JP2010144184A - Biomedical cast substrate of cobalt-chromium-based alloy superior in diffusion hardening treatability, biomedical sliding alloy member, and artificial joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biomedical cast substrate of a cobalt-chromium-based alloy, of which the surface can be uniformly and sufficiently hardened when the substrate has been subjected to diffusion hardening treatment such as carburizing treatment and nitriding treatment, and to provide a biomedical sliding alloy member which is obtained by subjecting the cast substrate of the cobalt-chromium-based alloy to the diffusion hardening treatment such as the carburizing treatment and the nitriding treatment and stably shows excellent wear resistance. <P>SOLUTION: The biomedical cast substrate of the cobalt-chromium-based alloy superior in diffusion hardening treatability is a biomedical cast substrate formed from a cobalt-chromium-based alloy; and includes 0.1 mass% or more nitrogen (N) and has a metallurgical structure in which an fcc (face centered cubic lattice) phase occupies 50% or more by a volume fraction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a biomedical cobalt-chromium based alloy cast base material, a biocompatible sliding alloy member, and an artificial joint, which are excellent in diffusion hardenability. For example, the base material is obtained by a diffusion hardening process such as carburizing or nitriding. Uniform surface hardening (in the present invention, such a characteristic is said to be “excellent in diffusion hardening process”), a cobalt-chromium alloy casting base for living body, and the cobalt-chromium alloy casting base A sliding alloy member for a living body that stably exhibits excellent wear resistance obtained by subjecting the material to diffusion hardening treatment such as carburizing treatment and nitriding treatment, and an artificial joint using the sliding alloy member for living body It is about.

  Cobalt-chromium-based alloys are excellent in biocompatibility, strength, wear resistance, and corrosion resistance among biomaterials, and have long been used for sliding members of artificial joints such as artificial hip joints and implant members. Yes. For example, Patent Document 1 discloses a cobalt-chromium-molybdenum alloy having a defined component composition. Patent Document 2 discloses a method for producing a Co-based alloy in which the component composition and the amount of γ phase are defined for the purpose of improving plastic workability.

  When such a cobalt-chromium-based alloy is used for a living body sliding member in particular, since the surface is easily worn, for example, carburizing treatment, nitriding treatment, etc. are generally performed as a treatment for surface hardening. . For example, Patent Document 3 and Patent Document 4 include a method of carburizing a cobalt-chromium-based alloy material, and characteristics achieved thereby (such as improving surface hardness and wear resistance without reducing corrosion resistance). It is shown.

Patent Document 5 discloses that a diffusion hardening treatment is performed on a metal material containing a Co—Cr—Mo alloy. Specifically, an internal oxidation method, an internal nitridation method, nitrogen, oxygen, or carbon is disclosed. It is described that the surface of the alloy was strengthened and hardened by an additional interstitial diffusion strengthening method using the above.
Japanese Patent Laid-Open No. 54-10224 JP 2008-1111177 A JP-T-2005-524772 JP 2007-277710 A Japanese Patent No. 3471401

  However, the base material made of a cobalt-chromium alloy has a large change in microstructure (hereinafter sometimes referred to as a metal structure or simply a structure) due to its manufacturing method, amount of added elements, heat treatment, etc., and as a result, the characteristics also change greatly. To do. Among them, in particular, the as-cast state obtained by melting the metal, which is a representative substrate manufacturing method, pouring into a mold and solidifying it, has a very uneven structure (the process of solidifying the molten metal) This means a state in which there is a deviation (segregation) in the element concentration that occurs in the above.

  An example of a method for making the structure in the non-uniform state uniform is to heat-treat the as-cast alloy at a high temperature for a long time. On the other hand, in recent years, as a typical combination of sliding members of artificial joints, there are cases where a cobalt-chromium based alloy sliding member and a cobalt-chromium based alloy sliding member are combined. It has been found that the wear resistance is improved by increasing the amount of carbon in the cobalt-chromium-based alloy and dispersing more carbide, which is a compound of carbon and metal. Therefore, heat treatment at a high temperature at which the carbide disappears is often not performed.

