Nickel-free hyperelastic titanium alloy containing Ti-Hf-Nb-Mo-Sn components and preparation method of nickel-free hyperelastic titanium alloy

Abstract

The invention relates to the technical field of biomedical materials, and discloses a nickel-free hyperelastic titanium alloy containing Ti-Hf-Nb-Mo-Sn and a preparation method thereof, the expression of the alloy is Ti-Hf-Nb-Mo-Sn, and the alloy meets the following conditions: a is 61%-71%; b is 12%-22%; c is 5%-15%; d is 1%-4%; e is 1-3%, and a + b + c + d + e = 100; the specific preparation method comprises the following steps: S1, smelting ingredients; s2, homogenizing and annealing; s3, carrying out hot forging on the sheath; s4, intermediate annealing; s5, cold rolling processing; s6, solid solution heat treatment; by adjusting the content of each main element and the heat treatment temperature and time, excellent hyperelasticity is obtained, the recovery dependent variable of the hyperelasticity alloy can reach 4%, and the hyperelasticity alloy shows good hyperelasticity.

Description

Technical Field

[0001] This invention relates to the field of biomedical materials technology, specifically to a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition and its preparation method. Background Technology

[0002] Biomedical titanium alloys have become core materials in the field of human tissue repair due to their excellent biocompatibility, corrosion resistance, and mechanical properties. Early medical titanium alloys were mainly pure titanium and Ti-6Al-4V alloys. Although pure titanium has good biocompatibility, it has low strength and no superelasticity, making it difficult to meet the requirements of dental orthodontics and minimally invasive orthopedic fixation, which require materials with good deformation recovery capabilities. Ti-6Al-4V alloys have high strength, but because they contain vanadium, long-term implantation may cause cytotoxic reactions, limiting their application in long-term implantable devices. With the development of materials technology, TiNi shape memory alloys, with their excellent superelasticity and shape memory effect, have been rapidly adopted in fields such as dental orthodontics and vascular stents. Chinese patent application No. 200810055021.8 discloses a medical NiTi shape memory alloy and its preparation method. This type of alloy solves the problem of traditional titanium alloys lacking superelasticity. However, the nickel element it contains has a significant defect—nickel ions are easily released from the alloy. When the concentration of nickel ions in the body exceeds 0.5 μg / mL, it will inhibit osteoblast proliferation, trigger allergic reactions, and in severe cases, even lead to cell carcinogenesis. Clinical data show that about 10%-15% of patients are sensitive to nickel and cannot use TiNi alloy devices.

[0003] To address the issue of nickel toxicity, researchers have developed Ti-Nb-based nickel-free β-titanium alloys. While eliminating the risk associated with nickel, these alloys suffer from unsatisfactory hyperelastic properties, easily undergoing irreversible plastic deformation when strain exceeds 3%, and exhibiting poor β-phase stability, leading to tissue phase transformation and mechanical property degradation after long-term implantation. Furthermore, some Ti-Nb-based alloys have poor machinability, are prone to cracking during cold rolling, and are difficult to fabricate into complex shapes such as thin-walled scaffolds or fine dental archwires. In addition, existing nickel-free titanium alloys often suffer from insufficient X-ray imaging performance, making precise placement during surgery difficult and increasing surgical complexity. The core shortcomings of existing technologies lie in the toxicity risks of nickel-containing alloys and the problems of insufficient hyperelasticity, poor machinability, weak imaging performance, and low β-phase stability in nickel-free alloys, failing to simultaneously meet the medical requirements of "non-toxicity, high elastic recovery, easy processing, imaging capability, and long-term stability." This invention overcomes these shortcomings by optimizing the alloy composition system and preparation process, providing a nickel-free hyperelastic titanium alloy with excellent comprehensive performance and its preparation method. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition and its preparation method. It has the advantages of being nickel-free and non-toxic, having excellent superelasticity, good processability, good imaging performance, and stable β phase, thus solving the problems of toxicity risks of existing nickel-containing alloys, insufficient superelasticity of nickel-free alloys, and processing difficulties.

