta titanium alloy in wide-temperature-range solid-state refrigeration, and belongs to the technical field of solid-state refrigeration. The metastable beta titanium alloy serves as a solid-state refrigeration working medium, transformation from a body-centered cubic structure to an orthogonal structure occurs under stress driving, and a heat effect is generated to achieve refrigeration. The alloy comprises the following components in percentage by mass: 20-36% of Nb, 2-5% of Zr, 6-10% of Sn and the balance of Ti and inevitable impurities. The material can realize adiabatic temperature change of 4.2 K at most in a temperature range of 1.59-298 K, and the fatigue life at room temperature exceeds 1 million weeks, and also exceeds 0.5 million weeks in a low-temperature environment, so that the material is obviously superior to other elastic and thermal material systems. Meanwhile, the alloy shows excellent electrochemical stability, and the pitting potential in a 3.5 wt% NaCl solution exceeds 10 V (relative to an Ag / AgCl electrode).

Description

Technical Field

[0001] This invention relates to the field of solid-state refrigeration technology, and more specifically to the application of a metastable β-titanium alloy in solid-state refrigeration over a wide temperature range. Background Technology

[0002] Cryogenic refrigeration plays a crucial supporting role in fields such as superconductivity, quantum information, high magnetic field scientific facilities, deep space exploration, and high-sensitivity detection. Especially in the operation of superconducting magnets, superconducting power, and superconducting electronic devices, a stable, continuous, and controllable cryogenic environment (such as the liquid helium temperature range and its vicinity) is often required to meet the critical temperatures of materials and the thermal stability requirements of the system. However, traditional cryogenic methods are highly dependent on helium and its related refrigeration chains: on the one hand, liquid helium, as a non-renewable strategic resource with a concentrated supply chain and continuously rising costs, faces long-term supply shortages and price fluctuations; on the other hand, cryogenic refrigeration equipment using helium as the working fluid is typically complex in structure, large in size, energy-intensive, and requires stringent maintenance, and in some application scenarios, is limited by resupply and operating costs. With the development of the superconducting and quantum technology industries, the demand for "helium-free" or "low-helium-dependent" cryogenic refrigeration solutions is becoming increasingly urgent, necessitating the development of new cryogenic refrigeration technologies to reduce dependence on helium resources and improve system energy efficiency and engineering deployability.

[0003] Solid-state refrigeration technology, due to its advantages such as not requiring volatile working fluids, high potential efficiency, and ease of modular integration, is considered one of the important directions for overcoming the bottlenecks in cryogenic refrigeration. Solid-state refrigeration mainly utilizes the thermodynamic response of materials under external fields, including magnetocaloric, electrothermal, compressive, and elastothermal effects. Among them, the elastothermal effect achieves heating / cooling cycles through the entropy and temperature changes accompanying the reversible phase transition of materials during stress loading / unloading. Compared with refrigeration methods that rely on high magnetic or electric fields, elastothermal refrigeration has greater potential advantages in device integration and engineering implementation; however, existing elastothermal material systems still have key limitations: typical materials have a narrow effective temperature range, insufficient cycle stability and fatigue life, and there is a risk of corrosion when used in cryogenic regions with low-freezing-point heat transfer fluids. These problems restrict the promotion of elastothermal refrigeration in wide-temperature range and high-reliability applications.

[0004] Against this backdrop, metastable β-titanium alloys, due to their designable metastableness and stress-induced reversible phase transition characteristics, are considered one of the potential material systems for achieving cryogenic elasto-thermal cooling. The stability of the β-phase in these alloys can be controlled through composition and heat treatment, allowing them to undergo a reversible stress-induced phase transition under applied stress, thus producing a significant elasto-thermal effect. Simultaneously, titanium alloy systems possess characteristics such as low density, high specific strength, corrosion resistance, and mature engineering processing capabilities, providing a material and manufacturing foundation for realizing integrable, scalable, and long-term cyclic solid-state cooling devices. Furthermore, if a balance between high reversible entropy / temperature change, low hysteresis loss, and excellent fatigue life can be achieved over a wide temperature range, and a material design and process window matching the device's cycling performance can be established, this will provide a new technological path for "helium-free" cryogenic cooling, especially for obtaining the cryogenic environment required for superconducting systems. Summary of the Invention

