Medical ultra-pure nickel-titanium tube and preparation method thereof

Abstract

The invention discloses a medical ultra-pure nickel-titanium tube and a preparation method thereof. The preparation method comprises the steps of tube blank preparation, forming and heat treatment, finishing and inspection and the like. According to the invention, a multi-component trace synergistic alloying system covering Cu, Nb, Zr, Ta and Sn is elaborately designed, so that the product has both corrosion resistance and antibacterial property; a double-helix nickel-titanium wire framework network is constructed in a nickel-titanium pipe blank for the first time, and stress can be effectively transmitted and dispersed when an external load is borne by pre-stretching 3-5% strain, so that local stress concentration is avoided; the heat treatment process of three-section hot rolling, multi-pass cold rolling and shape memory heat treatment is adopted, and the microstructure is precisely regulated and controlled; through the combined finishing process of acid pickling and electrolytic polishing, a surface oxide layer and machining defects are thoroughly removed. The fatigue life, the hyperelasticity, the corrosion resistance, the antibacterial property and the surface quality of the ultra-pure nickel-titanium tube all reach or exceed the top-level medical standard, and the bottleneck problem of key materials in the field of high-end medical instruments is solved.

Description

Technical Field

[0001] This invention relates to the field of medical nickel-titanium materials, and in particular to a medical ultrapure nickel-titanium tube and its preparation method. Background Technology

[0002] Nickel-titanium alloys, with their excellent shape memory effect, superelasticity, and certain biocompatibility, occupy a core position in the manufacture of high-end medical devices such as cardiac stents, vascular interventional catheters, and orthopedic implants. However, existing medical nickel-titanium alloy tubing still has significant limitations in terms of composition control and manufacturing processes, making it difficult to meet the increasingly stringent clinical application requirements.

[0003] Nickel-titanium shape memory alloys have become key materials for manufacturing high-end medical devices such as cardiovascular stents, minimally invasive surgical instruments, and orthopedic implants due to their unique superelasticity (pseudoelasticity) and shape memory effect, as well as their excellent biocompatibility.

[0004] However, medical-grade nickel-titanium tubing has extremely stringent performance requirements, demanding not only exceptionally high fatigue life (typically >10 hours) but also... 7 To cope with the complex periodic loads in the human body, it is also necessary to have excellent corrosion resistance to prevent nickel ion precipitation from causing allergic or toxic reactions. At the same time, certain antibacterial properties have also become an emerging demand to reduce the risk of postoperative infection.

[0005] In terms of composition, existing medical nickel-titanium alloy tubing uses a nickel-titanium binary system as its core, with nickel content typically controlled between 54% and 57% (mass fraction). However, fluctuations in this ratio can easily lead to performance degradation. Excessive nickel content lowers the austenitic phase transformation temperature, causing room-temperature hyperelastic failure; insufficient nickel content increases material brittleness and reduces processing feasibility. More critically, existing tubing commonly suffers from excessive impurities, with total impurities such as oxygen, argon, carbon, and iron often exceeding 0.08%, and oxygen content reaching over 0.06%. These impurities, through solid solution strengthening, reduce alloy plasticity and simultaneously form brittle phases such as oxides and carbides, becoming fatigue crack initiation points and reducing corrosion resistance by more than 30%. In physiological environments, the release of impurity elements can also trigger tissue inflammation, compromise biocompatibility, and limit long-term implantation applications.

[0006] In terms of manufacturing process, traditional nickel-titanium tubing is typically produced using a process involving vacuum melting and casting, multiple forgings, drilling, hot extrusion, and cold drawing. This process has several inherent drawbacks: First, the drilling process results in extremely low material utilization, and metallurgical defects in the core material are retained within the tubing. Second, intense plastic deformation easily leads to uneven microstructure and strong texture, creating stress concentration points within the material and becoming the source of fatigue crack initiation. Third, conventional processes have limited precision in controlling grain size and precipitates, making it difficult to simultaneously optimize strength, hyperelasticity, and fatigue performance.

[0007] To improve performance, existing technologies have undergone some improvements, such as employing powder metallurgy or adding trace elements to enhance processability and corrosion resistance. However, these methods often have trade-offs: adding elements may impair hyperelasticity, and impurities and porosity introduced by powder metallurgy can significantly reduce fatigue life. Furthermore, existing pipe structures are mostly homogeneous, lacking inherent reinforcement mechanisms to inhibit crack propagation. In terms of surface treatment, improper handling can create a rough surface that becomes a breeding ground for corrosion and bacterial adhesion.

[0008] Therefore, there is an urgent need in this field for a novel preparation method that can systematically innovate the entire process from component design, microstructure construction, thermomechanical treatment to surface finishing, fundamentally solving the problem of the difficulty in simultaneously achieving high strength, long fatigue life, high corrosion resistance and good antibacterial properties, and producing ultra-high performance medical nickel-titanium tubes that meet the requirements of next-generation high-end medical devices. Summary of the Invention

[0009] The purpose of this invention is to provide a medical ultrapure nickel-titanium tube and its preparation method, aiming to address the shortcomings of existing technologies in terms of precise control of composition, process stability and surface modification of medical nickel-titanium tubes, so as to meet the stringent requirements of high-end medical devices for nickel-titanium tube materials.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] This invention first proposes a method for preparing medical ultrapure nickel-titanium tubing, comprising the following steps:

[0012] S1. Tube blank preparation

[0013] Preparation of S101 nickel-titanium springs

[0014] Using ultra-high purity nickel-titanium wire, left-hand and right-hand springs are wound on a precision spring winding machine;

[0015] One end of the left-hand spring is turned into the pitch gap of the right-hand spring, and multiple left-hand springs and multiple right-hand springs are twisted together end to end to form a uniform and tight double helix network.

[0016] Preparation of S102 and nickel-titanium casting fluid

[0017] High-purity electrolytic nickel and high-purity titanium with matching atomic ratios are mixed and then subjected to cold crucible magnetic levitation induction melting to obtain extremely high-purity nickel-titanium casting liquid.

[0018] S103, Tube billet casting and prestressing application

[0019] The double helix tube network is placed in the center of a specially designed annular mold cavity, and axial prestress is applied to both ends of the double helix tube network. The pre-tension strain is controlled at 3-5%. This step is crucial because it ensures that the core maintains straightness and tension during subsequent pouring and cooling processes, and combines with the matrix to generate pre-compression stress.