[0005] To achieve the aforementioned objectives of nickel-free and non-toxic, superior superelasticity, good processability, excellent imaging performance, and stable β-phase, this invention provides the following technical solution: a method for preparing a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition, wherein the nickel-free superelastic titanium alloy is composed of five elements: Ti, Hf, Nb, Mo, and Sn, and each element, in atomic percentage, satisfies the following: Ti 61%-71%, Hf 12%-22%, Nb 5%-15%, Mo 1%-4%, and Sn 1%-3%, and the sum of the atomic percentages of Ti, Hf, Nb, Mo, and Sn is 100%; the specific method includes the following steps: S1. Batching and Melting: According to the atomic percentage of the nickel-free superelastic titanium alloy composition, select Ti, Hf, Nb, Mo, and Sn metals, and place them into the crucible of a vacuum arc melting furnace in order of increasing melting point. Melt the mixture under a vacuum degree ≤ 5× The furnace is smelted 4-5 times, with electromagnetic stirring activated during each smelting. After smelting, the furnace is cooled to obtain an ingot. S2. Homogenization annealing: The ingot is placed in a sealed quartz tube filled with argon gas and held at 900-1373K for 12-36h. After holding, it is water-cooled to obtain a solid solution β single-phase alloy. S3. Hot forging with a sheath: A high-temperature resistant metal is used to make a sheath shell, which completely wraps and welds the homogenized alloy ingot. The sheath is heated to 900-1000℃ and hot forged on a forging hammer. After forging, the sheath is removed by milling to obtain a plate-shaped alloy. S4. Intermediate annealing: Place the plate alloy in a vacuum annealing furnace and hold it at 973-1173K for 20-60 minutes, then cool it with water. S5. Cold rolling: The alloy after intermediate annealing is repeatedly cold rolled at room temperature, and the cold rolling deformation is controlled to be 60%-75% to obtain a thin plate with a thickness of 1-1.5mm. S6. Solution heat treatment: The cold-rolled sheet is placed in a vacuum heat treatment furnace and held at 673-1073K for 10-30 minutes. After holding, it is water-cooled to obtain a superelastic finished alloy.

[0006] Preferably, the melting current of the vacuum arc melting furnace in S1 is 200-300A, and the melting time for each melting is 5-8 minutes.

[0007] Preferably, the homogenization annealing temperature in S2 is 1173-1273K, and the holding time is 24-30h.

[0008] Preferably, the high-temperature resistant metal in S3 is pure titanium or stainless steel, and the sheath welding is performed using argon arc welding, resulting in a vacuum degree ≤1× Pa.

[0009] Preferably, in S4, the cold rolling is performed using multi-pass rolling, with each pass having a deformation amount of 10%-15% and an interval of 5-10 minutes between passes.

[0010] Preferably, the solution heat treatment temperature in S5 is 973-1173K, and the holding time is 15-20min.

[0011] A nickel-free superelastic titanium alloy with a composition of Ti-Hf-Nb-Mo-Sn is prepared by the above-mentioned method. The alloy has the expression Ti-Hfb-Nbc-Mod-Sne and satisfies the following conditions: a is 61%-71%; b is 12%-22%; c is 5%-15%; d is 1%-4%; e is 1-3%, and a+b+c+d+e=100.

[0012] Preferably, the atomic percentages of each element in the alloy are 65%-68% Ti, 15%-17% Hf, 10%-13% Nb, 2%-3% Mo, and 2%-3% Sn.

[0013] Preferably, the atomic percentage of the Hf element is not less than 15%.

[0014] Preferably, the atomic percentage of the Mo element is 2%-3%.

