Preparation method of ultra-pure nickel-titanium alloy thin-wall pipe for heart valve

Abstract

The invention discloses a preparation method of an ultra-pure nickel-titanium alloy thin-wall pipe for a heart valve. The method comprises the following steps: 1, preparing materials, and carrying out magnetic suspension induction melting to obtain a cast ingot; 2, gradually performing hot forging and rolling on the cast ingot to obtain a round bar; thirdly, the round bar is manufactured into a pipe blank, honing and polishing are conducted, and the nickel-titanium pipe is obtained; 4, assembling the nickel-titanium pipe into the titanium pipe to obtain a combined pipe; 5, heat treatment of the combined pipe; 6, three-roller precise cold rolling; 7, repeating to obtain a pipe semi-finished product; and 8, straightening and cylindrical grinding are performed to remove the titanium pipe. According to the method, the high-purity nickel-titanium alloy cast ingot is prepared through magnetic suspension induction melting, the outer-layer titanium pipe and the inner-layer nickel-titanium pipe are introduced to be assembled, the pass deformation is increased through the restraining and protecting effects of the titanium pipes, the number of times of rolling and heat treatment is reduced, and the machining period is shortened; the obtained ultra-pure nickel-titanium alloy thin-wall pipe is high in purity, high in size precision, good in surface quality, high in wall thickness uniformity and good in comprehensive mechanical property and is suitable for the field of heart valves.

Description

Technical Field

[0001] The invention belongs to the technical field of thin-walled tube processing, and in particular relates to a method for preparing an ultra-pure nickel-titanium alloy thin-walled tube for a heart valve. Background Art

[0002] Nickel-titanium alloy tubes have excellent physical properties, biocompatibility, unique shape memory effect and superelasticity, and have been widely used in medical devices in many fields such as cardiovascular and peripheral vascular. Especially in the field of heart valves, nickel-titanium alloy heart valve stents can be compressed to a very small size at room temperature, which is convenient for automatic restoration of the predetermined shape after being delivered to the target position through a catheter to ensure smooth blood flow. Superelasticity ensures that the stent is not easy to deform or break when subjected to force, which greatly reduces the high risks of open-chest surgery, especially for some elderly patients with multiple comorbidities and underlying diseases.

[0003] However, the high-quality nickel-titanium alloy thin-walled tubes used in heart valve stents are still highly dependent on imports. In addition to the high-cleanliness smelting technology of nickel-titanium alloys, the preparation of thin-walled tubes involves both multiple composite deformation mechanisms and complex phase changes, which is very demanding on the preparation process, expensive, and has a long delivery time, which seriously restricts the development of domestic high-end equipment.

[0004] Traditional nickel-titanium alloy melting technologies include vacuum consumable melting and induction melting. Vacuum consumable melting is generally used to make master alloys, and then vacuum induction melting is used. The use of graphite crucibles in induction melting will increase the C content, and oxide crucibles are easy to react with titanium and introduce oxygen. Impurity elements will cause changes in the composition of nickel-titanium alloys, thereby affecting the phase change temperature and mechanical properties. For nickel-titanium alloys used in heart valves, in addition to the excellent mechanical properties of nickel-titanium alloys, long-term fatigue performance is also an important parameter, and fatigue performance is inevitably related to impurity elements.

[0005] The preparation of nickel-titanium alloy tube blanks includes hot extrusion, hot rolling and warm rolling. The deformation resistance of nickel-titanium alloy is reduced at a certain temperature, but the dimensional accuracy and surface quality are poor, and titanium is very active and easily reacts with high-temperature graphite lubricant or oxygen in the air, introducing impurities, which brings trouble to subsequent processing and requires pickling to remove, which may cause environmental pollution. For example, Chinese patent CN114850219A discloses a preparation of a high-precision, thin-diameter, thin-walled nickel-titanium alloy tube, which uses warm rolling to obtain a semi-finished tube, and a finished tube is obtained by drawing with a moving core head. The key process is that warm rolling improves the plastic processing properties of the material and reduces the number of processing passes. However, the nickel-titanium tube blank uses graphite lubrication, and warm processing uses hydrogen heating. The rolling temperature is 500℃~700℃. The rolling process is very easy to absorb hydrogen and increase carbon, causing alloy component pollution, and it is difficult to meet the requirements of low inclusion elements for medical implant-grade nickel-titanium alloy.