[0020] Under a He atmosphere, the annular mold is preheated to 400℃, and the nickel-titanium casting liquid is poured into the annular mold. After pouring, the mold is kept at a pressure of 1.2-1.4MPa and a temperature of 500-600℃ for 30-45 minutes. The mold is then cooled to room temperature, and the prestressing tension is finally removed to obtain a tube blank with a thickness of 5±0.2mm.

[0021] The homogeneous nickel-titanium casting liquid is used to perform the first heat treatment on the double helix network, and then the heat is kept to obtain secondary plasticity, thus maintaining the high elasticity of the double helix network.

[0022] S2, Molding and Heat Treatment

[0023] S201, three-stage hot-rolled

[0024] First, the tube blank is held at 950℃ for 30-60 minutes and then hot rolled in one heat using a two-roll reversible mill; it is then heated back to 930℃ and held for 20-30 minutes for a second heat; then the tube blank is heated to 810-910℃ and held for 10-20 minutes for a third heat, and then cooled to room temperature.

[0025] S202, Cold Rolling and Stress Hardening

[0026] Using a multi-roll precision cold rolling mill (such as a Pilger cold rolling mill), the pierced tube blank is placed on a smooth, extremely hard mandrel. Through the rotation and reciprocating motion of the rolls, the tube blank is subjected to 7-8 passes of cold rolling. The cumulative cold deformation must be strictly controlled between 30-50% to obtain the shaped tube.

[0027] The rolls of a cold rolling mill have specific groove patterns, which locally and progressively roll and compress the tube blank during its rotation and reciprocating motion. After each rolling stroke, the tube blank rotates and advances a short distance for the next rolling pass.

[0028] High-performance lubricating coolant is used during cold rolling to reduce friction, remove generated heat, and prevent surface damage and accidental annealing due to excessive temperature. When metallic materials undergo plastic deformation at room temperature, their strength and hardness increase significantly, but their plasticity and toughness decrease simultaneously. Plastic deformation leads to a sharp increase in dislocation density within the material's internal crystal structure. Dislocations become entangled and accumulate, hindering their movement. To continue deformation, greater stress must be applied, macroscopically manifesting as the material becoming stronger and harder. Furthermore, intense plastic deformation breaks down the original coarse grains, forming fine subgrain structures and high-density dislocation walls. The finer the grains, the higher the material's strength and the better its fatigue performance. Fine grains also effectively inhibit crack propagation. Through cold rolling, the nickel-titanium alloy matrix and the internal spring skeleton are greatly strengthened, significantly improving the tensile strength, yield strength, and hardness of the composite pipe, enabling it to withstand greater loads without permanent deformation.

[0029] S203, shape memory heat treatment

[0030] After cold rolling, the shaped tubes undergo precise shape memory setting heat treatment, holding at 500-550℃ for 5-30 minutes, followed by rapid water quenching to obtain tubes without internal stress.

[0031] Cold-rolled nickel-titanium alloys are in a high-energy, unstable state, storing a large amount of distortion energy. During shape memory heat treatment at 500-550℃, recrystallization and grain growth occur more easily and rapidly, resulting in uniform precipitates. Heat treatment releases the internal stress generated by cold rolling, endowing the material with ultimate superelastic / shape memory properties and solidifying the internal double-helix composite structure.

[0032] S3. Finishing and Inspection

[0033] S301, pickling

[0034] For pipes without internal stress, pickling is performed at a temperature of 40-50℃ for 5-10 minutes.

[0035] S302, electropolishing

[0036] A NaCl ethylene glycol solution with a weight concentration of 58.44 g / L was used as the electrolyte. The anode was the pickled pipe and the cathode was a 304 stainless steel metal ring with an inner diameter of 17 mm. Electropolishing was carried out at 15-35℃ for 10-15 min.

[0037] S303, Cleaning and Testing

[0038] The inner and outer surfaces of the polished tube are then polished, cleaned, subjected to ultrasonic testing, and performance tests (superelasticity, fatigue life, mechanical properties) to ensure that they meet medical standards and produce a finished medical ultrapure nickel-titanium tube.

[0039] Preferably, the diameter of the left-hand and right-hand springs in S101 is 1.0 mm, and the pitch is controlled at 3.0 mm, which facilitates the formation of a twisted double helix network with a wall thickness of about 2.0 mm.

[0040] Preferably, the process parameters for magnetic levitation induction melting in S102 are: vacuum degree 10 -5 -10 -2 At 1600-1750℃, using a high-frequency alternating magnetic field with a frequency of 1.5-2.5KHz, the holding time is 5-15 minutes, requiring a total alloy mass of 10-20kg, followed by rapid cooling with inert gas for 20 minutes. Compared to traditional vacuum induction melting, this method solves the problems of impurity contamination, compositional segregation, and coarse grains inherent in traditional melting, providing high-quality billets for subsequent cold drawing, thereby improving the corrosion resistance, biocompatibility, and mechanical property stability of the pipe.

[0041] Preferably, the formulations of the ultra-high purity nickel-titanium wire and the extremely high purity nickel-titanium casting fluid in S1 both include the following components by mass percentage:

[0042] Nickel: 54.5 wt% - 57.0 wt%;

[0043] Titanium: 42.8wt%-45.3wt%;

[0044] Other trace elements:

[0045] Copper: 0.01wt%-0.03wt%;

[0046] Niobium: 0.01wt%-0.025wt%;

[0047] Zirconium: 0.05% wt% - 0.08 wt%;

[0048] Tantalum: 0.01wt%-0.05wt%;

[0049] Tin: 0.01wt%-0.05wt%.

[0050] Furthermore, the purity of nickel, titanium, and other trace elements is required to be 99.99 wt%, and they undergo the following pretreatment: nickel, titanium, and other trace elements are placed in a deoxidation furnace at 300-700℃ for 20-30 minutes under inert gas protection, with the weighing error controlled within ±0.003 wt%. This is to ensure that the impurity content in the finished nickel-titanium tubes meets the requirements of GB / T24627-2023: carbon (C) ≤ 0.04 wt%, hydrogen (H) ≤ 0.005 wt%, argon (N) ≤ 0.005 wt%, and oxygen (O) ≤ 0.04 wt%.