[0005] The purpose of this invention is to realize the application of a durable and corrosion-resistant metastable β-titanium alloy refrigerant for solid-state elastothermal refrigeration, covering room temperature to deep cryogenic temperature range, and to provide feasible materials and technical pathways for low-helium / helium-free cryogenic refrigeration and related devices.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An application of a metastable β-titanium alloy in solid-state refrigeration over a wide temperature range, wherein the metastable β-titanium alloy, as a refrigerant in a solid-state refrigeration system, absorbs and releases heat through its elasto-thermal effect during the refrigeration cycle, thereby achieving a refrigeration effect.

[0007] By applying a loading-unloading cycle to the metastable β-titanium alloy as an external field drive, the alloy undergoes a stress-induced phase transformation from a body-centered cubic structure (β phase) to an orth structure (orth phase) during the stress process, and the phase transformation is reversed during the unloading process; the solid-state refrigeration cycle is completed by utilizing the isothermal entropy change and adiabatic temperature change generated during this reversible phase transformation process.

[0008] Through alloy composition and heat treatment design, the β phase of the metastable β titanium alloy remains stable in the temperature range of 298 K to 1.59 K, and ensures that the β phase can be transformed into an orthorhombic structure phase under stress in this temperature range, thereby achieving continuous elastothermal cooling capability from room temperature to deep cryogenic temperature.

[0009] When the metastable β-titanium alloy is used as the refrigerant, suitable adiabatic temperature variations can be obtained in different temperature zones by controlling the refrigeration cycle conditions (including loading method, strain amplitude, stress rate and heat transfer process, etc.).

[0010] The working strain of the metastable β-titanium alloy during refrigeration cycles is controlled to within approximately 2% to achieve high cycle stability and long service life. When used as a refrigerant at 298 K, its fatigue life exceeds 1 million cycles; at temperatures below 298 K, its fatigue life exceeds 500,000 cycles.

[0011] For low-freezing-point heat transfer fluids that may exist in actual service environments, the metastable β-titanium alloy exhibits good pitting corrosion resistance in 3.5 wt% NaCl solution, with a pitting potential exceeding 10 V (relative to Ag / AgCl electrode), thereby improving the reliability and service life of the refrigerant in complex environments.

[0012] An application of a metastable β-titanium alloy in wide-temperature-range solid-state refrigeration, wherein the metastable β-titanium alloy, as a solid-state refrigerant, can achieve wide-temperature-range refrigeration based on the elastothermal effect.

[0013] The composition and structure of the alloy include: The metastable β-titanium alloy composition, by mass fraction, is: 20-36% Nb (preferably 20-30%, more preferably 21-25%), 2-5% Zr (preferably 2.5-4.5%, more preferably 3-4%), 6-10% Sn (preferably 6.5-8.5%, more preferably 7-8%), with the balance being Ti and unavoidable impurity elements; the alloy has a single-phase body-centered cubic structure.

[0014] The preparation process of the alloy includes: After being fed into the target composition, the material is melted into ingots in a vacuum non-consumable arc furnace at 1273 K-2500 K (preferably 1973 K-2400 K, more preferably 2100 K-2300 K). The ingots are then remelted at the same temperature 1-5 times (preferably 2-4 times, more preferably 2-3 times). Subsequently, the material is forged into round bars with a diameter of 50 mm-60 mm (preferably 52 mm-58 mm, more preferably 55 mm ± 1 mm) at 1123 K (preferably 1103 K-1200 K, more preferably 1123 K ± 20 K). Finally, the material is hot-rolled into round bars with a diameter of 10 mm-14 mm (preferably 11 mm-13 mm, more preferably 12 mm ± 0.5 mm) at 1023 K-1123 K (preferably 1053 K-1093 K, more preferably 1073 K ± 10 K).

[0015] The body-centered cubic phase of the metastable β-titanium alloy exists stably in the range of 298 K to 1.59 K and can be reversibly transformed into an orthorhombic phase under stress.

