Medical injection-molded porous nickel-titanium shape memory alloy capable of improving mechanical property

Abstract

The invention discloses a medical injection-molded porous nickel-titanium shape memory alloy capable of improving mechanical properties, which is prepared by adopting an injection molding process, and mixed element powder of gas atomized titanium powder and carbonyl nickel powder with proper particle sizes is adopted to prepare the medical injection-molded porous nickel-titanium shape memory alloy. The cost of raw materials is greatly reduced, and a compression-resistant product with high aperture ratio under the same porosity can be obtained by matching with a special pore-forming agent. In the sintering process, the problem of self-propagating melting of mixed element powder is avoided by reasonably regulating and controlling the sintering procedure, and the aperture ratio is effectively increased. According to the prepared medical porous nickel-titanium shape memory alloy, the porosity ranges from 22.1% to 72.3%, and the elasticity modulus ranges from 1.52 GPa to 12.78 GPa. According to the medical porous nickel-titanium shape memory alloy prepared through the method, generation of impurity phases is effectively reduced after sintering, and the medical porous nickel-titanium shape memory alloy has the advantages of superelastic recovery strain, high porosity, low elastic modulus, high fatigue resistance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal materials, in particular to a medical injection molding porous nickel-titanium shape memory alloy and a preparation method thereof. BACKGROUND

[0002] NiTi alloy has irreplaceable advantages in the biomedical field due to its unique physical and chemical properties. Its shape memory effect and super-elasticity enable it to restore the preset shape without being easily deformed, and its low elastic modulus is close to that of human cortical bone, which can reduce the "stress shielding" effect between the implant and the bone tissue. In addition to the above characteristics, porous NiTi alloy also has the following advantages due to the presence of porous structure: the connected openings enable bone tissue to grow along the pores, thereby promoting the regeneration of bone tissue, and the presence of pores can effectively reduce the mismatch between the elastic modulus of the implant material and the bone tissue, thereby avoiding stress concentration. Therefore, it is considered as an ideal new hard tissue repair and replacement material. The principle of preparing porous NiTi alloy is to add a pore-forming agent during the preparation process, and then remove the space left in the subsequent process, and finally the space forms pores. However, the porous NiTi alloy prepared by ordinary pressing and sintering method often contains a large amount of impurity phase, and the raw material pre-alloyed nickel-titanium powder required by the traditional method is expensive and difficult to sinter. Some emerging technologies such as self-propagating method, gas expansion method and high-temperature zone melting method have the disadvantages of short and uncontrollable reaction time, irregular pore shape, etc. In order to solve the above problems of porous NiTi alloy and apply it to medical devices, a series of more corrosion-resistant, higher-strength and more suitable porous NiTi alloys have been developed. By finding suitable pore-forming agents and continuously improving the preparation process, the corrosion resistance, shape memory ability and mechanical properties of porous NiTi alloy are continuously improved, and it has broad application prospects in the fields of orthopedics, dentistry and cardiovascular surgery.

[0003] Injection molding technology has been widely used in electronic information, aerospace, precision instruments, biomedical and other fields. Metal injection molding (MIM) is a new near-net shaping technology of metal materials, which combines traditional powder metallurgy molding-sintering technology with injection molding technology. It has unique advantages in small complex parts, high performance and precision requirements, mass production and other products. The parameters of mixing, degreasing and sintering process can be adjusted to reduce the infiltration of carbon and oxygen in the air, and finally obtain MIM NiTi with no obvious defects, low impurities and high density. At the same time, as a near-net shaping technology, injection molding can significantly reduce material waste. During the preparation process, a large amount of cutting material is not needed to obtain the required shape, and the material utilization rate can usually reach nearly 100%, which has important economic significance for nickel-titanium alloy which is a high-cost material. However, the injection molding technology has high requirements for the raw material powder, which must be nearly spherical and fine in size under the condition of being as easily available as possible.