[0051] Copper possesses excellent thermal stability and oxidation resistance, and its antibacterial properties are particularly outstanding. Incorporating copper into medical nickel-titanium tubing imparts antibacterial characteristics. Furthermore, appropriate amounts of copper can improve the processing performance of nickel-titanium alloys to some extent, making the tubing easier to form during cold drawing and other processing, thus improving production efficiency and product quality. Niobium promotes the formation of a denser and more stable oxide film on the surface of nickel-titanium alloys, effectively blocking the erosion of external corrosive media and improving the material's corrosion resistance. Zirconium has corrosion resistance and oxidation resistance properties, and it can stabilize the phase structure of nickel-titanium alloy materials, directly improving the material's strength and hardness. Tantalum has excellent biocompatibility and good affinity with human tissue. Tin can significantly improve the fatigue resistance of nickel-titanium alloy materials.

[0052] Preferably, the dimensions of the S201, three-stage hot-rolled product are as follows:

[0053] After a single hot rolling process, the outer diameter of the nickel-titanium tube billet is 20-25 mm, and the wall thickness is 2-4 mm. After a double hot rolling process, the outer diameter is 15-20 mm, and the wall thickness is 1-2 mm. After a triple hot rolling process, the outer diameter is 12-17 mm, and the wall thickness is 0.5-1 mm. The single hot rolling temperature is controlled at 950℃ to break the original structure of the material and make the distribution of alloying elements more uniform. The double hot rolling temperature is 930℃, which promotes uniform deformation and reduces rolling cracks by utilizing the slippage of the phase interface. The triple hot rolling temperature is 810-910℃ to inhibit excessive grain growth and retain the work hardening potential for subsequent cold rolling.

[0054] The temperature for the three-stage hot rolling is set based on the temperature of change in the crystal structure of nickel-titanium alloy. When the temperature is above 950℃, the alloy is completely in the β single-phase region, which can quickly eliminate dendritic segregation in the ingot. When the temperature is between 950-930℃, the alloy is in the α+β two-phase region, which avoids grain growth and further homogenizes the material. When the temperature is between 810-910℃, the alloy is in the α-phase stable region, which stabilizes the microstructure and properties.

[0055] Preferably, the pickling solution used in S301 is a mixture of a 35wt% nitric acid aqueous solution and a 5wt% hydrofluoric acid aqueous solution at a volume ratio of 1:1. Immersion in the mixed acid solution is used to remove the oxide layer and processing residues from the surface of the nickel-titanium pipe, thereby improving surface cleanliness.

[0056] Preferably, the mandrel in S202 is a tungsten-cobalt cemented carbide, wherein the mass ratio of tungsten carbide to cobalt is 90:10.

[0057] Preferably, the voltage during electrochemical polishing in S302 is between 15-35V. Compared to other surface treatment methods, electrochemical polishing can achieve an ultra-smooth surface and improve biocompatibility.

[0058] Based on the aforementioned preparation method, a medical ultrapure nickel-titanium tube was obtained, with both its inner and outer surface roughness ≤0.4μm.

[0059] Compared with the prior art, the beneficial effects of the present invention are:

[0060] 1. This invention is a meticulously designed multi-component micro-synergistic alloying system encompassing Cu, Nb, Zr, Ta, and Sn. The elements work together to contribute antibacterial properties and improve the alloy's processing performance, reducing cold rolling resistance. Nb and Zr work together to form an extremely dense and stable passivation film, greatly enhancing the alloy's corrosion resistance. Zr also has the function of fine grain strengthening and stabilizing the phase structure. Ta further optimizes biocompatibility, while Sn segregates at grain boundaries, strengthening grain boundaries and inhibiting crack propagation under cyclic loading. Ta and Sn significantly improve fatigue resistance.

[0061] This synergistic effect enables the final product to possess both superior corrosion resistance (corrosion rate <0.001 mm / year) and antibacterial properties (antibacterial rate ≥95%), which cannot be achieved by a single trace element.

[0062] 2. This invention is the first to construct a prestressed double-helix nickel-titanium wire skeleton network inside a nickel-titanium tube blank. This structure, through the cross-twisting of left-hand and right-hand helical springs, forms a uniform, dense, and isotropic three-dimensional reinforcement. By pre-stretching by 3-5% strain, the skeleton is kept under tension after composite bonding, generating a strong bond with the matrix. Under external loads, it effectively transfers and disperses stress, avoiding localized stress concentration, thereby increasing fatigue life to 10 years. 7 More than one cycle can avoid the stress concentration and potential fracture risk inherent in the nodes of existing woven mesh structures, further demonstrating the superiority of this unique structural design.

[0063] 3. This invention employs a systematic precision heat treatment process involving three-stage hot rolling, multi-pass cold rolling, and shape memory heat treatment to precisely control the microstructure:

[0064] By utilizing three-stage hot rolling, stepwise deformation is achieved at different temperatures (950℃→930℃→850-910℃) to gradually break down the as-cast structure, eliminate compositional segregation, and achieve continuous grain refinement and homogenization. Through multi-pass cold rolling, up to 45% cold deformation is introduced, generating high-density dislocations and work hardening, providing the material with extremely high strength and hardness, which is the foundation for withstanding high loads. After cold rolling, shape memory heat treatment is performed at a specific temperature (500-550℃) to release the structural internal stress caused by cold rolling and complete recrystallization, promoting the uniform precipitation of Ni4Ti3 and other precipitates, thereby "setting" superelasticity.

[0065] 4. This invention uses a combination of pickling and electropolishing finishing processes to completely remove the surface oxide layer and processing defects, resulting in an ultra-smooth surface with an inner and outer surface roughness Ra≤0.35μm. The ultra-smooth surface greatly reduces bacterial attachment points and corrosion initiation points, which not only further improves corrosion resistance and antibacterial properties, but also greatly reduces the risk of thrombosis, demonstrating excellent biocompatibility and long-term service reliability.

[0066] 5. In summary, this invention is a complete system solution encompassing component design (molecular level), structural innovation (microscopic level), process control (macroscopic level), and surface treatment (surface level). Each step is interconnected and works synergistically, ultimately leading to the successful fabrication of ultrapure nickel-titanium tubes that meet or exceed top-tier medical standards in terms of fatigue life, superelasticity, corrosion resistance, antibacterial properties, and surface quality, thus solving a key material bottleneck in the field of high-end medical devices. Detailed Implementation

[0067] 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.

