Medical cobalt-based alloy with high strength and high specific gravity

Abstract

The invention discloses a medical cobalt-based alloy with high strength and high specific gravity, which relates to the field of cobalt-based alloys and comprises the following chemical components in percentage by mass: 19.0 to 21.0 weight percent of Cr, 9.0 to 11.0 weight percent of Ni, 14.0 to 16.0 weight percent of W, 2.0 to 11.0 weight percent of Ta, 1.5 to 2.5 weight percent of Cu, 1.0 to 3.0 weight percent of Fe, less than or equal to 0.05 weight percent of C, less than or equal to 0.4 weight percent of Si, less than or equal to 0.01 weight percent of P, less than or equal to 0.01 weight percent of S and the balance of Co. A proper amount of Ta and Cu elements are added into the cobalt-based alloy, the characteristics of solid solution strengthening and high density of the Ta element are utilized, and the biological function of the Cu element is combined, so that the cobalt-based alloy for the intravascular stent with high strength, high density and the function of inhibiting in-stent restenosis is developed, and the cobalt-based alloy has an excellent developing effect under X-rays and can be used for preparing the intravascular stent. Meanwhile, the excellent mechanical property is also realized.

Description

Technical Field

[0001] The present invention relates to the field of cobalt-based alloys, and in particular to a medical cobalt-based alloy having the characteristics of high strength and high specific gravity. The strength and density of the material are significantly improved by adding tantalum elements, thereby improving its developability under X-rays. At the same time, the biological functionalization effect of copper elements is utilized to increase the speed of vascular endothelialization and inhibit the occurrence of restenosis in the stent. Background Art

[0002] Medical cobalt-based alloys are widely used in implantable medical devices such as cardiovascular stents due to their excellent mechanical properties, corrosion resistance and biocompatibility. Traditional medical cobalt-based alloys, such as L605 cobalt-based alloys, still face the problem of in-stent restenosis when used as cardiovascular stent materials. It is reported that the incidence of in-stent restenosis of bare metal stents is about 20%, and the incidence of in-stent restenosis of drug-eluting stents coated with drug coatings is also 5-10%, which is far from being controlled within a satisfactory range. In addition, drug-eluting stents inhibit the proliferation of endothelial cells while inhibiting the proliferation of smooth muscle cells, increasing the risk of late thrombosis. Medical research believes that under the condition of similar stent shape design, thinner stent wall design can reduce the stimulation of stent materials on vascular intima tissue, thereby significantly reducing the incidence of in-stent restenosis, but thin-walled stents also put forward higher requirements on the strength of the material to meet the radial support force requirements during service. In addition, thin-walled stents also reduce their development and visibility under X-rays, increasing the difficulty of positioning during stent implantation. Therefore, there is an urgent need in clinical practice to develop medical cobalt-based alloys for vascular stents that have both high strength and high developability.

[0003] At present, relevant research has been conducted on the development of new cardiovascular stent materials with high development properties and inhibition of restenosis in stents. For example, in the patents with publication numbers CN104451269A, CN104651670A, CN102618796A and CN104651669A, by adding an appropriate amount of copper elements and using the continuous trace release of copper ions, the coronary stents are given the function of anti-restenosis, but their density is equivalent to that of traditional stainless steel or cobalt-based alloys, and the development properties under X-rays are still very low. In the patent with publication number US20020144757A1, a large amount of platinum elements are added to traditional stainless steel to develop high-platinum medical stainless steel. In the patents with publication numbers EP 1404391B2 and CA2442200A, heavy metal elements are also added to traditional stainless steel to improve its development properties, but the strength of these stainless steel materials is still relatively low, which limits the design of thinner stents.