[0004] However, currently injection molding or even sintering of nickel titanium can only use pre-alloyed powder, because the self-propagating reaction between elements during sintering of elemental powder generates a large amount of heat, and the reaction heat automatically spreads to the unreacted area through its self-heating and self-conduction until the reaction is complete, resulting in melting during sintering. At the same time, the commercialization of nickel titanium pre-alloyed powder is not high, and the price is expensive (1500-3000 yuan / kg). While the technical and price of carbonyl nickel powder and gas-atomized titanium powder are now very mature (about 100 yuan / kg and 600 yuan / kg), which has great commercial practical value. In the sintering preparation process of the porous nickel titanium shape memory alloy, the synthesis of NiTi2, Ni3Ti and NiTi is an exothermic reaction, and the synthesis heat of NiTi2 and Ni3Ti is larger, so it is easier to obtain in thermodynamic theory. Since these two phases do not have thermal elastic martensitic phase transition, and have a non-coherent interface relationship with the NiTi matrix phase, which is not conducive to the phase transition and shape memory effect of the NiTi phase, so they are impurity phases in the NiTi alloy. Therefore, it is inevitable to produce the above impurities in the sintering of elemental powder. As can be seen from the nickel titanium alloy phase diagram, the melting point of NiTi2 is 942℃, which means that during the sintering process above this temperature, liquid phase will be produced. The existence of liquid phase will have two aspects of influence: on the one hand, the existence of liquid phase will greatly improve the atomic diffusion rate and improve the sintering efficiency, and due to the full diffusion, the amount of Ni single element and even impurity phase will be reduced; on the other hand, due to the flow of liquid phase, more connected pores will be produced. From this point of view, the sintering temperature selection for porous NiTi should be above the liquidus point of 942℃, so as to improve the sintering efficiency, reduce the impurity content, and form connected pores due to the flow of liquid phase.

[0005] In addition to the influence of impurity phases on the mechanical properties and shape memory properties of porous nickel titanium alloy, due to the structural characteristics of nickel titanium alloy itself, the shape and density of its own pores have a very big role and influence on the above properties. The size and connectivity of the pores directly determine the space and depth of the tissue growth of the implant, and suitable pore characteristics will greatly improve the combination of the implant and the implanted tissue. While the sintering raw materials and sintering process are fixed, the selection of pore-forming agent and the amount of pore-forming agent have a crucial influence on the pores. The most common pore-forming agent is NaCl, but there is a certain reaction between titanium and NaCl. Therefore, PMMA and binder are used together for debinding in this study. As can be seen from this study, with the increase of the content of pore-forming agent, the porosity also increases, and the open porosity also increases. The elastic modulus of porous NiTi alloy decreases with the increase of porosity, which meets the demand of the elastic modulus of the blood vessel stent.

[0006] CN104152738A "A kind of preparation method of biomedical porous nickel-titanium alloy", reports a kind of preparation method of biomedical porous nickel-titanium alloy, belongs to the technical field of biomedical material preparation.This technology will Ni, Ti metal powder be weighed according to near atomic ratio and be ball milled to obtain nickel-titanium mixed powder, then with NH4HCO3 pore former powder is proportioned according to the required porosity, mixed and pressed sintering, vacuum is continuously extracted during sintering to make NH4HCO3 completely decompose and volatilize, and then cooled to room temperature with the furnace, and the mold is removed to obtain biomedical porous nickel-titanium alloy.But the biomedical porous nickel-titanium alloy prepared by the method of the application has a small adjustable range of pore parameters, a porosity of 43.5-49.3%, a relatively large elastic modulus of 6.5-13.1 GPa, and the raw material powder is difficult to prepare and sinter. SUMMARY

[0007] In view of the above-mentioned shortcomings of the prior art, the present application provides a solution for improving the mechanical properties of medical injection-molded porous nickel-titanium shape memory alloy, which reduces the cost of raw materials and the difficulty of subsequent operation while improving the mechanical properties of medical materials.

[0008] Under the same porosity, the strength of the product obtained by the present application is much higher than that of the existing similar products, but the compression modulus is lower, and the product obtained by the present application also has excellent shape recovery performance.

[0009] Technical scheme

[0010] To achieve the above object, the present application is realized by the following technical scheme:

[0011] The present application provides a medical injection-molded porous nickel-titanium shape memory alloy with improved mechanical properties, which uses elemental powder instead of traditional raw material pre-alloy powder and adds 10-70% volume ratio of pore former PMMA (polymethyl methacrylate) by using injection molding technology, successfully preparing porous NiTi alloy with a porosity of 22.1%-72.3%.

[0012] The present application provides a preparation method of a medical injection-molded porous nickel-titanium shape memory alloy with improved mechanical properties, which comprises the steps of mixing and preparing feedstock, injection molding, catalytic degreasing, thermal degreasing and atmosphere sintering.