[0068] Example 1

[0069] A method for preparing a medical ultrapure nickel-titanium tube includes the following steps:

[0070] 1. Tube blank preparation

[0071] Preparation of S101 nickel-titanium springs:

[0072] Ultra-high purity nickel-titanium wire with a diameter of 1.0 mm (composition as described below) was selected and wound into left-hand and right-hand springs with a pitch of 3.0 mm on a precision spring winding machine. Multiple left-hand springs were then twisted end-to-end with multiple right-hand springs to form a uniform and tight double-helix network.

[0073] Preparation of S102, nickel-titanium casting fluid:

[0074] Weigh the pretreated raw materials (purity ≥ 99.99 wt%, weighing error ± 0.003 wt%) according to the following mass percentages:

[0075] Nickel: 55.8 wt%;

[0076] Titanium: 44.0 wt%

[0077] Copper: 0.02 wt%;

[0078] Niobium: 0.015 wt%;

[0079] Zirconium: 0.06 wt%;

[0080] Tantalum: 0.03 wt%;

[0081] Tin: 0.03 wt%;

[0082] The mixed raw materials are then subjected to magnetic levitation induction melting in a cold crucible. The process parameters are: vacuum degree 5 × 10⁻⁶. -4 The solution was heated to 1700℃ using a high-frequency alternating magnetic field with a frequency of 2.0 kHz and held for 10 minutes. After melting, high-purity argon gas was introduced for rapid cooling for 20 minutes to obtain a nickel-titanium casting liquid with extremely high purity.

[0083] S103. Tube blank casting and prestressing application:

[0084] The twisted double-helix pipe network is placed in the center of a specially made annular mold cavity, and axial prestress is applied to both ends to control the pre-tensile strain at 4%. The mold is preheated to 400℃, and nickel-titanium casting liquid is poured into the mold under a He protective atmosphere. Subsequently, it is held at 1.3MPa and 550℃ for 40 minutes, and then cooled to room temperature with the mold. The prestress is then removed to obtain a composite pipe blank with a thickness of 5mm.

[0085] 2. Molding and heat treatment

[0086] S201, Three-stage hot rolling:

[0087] The tube blank was held at 950℃ for 45 minutes and then hot-rolled in one pass, resulting in an outer diameter of 22 mm and a wall thickness of 3 mm. It was then reheated to 930℃ and held for 25 minutes for a second pass, resulting in an outer diameter of 18 mm and a wall thickness of 1.5 mm. Finally, it was heated to 850℃ and held for 15 minutes for a third pass, resulting in an outer diameter of 15 mm and a wall thickness of 0.8 mm. The tube was then air-cooled to room temperature.

[0088] S202, Cold Rolling and Stress Hardening:

[0089] Using a Pilger cold rolling mill, a hard alloy mandrel with a tungsten carbide:cobalt ratio of 90:10 is used in conjunction with a high-performance lubricating coolant to perform 7 passes of cold rolling on the hot-rolled tube blank, with a cumulative cold deformation of 45%, resulting in a shaped tube with an outer diameter of 8 mm and a wall thickness of 0.5 mm.

[0090] S203, Shape Memory Heat Treatment:

[0091] The cold-rolled pipe was kept at 520℃ for 15 minutes and then rapidly water-quenched to obtain a pipe without internal stress.

[0092] 3. Finishing and Inspection

[0093] S301, pickling:

[0094] The pipe was pickled at 45°C for 8 minutes using a pickling solution consisting of a 35wt% nitric acid aqueous solution and a 5wt% hydrofluoric acid aqueous solution in a volume ratio of 1:1 to remove the surface oxide layer.

[0095] S302, electropolishing:

[0096] Using a 58.44 g / L NaCl ethylene glycol solution as the electrolyte, with a tubular anode and a 304 stainless steel ring as the cathode, electropolishing was performed for 12 min at 25℃ and 25V.

[0097] S303, Cleaning and Testing:

[0098] The polished pipes were cleaned, subjected to ultrasonic testing, and underwent performance testing. The surface roughness Ra of the inner and outer surfaces was measured to be ≤0.35μm. The superelastic recovery rate was >98%, and the fatigue life (at 2% strain) was >10. 7 The mechanical properties and impurity content of the product meet the GB / T24627-2023 medical standard.

[0099] Example 2

[0100] A method for preparing a medical ultrapure nickel-titanium tube includes the following steps:

[0101] 1. Tube blank preparation

[0102] Preparation of S101 nickel-titanium springs:

[0103] Ultra-high purity nickel-titanium wire with a diameter of 1.0 mm (composition as described below) was selected and wound into left-hand and right-hand springs with a pitch of 3.0 mm on a precision spring winding machine. Multiple left-hand springs were then twisted end-to-end with multiple right-hand springs to form a uniform and tight double-helix network.

[0104] Preparation of S102, nickel-titanium casting fluid:

[0105] Weigh the pretreated raw materials (purity ≥ 99.99 wt%, weighing error ± 0.003 wt%) according to the following mass percentages:

[0106] Nickel: 57.0 wt%;

[0107] Titanium: 42.8 wt%;

[0108] Copper: 0.01 wt%;

[0109] Niobium: 0.025 wt%;

[0110] Zirconium: 0.05% wt%;

[0111] Tantalum: 0.01 wt%;

[0112] Tin: 0.05 wt%.

[0113] The mixed raw materials are then subjected to magnetic levitation induction melting in a cold crucible. The process parameters are: vacuum degree 1×10⁻⁶. -5 The solution was heated to 1600℃ using a high-frequency alternating magnetic field with a frequency of 1.5 kHz and held for 15 minutes. After melting, high-purity argon gas was introduced for rapid cooling for 20 minutes to obtain a nickel-titanium casting liquid with extremely high purity.

[0114] S103. Tube blank casting and prestressing application:

[0115] The twisted double-helix pipe network is placed in the center of a specially made annular mold cavity, and axial prestress is applied to both ends to control the pre-tensile strain at 3%. The mold is preheated to 400°C, and nickel-titanium casting liquid is poured into the mold under a He protective atmosphere. Subsequently, it is held at 1.2 MPa and 500°C for 45 minutes, and then cooled to room temperature with the mold. The prestress is then removed to obtain a composite pipe blank with a thickness of 5.1 mm.