[0004] Therefore, in order to obtain a new cardiovascular stent material with high developability and inhibition of restenosis in the stent, the present invention provides a medical cobalt-based alloy with both high strength and high specific gravity. By adding appropriate amounts of tantalum and copper elements, utilizing the solid solution strengthening and high density characteristics of tantalum elements, and combining the biological functions of copper elements, a cobalt-based alloy for vascular stents with high strength, high density and inhibition of restenosis in the stent is designed and prepared. The results of the present invention have brought new foundations and opportunities for the development of new cobalt-based alloy stent materials. Summary of the invention

[0005] The purpose of the present invention is to provide a medical cobalt-based alloy with both high strength and high specific gravity, which utilizes the biological function of copper elements and combines the solid solution strengthening and high specific gravity characteristics of tantalum elements to improve the strength of the material and the development performance under X-rays, while being able to significantly inhibit the incidence of restenosis in the stent.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A high-strength and high-density medical cobalt-based alloy, whose chemical composition, by mass percentage, is as follows: chromium Cr: 19.0-21.0wt.%, nickel Ni: 9.0-11.0wt.%, tungsten W: 14.0-16.0wt.%, tantalum Ta: 2.0-11.0wt.%, copper Cu: 1.5-2.5wt.%, iron Fe:

[0008] 1.0-3.0wt.%, carbon C≤0.05wt.%, silicon Si≤0.4wt.%, phosphorus P≤0.01wt.%, sulfur S≤0.01wt.%, and the balance is Co.

[0009] The high-strength and high-density medical cobalt-based alloy preferably contains 4.0-8.0wt.% tantalum Ta in terms of mass percentage.

[0010] The high-strength and high-density medical cobalt-based alloy is smelted in a vacuum induction furnace or a vacuum suspension furnace.

[0011] The high-strength and high-density medical cobalt-based alloy is solution treated at 1175-1250° C. for 1-4 hours and air-cooled or water-cooled to room temperature, and its microstructure is a single-phase austenite structure.

[0012] The high-strength and high-specific-gravity medical cobalt-based alloy significantly reduces the incidence of restenosis in the stent by adding copper elements and utilizing trace and continuous release of copper ions.

[0013] The high-strength and high-specific-gravity medical cobalt-based alloy is added with the heavy metal element tantalum, which significantly improves the strength and specific gravity of the alloy, increases its development performance under X-rays, and improves its positioning accuracy during implantation.

[0014] The design concept of the present invention:

[0015] Ta: Adding heavy metal Ta element can significantly increase the specific gravity of the material. At the same time, Ta addition can also play a significant solid solution strengthening effect, significantly improving the strength of the alloy. In addition, Ta is also an austenite stabilizing element in cobalt-based alloys, which can reduce the transformation temperature of austenite to martensite. The maximum solid solubility of Ta in cobalt is about 11.5wt.%. Too little Ta addition has little effect on the specific gravity of cobalt-based alloys, and too much Ta addition will produce Ta-rich brittle phases that affect the mechanical properties of the alloy. Therefore, the addition of Ta element should be controlled between 2-11wt.%.

[0016] C: Adding C element can form carbides in the alloy matrix, significantly improving the strength of the alloy. However, Ta is a strong carbide-forming element. When too much C element is added, a large amount of carbides will be formed, which will greatly reduce the plasticity of the alloy. Therefore, the addition amount of C element should be controlled below 0.05wt.%.

[0017] Cu: Adding Cu element can give the alloy excellent biological function. Too little Cu element addition will affect the biological function of the alloy, and too much Cu element addition will significantly reduce the strength of the alloy. Therefore, the addition amount of Cu element should be controlled between 1.5-2.5wt.%.

[0018] The contents of other alloying elements are comparable to those of conventional L605 cobalt-based alloys, and the impurity elements S and P are controlled below 0.01wt.% to ensure the excellent comprehensive properties of the alloy.

[0019] Beneficial effects of the present invention:

[0020] The present invention has developed a medical cobalt-based alloy with both high strength and high specific gravity. The strength and density of the cobalt-based alloy are improved by utilizing the significant solid solution strengthening effect and high density characteristics of the Ta element, so that it can meet the requirements of thin-walled stent design and X-ray development. Through the thin-walled stent design and the biofunctionalization of Cu, the incidence of restenosis in the stent is synergistically reduced. At the same time, it also has excellent mechanical properties, providing a research direction for the development of new metal materials for stents that inhibit restenosis in the stent. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The microstructure of the high-strength and high-density cobalt-based alloy after solution treatment at 1200℃ for 1h shows a single-phase austenite structure;

[0022] Figure 2 The developability of L605 with different thicknesses and Ta-containing cobalt-based alloys under X-rays. The Ta-containing cobalt-based alloy exhibits excellent developability. 2Ta and 4Ta indicate that the mass percentage of Ta in the alloy is 2.1wt.% and 4.1wt.%, respectively. DETAILED DESCRIPTION

[0023] The present invention is further described below with examples. These examples are merely descriptions of the best mode for carrying out the present invention and are not intended to limit the scope of the present invention in any way.