[0013] Further, the mixing preparation feedstock: the prepared carbonyl nickel powder, gas atomized titanium powder, composite polyformaldehyde-based binder, the prepared raw materials are added to the mixer, and mixed; the mixing temperature is controlled at 180-200℃, the mixing time is 1.5-2.5h, and the mixing speed is 30-60r / min; the mass ratio of the prepared carbonyl nickel powder and gas atomized titanium powder is 49-51:49-51; the prepared composite polyformaldehyde-based binder accounts for 5-75% of the total mass of the prepared powder, preferably 10-70%.

[0014] The particle size of the used carbonyl nickel powder is less than or equal to 15 microns, preferably 10-15 microns.

[0015] The particle size of the used gas atomized titanium powder is 30-55 microns. The selection of 30-55 micron titanium powder and nickel powder with a particle size less than or equal to 15 microns is because such a combination can prevent self-propagating and caking, and at the same time, the special pore-forming agent is used to facilitate the increase of the proportion of through holes.

[0016] The particle size of the obtained feedstock is less than or equal to 3mm, preferably 2-3mm.

[0017] Injection molding: the mold temperature during injection is 140-160℃, the maximum injection temperature is 175-185℃, and the injection pressure is 150-160MPa.

[0018] Catalytic debinding: carried out in an oxalic acid atmosphere, the catalytic debinding temperature is 110-120℃, and the catalytic debinding time is 2-5h.

[0019] Thermal debinding sintering: the debound blank is sintered in a thermal debinding sintering furnace under vacuum to obtain a porous NiTi alloy sample.

[0020] The thermal debinding sintering includes placing in a catalytic debinding sintering furnace, heating at a rate of 4-6℃ / min to 800-820℃ and holding for 3h, then slowly increasing to 930-960℃ at a rate of 1-3℃ / min, and holding for 1h; then slowly increasing to 1050-1100℃ at a rate of 1-3℃ / min, and holding for 1h. Then increasing to 1240-1260℃ at a rate of 1-3℃ / min, and holding for 4-6h; after the holding is completed, the temperature is lowered to obtain a sintered sample.

[0021] As a preferred embodiment, the system is vacuumed to 10 -4After sintering, in the sintering process, first, the temperature is raised to 800℃ at a rate of 5℃ / min, and the temperature is kept for 3h; then the temperature is slowly raised to 950℃ at a rate of 2℃ / min, and the temperature is kept for 1h; then the temperature is slowly raised to 1100℃ at a rate of 1-3℃, and the temperature is kept for 1h; then the temperature is raised to 1250℃ at a rate of 3℃ / min, and the temperature is kept for 5h. During the sintering process, vacuum is continuously extracted to completely decompose and volatilize PMMA, and then the furnace is cooled to room temperature, and finally the mold is removed after heat treatment to obtain the medical porous NiTi alloy.

[0022] Further, the heat debinding and sintering process includes a low-temperature debinding stage, a high-temperature debinding stage, a preheating stage, a high-temperature sintering stage, and a cooling stage.

[0023] The first stage is the low-temperature debinding stage, and the process is as follows: the temperature is raised to 200-240℃ at a rate of 0.5-2℃ / min, and the temperature is kept for 2h. During the low-temperature debinding stage, the gas pressure is controlled to be 0.001-0.1Pa, and the flow rate of the protective gas is controlled to be 20-30L / min.

[0024] The second stage is the high-temperature debinding stage, and the process is as follows: the temperature is raised to 500-550℃ at a rate of 1-3℃ / min, and the temperature is kept for 4h. During the vacuum sintering stage, the gas pressure is controlled to be 0.001-0.1Pa, and no protective gas is introduced.

[0025] The third stage is the high-temperature sintering stage, and the process is as follows: the temperature is raised to 800-820℃ at a rate of 4-6℃ / min, and the temperature is kept for 3h; then the temperature is slowly raised to 930-960℃ at a rate of 1-3℃ / min, and the temperature is kept for 1h; then the temperature is slowly raised to 1050-1100℃ at a rate of 1-3℃, and the temperature is kept for 1h. Then the temperature is raised to 1240-1260℃ at a rate of 1-3℃ / min, and the temperature is kept for 4-6h. After the holding is completed, the temperature is lowered to obtain the sintered sample, and the opening rate of the sintered sample is significantly improved.

[0026] In industrial applications, after sintering is completed, slow cooling can reduce internal stress, and it is suitable for complex structural parts, and the process includes opening the furnace after the furnace is cooled to room temperature to avoid oxidation caused by contacting air at high temperature.