[0006] Nickel-titanium alloy finished pipes are processed by hot drawing or cold drawing. The drawing process is simple, the mold can be easily disassembled and replaced, and it is suitable for the production of pipes, but the requirements for lubricants are high. Chinese patent CN 103394532A discloses a continuous hot drawing forming method for nickel-titanium alloy pipes, which uses induction heating to achieve continuous hot drawing of nickel-titanium alloy pipes (with mandrels), and then plastically stretches the mandrels to reduce the diameter of the mandrels and remove them to obtain nickel-titanium alloy pipes. The key process is to use induction heating to achieve continuous hot drawing, which improves production efficiency; however, the induction heating process will cause uneven heating of the pipes, the precision and surface quality of the pipes are not high, and the content of impurity elements may also increase. Chinese patent CN115870365A discloses a processing method for medical nickel-titanium pipes, which uses nickel-titanium tube blanks + hard mandrels for one or more cold drawing, overall annealing, and hardening of the core to obtain medical nickel-titanium pipe products. The key process is to use hard mandrels to improve the inner surface quality of the pipes. However, there is a large clamping force between the tube and the mandrel after drawing, which makes it difficult to remove the mandrel, and there is a risk of contamination caused by element diffusion at the interface of the mandrel and tube when the two materials are heat treated together.

[0007] The stress state provided by cold rolling is most suitable for the plastic deformation of metal pipes. The quality and dimensional accuracy of the inner and outer surfaces of the obtained pipes are much better than those of cold drawing. It belongs to precision cold processing. However, nickel-titanium alloy hardens very quickly during cold processing, and the processing amount per pass is small. In particular, the outer surface of the pipe is deformed greatly, which is easy to form cracks. The deformation should be strictly controlled between 15% and 20% during rolling (such as reference: Hu Jie et al. Research on the processing technology of titanium-nickel shape memory alloy capillary [J]. New Technology and New Process, 2006, 6: 51-52).

[0008] Therefore, it is urgent to develop a full-process preparation technology for ultra-pure nickel-titanium alloy thin-walled tubes to improve the deep processing technology level of high-end medical devices. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a method for preparing ultra-pure nickel-titanium alloy thin-walled tubes for heart valves in view of the deficiencies of the above-mentioned prior art. The method adopts magnetic levitation induction melting to prepare high-purity nickel-titanium alloy ingots and prepares nickel-titanium tubes, which are then assembled and combined as inner and outer titanium tubes for cold rolling. By introducing the outer titanium tube, the cold rolling deformation is increased without introducing new impurity elements, and the processing cycle is shortened to obtain ultra-pure nickel-titanium alloy thin-walled tubes with high purity, high dimensional accuracy, good surface quality, high wall thickness uniformity, and good comprehensive mechanical properties, solving the problems of conventional nickel-titanium alloy tubes that introduce impurity elements during hot (warm) rolling and drawing, low cold rolling efficiency, and poor cold drawing dimensional accuracy.

[0010] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an ultrapure nickel-titanium alloy thin-walled tube for a heart valve, characterized in that the method comprises the following steps:

[0011] Step 1: using grade 0 small particle titanium sponge and nickel plate with a purity of 99.99% and then using magnetic levitation induction melting to prepare a nickel-titanium alloy ingot; the magnetic levitation induction melting is repeated 2 to 3 times;

[0012] Step 2, hot forging the nickel-titanium alloy ingot obtained in step 1 into a square rod, and then rolling it into a nickel-titanium alloy round rod; the nickel-titanium alloy round rod has a diameter of 20 mm to 25 mm;

[0013] Step 3: Prepare the nickel-titanium alloy round rod obtained in step 2 into a tube blank by deep hole drilling, and perform inner surface honing and outer surface polishing until the inner and outer surface roughnesses are both less than 0.4 μm, to obtain a nickel-titanium tube;

[0014] Step 4: Select a titanium tube with an inner and outer surface roughness of no more than 0.4 μm and a processed microstructure, and assemble the nickel-titanium tube obtained in step 3 into the titanium tube so that the inner diameter of the titanium tube and the outer diameter of the nickel-titanium tube are fitted with a clearance fit, and the clearance is 0.05 mm to 0.1 mm, to obtain a combined tube;