[0016] When the metastable β-titanium alloy is used as the refrigerant for a stretch-unload operation, the maximum adiabatic temperature change is 4 K at 298 K; 1.7 K at 137 K; and 4.2 K at 38 K.

[0017] At a temperature of 298 K and a strain of 2%, the fatigue life of this alloy exceeds 1 million cycles. At a temperature of 137 K and a strain of 2%, its fatigue life exceeds 500,000 cycles.

[0018] The metastable β-titanium alloy has a pitting potential exceeding 10 V in 3.5 wt% NaCl solution (relative to Ag / AgCl electrode).

[0019] The alloy is used in a temperature range of 298 K to 1.59 K (preferably 273 K–1.59 K, more preferably 137 K–38 K).

[0020] The advantages and beneficial effects of this invention are as follows: 1. This invention uses metastable β-titanium alloy as the refrigerant, and achieves refrigeration based on the elastothermal effect. The working temperature range covers from room temperature to deep cryogenic temperature (298 K to 1.59 K). It provides a potential "low-helium / helium-free" solid-state refrigeration material and technology path for the needs of superconducting and quantum devices for deep cryogenic environments, which helps to reduce the dependence on liquid helium resources and traditional deep cryogenic refrigeration links.

[0021] (Comparison: The usable operating temperature range of commercial Ti-Ni alloys is limited to room temperature.) Applied Physics Lett. 127,161905 (2025)].

[0022] 2. The metastable β-titanium alloy used in this invention can undergo a phase transition from a body-centered cubic structure to an orthorhombic structure under uniaxial stress, and achieves stress-induced transformation in the temperature range of 298 K to 1.59 K. Therefore, it can maintain an effective elastothermal response in different temperature ranges, enabling the cooling effect to have continuous temperature range coverage and scalability.

[0023] 3. This invention clarifies the adiabatic temperature change range under key temperature zones: a maximum of 4 K at 298 K, a maximum of 1.7 K at 137 K, and a maximum of 4.2 K at 38 K. Significant temperature changes can still be achieved, especially at low temperatures (such as 38 K), providing direct performance support for cooling in deep cryogenic regions and expanding the applicability of elastothermal materials in the cryogenic field.

[0024] 4. The metastable β-titanium alloy used in this invention has a fatigue life of over 1 million cycles in the 298 K temperature range under approximately 2% strain conditions, and over 500,000 cycles in the temperature range below 298 K (such as 137 K). It exhibits excellent cycle stability and durability, which is beneficial for constructing solid-state refrigeration devices that can operate continuously for a long time, reducing maintenance costs and improving reliability.

[0025] (Comparison: The fatigue life of commercial Ti-Ni alloys at room temperature is approximately -10°C) 5 Week [ J. Phys. D: Appl. Phys [50, 424006 (2017)]; The fatigue life of Cu-Al-Mn alloy and Heusler alloy is only maintained at -10. 3 Week [ Scripta Mater. [252, 116227 (2024)]. 5. Compared with solid-state cooling methods that rely on magnetic fields, electric fields or hydrostatic pressure fields, this invention uses uniaxial stress / strain as the driving field, which is easier to integrate with mechanical loading mechanisms, flexible structures or micro actuators. It has the advantages of clear implementation path, easy modularization and potential miniaturization, and is suitable for application in space-constrained or distributed cooling scenarios.

[0026] 6. The metastable β-titanium alloy used in this invention has a pitting potential exceeding 10 V in 3.5 wt% NaCl solution (relative to Ag / AgCl electrode), demonstrating excellent pitting resistance. This is beneficial for maintaining stable service in complex environments such as those containing chlorine or low-freezing-point heat transfer fluids, thereby improving the environmental adaptability and service life of the refrigeration system.