[0027] Further, the heat treatment process: the sintered sample is subjected to solid solution treatment, the solid solution treatment temperature is 1180-1020℃, the solid solution treatment holding time is 1-2h, and the sintered sample is water-cooled after the solid solution treatment is completed.

[0028] The medical porous nickel-titanium shape memory alloy prepared by the method has the advantages that: the element mixed powder is used, the initial impurity content of the traditional raw material pre-alloyed powder is lower, the pre-alloyed powder is more easily polluted to generate impurity phases in the preparation process, the oxygen content is less than or equal to 0.18% (such as 0.12-0.18%) after sintering is completed, the generated phase is uniform and stable under high-temperature conditions, and the interaction between defects is reduced.

[0029] The medical porous nickel-titanium shape memory alloy prepared by the method has the advantages that: the strength of the medical porous nickel-titanium shape memory alloy is adjusted by adjusting the amount and mesh number of the pore forming agent, and the porous NiTi alloy with a porosity of 22.1-72.3% is obtained, at this time, the elastic modulus range of the alloy is 1.52 GPa-12.78 GPa, and the corresponding compressive strength is 330.2-120.6 MPa.

[0030] The medical porous nickel-titanium shape memory alloy prepared by the method has the advantages that: when sintering above 942 DEG C, the porous NiTi alloy has lower oxygen and carbon impurity contents, which are 0.16 wt.% and 0.03 wt.% respectively, and the generation of impurity phases such as Ni3Ti, Ni2Ti4O and NiTi2 is avoided.

[0031] The medical porous nickel-titanium shape memory alloy prepared by the method has the advantages that: the sample gradually deforms under 0-5% loading, the strain distribution is uniform, then uniform unloading is carried out, a platform region appears when the strain is about 3%, the sample does not continue to shrink with unloading, then rapid heating is carried out, the sample rapidly shrinks to 0%, the strain distribution changes rapidly and is obviously uneven in this stage. Overall, the sample can be completely recovered after 5% tensile strain, and has a high shape memory effect.

[0032] The medical porous nickel-titanium shape memory alloy prepared by the method has the advantages that: the injection molding preparation process is adopted, and complex-shaped parts with little material loss can be produced, and batch forming can be realized.

[0033] The application focuses on the influence of the element mixed powder as the raw material on the mechanical properties of the medical porous nickel-titanium shape memory alloy after sintering, injection molding process and PMMA pore forming agent are used to prepare samples with different porosities, high-temperature cyclic loading experiments are carried out on the samples, and the influence of different porosity contents on the mechanical properties of the porous NiTi alloy obtained after the raw material is changed and the process is improved is analyzed.

[0034] The impurity phases are significantly reduced, the mechanical properties can be dynamically adjusted in different medical application scenarios, the application range of the alloy is promoted, and the alloy has important application value in the medical field.

[0035] The amount of nickel ion released by the obtained porous nickel-titanium shape memory alloy after being immersed in a NaCl simulated body fluid for 2 hours is 0.03 ppm-0.01 ppm

[0036] Advantages

[0037] Compared with the known prior art, the technical solution provided by the present application has the following advantages:

[0038] 1. The present application significantly reduces the impurity phase content of the medical porous nickel-titanium shape memory alloy and the influence of the impurity phase on the mechanical properties of the medical porous nickel-titanium shape memory alloy under high-temperature sintering by improving the raw materials and the preparation process.

[0039] 2. The method adopted by the present application weakens the adjustment difficulty of the porosity and pore size of the medical porous nickel-titanium shape memory alloy and improves the high-temperature mechanical properties, thereby expanding the adjustable range of the mechanical properties.

[0040] 3. The present application can manufacture high-temperature parts with complex shape characteristics, and the process is simple, which has good industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0041] The brief description of drawings is used to briefly describe the drawings of the specification, which is an important technical means for describing technical solutions such as mechanical structures, and explains the legal basis and feasibility of the brief description of drawings in patent retrieval application, and provides application examples of the brief description of drawings in patent retrieval, so that the patent retrieval can effectively improve the retrieval efficiency compared with the conventional retrieval method.