[0015] Compared with the prior art, the present invention provides a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition and its preparation method, which has the following beneficial effects: 1. The nickel-free superelastic titanium alloy with the composition Ti-Hf-Nb-Mo-Sn and its preparation method completely eliminate nickel and use five biosafe elements, Ti, Hf, Nb, Mo, and Sn, fundamentally avoiding the cytotoxicity and allergy risks caused by nickel ion precipitation. The biocompatibility meets the first-level standard of GB / T 16886.1-2022 for biocompatibility evaluation of medical materials. At the same time, the introduction of Hf gives the alloy good X-ray imaging performance, which allows for precise positioning of implanted devices during surgery using imaging equipment, solving the problem of blurred imaging in existing nickel-free titanium alloys and reducing the difficulty of surgical operation.

[0016] 2. The nickel-free superelastic titanium alloy with Ti-Hf-Nb-Mo-Sn composition and its preparation method effectively eliminate the compositional segregation of the alloy ingot through a process of "vacuum arc melting 4-5 times + electromagnetic stirring", improving the uniformity of element distribution to over 98%. Combined with the processing method of "intermediate annealing to restore plasticity + multi-pass cold rolling to control deformation", the cold rolling deformation of the alloy is stabilized at 60%-75%, successfully producing thin-walled plates of 1-1.5mm, solving the problems of easy cracking and poor machinability of traditional nickel-free titanium alloys during cold rolling. Finally, through solution heat treatment at 673-1173K, the internal microstructure of the alloy is controlled, so that the superelastic recovery strain reaches 4% and the fracture strength is stabilized at 580-700MPa, meeting the dual requirements of "high elastic recovery + high strength" for materials in dental orthodontics, minimally invasive orthopedic fixation and other scenarios.

[0017] 3. Compared with existing Ti-Nb-based nickel-free alloys, the β-phase stability of this nickel-free superelastic titanium alloy and its preparation method are significantly improved. After being placed in a human body temperature environment of 37°C for 12 months, the β-phase content still remains above 95% with no obvious phase transformation. At the same time, the elastic modulus of the alloy is controlled at 45-70 GPa, which is closer to the elastic modulus of human bone tissue. This can reduce the "stress shielding effect", promote bone tissue healing, and overcome the bone resorption problem caused by the excessively high elastic modulus of traditional TiNi alloys. Attached Figure Description

[0018] Figure 1 The X-ray diffraction patterns of the structural evolution of the alloy of the present invention before and after tensile loading and unloading are shown. Figure 2 This is a tensile curve of the alloy of the present invention; Figure 3 This is a tensile cyclic loading and unloading curve of the alloy of the present invention; Figure 4 This is a sample image after machining according to the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0020] Example 1

[0021] A nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition and its preparation method are described below: S1: Batching and Melting: Based on the atomic percentages of Ti 61%, Hf 22%, Nb 11%, Mo 3%, and Sn 3%, select 30.5g of Ti (99.9% purity), 22g of Hf (99.8% purity), 5.5g of Nb (99.9% purity), 1.5g of Mo (99.9% purity), and 1.5g of Sn (99.99% purity). Place the metals in the crucible of vacuum arc melting furnace 1 in the order of Sn, Ti, Nb, Mo, and Hf (melting point from lowest to highest). After closing the furnace door, evacuate to 3× Pa, set the melting current to 250A, melt for 6 minutes each time, turn on the electromagnetic stirring, repeat the melting 4 times, and cool with the furnace after melting to obtain an ingot 2 with a diameter of about 20mm.

[0022] S2: Homogenization annealing: Place the ingot 2 into a sealed quartz tube filled with argon gas, place it in a homogenization annealing furnace 3, heat it to 1273K, hold it for 24h, and immediately water cool it after the holding period to obtain a solid solution β single-phase alloy.

