JPS6214213B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an iron-chromium-aluminum medical implant alloy. The alloy of the present invention is useful as a medical implant material. Prior Art Orthopedic implant materials are required to have the following properties. (1) Not dissolved or absorbed in the body. (2) Excellent corrosion resistance. (3) It has excellent mechanical properties and does not deteriorate over a long period of time. (4) Be non-toxic and non-irritating. This is a problem that should be understood as a comprehensive phenomenon, not just a direct or local phenomenon. (5) Be well organized with surrounding living tissues. That is, it is necessary to have excellent compatibility with tissues, that is, with the living body. If the heterogeneity is strong, fibrous tissue will be generated in the living body using the implant material to embed and isolate the implant material, resulting in loosening between the implant material and the living body, resulting in various problems. Iron-nickel-chromium austenitic stainless steel has traditionally been used as an implant material. However, although this has good mechanical properties, there are problems with compatibility with living organisms, and furthermore, stress corrosion cracking resistance, pitting corrosion resistance, crevice corrosion resistance, and other corrosion resistance are not necessarily sufficient. Limited to short-term use. In addition, there is a problem that eluted metal ions, especially nickel ions, are harmful to the human body. Furthermore, in recent years, ceramic materials mainly composed of α-Al ₂ O ₃ have been used on a trial basis. It has many advantages, such as excellent corrosion resistance, long-term stability in living organisms, non-toxicity to living organisms, and high affinity. but,
It has a major drawback of poor mechanical properties, particularly poor anti-deposition resistance. Composition of the Invention In view of the current situation, the present inventor has conducted various studies and has developed a new material that combines the good mechanical properties of stainless steel materials and the excellent affinity for the human body and high corrosion resistance of ceramic materials. We have now completed a new implant alloy. That is, in the present invention, Cr20-32% by weight, Al 0.5-32% by weight
This relates to an iron-chromium-aluminum medical implant alloy consisting of 5.0% by weight, Mo 0.5-4.0% by weight, 0.05-0.5% by weight of at least one of Zr, Hf and Y, and the balance Fe. The implant alloy of the present invention contains Al, Zr,
Since it contains an appropriate amount of at least one of Hf and Y, it can be heat-treated in air or oxygen to form α-Al ₂ O ₃ with a dense surface and excellent adhesion.
Forms an oxide film mainly composed of This oxide film has excellent properties in terms of affinity with living organisms and also exhibits excellent corrosion resistance. Furthermore, in terms of mechanical properties, the implant alloy of the present invention is SUS316L, which has been conventionally used as a biomedical implant material, or the basic alloy of the present alloy.
Compared to Fe-30Cr-Mo alloys, it is not inferior in practicality and has sufficient strength as an implant material. Regarding the elements contained in the implant alloy of the present invention,
Its content and effect will be explained in detail below. (1) Cr: 20 to 32% by weight Cr is an essential element for improving the corrosion resistance of iron-based alloys as a component that forms a stable passive film, and as its amount increases, the corrosion resistance increases.
However, coexistence with elements such as Al and Mo synergistically causes embrittlement of the alloy, so the upper limit is set at 32% by weight. In addition, there are cases in which the present alloy is used for in-vivo implants for a short period of about 2 to 3 months, and in this case, the required level of corrosion resistance is slightly relaxed, but at least 18Cr
The lower limit is set at 20% by weight, as corrosion resistance higher than that of grade high-purity ferritic stainless steel is required. (2) Al: 0.5 to 5.0% by weight In a Fe-Cr alloy system, when the Cr content is about 30% by weight, the toughness and cold and hot workability decrease rapidly due to the addition of elements such as Al and Mo. do. Al
Therefore, the upper limit is set at 5% by weight. Also, if the Al content is low,
α-Al ₂ O ₃ generated by heat treatment is reduced,
The amount of Cr ₂ O ₃ produced increases. When the ratio of Cr ₂ O ₃ increases, the phase boundary between the two types of oxides increases, the toughness of the surface oxide film deteriorates, and the material function decreases. Therefore, from this point of view, when performing heat treatment in air or oxygen,
Al is preferably about 2% by weight or more. In addition, when performing heat treatment by adjusting the atmosphere to a pressure lower than atmospheric pressure, the lower limit of the amount of Al should be 0.5% by weight.
It can be done. (3) Mo: 0.5 to 4.0% by weight Mo has a remarkable effect on improving corrosion resistance, especially pitting corrosion resistance and crevice corrosion resistance.
0.5% by weight or more is required. On the other hand, increasing the amount of Mo tends to cause embrittlement, and furthermore, Cr,
The upper limit is set at 4.0% by weight because coexistence with Al particularly promotes deterioration of workability. (4) At least one of Zr, Hf and Y: 0.05 to 0.5
Weight% The main roles of Zr, Hf and Y are α-
It enters the Al ₂ O _3- based film and gives high toughness to the film, which is originally very brittle, and has a slightly higher affinity with oxygen than Al, so it oxidizes internally and becomes fine oxide particles. This may improve the adhesion of the surface oxide layer to the alloy matrix. However, when the content of these elements increases, their degree of incorporation into the film increases, deteriorating the density of the film, and also having a negative effect on the corrosion resistance of the alloy matrix, cold and hot workability, and toughness of the alloy. It turns out. Therefore, the content of Zr, Hf and Y is the total amount
The upper limit is 0.5% by weight. On the other hand, if the content of these elements is too small, the toughness and adhesion of the film will be insufficient, so it is necessary to contain at least 0.05% by weight of at least one of Zr, Hf and Y. (5) Others Si causes alloy embrittlement, and during heat treatment
Since it becomes SiO ₂ and mixes into the α-Al ₂ O ₃ film, reducing its functionality, the content is preferably 0.3% by weight or less. C and N are easily removed by heat treatment.
Reacts with Cr to form Cr-based compounds. This Cr
These compounds have a strong tendency to form at grain boundaries of alloys, leading to a decrease in Cr concentration in the vicinity and inducing intergranular corrosion. Furthermore, C becomes CO or CO ₂ gas and has the effect of destroying the α-Al ₂ O ₃ film.
From these points, C is 0.008% by weight or less, and N is
The content is preferably 0.015% by weight or less. Since P impairs the toughness of steel, it is preferable to limit it to 0.025% by weight or less. Since S also impairs the toughness of steel, it is preferable to limit it to 0.025% by weight or less. (6) The remainder is Fe. The method for producing the implant alloy of the present invention is not particularly limited, and implant alloys within the above-mentioned composition range can be produced by conventional methods. The alloy of the present invention is used as an implant material after being subjected to heat treatment. This heat treatment produces an oxide film mainly composed of α-Al ₂ O ₃ that is dense and has excellent adhesion to the alloy matrix.
The heat treatment is usually performed in air at atmospheric pressure or in oxygen at a temperature of about 1100 to 1300°C. however
When the Al content is about 0.5 to 2% by weight, it is preferable to perform the heat treatment under a pressure lower than atmospheric pressure. The heat treatment time may be appropriately selected from about 0.5 to 30 hours depending on the required thickness of the oxide film. Effects of the Invention The implant alloy of the present invention has excellent compatibility with the human body and high corrosion resistance due to the oxide film formed by heat treatment. Furthermore, the alloy matrix itself also exhibits excellent corrosion resistance. Furthermore, the mechanical properties are sufficient for practical use as an implant material. Therefore, it satisfies the requirements as an implant material.
Can be used effectively. Examples Next, examples will be shown regarding the implant alloy of the present invention. Example 1 Iron-chromium-aluminum implant alloys having the compositions shown in Table 1 were prepared according to a conventional method.