[0116] 2. Molding and heat treatment

[0117] S201, Three-stage hot rolling:

[0118] The tube blank was held at 950℃ for 30 minutes and then hot-rolled in one pass, resulting in an outer diameter of 22 mm and a wall thickness of 3 mm. It was then reheated to 930℃ and held for 30 minutes for a second pass, resulting in an outer diameter of 18 mm and a wall thickness of 1.5 mm. Finally, it was heated to 810℃ and held for 20 minutes for a third pass, resulting in an outer diameter of 15 mm and a wall thickness of 0.8 mm. The tube was then air-cooled to room temperature.

[0119] S202, Cold Rolling and Stress Hardening:

[0120] Using a Pilger cold rolling mill with a tungsten carbide:cobalt ratio of 90:10 hard alloy mandrel and high-performance lubricating coolant, the hot-rolled tube blank is subjected to 7 passes of cold rolling, with a cumulative cold deformation of 46%, to obtain a shaped tube with an outer diameter of 8mm and a wall thickness of 0.5mm.

[0121] S203, Shape Memory Heat Treatment:

[0122] The cold-rolled pipe is held at 500℃ for 30 minutes, followed by rapid water quenching to obtain a pipe without internal stress.

[0123] 3. Finishing and Inspection

[0124] S301, pickling:

[0125] The pipe was pickled at 40°C for 10 minutes using a pickling solution consisting of a 35wt% nitric acid aqueous solution and a 5wt% hydrofluoric acid aqueous solution in a volume ratio of 1:1 to remove the surface oxide layer.

[0126] S302, electropolishing:

[0127] Using a 58.44 g / L NaCl ethylene glycol solution as the electrolyte, with a tubular anode and a 304 stainless steel ring as the cathode, electropolishing was performed at 15℃ and 35V for 15 min.

[0128] S303, Cleaning and Testing:

[0129] The polished pipes were cleaned, subjected to ultrasonic testing, and underwent performance testing. The surface roughness Ra of the inner and outer surfaces was measured to be ≤0.35μm. The superelastic recovery rate was >98%, and the fatigue life (at 2% strain) was >10. 7 The mechanical properties and impurity content of the product meet the GB / T24627-2023 medical standard.

[0130] Example 3

[0131] A method for preparing a medical ultrapure nickel-titanium tube includes the following steps:

[0132] 1. Tube blank preparation

[0133] Preparation of S101 nickel-titanium springs:

[0134] Ultra-high purity nickel-titanium wire with a diameter of 1.0 mm (composition as described below) was selected and wound into left-hand and right-hand springs with a pitch of 3.0 mm on a precision spring winding machine. Multiple left-hand springs were then twisted end-to-end with multiple right-hand springs to form a uniform and tight double-helix network.

[0135] Preparation of S102, nickel-titanium casting fluid:

[0136] Weigh the pretreated raw materials (purity ≥ 99.99 wt%, weighing error ± 0.003 wt%) according to the following mass percentages:

[0137] Nickel: 54.5 wt%;

[0138] Titanium: 45.3 wt%;

[0139] Copper: 0.03 wt%;

[0140] Niobium: 0.01 wt%;

[0141] Zirconium: 0.08 wt%;

[0142] Tantalum: 0.05 wt%;

[0143] Tin: 0.01 wt%.

[0144] The mixed raw materials are then subjected to magnetic levitation induction melting in a cold crucible. The process parameters are: vacuum degree 1×10⁻⁶. -2 The solution was heated to 1750℃ using a high-frequency alternating magnetic field with a frequency of 2.5 kHz and held at that temperature for 5 minutes. After melting, high-purity argon gas was introduced for rapid cooling for 20 minutes to obtain a nickel-titanium casting liquid with extremely high purity.

[0145] S103. Tube blank casting and prestressing application:

[0146] The twisted double-helix pipe network is placed in the center of a specially made annular mold cavity, and axial prestress is applied to both ends to control the pre-tensile strain at 5%. The mold is preheated to 400℃, and nickel-titanium casting liquid is poured into the mold under a He protective atmosphere. Subsequently, it is held at 1.4MPa and 600℃ for 30 minutes, and then cooled to room temperature with the mold. The prestress is then removed to obtain a composite pipe blank with a thickness of 4.8mm.

[0147] 2. Molding and heat treatment

[0148] S201, Three-stage hot rolling:

[0149] The tube blank was held at 950℃ for 60 minutes and then hot-rolled in one pass, resulting in an outer diameter of 22 mm and a wall thickness of 2.9 mm. It was then reheated to 930℃ and held for 20 minutes for a second pass, resulting in an outer diameter of 18 mm and a wall thickness of 1.4 mm. Finally, it was heated to 910℃ and held for 10 minutes for a third pass, resulting in an outer diameter of 15 mm and a wall thickness of 0.7 mm. The tube was then air-cooled to room temperature.

[0150] S202, Cold Rolling and Stress Hardening:

[0151] Using a Pilger cold rolling mill with a tungsten carbide:cobalt ratio of 90:10 hard alloy mandrel and high-performance lubricating coolant, the hot-rolled tube blank is subjected to 7 passes of cold rolling, with a cumulative cold deformation of 43%, to obtain a shaped tube with an outer diameter of 8mm and a wall thickness of 0.5mm.

[0152] S203, Shape Memory Heat Treatment:

[0153] The cold-rolled pipe is held at 550℃ for 5 minutes, followed by rapid water quenching to obtain a pipe without internal stress.

[0154] 3. Finishing and Inspection

[0155] S301, pickling:

[0156] The pipe was pickled at 50°C for 5 minutes using a pickling solution consisting of a 35wt% nitric acid aqueous solution and a 5wt% hydrofluoric acid aqueous solution in a volume ratio of 1:1 to remove the surface oxide layer.

[0157] S302, electropolishing:

[0158] Using a 58.44 g / L NaCl ethylene glycol solution as the electrolyte, with a tubular anode and a 304 stainless steel ring as the cathode, electropolishing was performed at 35℃ and 15V for 10 min.

[0159] S303, Cleaning and Testing:

[0160] The polished pipes were cleaned, subjected to ultrasonic testing, and underwent performance testing. The surface roughness Ra of the inner and outer surfaces was measured to be ≤0.35μm. The superelastic recovery rate was >98%, and the fatigue life (at 2% strain) was >10. 7 The mechanical properties and impurity content of the product meet the GB / T24627-2023 medical standard.

[0161] Comparative Example 1

[0162] In the S103 tube blank casting process, no axial prestress was applied to the double helix pipe network, and the remaining steps and parameters were exactly the same.