[0015] Step 5, heat treating the combined tube obtained in step 4, so that the outer diameter of the inner layer of the nickel-titanium tube in the combined tube increases by 0.15 mm to 0.2 mm due to the memory effect, and achieves an interference fit with the outer layer of the titanium tube; the heat treatment temperature is 650° C. to 700° C., and the holding time is 30 min to 45 min;

[0016] Step 6: The combined pipe after heat treatment in step 5 is subjected to three-roll precision cold rolling, the deformation amount of a single pass is 25% to 33%, and an intermediate heat treatment is performed after each cold rolling, the intermediate heat treatment temperature is 600°C to 645°C, and the last intermediate heat treatment temperature is 350°C to 400°C;

[0017] Step 7: Repeat the cold rolling and intermediate heat treatment process in step 6 until the target size is obtained to obtain a semi-finished pipe;

[0018] Step 8: Straighten the semi-finished pipe obtained in step 7 to a straightness of no more than 0.3 mm / 300 mm, and then use a centerless grinder to remove the titanium pipe by cylindrical grinding, with a grinding amount of 0.1 mm to 0.2 mm to obtain an ultra-pure nickel-titanium alloy thin-walled pipe.

[0019] The above-mentioned method for preparing ultrapure nickel-titanium alloy thin-walled tube for heart valve is characterized in that the process parameters of magnetic suspension induction melting in step 1 are: the vacuum degree does not exceed 2×10 -2 Pa, electromagnetic induction heating frequency 1800Hz ~ 2200Hz, insulation power 320kW ~ 350kW, insulation time 10min ~ 15min, cooling time 60min ~ 90min, the weight of the nickel-titanium alloy ingot is 10kg ~ 20kg. By controlling the process parameters of magnetic levitation induction melting and the weight of the nickel-titanium alloy ingot, the melt of the nickel-titanium alloy ingot is suspended, ensuring the smooth progress of magnetic levitation induction melting, while increasing the single processing volume of ultra-pure nickel-titanium alloy thin-walled pipes, ensuring the preparation efficiency.

[0020] The above-mentioned method for preparing an ultrapure nickel-titanium alloy thin-walled tube for a heart valve is characterized in that the wall thickness of the titanium tube in step 4 is 0.1 mm to 0.2 mm. The present invention uses a titanium tube as a protective layer for the nickel-titanium tube to avoid damage to the nickel-titanium tube by direct contact with the mold during early rolling, to avoid excessive stress on the nickel-titanium tube, and to facilitate removal of the titanium layer by centerless grinding in the later stage.

[0021] The above-mentioned method for preparing an ultrapure nickel-titanium alloy thin-walled tube for heart valves is characterized in that the composition of the ultrapure nickel-titanium alloy thin-walled tube in step eight complies with ASTM F2063-2018 "Standard Specification for Forged Nickel-Titanium Shape Memory Alloys for Medical Devices and Surgical Implants", wherein the mass percentage of impurity elements is: C≤0.005%, H≤0.0005%, N≤0.005%, O≤0.02%. The mass percentage of impurity elements in the ultrapure nickel-titanium alloy thin-walled tube prepared by the present invention is lower than the requirements of ASTM F2063-2018 standard specification, meeting the requirements of metal tubes for heart valves.

[0022] The method for preparing the ultrapure nickel-titanium alloy thin-walled tube for heart valves is characterized in that the outer diameter of the ultrapure nickel-titanium alloy thin-walled tube in step eight is 4 mm to 12 mm, and the wall thickness is 0.1 mm to 0.5 mm. The size of the ultrapure nickel-titanium alloy thin-walled tube prepared by the present invention meets the requirements of medical metal tubes, especially metal tubes for heart valves.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention first selects high-purity raw materials to prepare high-purity nickel-titanium alloy ingots through magnetic levitation induction melting, hot forging and rolling them into round bars, and deep drilling them into nickel-titanium tubes. The nickel-titanium tubes are then assembled into the interior of the titanium tubes for heat treatment, and the shape memory effect of the nickel-titanium alloy is used to ensure that the nickel-titanium tubes are tightly combined with the titanium tubes. A large deformation cold rolling combined with intermediate heat treatment is then performed to make the tubes close to the finished product size. After straightening, the outer layer of the titanium tube is removed by centerless grinding. In this preparation process, the outer layer of the titanium tube is introduced, that is, no new impurity elements are introduced, and the cold rolling deformation of the nickel-titanium alloy tube is increased, the processing cycle is shortened, and the purity and dimensional accuracy of the product nickel-titanium alloy thin-walled tube are guaranteed.