[0023] S3: Hot forging of the sheath: The outer shell 4 is made of pure titanium plate with a thickness of 2mm. The homogenized alloy ingot is placed inside the sheath and sealed by argon arc welding. After welding, a vacuum of 5× is applied. Pa; The entire sheath is placed in the hot forging equipment 5, heated to 950℃, held for 30 minutes, and then hot forged three times with a forging hammer. After forging, the sheath shell 4 is peeled off by milling to obtain a plate-shaped alloy with a thickness of 8mm.

[0024] S4: Intermediate annealing: Place the plate alloy into intermediate annealing furnace 6, heat to 1073K, hold for 40 minutes, and then water cool to restore the alloy's plasticity.

[0025] S5: Cold rolling: The plate alloy after intermediate annealing is placed into the cold rolling mill 7 and cold rolled in 5 passes at room temperature. The deformation amount of each pass is 15%, and the interval between passes is 8 minutes. Finally, an alloy sheet with a thickness of 1.2 mm is obtained.

[0026] S6: Solution heat treatment: Place the alloy sheet into heat treatment furnace 8, heat it to 973K, hold it for 10 minutes, and then cool it with water to obtain the finished alloy sheet 9.

[0027] The alloy prepared in this embodiment was subjected to performance tests: superelastic recovery strain of 2.6%, fracture strength of 700 MPa, elongation of 47%, elastic modulus of 65 GPa at 310 K, and clear X-ray imaging, meeting the requirements for use in dental fixation devices.

[0028] Example 2

[0029] A nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition and its preparation method are described below: S1: Batching and Melting: Based on the atomic percentages of Ti 65%, Hf 17%, Nb 13%, Mo 2%, and Sn 3%, select 32.5g of Ti (99.9% purity), 17g of Hf (99.8% purity), 6.5g of Nb (99.9% purity), 1g of Mo (99.9% purity), and 1.5g of Sn (99.99% purity). Place the metals in the crucible of vacuum arc melting furnace 1 in the order of Sn, Ti, Nb, Mo, and Hf, and evacuate to 4× Pa, melting current 280A, each melting time 7min, electromagnetic stirring turned on, repeated melting 5 times, and then cooled with the furnace to obtain ingot 2.

[0030] S2: Homogenization annealing: Place the ingot 2 into an argon-sealed quartz tube, place it in a homogenization annealing furnace 3, heat it to 1173K, hold it for 30h, and then water cool it to obtain a β single-phase alloy.

[0031] S3: Hot forging of the sheath: The outer shell of the sheath is made of stainless steel plate, sealed by argon arc welding, and then vacuumed to 8× Pa is placed in a hot forging machine 5 and heated to 980℃. After holding at that temperature for 25 minutes, it is hot forged. After forging, the cladding is milled off to obtain a plate-shaped alloy with a thickness of 10mm.

[0032] S4: Intermediate annealing: Place the plate alloy into intermediate annealing furnace 6, heat to 1123K, hold for 30 minutes, and then water cool.

[0033] S5: Cold rolling: Six passes of cold rolling are performed in cold rolling mill 7, with a deformation of 12% per pass and an interval of 10 minutes between passes, to obtain an alloy sheet with a thickness of 1.0 mm.

[0034] S6: Solution heat treatment: Place the alloy sheet into heat treatment furnace 8, heat it to 1073K, hold it for 20 minutes, and then water cool it to obtain the finished product 9.

[0035] Performance test results: Superelastic recovery strain 4.0%, breaking strength 580MPa, elongation 24%, elastic modulus at 310K 60GPa, excellent machinability, suitable for manufacturing orthopedic bone screws.

[0036] Example 3

[0037] A nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition and its preparation method are described below: S1: Batching and Melting: Based on the atomic percentages of Ti 71%, Hf 12%, Nb 13%, Mo 3%, and Sn 1%, select 35.5g of Ti (99.9% purity), 12g of Hf (99.8% purity), 6.5g of Nb (99.9% purity), 1.5g of Mo (99.9% purity), and 0.5g of Sn (99.99% purity). The metals are placed into vacuum arc melting furnace 1 in the order of Sn, Ti, Nb, Mo, and Hf, and the furnace is evacuated to 2× Pa, melting current 220A, each melting for 5 minutes, electromagnetic stirring turned on, repeated melting 4 times, and then cooled with the furnace to obtain ingot 2.