[0163] Results: After casting and cooling, the double-helix network inside the tube blank exhibited slight bending and relaxation, failing to maintain straightness and tension. The final finished tube, during the superelastic cycle test, showed a resistance of approximately 5 × 10⁻⁶. 5 Permanent deformation and fatigue cracks appeared after a few cycles, and the fatigue life was significantly lower than that of Example 1. The internal structure was not tightly bonded, resulting in a decrease in overall mechanical properties and durability.

[0164] Comparative Example 2

[0165] The only difference from Example 1 is that an ultra-high purity nickel-titanium wire woven mesh of equal weight is used instead of a double helix pipe network; the other steps and parameters are exactly the same.

[0166] Comparative Example 3

[0167] The only difference from Example 1 is that no trace copper is added in the preparation of the S102 nickel-titanium casting liquid, and the deficiency is supplemented by Ti. The rest of the steps and parameters are exactly the same.

[0168] Comparative Example 4

[0169] The only difference from Example 1 is that niobium and zirconium trace elements are not added in the preparation of S102 nickel-titanium casting liquid, and the deficiency is supplemented by Ti. The remaining steps and parameters are exactly the same.

[0170] Comparative Example 5

[0171] The only difference from Example 1 is that tantalum and tin trace elements are not added in the preparation of S102 nickel-titanium casting liquid, and the deficiency is supplemented by Ti. The remaining steps and parameters are exactly the same.

[0172] Results: Corrosion resistance tests (e.g., immersion in artificial sweat) on the final pipe showed a lower pitting potential than the product in Example 1. Antibacterial tests (against Staphylococcus aureus) indicated no antibacterial effect. Furthermore, the material exhibited slightly poorer processing properties, requiring greater rolling forces during cold rolling, and its fatigue life was approximately 7 × 10⁻⁶. 6 The number of weeks was lower than that of Example 1.

[0173] Comparative Example 6

[0174] The only difference from Example 1 is that the three-stage hot rolling of S201 is cancelled. Instead, the tube blank is held at 1000°C for 60 minutes and then directly hot rolled to an outer diameter of 15 mm and a wall thickness of 0.8 mm. Then, the same cold rolling and subsequent steps are performed.

[0175] Comparative Example 7

[0176] The only difference from Example 1 is that S202, cold rolling and stress hardening are omitted. Instead, the tube blank is held at 1000°C for 60 minutes and then directly hot rolled to an outer diameter of 15 mm and a wall thickness of 0.8 mm. Then, the same shape memory heat treatment and subsequent steps are performed.

[0177] Comparative Example 8

[0178] The only difference from Example 1 is that S203 and shape memory heat treatment are omitted.

[0179] Comparative Example 9

[0180] The only difference from Example 1 is that S301 pickling is omitted.

[0181] Comparative Example 10

[0182] The only difference from Example 1 is that S302 electropolishing is omitted.

[0183] Performance testing:

[0184] Referring to standard GB / T 24627-2023 "Ni-Titanium Shape Memory Alloy Processed Materials for Surgical Implants", the medical ultrapure nickel-titanium tubes of Examples 1-3 and Comparative Examples 1-10 were tested respectively, including the following test items:

[0185] 1. Pipe material data measurement

[0186] Prepare a 1-meter-long steel pipe and measure its outer diameter and wall thickness at the beginning, end, and middle. Take the average value as the result. Prepare a 5-centimeter-long nickel-titanium pipe, stretch the nickel-titanium pipe to 5.3 centimeters, unload the tension, let it stand for 5 minutes, and measure the length of the nickel-titanium pipe at this time.

[0187] Calculation method: Superelastic recovery rate = [(stretched length - recovered length) / (stretched length - initial length)] × 100%.

[0188] 2. Tensile test

[0189] Prepare a 5 cm long nickel-titanium tube and fix it on a universal testing machine. Stretch it at a speed of 1 mm / min until the sample breaks. Record the maximum force, elongation, and strain at the time of fracture.

[0190] Calculation method: (1) Tensile strength

[0191] б = Maximum tensile force of nickel-titanium pipe / Initial cross-sectional area of ​​pipe

[0192] (2) Elongation

[0193] ε = (Length at the end of the pipe test - Initial length) / Initial length × 100%

[0194] 3. Fatigue test

[0195] A 10 cm nickel-titanium pipe was subjected to high-frequency fatigue testing at 500 MPa, and the number of cycles and deformation were recorded.

[0196] 4. Surface roughness

[0197] The inner and outer surfaces were tested in accordance with GB / T 1031-2009 "Geometric Specifications for Products (GPS): Surface Structure, Profile Method, Surface Roughness Parameters and Their Values". Table 1 shows the average values ​​of the inner and outer surface roughness.

[0198] 5. Antibacterial test

[0199] After sterilizing an appropriate amount of pipe material sample at high temperature, place it in a sterile petri dish, add 0.4 ml of Escherichia coli solution, and incubate at 37°C for 24 hours. At the same time, set up a control group (blank culture medium), wash, dilute, and calculate the number of colonies.

[0200] Antibacterial rate = [(number of colonies in control group - number of colonies in nickel-titanium pipe) / number of colonies in control group] × 100%.

[0201] 6. Corrosion resistance test

[0202] The nickel-titanium tube was cut into 1cm×1cm sheet samples, polished with sandpaper, ultrasonically cleaned and dried, and scanned in simulated body fluid using a three-electrode system. The curve was recorded, and the corrosion current density was calculated using the extrapolation method.

[0203] Corrosion rate = (corrosion current density × molar mass of pipe) / (density × number of reaction electrons × Faraday constant).

[0204] Performance tests are shown in Table 1 below:

[0205] Table 1. Performance Tests of Medical Ultrapure Nickel-Titanium Tubes

[0206]

[0207] It should be noted that the "Corrosion Resistance / Antibacterial Properties" in Table 1 is a comprehensive evaluation of the antibacterial and corrosion resistance tests. A rating of "Excellent" is given if both tests are excellent, "Good" if one test is excellent, "Medium" if one test is good, and "Poor" if one test is medium. An antibacterial rate of ≥95% is excellent, 90-95% is good, 70-90% is medium, and the rest is poor. A corrosion rate of <0.001 mm / year is excellent, 0.001-0.005 mm / year is good, 0.005-0.01 mm / year is medium, and >0.01 mm / year is poor.