[0025] 2. The present invention adopts magnetic levitation induction melting to prepare nickel-titanium alloy ingots, and utilizes high-frequency magnetic field heating and melt stirring to improve the composition uniformity and accuracy of the nickel-titanium alloy ingots. The melting process does not contact the crucible, eliminating crucible contamination, reducing the content of C, H, O, and N impurity elements, and controlling the content of inclusions from the source. At the same time, due to the effect of electromagnetic induction, the melt will roll up and down during the melting process, which plays a stirring role, making the nickel-titanium alloy composition more uniform, which is beneficial to improving the long-term fatigue performance of the heart valve stent produced therefrom.

[0026] 3. In view of the defects that the titanium-nickel alloy hardens very quickly during work hardening, is extremely sensitive to deformation, has a small deformation during single rolling (single deformation of 15% to 20%), requires frequent annealing during cold working, and is very easy to crack due to the large processing stress on the outer surface of the pipe during cold rolling, especially the end of the pipe, which is very easy to crack due to the instantaneous stress of contacting the mold. The present invention assembles the nickel-titanium pipe into a titanium pipe with better processing performance and performs cold rolling after achieving interference fit. During cold rolling, the outer layer of the titanium pipe is subjected to large force and the inner layer of the nickel-titanium pipe is relatively slightly deformed, thereby achieving protection of the nickel-titanium pipe. and stress constraints, improving the processability of the outer side of the nickel-titanium tube, so that the nickel-titanium tube is not prone to defects such as cracks and folds during the rolling process. At the same time, the titanium tube has high biocompatibility, will not introduce new elements, and avoid pollution. In addition, due to the above-mentioned effect of the outer titanium tube, the single-pass deformation during cold rolling of the present invention is significantly increased (the single-pass deformation is 25% to 33%, which is about 1.6 times the cold-rolled deformation of the original nickel-titanium tube), and the number of intermediate heat treatments is reduced, thereby effectively shortening the processing cycle, improving the yield rate, and reducing costs.

[0027] 4. The cold rolling process of the present invention does not introduce elements such as C, H, O, and N, thereby ensuring the composition of the ultra-pure nickel-titanium alloy thin-walled tube; at the same time, compared with the traditional drawing method, it eliminates the processes such as surface lubrication and subsequent core removal, thus simplifying the process.

[0028] 5. The ultra-pure nickel-titanium alloy thin-walled tube prepared by the present invention has high purity, high dimensional accuracy, good surface quality, high wall thickness uniformity, and good comprehensive mechanical properties, and is suitable for the field of heart valves.

[0029] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a physical picture of the nickel-titanium alloy ingot prepared in Example 1 of the present invention.

[0031] Figure 2 This is a physical picture of the ultra-pure nickel-titanium alloy thin-walled tube prepared in Example 1 of the present invention.

[0032] Figure 3 This is a physical picture of the ultra-pure nickel-titanium alloy thin-walled tube prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] Example 1

[0034] This embodiment includes the following steps:

[0035] Step 1: Use grade 0 small particle titanium sponge and nickel plate with a purity of 99.99% and then use magnetic levitation induction melting to prepare a nickel-titanium alloy ingot. Figure 1 As shown; the magnetic levitation induction melting is repeated twice; the process parameters of the magnetic levitation induction melting are: the vacuum degree does not exceed 2×10 -2 Pa, electromagnetic induction heating frequency 1800 Hz, holding power 320 kW, holding time 10 min, cooling time 60 min, the weight of the nickel-titanium alloy ingot is 10 kg;

[0036] Step 2, hot forging the nickel-titanium alloy ingot obtained in step 1 into a square rod, and then rolling it into a nickel-titanium alloy round rod with a diameter of 2 mm;

[0037] Step 3: The nickel-titanium alloy round rod obtained in step 2 is prepared into a tube blank by deep hole drilling, and the inner surface is honed and the outer surface is polished until the inner and outer surface roughnesses are both less than 0.4 μm, so as to obtain a nickel-titanium tube with an outer diameter × wall thickness of Φ17.0 mm × 1.2 mm;