  As described above, there is a tendency not to perform high-temperature heat treatment to improve wear resistance, but without performing heat treatment at the high temperature, diffusion such as carburizing treatment, nitriding treatment, etc., on a substrate having a non-uniform structure. A curing process is performed. However, if diffusion hardening treatment is applied to a substrate with a non-uniform structure, local hardening may occur on the same treated surface, or solid solution elements (for example, carbon in carburizing treatment) in the thickness direction of the hardening treatment layer. However, there is a problem that the wear resistance tends to vary due to, for example, an element concentration distribution with no reproducibility.

  The present invention has been made in view of such circumstances, and its purpose is to provide a bio-cobalt-chromium group that can sufficiently achieve uniform curing of the substrate surface when subjected to diffusion hardening treatment. Alloy casting base material, sliding alloy member for living body which is obtained by subjecting the cobalt-chromium based alloy casting base material to the above diffusion hardening treatment, and which exhibits excellent wear resistance stably, and the sliding alloy for living body An object of the present invention is to provide a highly reliable artificial joint obtained by using a member.

  The living body cobalt-chromium based alloy casting base material according to the present invention is a living body casting base material made of a cobalt-chromium base alloy, containing 0.1% by mass or more of nitrogen (N), and in a metal structure. It is characterized in that the volume fraction of the fcc (face centered cubic lattice) phase is 50% or more (in the metal structure,% indicates volume%, the same applies hereinafter).

  The upper limit of the N content of the cobalt-chromium-based alloy is preferably 0.25% by mass, and the content of elements other than N is preferably within the range specified in ASTM F75-07.

  The cobalt-chromium based alloy cast base material of the present invention is also one having an average crystal grain size of the metal structure of 1000 μm or more.

  The present invention also includes living body sliding alloy members obtained by subjecting the above-described cobalt-chromium-based alloy cast base material to an as-cast state by diffusion hardening treatment (for example, carburization treatment). Further, the two sliding members constituting the sliding surface are artificial joints made of a cobalt-chromium based alloy sliding member, and at least one of the cobalt-chromium based alloy sliding members is the living body sliding An artificial joint characterized in that it is an alloy member is also included.

  According to the present invention, a uniform hardened layer is formed by the diffusion hardening process even when the as-cast cobalt-chromium base alloy casting base material, which is likely to have a non-uniform structure, is subjected to the diffusion hardening process. A sliding alloy member for a living body can be obtained. As a result, a sliding alloy member for a living body that continues to exhibit high strength, excellent wear resistance, and further excellent corrosion resistance, and a highly reliable artificial joint obtained by using the sliding alloy member for living body Etc. can be provided.

  The present inventor has intensively studied to realize a cobalt-chromium based alloy casting base material for biomedical use capable of obtaining a uniform hardened layer without local shortage of hardening, in particular, by diffusion hardening treatment. As a result, the metal structure of the cobalt-chromium based alloy cast base material may be a structure in which a phase (also referred to as fcc phase or γ phase) having a crystal structure of fcc (face-centered cubic lattice) occupies a certain amount or more. I found. Hereinafter, the present invention will be described in detail. In the following, a case where carburizing treatment is performed as a representative example of diffusion hardening treatment is described. However, the present invention is not limited to this, and as will be described later, as diffusion hardening treatment, nitriding treatment, boride treatment, oxidation treatment is performed. The case where processing is performed is also included in the technical scope of the present invention.

  First, the present inventor considers that the occurrence of local insufficiency is caused by the metal structure, and produces cobalt-chromium based alloy cast base materials (as cast) having various metal structures, which will be described later. After carburizing by the method shown in the examples, Vickers hardness (hereinafter sometimes simply referred to as hardness) at a plurality of locations was measured in the same plane of the carburized material. The measurement was carried out using a Vickers hardness measuring apparatus and measuring 10 arbitrary points per sample with a load of 50 gf.