[Table] This alloy was heat treated in oxygen to form an oxide film. FIG. 1 shows the relationship between heat treatment time, oxidation weight gain, and thickness of the formed film. Furthermore, as a result of examining the cross-sectional structure of this oxide film, the boundary between the alloy matrix and the surface oxide layer is complicated;
It was found that the adhesion was very excellent. Similar results were obtained when heat-treated in air. (i) Mechanical properties Table 2 shows the mechanical properties of the alloys of the present invention before heat treatment. For comparison, the mechanical properties of SUS316L, which has been conventionally used as a biological implant material, are also shown. The tensile strength and elongation were tested according to JIS-Z-2201, and the hardness was tested according to JIS-Z-2244.

[Table] From the results shown in Table 2, it is clear that the alloy of the present invention has mechanical properties equivalent to those of conventional products. Table 3 shows changes in mechanical properties when the alloy of the present invention was heat treated at 1250° C. in the atmosphere.

[Table] From the results shown in Table 3, even if the heating time becomes longer, the mechanical properties of the alloy of the present invention do not change much;
It is clear that there is no problem in practical use. (ii) Corrosion resistance test Regarding corrosion resistance, it has been experimentally found that good corrosion resistance is exhibited when covered with an oxide film due to heat treatment. That is, no corrosion or wear was observed in the corrosion resistance test items shown in Tables 4 and 5 below. Here, we investigated corrosion resistance when the alloy matrix is exposed due to damage caused by mechanical impact or abrasion caused by screw fastening. First, the crevice corrosion of a sample of the alloy of Example 1 before heat treatment was investigated. That is, a flat plate sample is immersed in a 10% FeCl ₃ aqueous solution, and 50% is placed on the sample plate.
A mmφ glass rod was placed and the corrosion state occurring in the gap between the sample and the glass rod after 24 hours was observed. The results are shown in Table 4.