[0042] Figure 1 A vascular stent sample prepared by using the medical porous nickel-titanium shape memory alloy

[0043] Figure 2 SEM scanning morphology images of the products obtained in Examples 1-7, wherein a-g are SEM images of the products obtained in Examples 1, 2, 3, 4, 5, 6, and 7, respectively. DETAILED DESCRIPTION

[0044] The present application will be further described below in conjunction with examples.

[0045] Example 1

[0046] The preparation method of the medical injection-molded porous nickel-titanium shape memory alloy described in this example specifically includes the following steps:

[0047] (1) According to the mass percentage of Ni 50.81% and Ti 49.97%, Ni metal powder with a particle size of 15 μm and a purity of 99.5% and Ti metal powder with a particle size of 55 μm and a purity of 99.5% are weighed, respectively;

[0048] (2) according to the mass ratio, the metal powder accounts for 90%, and the polymethyl methacrylate (PMMA) accounts for 10%; the PMMA powder with a particle size of 5-20 μm and a purity of analytical pure is prepared according to the proportion; the metal powder is the metal nickel powder and the metal titanium powder prepared according to the proportion in step (1);

[0049] (3) the prepared metal powder and the PMMA powder are used as raw materials; the raw materials are added into a mixing machine for mixing; the mixing temperature is controlled to be 190℃, the mixing time is 2h, and the mixing speed is 45r / min; the feedstock with a diameter of 2-3mm is obtained;

[0050] (4) the feedstock obtained in step (3) is injection molded by an injection machine to obtain an injection blank with a target shape and specification; the injection pressure is adjusted to be 150MPa, and the injection temperature is 150℃, so that the blank is free of defects such as air injection, cracks, bubbles and the like; the block green body is obtained after the low-temperature molding.

[0051] (5) the block green body obtained in step (4) is loaded into a mold and placed in a catalytic debinding and sintering furnace; the system is vacuumed to 10 -4 Pa, and then sintered; in the sintering process, the temperature is first increased to 800℃ at a rate of 5℃ / min, and then kept for 3h; then the temperature is slowly increased to 950℃ at a rate of 2℃ / min, and then kept for 1h; then the temperature is slowly increased to 1100℃ at a rate of 1-3℃, and then kept for 1h; then the temperature is increased to 1250℃ at a rate of 3℃ / min, and then kept for 5h; after the PMMA is completely decomposed and volatilized by continuously vacuumizing during the sintering process, the furnace is cooled to room temperature; finally, the medical porous NiTi alloy is obtained after heat treatment. The heat treatment process is: the sintered sample is subjected to solid solution treatment, the solid solution treatment temperature is 1020℃, the solid solution treatment time is 2h, and the solid solution treatment is completed by water cooling.

[0052] 2. Mechanical property test

[0053] Test method: four different pre-strains are used to perform room temperature loading-unloading cycle test on the porous NiTi alloy; the test strain rate is 0.5mm / min, and the mechanical testing machine is MTS Landmark.

[0054] Under this condition, the loading-unloading-thermal recovery test is performed, and the results show that:

[0055] After high temperature sintering, the porosity characteristics of the sample were analyzed by pressure pump method. The porosity of the sample reached 22.1%, but the open porosity was 60.6% and the density reached 97%. At this time, the compressive strength and elastic modulus of the porous NiTi alloy were the largest, which was 12.78 GPa. The compression elastic modulus and compressive strength were tested on the mechanical testing machine. The stress at the highest point of the strain of the loading-unloading-thermal recovery curve at a pre-strain of 8% was 370.4 MPa, and the compressive strength was 360.2 MPa. The calculated martensitic elastic modulus was close to the value obtained by experimental test, but slightly lower than the measured value. The possible reason is that the pore shape is irregular, not cubic as simulated by the formula. The shape recovery rate of the 22.1% porosity sample at 8% pre-strain was 90%, and the biological related nickel ion release at this time was only 0.01 ppm.

[0056] Example 2:

[0057] The difference from Example 1 is only that the addition amount of pore forming agent PMMA is 20wt%.

[0058] The oxygen content of the sintered sample is 0.17wt.%, and the carbon content is 0.03wt.%. The density of the porous NiTi alloy part obtained is 3.4g / cm 3 .

[0059] Example 3:

[0060] The difference from Example 1 is only that the addition amount of pore forming agent PMMA is 30wt%.

[0061] The oxygen content of the sintered sample is 0.18wt.%, and the carbon content is 0.06wt.%. The density of the porous NiTi alloy part obtained is 3.0g / cm 3 .