[0038] S2: Homogenization annealing: After the ingot 2 is sealed with argon gas, it is placed in the homogenization annealing furnace 3, heated to 1373K, held for 12h, and water-cooled to obtain β single-phase alloy.

[0039] S3: Hot forging of the sheath: Pure titanium sheath shell, after 4-fold sealing, is vacuumed to 3× Pa, hot forging equipment 5 heats to 1000℃, holds for 20 minutes and then hot forges, and after milling, a plate-shaped alloy with a thickness of 9mm is obtained.

[0040] S4: Intermediate annealing: Heat intermediate annealing furnace 6 to 1173K, hold for 20 minutes, and then water cool.

[0041] S5: Cold rolling process: Cold rolling mill 7 performs 4 passes of cold rolling, with a deformation of 18% per pass and an interval of 5 minutes between passes, to obtain an alloy sheet with a thickness of 1.5 mm.

[0042] S6: Solution heat treatment: Heat treatment furnace 8 is heated to 1173K, held for 30 minutes, and then water-cooled to obtain the finished product 9.

[0043] Performance test results: Superelastic recovery strain 3.2%, breaking strength 700MPa, elongation 25%, elastic modulus at 310K 70GPa, high mechanical strength, suitable for use in neurovascular stents.

[0044] Working principle: This invention uses a five-element composition system design, utilizing Hf and Nb to stabilize the β phase and improve imaging properties, and Mo and Sn to improve processability and superelasticity. During the preparation process, vacuum arc melting ensures uniform composition, homogenization annealing eliminates ingot stress, cladding hot forging prevents oxidation, intermediate annealing restores plasticity, cold rolling controls plate thickness, and solution heat treatment regulates microstructure. Ultimately, the alloy possesses comprehensive properties of "nickel-free and non-toxic, high elastic recovery, easy processing, and imaging capability", making it suitable for various medical applications.

[0045] In summary, this nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition and its preparation method, by completely eliminating nickel and using five biosafe elements—Ti, Hf, Nb, Mo, and Sn—fundamentally avoids the cytotoxicity and allergy risks caused by nickel ion release, achieving biocompatibility meeting GB / T standards. Standard 16886.1-2022, Level 1 Standard for Biological Evaluation of Medical Materials; Simultaneously, the introduction of Hf element gives the alloy excellent X-ray imaging properties, allowing for precise positioning of implanted devices during surgery using imaging equipment, solving the problem of blurred imaging in existing nickel-free titanium alloys and reducing the difficulty of surgical procedures; through a process of "vacuum arc melting 4-5 times + electromagnetic stirring," the compositional segregation of the alloy ingot is effectively eliminated, increasing the uniformity of element distribution to over 98%; combined with a processing method of "intermediate annealing to restore plasticity + multi-pass cold rolling to control deformation," the cold rolling deformation of the alloy is stabilized at 60%-75%, successfully producing thin-walled plates of 1-1.5mm, solving the problems of easy cracking and poor machinability in traditional nickel-free titanium alloys during cold rolling. The problem was solved by solution heat treatment at 673-1173K to regulate the internal microstructure of the alloy, achieving a superelastic recovery strain of 4% and a fracture strength of 580-700MPa. This meets the dual requirements of "high elastic recovery + high strength" for materials used in dental orthodontics and minimally invasive orthopedic fixation. Compared to existing Ti-Nb-based nickel-free alloys, the stability of the β phase is significantly improved. After being placed at a human body temperature of 37℃ for 12 months, the β phase content remains above 95%, with no significant phase transformation. At the same time, the elastic modulus of the alloy is controlled at 45-70GPa, which is closer to the elastic modulus of human bone tissue. This reduces the "stress shielding effect," promotes bone tissue healing, and overcomes the bone resorption problem caused by the excessively high elastic modulus of traditional TiNi alloys.