[Table] ○: No crevice corrosion △: Evidence of crevice corrosion ×: Severe crevice corrosion occurred Next, the alkali resistance, intergranular corrosion resistance, acid resistance, and stress corrosion resistance of the samples that had not been heat treated were investigated. The results are shown in Table 5. The test was conducted in accordance with JIS-G-0573.

[Table] Furthermore, as a result of a dissolution test in physiological saline (3% NaCl), Fe, Cr and
The amount of Al eluted was less than 1 ppm, and when immersed in boiling liquid for 5 hours, Fe was 2 ppm and the others were less than 1 ppm. From the above results, it can be seen that the corrosion resistance of the alloy of the present invention is superior to conventional products even in a state where no oxide film is formed by heat treatment. Furthermore, it was found that the corrosion resistance of the alloy matrix after heat treatment was also comparable to that before treatment. For example, after heat treating the alloy shown in Table 1 at 1250°C for 5 hours in the air, the oxide film was completely removed by polishing, and the tests for each item in Tables 4 and 5 were conducted. No difference was observed from the results shown in Tables 4 and 5. Example 2 For each of the alloys shown in Table 1 of Example 1 in which Zr was replaced with Hf and Zr was replaced with Y,
A test similar to Example 1 was conducted. Both the Hf-containing alloy and the Y-containing alloy had less weight gain due to oxidation when heat-treated than the alloy of Example 1. For example, when heat treated at 1200°C for 20 hours, the weight gain due to oxidation is approximately 2.0 for Hf-containing alloys.
mg/cm ² , and about 1.0 mg/cm ² for the Y-containing alloy.
The adhesion of this oxide film was as excellent as in Example 1. Subsequently, mechanical properties and corrosion resistance were tested in the same manner as in Example 1. As a result, almost the same results as in Example 1 were obtained for both the Hf-containing alloy and the Y-containing alloy. Example 3 Iron-chromium-aluminum implant alloys having the compositions shown in Table 6 below were produced according to a conventional method. In addition, Si, C, N and O mixed as impurities
The amount of was comparable to that of the implant alloy of Example 1.

【table】

[Table] For each alloy No. 1 to 13 above, in the atmosphere
Heat treatment was performed at 1200℃ to form an Al ₂ O ₃ film, and for samples where a uniform Al ₂ O ₃ film was not formed by heat treatment in the atmosphere, the sample was heated at 1200℃ under a reduced pressure of 2 × 10 ^-2 Torr. A heat treatment was performed to form an Al ₂ O ₃ film. The results are shown in Table 7 using the symbols below. 〇: Uniform Al ₂ O ₃ film formed in the atmosphere △: Uniform Al ₂ O ₃ film formed under reduced pressure ×: Uniform Al ₂ O ₃ film not formed In addition, each of the above alloys No. 1 to 13 The samples were tested for tensile strength, crevice corrosion resistance, alkali resistance, intergranular corrosion resistance, acid resistance, and stress corrosion cracking resistance in the same manner as in Example 1. For tensile strength, measured values are shown, and for other test results, comparison results with test results for SUS316L are shown in Table 7 using the symbols below. ◎: Significantly better than SUS316L 〇: Slightly better than SUS316L △: Same as SUS316L ×: Inferior to SUS316L

【table】

[Table] Additionally, various tests described above were conducted on alloys containing Hf or Y in place of Zr.
The results were almost the same. Comparative example 1 Cr20.5% by weight, Al 0.3% by weight, Mo1% by weight,
Regarding the alloy consisting of 0.1% by weight of Zr and the balance Fe,
Heating was performed in the air and under reduced pressure in a temperature range of 1100 to 1250°C, but no uniform Al ₂ O ₃ film was formed under any of the conditions.
The above alloys are therefore unsuitable as implant materials. Comparative example 2 Cr32% by weight, Al 6.0% by weight, Mo5.0% by weight,
An alloy consisting of 0.6% by weight of Zr and the balance Fe was prepared,
When cold working was performed, workability was poor and cracks occurred.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between heat treatment time, oxidation weight gain, and oxide film thickness.

Claims (1)

[Claims] 1 Cr20-32% by weight, Al 0.5-5.0% by weight,
An iron-chromium-aluminum medical implant alloy consisting of 0.5-4.0% by weight of Mo, 0.05-0.5% by weight of at least one of Zr, Hf and Y, and the balance Fe.