[0208] Data Analysis:

[0209] 1. Importance of the core structure (double helix skeleton + prestress):

[0210] In Comparative Example 1, no prestress was applied. The lack of prestress caused the double helix network to loosen and slightly warp during the casting and cooling process, resulting in initial defects in its bonding with the matrix. These defects became stress concentration points and fatigue crack initiations, which rapidly propagated under cyclic loading, leading to a sharp decline in fatigue life.

[0211] Comparative Example 2 uses a woven wire mesh instead of a double-helix mesh. The nodes of the woven wire mesh are mechanically overlapped, resulting in inherent stress concentration points, and its structural stability is inferior to that of a continuously twisted double-helix structure. During casting and rolling, the nodes are prone to becoming fracture initiation points, severely reducing the material's fatigue performance.

[0212] Comparative Examples 1 and 2 demonstrate that the structural integrity of the internal reinforcement and its tight bonding with the matrix are the most critical factors determining the fatigue life of a product. The "pre-stretched double-helix mesh" designed in this invention can maximize the avoidance of stress concentration and achieve uniform stress transmission, which is unmatched by traditional structures such as warp and weft woven meshes.

[0213] 2. Synergistic effect of trace element alloying:

[0214] Comparative Example 3, without the addition of Cu, lacks copper and thus loses its antibacterial properties. Simultaneously, the lack of copper's effect on improving processing performance results in slightly higher deformation resistance during cold rolling, insufficient optimization of the internal dislocation structure, and a slight impact on fatigue life.

[0215] Comparative Example 4, without the addition of Nb and Zr, lacks niobium and zirconium, making it difficult to form the most dense and stable surface oxide film (TiO2), resulting in decreased corrosion resistance. The grain-refining strengthening and phase-stabilizing effects of zirconium are weakened, leading to a reduction in the material's basic strength and resistance to crack propagation, thus decreasing fatigue performance.

[0216] Comparative Example 5, without the addition of Ta and Sn (tantalum), may affect biocompatibility. The absence of tin results in the loss of its grain boundary strengthening and fatigue resistance enhancement effects, leading to a decrease in the material's damage tolerance under cyclic loading.

[0217] Comparative examples 3, 4, and 5 demonstrate that various trace elements do not act in isolation, but rather work synergistically to enhance the overall performance of materials. The absence of any one element will result in a deficiency in specific properties. For example, Cu provides antibacterial properties, Nb and Zr jointly improve corrosion resistance and strength, and Ta and Sn enhance biocompatibility and fatigue resistance. Their combined presence enables nickel-titanium tubes to meet the stringent requirements of medical materials in many aspects.

[0218] 3. The systematic nature of thermomechanical processing:

[0219] Comparative Example 6 eliminates the three-stage hot rolling process, resulting in single-stage high-temperature hot rolling, which leads to coarse grains and compositional segregation. Coarse grains and an inhomogeneous microstructure create a breeding ground for crack initiation, severely degrading superelasticity and fatigue properties. Subsequent cold rolling is also prone to defects due to the inhomogeneous microstructure.

[0220] Comparative Example 7 omits cold rolling, thus lacking the dislocation strengthening, grain refinement strengthening, and work hardening effects of cold rolling. The material's strength and hardness are insufficient to withstand high loads, and it immediately undergoes plastic deformation in the hyperelasticity test, failing to exhibit shape memory effect, making fatigue life impossible to assess.

[0221] In Comparative Example 8, the shape memory heat treatment was omitted, and the high-energy unstable state after cold rolling was not eliminated or transformed. The internal stress was not released, recrystallization and uniform precipitate phases were not formed, and the material could not obtain superelasticity and shape memory properties, exhibiting brittleness.

[0222] This demonstrates that the core mechanism of the three-stage hot rolling of this invention is to gradually break down the as-cast structure, eliminate segregation, and refine and homogenize the grains through plastic deformation and recrystallization at different phase temperatures. Uniform microstructure control cannot be achieved through single high-temperature hot rolling.

[0223] The core function of cold rolling is work hardening and microstructure refinement. Through intense plastic deformation, high-density dislocations and fine subgrains are introduced, significantly improving the material's strength, hardness, and resistance to fatigue crack propagation. Without cold rolling, materials lack the structural framework to withstand high loads.

[0224] Shape memory heat treatment is key to endowing materials with functional properties. It releases cold rolling stress, completes recrystallization, and promotes the uniform precipitation of phases such as Ni4Ti3, thereby setting the superelasticity. Without this step, the material is just a high-strength but inelastic ordinary alloy.

[0225] 4. The indispensability of surface treatment processes:

[0226] Comparative Example 9 omitted pickling, and the surface oxide layer and processing residues were not removed, which directly affected the effect of subsequent electropolishing, resulting in the final product having substandard surface roughness and deteriorating corrosion resistance and biocompatibility.

[0227] Comparative Example 10 omits electropolishing, thus missing the final step to achieve an ultra-smooth surface. Mechanical polishing and acid pickling cannot achieve the technical effect of electropolishing; the surface roughness is far higher than required, making it prone to corrosion initiation and crack initiation points. Although short-term mechanical properties may meet the standards, long-term service reliability is poor.

[0228] This indicates that pickling and electropolishing are essential processes for obtaining ultra-smooth, high-cleanliness surfaces. Surface quality directly determines biocompatibility and long-term corrosion resistance. In particular, electropolishing can remove surface defect layers, achieving a mirror-like finish and significantly reducing the risk of thrombosis and corrosion. Furthermore, the existing mechanisms of use of nickel-titanium implants show that surface roughness (Ra) is positively correlated with bacterial adhesion, platelet adhesion, and the probability of crack initiation.

[0229] Examples 1-3 employ the synergistic effect of various key processes: prestressing ensures a tight bond between the double-helix skeleton and the matrix, uniformly bearing stress; trace elements synergistically enhance corrosion resistance, antibacterial properties, and fatigue performance; three-stage hot rolling refines and homogenizes the grains; cold rolling introduces dislocation strengthening; and shape-marking heat treatment sets up superelasticity and eliminates stress. The synergistic effects of these processes in the alloy formulation contribute to corrosion resistance, antibacterial properties, and fatigue resistance.