[0027] (For comparison: the pitting potential of commercial Ti-Ni alloys under the same conditions is approximately 1.09 V–1.23 V (relative to Ag / AgCl electrodes).) 7. The metastable β-titanium alloy used in this invention has a mature processing and application foundation. It can be made into various engineering forms such as plates, bars, strips, foils or structured units, which is convenient for matching with heat exchange structures and loading mechanisms. This reduces the engineering threshold from material research and development to device realization and has the potential for large-scale application. Attached Figure Description

[0028] Figure 1 The flowchart shows the preparation process of the metastable β-titanium alloy in this embodiment. Figure 2 The electron backscattering diffraction pattern (a) and grain size distribution pattern (b) of the metastable β titanium alloy in the embodiment are shown. Figure 3 The in-situ synchrotron radiation results of the metastable β titanium alloy at 298 K in the examples are: stress-strain curve (a) and corresponding diffraction pattern (b). Figure 4 The results of in-situ synchrotron radiation of the metastable β titanium alloy at 298 K are shown in the example, with strain-strain curve (a) and corresponding diffraction pattern (b). Figure 5 The in-situ neutron diffraction results of the metastable β titanium alloy at 38 K in the embodiment are: stress-strain curve (a) and corresponding diffraction spectrum (b). Figure 6 The examples show the tensile-compressive true stress-true strain curves of the metastable β titanium alloy at 298 K, 137 K, and 38 K (a), and the variation of recoverable strain with external load at different temperatures (b). Figure 7 The measured temperature curves (a) of the metastable β-titanium alloy at 298 K, 137 K and 38 K in the examples, and the evolution of the adiabatic temperature change with true strain (b). Figure 8 The results of the metastable β titanium alloy under a million-cycle compression test at 298 K are shown in the examples: loading-unloading curve of the first cycle (a), curves at different cycle numbers (b), and sample length measurements before and after the cycle (c). Figure 9 The results of a 500,000-cycle fatigue test on a metastable β-titanium alloy at 137 K are shown in the examples. Figure 10 The polarization curve of the metastable β-titanium alloy in the example is shown in 3.5 wt% NaCl solution at room temperature (compared with commercial Ti-Ni alloy). Detailed Implementation

[0029] To further understand the present invention, the following description is provided with reference to examples. However, these examples are merely illustrative of the features and advantages of the present invention and are not intended to limit the scope of the claims. Unless otherwise stated, the raw materials, equipment, and testing methods used in the embodiments are all obtainable or achievable by conventional means in the art.

[0030] Example 1 A metastable β-titanium alloy was selected as the solid-state refrigerant (nominal alloy composition: Ti-24Nb-4Zr-8Sn, by mass fraction). Its preparation process is as follows: Figure 1 As shown: The alloy was melted in a vacuum non-consumable arc furnace at 2300 K, cooled in water to room temperature to obtain an ingot; it was then remelted three times at 2300 K (melting, then cooling in water to room temperature to obtain the ingot) to eliminate macroscopic compositional segregation; subsequently, the ingot was forged into a round bar with a diameter of 55 mm at 1123 K; finally, it was hot-rolled at 1073 K into a round bar with a diameter of 12 mm, obtaining an equiaxed grain structure with an average grain size of approximately 4 μm, and its body-centered cubic single-phase structure is as follows. Figure 2 As shown.

[0031] To verify the stability of the body-centered cubic phase over a wide temperature range, neutron diffraction was used to characterize the sample phase structure. At J-PARC beamline 19 in Japan, the sample (with structural dimensions identical to the tensile specimen in Example 2) was directly cooled in a vacuum chamber and tested at 298 K, 137 K, and 38 K. At the POWGEN beamline at Oak Ridge National Laboratory in the United States, the sample was machined into a cylinder (15 mm long, 5 mm in diameter) and placed in a vanadium box, then directly cooled to 100 K and 1.59 K for testing. The results show that the body-centered cubic structure of this alloy can be stably maintained from 298 K to 1.59 K, meeting the structural requirements for use as a cryogenic elastothermal refrigerant.

[0032] Example 2 The sample obtained in Example 1 was machined into a tensile specimen (total length 64 mm; M8 thread at both ends; gauge length 25 mm; cylinder diameter 4 mm) according to national standard GB / T 228.1-2021. A low-temperature tensile testing device was used (test method as follows: Acta Mater. (165, 109-117 (2019)) Tensile-unloading cycle tests were performed on the specimens. The vacuum chamber was brought to a vacuum level of 10... -7 After reaching mbar, cooling begins, and the temperature is held at that temperature for at least one hour to ensure stability. Subsequently, a tensile-unloading cycle is performed following a deformation sequence of 1%-unloading-2%-unloading-3%-unloading-4%-unloading-5% (deformation along the length direction, with 0% deformation after unloading), where the tensile strain rate is 2.32 × 10⁻⁶. -4 s -1 The unloading stress rate is -300 MPa / s.