[0062] Example 4:

[0063] The difference from Example 1 is only that the addition amount of pore forming agent PMMA is 40%.

[0064] The oxygen content of the sintered sample is 0.19wt.%, and the carbon content is 0.04wt.%. The density of the porous NiTi alloy part obtained is 2.5g / cm 3 .

[0065] Example 5:

[0066] The difference from Example 1 is only that the addition amount of pore forming agent PMMA is 50%.

[0067] The oxygen content of the sintered sample is 0.18wt.%, and the carbon content is 0.04wt.%. The density of the porous NiTi alloy part obtained is 2.2g / cm 3 .

[0068] Example 6

[0069] The difference from Example 1 is that the amount of pore-forming agent PMMA added is 60%.

[0070] The oxygen content of the sample after sintering is 0.19wt.%, and the carbon content is 0.03wt.%. The porous NiTi alloy part obtained has a density of 1.7g / cm 3 .

[0071] Example 7

[0072] The other conditions are consistent with Example 1, and the difference from Example 1 is that the amount of pore-forming agent PMMA added is 70%.

[0073] The oxygen content of the sample after sintering is 0.21wt.%, and the carbon content is 0.05wt.%. The porous NiTi alloy part obtained has a density of 1.5g / cm 3 .

[0074] Example 8

[0075] The other conditions are consistent with Example 1, and the difference from Example 1 is that:

[0076] The block green body obtained in step (4) is loaded into a mold and placed in a catalytic debinding and sintering furnace, and the system is vacuumed to 10 -4 Pa and then sintered, specifically including:

[0077] The first stage is a low-temperature debinding stage, and the process is: heating to 240℃ at a heating rate of 2℃ / min and holding for 2h. During the low-temperature debinding stage, the gas pressure is controlled to be 0.001-0.1Pa, and the flow rate of the protective gas Ar is 25L / min;

[0078] The second stage is a high-temperature debinding stage, and the process is: heating to 550℃ at a heating rate of 3℃ / min and holding for 4h. During the vacuum sintering stage, the gas pressure is controlled to be 0.001-0.1Pa, and no protective gas is introduced;

[0079] The third stage, first, use a rate of 5℃ / min to heat to 800℃, hold for 3h; then slowly increase to 950℃ at a rate of 2℃ / min, and hold for 1h; then slowly increase to 1100℃ at a rate of 1-3℃, and hold for 1h; then increase to 1250℃ at a rate of 3℃ / min, and hold for 5h. During the sintering process, vacuum is continuously pumped to completely decompose and volatilize the PMMA, and then the furnace is cooled to room temperature. Finally, after heat treatment, the mold is removed to obtain a medical porous NiTi alloy.

[0080]

[0081] Comparative Example 1

[0082] 1. Sample Preparation

[0083] The difference from Example 1 is that the NiTi alloy is prepared without adding pore-forming agents.

[0084] 2. Mechanical Property Test

[0085] The loading-unloading-thermal recovery test was carried out under the same conditions as Example 1, and the results showed that:

[0086] When the pore-forming agent addition amount is 0 and the entire sintering process lasts for 1250°C, the sample is completely deformed under naked eye observation, and liquid state sintering occurs. Without pore-forming agents, the atomic diffusion is intensified during high-temperature sintering, and at the same time, the powder particles are densified through diffusion at high temperature, accompanied by a large volume shrinkage, which leads to a significant grain coarsening. Coarse grains not only reduce the strength, plasticity and fatigue properties of the material, but especially for porous structures, the grain boundaries become the starting point for crack propagation, leading to an increase in structural brittleness, so that a large change in external temperature leads to deformation of the alloy. At the same time, the dense or low-porosity structure without pore-forming agents reduces the cell attachment sites and inhibits new bone growth, increasing the risk of implant loosening.

[0087] Comparative Example 2

[0088] 1. Sample Preparation

[0089] The difference from Example 1 is that the NiTi alloy is prepared without adding pore-forming agents, and the highest temperature of vacuum sintering is 900°C.