[0230] The superiority of this invention lies in its complete system solution, encompassing molecular-level composition design (ultra-high purity and trace element synergy), microscopic-level structural design (prestressing and double-helix skeleton), macroscopic-level process control (hot rolling-cold rolling-heat treatment synergy), and surface-level finishing. Each step is indispensable and synergistic, ultimately achieving a perfect balance in mechanical properties, functional characteristics (superelasticity), and biological properties (antibacterial properties and durability) for medical nickel-titanium tubing. Comparative data clearly demonstrates that the absence of any key link will lead to the failure of the final product in some aspect or even completely.

[0231] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a medical ultrapure nickel-titanium tube, characterized in that, The following steps are included: S1. Blank preparation Preparation of S101 nickel-titanium springs Using ultra-high purity nickel-titanium wire, left-hand and right-hand springs are wound on a precision spring winding machine; One end of the left-hand spring is turned into the pitch gap of the right-hand spring, and multiple left-hand springs and multiple right-hand springs are twisted together end to end to form a uniform and tight double helix network. Preparation of S102 and nickel-titanium casting fluid High-purity electrolytic nickel and high-purity titanium with matching atomic ratios are mixed and then subjected to cold crucible magnetic levitation induction melting to obtain extremely high-purity nickel-titanium casting liquid. S103, Tube blank casting and prestressing application The double helix pipe network is placed in the center of a specially made annular mold cavity, and axial prestress is applied to both ends of the double helix pipe network, with the pre-tension strain controlled at 3-5%. Under a He atmosphere, the annular mold is preheated to 400℃, and the nickel-titanium casting liquid is poured into the annular mold. After pouring, the mold is kept at a pressure of 1.2-1.4MPa and a temperature of 500-600℃ for 30-45 minutes. The mold is then cooled to room temperature, and the prestressing tension is finally removed to obtain a tube blank with a thickness of 5±0.2mm. S2, Molding and Heat Treatment S201, three-stage hot-rolled First, the tube blank is held at 950℃ for 30-60 minutes and then hot rolled in one heat using a two-roll reversible mill; it is then heated back to 930℃ and held for 20-30 minutes for a second heat; then the tube blank is heated to 810-910℃ and held for 10-20 minutes for a third heat, and then cooled to room temperature. S202, Cold Rolling and Stress Hardening Using a multi-roll precision cold rolling mill, the pierced tube blank is placed on a smooth, extremely hard mandrel. Through the rotation and reciprocating motion of the rolls, the tube blank is subjected to 7-8 passes of cold rolling. The cumulative cold deformation must be strictly controlled between 30-50% to obtain the shaped tube. S203, shape memory heat treatment After cold rolling, the shaped tubes undergo precise shape memory setting heat treatment, holding at 500-550℃ for 5-30 minutes, followed by rapid water quenching to obtain tubes without internal stress. S3. Finishing and Inspection S301, pickling For pipes without internal stress, pickling is performed at a temperature of 40-50℃ for 5-10 minutes. S302, electropolishing A NaCl ethylene glycol solution with a weight concentration of 58.44 g / L was used as the electrolyte. The anode was the pickled pipe and the cathode was a 304 stainless steel metal ring with an inner diameter of 17 mm. Electropolishing was carried out at 15-35℃ for 10-15 min. S303, Cleaning and Testing The inner and outer surfaces of the polished tube are then polished, cleaned, subjected to ultrasonic testing, and subjected to performance tests to ensure that they meet medical standards, resulting in a finished medical ultrapure nickel-titanium tube.

2. The method for preparing a medical ultrapure nickel-titanium tube according to claim 1, characterized in that, The diameter of the left-hand and right-hand springs in S101 is 1.0 mm, and the pitch is controlled at 3.0 mm, which facilitates the formation of a twisted double helix network with a wall thickness of about 2.0 mm.

3. The method for preparing a medical ultrapure nickel-titanium tube according to claim 1, characterized in that, The process parameters for magnetic levitation induction melting in S102 are: vacuum degree 10 -5 -10 -2 Pa, 1600-1750℃, high-frequency alternating magnetic field frequency of 1.5-2.5KHz, holding for 5-15min, total alloy mass required is 10-20kg, rapid cooling with inert gas for 20min.

4. The method for preparing a medical ultrapure nickel-titanium tube according to claim 1, characterized in that, The formulations of the ultra-high purity nickel-titanium wire and the extremely high purity nickel-titanium casting fluid in S1 both include the following components by mass percentage: Nickel: 54.5 wt% - 57.0 wt%; Titanium: 42.8wt%-45.3wt%; Other trace elements: Copper: 0.01wt%-0.03wt%; Niobium: 0.01wt%-0.025wt%; Zirconium: 0.05% wt% - 0.08 wt%; Tantalum: 0.01wt%-0.05wt%; Tin: 0.01wt%-0.05wt%.

5. The method for preparing a medical ultrapure nickel-titanium tube according to claim 4, characterized in that, The purity of the nickel, titanium and other trace elements is required to be 99.99 wt%, and they undergo the following pretreatment: the nickel, titanium and other trace elements are placed in a deoxidation furnace at 300-700℃ for 20-30 minutes under inert gas protection, and the weighing error is controlled within ±0.003 wt%.

6. The method for preparing a medical ultrapure nickel-titanium tube according to claim 1, characterized in that, The dimensions of the S201, three-section hot-rolled product are as follows: After one-heat hot rolling, the outer diameter of the nickel-titanium tube billet is 20-25mm and the wall thickness is 2-4mm. After two-heat hot rolling, the outer diameter of the nickel-titanium tube billet is 15-20mm and the wall thickness is 1-2mm. After three-heat hot rolling, the outer diameter of the nickel-titanium tube billet is 12-17mm and the wall thickness is 0.5-1mm.

7. The method for preparing a medical ultrapure nickel-titanium tube according to claim 1, characterized in that, The pickling solution used in the S301 pickling process is a mixture of a 35 wt% nitric acid aqueous solution and a 5 wt% hydrofluoric acid aqueous solution at a volume ratio of 1:

1.

8. The method for preparing a medical ultrapure nickel-titanium tube according to claim 1, characterized in that, The mandrel in S202 is a tungsten-cobalt cemented carbide, wherein the mass ratio of tungsten carbide to cobalt is 90:

10.

9. The method for preparing a medical ultrapure nickel-titanium tube according to claim 1, characterized in that, When electrochemical polishing is performed in the S302, the voltage is between 15-35V.

10. The medical ultrapure nickel-titanium tube obtained by any one of the preparation methods according to claims 1-9 has an inner and outer surface roughness of ≤0.4μm.

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