[0046] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition, characterized in that: The nickel-free superelastic titanium alloy is composed of five elements: Ti, Hf, Nb, Mo, and Sn. The atomic percentages of each element satisfy the following: Ti 61%-71%, Hf 12%-22%, Nb 5%-15%, Mo 1%-4%, and Sn 1%-3%, with the sum of the atomic percentages of Ti, Hf, Nb, Mo, and Sn being 100%. The specific preparation method includes the following steps: S1. Batching and Melting: Based on the atomic percentage of the nickel-free superelastic titanium alloy composition, select Ti, Hf, Nb, Mo, and Sn metals, and place them into the crucible of a vacuum arc melting furnace in order of increasing melting point. Melt the mixture under a vacuum degree ≤ 5× The furnace is smelted 4-5 times, with electromagnetic stirring activated during each smelting. After smelting, the furnace is cooled to obtain an ingot. S2. Homogenization annealing: The ingot is placed in a sealed quartz tube filled with argon gas and held at 900-1373K for 12-36h. After holding, it is water-cooled to obtain a solid solution β single-phase alloy. S3. Hot forging with a sheath: A high-temperature resistant metal is used to make a sheath shell, which completely encloses and welds the homogenized alloy ingot. The sheath is heated to 900-1000℃ and hot forged on a forging hammer. After forging, the sheath is removed by milling to obtain a plate-shaped alloy. S4. Intermediate annealing: Place the plate alloy in a vacuum annealing furnace and hold it at 973-1173K for 20-60 minutes, then cool it with water. S5. Cold rolling: The alloy after intermediate annealing is repeatedly cold rolled at room temperature, and the cold rolling deformation is controlled to be 60%-75% to obtain a thin plate with a thickness of 1-1.5mm. S6. Solution heat treatment: The cold-rolled sheet is placed in a vacuum heat treatment furnace and held at 673-1173K for 10-30 minutes. After holding, it is water-cooled to obtain a superelastic finished alloy.

2. The method for preparing a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 1, characterized in that: The vacuum arc melting furnace in S1 has a melting current of 200-300A and a melting time of 5-8 minutes per melting.

3. The method for preparing a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 1, characterized in that: The homogenization annealing temperature in S2 is 1173-1273K, and the holding time is 24-30h.

4. The method for preparing a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 1, characterized in that: The high-temperature resistant metal in S3 is pure titanium or stainless steel, and the sheath welding is performed using argon arc welding. The vacuum degree after welding is ≤1× Pa.

5. The method for preparing a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 1, characterized in that: The cold rolling process in S4 is a multi-pass rolling process, with a deformation of 10%-15% per pass and an interval of 5-10 minutes between passes.

6. The method for preparing a nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 1, characterized in that: The solution heat treatment temperature in S5 is 973-1173K, and the holding time is 15-20min.

7. A nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition, prepared by the method according to any one of claims 1-6, characterized in that: The alloy is expressed as Tia-Hfb-Nbc-Mod-Sne, and satisfies the following conditions: a = 61%-71%; b = 12%-22%; c = 5%-15%; d = 1%-4%; e = 1%-3%, and a+b+c+d+e = 100.

8. A nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 7, characterized in that: The atomic percentages of each element in the alloy are: Ti 65%-68%, Hf 15%-17%, Nb 10%-13%, Mo 2%-3%, and Sn 2%-3%.

9. A nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 7, characterized in that: The atomic percentage of the Hf element is not less than 15%.

10. A nickel-free superelastic titanium alloy with a Ti-Hf-Nb-Mo-Sn composition according to claim 7, characterized in that: The atomic percentage of the Mo element is 2%-3%.

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