[0024] Example:

[0025] Example 1-6 is a medical cobalt-based alloy with high strength and high specific gravity, and its chemical composition is shown in Table 1. According to the chemical composition range of the present invention, vacuum induction furnace smelting is carried out, and hot forging is carried out at 1250°C for 1 hour to prepare a rod with a diameter of 20 mm. Then, solution treatment is carried out, and the solution temperature is 1200°C and the solution time is 1 hour.

[0026] Comparative Example:

[0027] Comparative Example 1 is L605 cobalt-based alloy, and Comparative Examples 2-5 are other tantalum-containing cobalt-based alloys, whose chemical compositions are shown in Table 1, and their specific preparation processes and heat treatment processes are the same as those in the embodiment.

[0028] The mechanical properties and density values ​​of the materials of Examples 1-6 and Comparative Examples 1-5 are shown in Table 2.

[0029] Table 1 Chemical composition of materials in Examples and Comparative Examples (wt.%)

[0030]

[0031]

[0032] Table 2 Mechanical properties and density values ​​of the materials of the embodiments and comparative examples

[0033]

[0034] From the results in Table 2, it can be seen that the yield strength, tensile strength, elongation and density of the conventional L605 cobalt-based alloy (such as comparative example 1) are 460 MPa, 1015 MPa, 50.5% and 9.14 g / cm 3 The Ta-containing medical cobalt-based alloys of Examples 1-6 of the present invention all exhibit excellent strength, plasticity and density, and have excellent strength-plasticity matching. Their microstructures are single austenite structures (such as Figure 1 ), and exhibits excellent X-ray development performance at a thin thickness (such as Figure 2 ).

[0035] The appropriate amount of Ta added has an important influence on the strength, plasticity and density of the cobalt-based alloy. When the Cu element is added alone, the strength of the alloy will be slightly reduced, but the elongation of the alloy will be increased, and there will be no obvious effect on the density of the alloy (such as Example 2). When the amount of Ta added is too low, the solid solution strengthening effect of Ta is not obvious, and the effect on the strength is not significant. At the same time, the increase in density is also very limited (such as Example 3). When the amount of Ta added is too high, although the strength and density are significantly improved, its plasticity is greatly reduced (such as Example 4), which does not meet the processing performance requirements as a bracket material. In addition, excessive C addition will also significantly reduce the plasticity of the alloy due to the presence of a large amount of carbides (such as Example 5).

[0036] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-strength and high-density medical cobalt-based alloy, characterized in that: Calculated by mass percentage, its chemical composition is: Cr: 19.0-21.0wt.%, Ni: 9.0-11.0wt.%, W: 14.0-16.0wt.%, Ta: 2.0-11.0wt.%, Cu: 1.5-2.5wt.%, Fe: 1.0-3.0wt.%, C≤0.05wt.%, Si≤0.4wt.%, P≤0.01wt.%, S≤0.01wt.%, and the balance is Co.

2. A high-strength and high-density medical cobalt-based alloy according to claim 1, characterized in that: By mass percentage, Ta: 4.0-8.0wt.%.

3. The high-strength and high-density medical cobalt-based alloy according to claim 1, characterized in that: The cobalt-based alloy is smelted in a vacuum induction furnace or a vacuum suspension furnace.

4. The high-strength and high-density medical cobalt-based alloy according to claim 1, characterized in that: The cobalt-based alloy is solution treated at 1175-1250° C. for 1-4 hours and air-cooled or water-cooled to room temperature, and its microstructure is a single-phase austenite structure.

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