[0038] Step 4: Select a titanium tube with an inner and outer surface roughness of no more than 0.4 μm and a processed microstructure, and an outer diameter × wall thickness of Φ17.5 mm × 0.2 mm, and assemble the nickel-titanium tube obtained in step 3 into the titanium tube, so that the inner diameter of the titanium tube and the outer diameter of the nickel-titanium tube are assembled into a clearance fit, and the clearance is 0.05 mm, to obtain a combined tube with an outer diameter × wall thickness of Φ17.5 mm × 1.4 mm;

[0039] Step 5: heat-treating the combined tube obtained in step 4, so that the outer diameter of the inner nickel-titanium tube in the combined tube increases by 0.2 mm due to the memory effect, and an interference fit is achieved with the outer titanium tube; the heat treatment temperature is 700° C., and the holding time is 45 min;

[0040] Step 6: The combined pipe after heat treatment in step 5 is subjected to three-roll precision cold rolling. The change of outer diameter × wall thickness during cold rolling is: Φ17.5mm×1.4mm→Φ15.8mm×1.1mm→Φ14mm×0.9mm→Φ12.4mm×0.7mm (retaining the processed state), and an intermediate heat treatment is performed after each cold rolling, the intermediate heat treatment temperature is 645°C, the time is 15min, and the last intermediate heat treatment temperature is 400°C, and the time is 35min;

[0041] Step 7: Repeat the cold rolling and intermediate heat treatment process in step 6 until the target size is obtained to obtain a semi-finished pipe;

[0042] Step 8: Straighten the semi-finished pipe obtained in step 7 to a straightness of 0.2 mm / 300 mm, and then use a centerless grinder to remove the titanium pipe by cylindrical grinding, with a grinding amount of 0.2 mm to obtain an ultra-pure nickel-titanium alloy thin-walled pipe with an outer diameter × wall thickness of Φ12.0 mm × 0.5 mm, such as Figure 2 described.

[0043] After testing, the composition of the ultra-pure nickel-titanium alloy thin-walled tube prepared in this embodiment conforms to ASTM F2063-2018 "Standard Specification for Forged Nickel-Titanium Shape Memory Alloy for Medical Devices and Surgical Implants", wherein the mass percentage of impurity elements is: C≤0.005%, H≤0.0005%, N≤0.005%, O≤0.02%.

[0044] Example 2

[0045] This embodiment includes the following steps:

[0046] Step 1: Use grade 0 small particle titanium sponge and nickel plate with a purity of 99.99%, and then use magnetic levitation induction melting to prepare a nickel-titanium alloy ingot; the magnetic levitation induction melting is repeated 3 times; the process parameters of the magnetic levitation induction melting are: the vacuum degree does not exceed 2×10 -2 Pa, electromagnetic induction heating frequency 2100 Hz, holding power 345 kW, holding time 13 min, cooling time 80 min, the weight of the nickel-titanium alloy ingot is 16 kg;

[0047] Step 2, hot forging the nickel-titanium alloy ingot obtained in step 1 into a square rod, and then rolling it into a nickel-titanium alloy round rod with a diameter of 20 mm;

[0048] Step 3: The nickel-titanium alloy round rod obtained in step 2 is prepared into a tube blank by deep hole drilling, and the inner surface is honed and the outer surface is polished until the inner and outer surface roughnesses are both less than 0.4 μm, so as to obtain a nickel-titanium tube with an outer diameter × wall thickness of Φ11.2 mm × 0.5 mm;

[0049] Step 4: Select a titanium tube with an inner and outer surface roughness of no more than 0.4 μm and a processed microstructure, and an outer diameter × wall thickness of Φ11.5 mm × 0.1 mm, and assemble the nickel-titanium tube obtained in step 3 into the titanium tube, so that the inner diameter of the titanium tube and the outer diameter of the nickel-titanium tube are assembled into a clearance fit, and the clearance is 0.1 mm, to obtain a combined tube with an outer diameter × wall thickness of Φ11.5 mm × 0.6 mm;

[0050] Step 5: heat-treating the combined pipe obtained in step 4, so that the outer diameter of the inner layer of the nickel-titanium pipe in the combined pipe increases by 0.15 mm due to the memory effect, and an interference fit is achieved with the outer layer of the titanium pipe; the heat treatment temperature is 680° C., and the holding time is 45 minutes;