[0033] Figure 4 (298 K) and Figure 5 (38 K) are the in-situ synchrotron radiation results obtained at SPring-8 13XU beamline in Japan and the in-situ neutron diffraction results obtained at J-PARC 19 beamline in Japan, respectively, including stress-strain curves and corresponding diffraction spectra. It can be clearly observed that the body-centered cubic structure transforms into an orthogonal structure during loading and then reverses into a body-centered cubic structure during unloading, forming a reversible phase transition cycle. Figure 6 (a) shows the tensile-unloading stress-strain curves at different temperatures. By calculating the strain corresponding to the maximum load and the recoverable strain after unloading, the following results are obtained. Figure 6 The result shown in (b) (calculation method as follows:) Science353, 368-370 (2016). The results show that at 298 K, 137 K and 38 K, 3% strain (i.e. deformation) can achieve about 3% recoverable strain, indicating that the above phase transformation path is basically completely reversible at 3% total deformation.

[0034] During the unloading process described above (stress rate approximately -300 MPa / s), an E-type thermocouple (purchased from Omega Engineering Inc.) spot-welded to the center of the gauge length was used to monitor the temperature change of the sample. The test results are as follows: Figure 7 As shown (test method reference:) Applied Physics Lett. 127, 161905 (2025)). The adiabatic temperature change of this metastable β-titanium alloy during elastothermal cycling was measured as follows: (1) At a temperature of 298 K, the adiabatic temperature changes to 1 to 4 K; (2) At a temperature of 137 K, the adiabatic temperature changes from 0.3 to 1.7 K; (3) At a temperature of 38 K, the adiabatic temperature changes to 2.4 to 4.2 K.

[0035] This demonstrates that the metastable β-titanium alloy can achieve the temperature variation output required for elastothermal cooling in the temperature range of 298 K to 38 K.

[0036] Example 3 In the 298 K temperature range, the sample obtained in Example 1 was wire-cut into cuboid compression fatigue specimens (10 mm long, 5 mm wide, and 5 mm high), which were then subjected to repeated tensile-unloading cyclic tests along their length as a refrigerant. A Shimadzu fatigue testing machine was used, with the maximum strain (i.e., deformation) set to 2% (corresponding to a stress of approximately 670 MPa), a cycle frequency of 10 Hz, and a stress ratio of 0.1. The test results showed that after 1 million cycles, the sample length changed from 9.979 mm to 9.960 mm, a change (i.e., deformation) of 0.19%. Data are as follows: Figure 8 As shown, this indicates that the material has a stable structure and possesses cyclic durability suitable for continuously operating refrigeration systems.

[0037] Example 4 In a temperature range below 298 K (taking 137 K as an example), the sample obtained in Example 1 was machined into fatigue tensile specimens (total length 50 mm; M8 threads at both ends; gauge length 10 mm; cylinder diameter 4 mm) according to the national standard GB / T 228.1-2010. These specimens were used as the refrigerant for tensile-unloading cyclic testing along their length. An MTS fatigue testing machine was used, with the maximum strain set to 2% (corresponding to a stress of approximately 385 MPa), a cycle frequency of 1 Hz, and a stress ratio of 0.1. The results are as follows: Figure 9As shown, the sample did not break after more than 500,000 cycles, indicating that the material still has good cycling reliability under low temperature conditions and is suitable for cryogenic solid-state thermo-elastomeric refrigeration scenarios.