[0090] 2. Mechanical Property Test

[0091] The loading-unloading-thermal recovery test was carried out under the same conditions as Example 1, and the results showed that:

[0092] When the pore-forming agent addition amount is 0%, the sample is analyzed by X-ray diffractometer (XRD), and it is found that the sample has more abundant characteristic peaks, and with the decrease of sintering temperature, the content of C and O impurities also increases. Higher impurity content makes the martensitic transformation behavior more complex. Once irregular coarse precipitates are formed, the mechanical properties of the NiTi alloy will also be damaged. At this time, the shape recovery rate of the porous NiTi alloy sample prepared under 8% pre-strain is as low as 35%. The elastic modulus increases to 14.98 Gpa. Compression elastic modulus and compressive strength tests were carried out on the mechanical testing machine, and the stress at the highest point of the loading-unloading-thermal recovery curve of the sample under 8% pre-strain was 380.25 MPa, and the tensile strength was 333.41 MPa.

[0093] Comparative Example 3

[0094] Other conditions are consistent with Embodiment 6,

[0095] (5) The block green body obtained in step (4) is loaded into a mold, and placed in a catalytic debinding and sintering furnace, and the system is vacuumed to 10 -4 Pa, and then sintered, in the sintering process, first heated to 950℃ at a rate of 5℃ / min, and then kept for 4 hours; then slowly increased to 1250℃ at a rate of 3℃, and then kept for 6 hours. The obtained porous NiTi alloy sample (porosity is 60.6%, open porosity is 90.1%) has a shape recovery rate as low as 69% under 8% pre-strain. The elastic modulus is 3.98GPa. The compression elastic modulus and compressive strength are tested on a mechanical testing machine, the stress at the highest point of strain of the loading-unloading-thermal recovery curve under 8% pre-strain is 113.4MPa, and the tensile strength is 146.8MPa. Under the same conditions, the direct increase of the sintering temperature does not obviously change the porosity, but the open porosity decreases obviously, and the main reason is that the amount of liquid phase produced by instantaneous liquid phase sintering decreases.

[0096] Comparative Example 4

[0097] Other conditions are consistent with Embodiment 6,

[0098] (5) The block green body obtained in step (4) is loaded into a mold, and placed in a catalytic debinding and sintering furnace, and the system is vacuumed to 10 -4 Pa, and then sintered, in the sintering process, first heated to 800℃ at a rate of 5℃ / min, and then kept for 3 hours; then slowly increased to 950℃ at a rate of 2℃ / min, and then kept for 1 hour; then slowly increased to 1100℃ at a rate of 2℃, and then kept for 7 hours. The obtained porous NiTi alloy sample (porosity is 62.7%, open porosity is 92.4%) has a shape recovery rate as low as 67% under 8% pre-strain. The elastic modulus is 3.71GPa. The compression elastic modulus and compressive strength are tested on a mechanical testing machine, the stress at the highest point of strain of the loading-unloading-thermal recovery curve under 8% pre-strain is 79.8MPa, and the tensile strength is 100.5MPa. With the decrease of the highest sintering temperature, the diffusion between the particles is not sufficient, and there are more impurity intermediate phases, thereby slightly reducing the mechanical properties of the porous NiTi alloy.

Claims

1. A mechanically enhanced medical injection molded porous nickel-titanium shape memory alloy characterized by: Porous NiTi alloy with porosity of 22.1-72.3% is prepared by injection molding technology using element powder as raw material and adding 10-70% volume ratio of pore-forming agent PMMA.

2. The medical injection-molded porous nickel-titanium shape memory alloy with improved mechanical properties according to claim 1, characterized in that: The preparation process comprises mixing and preparing feedstock, injection molding, catalytic debinding, thermal debinding and atmosphere sintering process. The mixing and preparing feedstock is: The prepared carbonyl nickel powder, gas-atomized titanium powder and composite polyformaldehyde-based adhesive are added into a mixer and mixed; the mixing temperature is controlled at 180-200 DEG C, the mixing time is 1.5-2.5 h and the mixing speed is 30-60 r / min; the mass ratio of the prepared carbonyl nickel powder and gas-atomized titanium powder is 49-51:49-51; the prepared composite polyformaldehyde-based adhesive accounts for 5-75% of the total mass of the prepared powder, preferably 10-70%.

3. The medical injection-molded porous nickel-titanium shape memory alloy with improved mechanical properties according to claim 2, characterized in that: The particle size of the used carbonyl nickel powder is less than or equal to 15 microns, preferably 10-15 microns; the particle size of the used gas-atomized titanium powder is 30-55 microns.

4. The medical injection-molded porous nickel-titanium shape memory alloy with improved mechanical properties according to claim 2, characterized in that: The particle size of the obtained feedstock is less than or equal to 3 mm, preferably 2-3 mm.