[0051] Step 6: The combined pipe after heat treatment in step 5 is subjected to three-roll precision cold rolling. The change of outer diameter × wall thickness during cold rolling is: Φ11.5mm×0.6mm→Φ10.2mm×0.5mm→Φ9.2mm×0.3mm→Φ8.2mm×0.3mm (retaining the processed state), and an intermediate heat treatment is performed after each cold rolling, the intermediate heat treatment temperature is 620°C, the time is 10min, and the last intermediate heat treatment temperature is 380°C, and the time is 30min;

[0052] Step 7: Repeat the cold rolling and intermediate heat treatment process in step 6 until the target size is obtained to obtain a semi-finished pipe;

[0053] Step 8: Straighten the semi-finished pipe obtained in step 7 to a straightness of 0.1 mm / 300 mm, and then use a centerless grinder to remove the titanium pipe by cylindrical grinding, with a grinding amount of 0.1 mm to obtain an ultra-pure nickel-titanium alloy thin-wall pipe with an outer diameter × wall thickness of Φ8.0 mm × 0.2 mm, such as Figure 3 shown.

[0054] After testing, the composition of the ultra-pure nickel-titanium alloy thin-walled tube prepared in this embodiment conforms to ASTM F2063-2018 "Standard Specification for Forged Nickel-Titanium Shape Memory Alloy for Medical Devices and Surgical Implants", wherein the mass percentage of impurity elements is: C≤0.005%, H≤0.0005%, N≤0.005%, O≤0.02%.

[0055] Example 3

[0056] This embodiment includes the following steps:

[0057] Step 1: Use grade 0 small particle titanium sponge and nickel plate with a purity of 99.99%, and then use magnetic levitation induction melting to prepare a nickel-titanium alloy ingot; the magnetic levitation induction melting is repeated 3 times; the process parameters of the magnetic levitation induction melting are: the vacuum degree does not exceed 2×10 -2 Pa, electromagnetic induction heating frequency 2200 Hz, holding power 350 kW, holding time 15 min, cooling time 90 min, the weight of the nickel-titanium alloy ingot is 20 kg;

[0058] Step 2, hot forging the nickel-titanium alloy ingot obtained in step 1 into a square rod, and then rolling it into a nickel-titanium alloy round rod with a diameter of 20 mm;

[0059] Step 3: The nickel-titanium alloy round rod obtained in step 2 is prepared into a tube blank by deep hole drilling, and the inner surface is honed and the outer surface is polished until the inner and outer surface roughnesses are both less than 0.4 μm, so as to obtain a nickel-titanium tube with an outer diameter × wall thickness of Φ5.95 mm × 0.3 mm;

[0060] Step 4: Select a titanium tube with an inner and outer surface roughness of no more than 0.4 μm and a processed microstructure, and an outer diameter × wall thickness of Φ6.2 mm × 0.1 mm, and assemble the nickel-titanium tube obtained in step 3 into the titanium tube, so that the inner diameter of the titanium tube and the outer diameter of the nickel-titanium tube are assembled into a clearance fit, and the clearance is 0.05 mm, to obtain a combined tube with an outer diameter × wall thickness of Φ6.2 mm × 0.4 mm;

[0061] Step 5, heat-treating the combined tube obtained in step 4, so that the outer diameter of the inner layer of the nickel-titanium tube in the combined tube increases by 0.15 mm due to the memory effect, and an interference fit is achieved with the outer layer of the titanium tube; the heat treatment temperature is 650° C., and the holding time is 35 minutes;

[0062] Step 6: The combined pipe after heat treatment in step 5 is subjected to three-roll precision cold rolling. The change of outer diameter × wall thickness during cold rolling is: Φ6.2mm×0.4mm→Φ5.5mm×0.3mm→Φ4.8mm×0.25mm→Φ4.2mm×0.2mm (retaining the processed state), and an intermediate heat treatment is performed after each cold rolling, the intermediate heat treatment temperature is 600°C, the time is 5min, and the last intermediate heat treatment temperature is 350°C, and the time is 20min;

[0063] Step 7: Repeat the cold rolling and intermediate heat treatment process in step 6 until the target size is obtained to obtain a semi-finished pipe;

[0064] Step 8: Straighten the semi-finished pipe obtained in step 7 to a straightness of 0.1 mm / 300 mm, and then use a centerless grinder to remove the titanium pipe by cylindrical grinding, with a grinding amount of 0.1 mm to obtain an ultra-pure nickel-titanium alloy thin-walled pipe with an outer diameter × wall thickness of Φ4.0 mm × 0.1 mm.