[0038] Example 5 To verify the suitability of the material in low freezing point environments, the sample obtained in Example 1 was processed into a cylindrical working electrode (3 mm long, 7.8 mm in diameter) for potentiodynamic polarization testing. The sample surface was initially polished with 180-grit silicon carbide sandpaper, then titanium wire (with heat-shrink tubing on the outer surface) was spot-welded in, inlaid with epoxy resin and mirror-polished, and finally finely polished with 2000-grit sandpaper and ultrasonically cleaned. Before testing, all samples were immersed in a 3.5 wt% NaCl solution for 24 hours. The tests were conducted using a PARSTAT 4000 electrochemical workstation at room temperature (approximately 288 K) using a standard three-electrode system: a 20 mm × 20 mm platinum mesh as the counter electrode and an Ag / AgCl electrode as the reference electrode. Before testing, the device was pretreated at -1.5 V (relative to the reference electrode) for 300 seconds. Then, the open circuit potential was measured until the drift rate was below 0.0001 mV / min. Finally, a potentiodynamic polarization scan was performed at a scan rate of 0.5 mV / s, with the potential range from -0.5 V to 2-10 V.

[0039] Test results are as follows Figure 10 As shown, the pitting potential of this metastable β-titanium alloy exceeds 10 V (relative to an Ag / AgCl electrode). A commercially available TiNi alloy (nominal composition Ti-55.87Ni, purchased from Baoji Runyang Rare Metals Co., Ltd.) tested under the same conditions pitted at 1.09 V and 1.23 V. This indicates that the alloy of this invention has significantly superior pitting resistance compared to commercially available TiNi alloys, which is beneficial for improving the reliability and service life of the refrigerant in complex environments.

[0040] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An application of a metastable β-titanium alloy in solid-state refrigeration over a wide temperature range, characterized in that: The metastable β-titanium alloy, used as a solid refrigerant, can achieve wide-temperature-range cooling based on the elastothermal effect.

2. The application according to claim 1, characterized in that: The composition and structure of the alloy include: The metastable β-titanium alloy composition, by mass fraction, is: 20-36% Nb (preferably 20-30%, more preferably 21-25%), 2-5% Zr (preferably 2.5-4.5%, more preferably 3-4%), 6-10% Sn (preferably 6.5-8.5%, more preferably 7-8%), with the balance being Ti and unavoidable impurity elements; the alloy has a single-phase body-centered cubic structure.

3. The application according to claim 1 or 2, characterized in that: The preparation process of the alloy includes: After being fed into the target composition, the material is melted into ingots in a vacuum non-consumable arc furnace at 1273 K-2500 K (preferably 1973 K-2400 K, more preferably 2100 K-2300 K). The ingots are then remelted at the same temperature 1-5 times (preferably 2-4 times, more preferably 2-3 times). Subsequently, the material is forged into round bars with a diameter of 50 mm-60 mm (preferably 52 mm-58 mm, more preferably 55 mm ± 1 mm) at 1123 K (preferably 1103 K-1200 K, more preferably 1123 K ± 20 K). Finally, the material is hot-rolled into round bars with a diameter of 10 mm-14 mm (preferably 11 mm-13 mm, more preferably 12 mm ± 0.5 mm) at 1023 K-1123 K (preferably 1053 K-1093 K, more preferably 1073 K ± 10 K).

4. The application according to claim 1, 2 or 3, characterized in that: The body-centered cubic phase of the metastable β-titanium alloy exists stably in the range of 298 K to 1.59 K and can be reversibly transformed into an orthorhombic phase under stress.

5. The application according to claim 1 or 4, characterized in that: When the metastable β-titanium alloy is used as the refrigerant for a stretch-unload operation, the maximum adiabatic temperature change is 4 K at 298 K; 1.7 K at 137 K; and 4.2 K at 38 K.

6. The application according to claim 5, characterized in that: At a temperature of 298 K and a strain of 2%, the fatigue life of this alloy exceeds 1 million cycles. At a temperature of 137 K and a strain of 2%, its fatigue life exceeds 500,000 cycles.

7. The application according to claim 1, 2 or 3, characterized in that: The metastable β-titanium alloy has a pitting potential exceeding 10 V in 3.5 wt% NaCl solution (relative to Ag / AgCl electrode).

8. The application according to claim 1, characterized in that: The alloy is used in a temperature range of 298 K to 1.59 K (preferably 273 K–1.59 K, more preferably 137 K–38 K).

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