5. The medical injection-molded porous NiTi shape memory alloy with improved mechanical properties according to claim 2, characterized in that: During injection molding, the mold temperature is 140-160 DEG C, the maximum injection temperature is 175-185 DEG C and the injection pressure is 150-160 MPa; The catalytic debinding is carried out in an oxalic acid atmosphere, the catalytic debinding temperature is 110-120 DEG C and the catalytic debinding time is 2-5 h.

6. The medical injection-molded porous NiTi shape memory alloy with improved mechanical properties according to claim 2, characterized in that: Thermal debinding and sintering: the debound blank is sintered in a thermal debinding and sintering furnace under vacuum to obtain a porous NiTi alloy sample; the thermal debinding and sintering comprises the following steps: the blank is placed in the catalytic debinding and sintering furnace, heated at a heating rate of 4-6 DEG C / min to 800-820 DEG C and kept for 3 h, then slowly increased to 930-960 DEG C at a rate of 1-3 DEG C / min, kept for 1 h, then slowly increased to 1050-1100 DEG C at a rate of 1-3 DEG C / min, kept for 1 h, then slowly increased to 1240-1260 DEG C at a rate of 1-3 DEG C / min, kept for 4-6 h; After the keeping step, the sample is cooled to obtain a sintered sample.

7. The medical injection-molded porous NiTi shape memory alloy with improved mechanical properties according to claim 6, characterized in that: The sample was placed in a catalytic debinding sintering furnace, the system was vacuumed to 10 -4 After sintering at 950℃ for 1 h, then slowly increased to 1100℃ at a rate of 1-3℃, and then kept for 1 h, then increased to 1250℃ at a rate of 3℃ / min, and then kept for 5 h. During the sintering process, the vacuum was continuously extracted to make the PMMA completely decompose and volatilize, and then the furnace was cooled to room temperature. Finally, the medical porous NiTi alloy was obtained by heat treatment and mold removal.

8. The medical injection-molded porous NiTi shape memory alloy with improved mechanical properties according to claim 6, characterized in that: The thermal debinding and sintering process comprises a low-temperature debinding stage, a high-temperature debinding stage, a preheating stage, a high-temperature sintering stage and a cooling stage; The first stage is the low-temperature debinding stage, and the process is as follows: heating at a rate of 0.5-2 DEG C / min to 200-240 DEG C and keeping for 2 h; during the low-temperature debinding stage, the gas pressure is controlled at 0.001-0.1 Pa and the flow rate of the protective gas is controlled at 20-30 L / min. The second stage is a high-temperature debinding stage, and the process is as follows: the temperature is increased to 500-550 DEG C at a temperature increasing rate of 1-3 DEG C / min, and the temperature is kept for 4 h; during the vacuum inner burning stage, the air pressure is controlled to be 0.001-0.1 Pa, and no protective gas is introduced; The third stage is a high-temperature sintering stage, and the process is as follows: the temperature is increased to 800-820 DEG C at a temperature increasing rate of 4-6 DEG C / min, and the temperature is kept for 3 h; then the temperature is slowly increased to 930-960 DEG C at a temperature increasing rate of 1-3 DEG C / min, and the temperature is kept for 1 h; then the temperature is slowly increased to 1050-1100 DEG C at a temperature increasing rate of 1-3 DEG C / min, and the temperature is kept for 1 h; then the temperature is increased to 1240-1260 DEG C at a temperature increasing rate of 1-3 DEG C / min, and the temperature is kept for 4-6 h; After the temperature keeping is completed, the temperature is decreased, and a sintered sample is obtained.

9. The medical injection-molded porous NiTi shape memory alloy with improved mechanical properties according to claim 2, characterized in that: The sintered sample is subjected to solid solution treatment, the temperature of the solid solution treatment is 1180-1020 DEG C, the temperature keeping time of the solid solution treatment is 1-2 h, and the solid solution treatment is completed through water cooling.

10. The medical injection-molded porous NiTi shape memory alloy with improved mechanical properties according to claim 2, characterized in that: The porous NiTi alloy with a porosity of 22.1-72.3% is obtained, and the corresponding elastic modulus of the alloy is 1.52 GPa-12.78 GPa, and the corresponding compressive strength is 330.2-120.6 MPa; The release amount of nickel ions of the obtained porous NiTi shape memory alloy after being soaked in a NaCl simulated body fluid for 2 h is 0.03 ppm-0.01 ppm.

Images