[0065] The composition of the ultra-pure nickel-titanium alloy thin-walled tube prepared in this embodiment conforms to ASTM F2063-2018 "Standard Specification for Forged Nickel-Titanium Shape Memory Alloys for Medical Devices and Surgical Implants", wherein the mass percentage of impurity elements is: C≤0.005%, H≤0.0005%, N≤0.005%, O≤0.02%.

[0066] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an ultrapure nickel-titanium alloy thin-walled tube for a heart valve, characterized in that: The method comprises the following steps: Step 1: using grade 0 small particle titanium sponge and nickel plate with a purity of 99.99% and then using magnetic levitation induction melting to prepare a nickel-titanium alloy ingot; the magnetic levitation induction melting is repeated 2 to 3 times; Step 2, hot forging the nickel-titanium alloy ingot obtained in step 1 into a square rod, and then rolling it into a nickel-titanium alloy round rod; the nickel-titanium alloy round rod has a diameter of 20 mm to 25 mm; Step 3: Prepare the nickel-titanium alloy round rod obtained in step 2 into a tube blank by deep hole drilling, and perform inner surface honing and outer surface polishing until the inner and outer surface roughnesses are both less than 0.4 μm, to obtain a nickel-titanium tube; Step 4: Select a titanium tube with an inner and outer surface roughness of no more than 0.4 μm and a processed microstructure, and assemble the nickel-titanium tube obtained in step 3 into the titanium tube so that the inner diameter of the titanium tube and the outer diameter of the nickel-titanium tube are fitted with a clearance fit, and the clearance is 0.05 mm to 0.1 mm, to obtain a combined tube; Step 5, heat treating the combined tube obtained in step 4, so that the outer diameter of the inner layer of the nickel-titanium tube in the combined tube increases by 0.15 mm to 0.2 mm due to the memory effect, and achieves an interference fit with the outer layer of the titanium tube; the heat treatment temperature is 650° C. to 700° C., and the holding time is 30 min to 45 min; Step 6: The combined pipe after heat treatment in step 5 is subjected to three-roll precision cold rolling, the deformation amount of a single pass is 25% to 33%, and an intermediate heat treatment is performed after each cold rolling, the intermediate heat treatment temperature is 600°C to 645°C, and the last intermediate heat treatment temperature is 350°C to 400°C; Step 7: Repeat the cold rolling and intermediate heat treatment process in step 6 until the target size is obtained to obtain a semi-finished pipe; Step 8: Straighten the semi-finished pipe obtained in step 7 to a straightness of no more than 0.3 mm / 300 mm, and then use a centerless grinder to remove the titanium pipe by cylindrical grinding, with a grinding amount of 0.1 mm to 0.2 mm to obtain an ultra-pure nickel-titanium alloy thin-walled pipe.

2. The method for preparing an ultrapure nickel-titanium alloy thin-walled tube for a heart valve according to claim 1, characterized in that: The process parameters of the magnetic suspension induction melting in step 1 are: the vacuum degree does not exceed 2×10 -2 Pa, electromagnetic induction heating frequency is 1800Hz-2200Hz, insulation power is 320kW-350kW, insulation time is 10min-15min, cooling time is 60min-90min, and the weight of the nickel-titanium alloy ingot is 10kg-20kg.

3. The method for preparing an ultrapure nickel-titanium alloy thin-walled tube for a heart valve according to claim 1, characterized in that: The wall thickness of the titanium tube in step 4 is 0.1 mm to 0.2 mm.

4. The method for preparing an ultrapure nickel-titanium alloy thin-walled tube for a heart valve according to claim 1, characterized in that: The composition of the ultra-pure nickel-titanium alloy thin-walled tube described in step eight complies with ASTM F2063-2018 "Standard Specification for Wrought Nickel-Titanium Shape Memory Alloys for Medical Devices and Surgical Implants", wherein the mass percentage of impurity elements is: C≤0.005%, H≤0.0005%, N≤0.005%, O≤0.02%.

5. The method for preparing an ultrapure nickel-titanium alloy thin-walled tube for a heart valve according to claim 1, characterized in that: The ultrapure nickel-titanium alloy thin-walled tube in step eight has an outer diameter of 4 mm to 12 mm and a wall thickness of 0.1 mm to 0.5 mm.

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