  As a result, it was found that there were samples in which the hardness varied in the same plane and samples in which the hardness variation hardly occurred. Therefore, the hardness varies in the same plane (hereinafter, the variation in hardness generated in the same plane may be referred to as “hardness unevenness”) (No. 2 in Examples described later), and the above The state of hardness unevenness and the cause of occurrence were examined for a sample (No. 7 in Examples described later) in which the hardness unevenness hardly occurred.

  First, with respect to the sample (No. 2) in which the hardness unevenness occurred, the Vickers hardness measured in the same plane was divided into a relatively high hardness and a relatively low hardness. It can be seen that the high hardness is measured around the precipitate (carbide) existing after casting, while the relatively low hardness is measured in a region away from the precipitate. It was. This is because No. 1 shown in FIG. It is also confirmed from the Vickers indentation photo of No. 2 (optical micrograph, indicating that the smaller the indentation, the harder the hardness), the Vickers indentation size is different between the periphery of the precipitate and the other areas. it can. No. Table 1 also shows the results of dividing the Vickers hardness measured in 7 into the periphery of the precipitate (carbide) and the other region (region away from the precipitate). No. The Vickers impression photograph of No. 7 is shown in FIG. For No. 7, it can be seen that the hardness is almost constant regardless of the measurement location.

  Furthermore, in order to find out the cause of the occurrence of the hardness unevenness, Two metallographic structures were examined. Specifically, No. before carburizing treatment is performed by an electron back scattering pattern (EBSP) method. The crystal orientation analysis of the base material of 2 was implemented. The result is shown in FIG. The blue region in FIG. 3A indicates the fcc phase region, and the red region in FIG. 3B indicates the hcp phase (also referred to as a hexagonal close-packed lattice or ε phase) region. From FIG. 3, it can be seen that the periphery of the amorphous precipitate is an fcc phase region, and the region away from the precipitate is an hcp phase.

  From the structure shown in FIG. 3 and the Vickers indentation photograph shown in FIG. 1, in the structure before carburizing treatment, the periphery of the precipitate that is the fcc phase is hard after carburizing treatment. It can be seen that the hardness after the carburizing treatment is lower in the region of the hcp phase away from the object than the surroundings of the precipitate.

  It should be noted that the Vickers hardness (Vickers indentation) is almost constant regardless of the measurement location. 7 shows the result of the crystal orientation analysis by EBSP. In FIG. 4, green, blue-green, and blue portions indicate fcc phase regions. From FIG. As for No. 7, it can be seen that the structure before the carburizing treatment is almost occupied by the fcc phase.

  It was also examined whether the hardness unevenness was caused by the carburizing process (before the carburizing process). That is, the above-mentioned No. 2 and no. About each base material before carburizing treatment of No. 7, as above-mentioned, while measuring the Vickers hardness, the photograph of the Vickers impression was photographed. The results are shown in Table 2 and FIG.

  From Table 2 and FIG. 2 and no. In both cases, the hardness in the same plane is almost uniform, and it can be seen that the hardness unevenness is caused by performing the carburizing process.

  From these results, when the proportion of the hcp phase in the structure of the base material before the carburizing treatment is significantly larger than that of the fcc phase, the hardness of the hcp phase region after the carburizing treatment becomes low, and thus the hardness unevenness becomes remarkable. It has been found that if the proportion of the fcc phase in the structure of the base material before carburizing is increased, a large area of high hardness can be secured and hardness unevenness can be suppressed when carburizing is performed.

  Therefore, the present inventor examined how much fcc phase that should have high hardness after carburizing treatment should be secured in the base material structure before carburizing treatment. Specifically, as shown in Table 3 of Examples described later, various cobalt-chromium based alloy cast base materials having different volume fractions of the fcc phase were prepared by changing the component composition, and the hardness of each base material I checked for unevenness. As a result, if the volume fraction of the fcc phase occupying the structure of the base material before carburizing is 50% or more, the Vickers hardness is almost constant within the same plane after carburizing regardless of the presence or location of carbides. Thus, it was found that a uniform cured layer without local curing deficiency was obtained.

  Since the in-plane uniformity of hardness increases as the proportion of the fcc phase increases, the volume fraction of the fcc phase is preferably 60% or more, more preferably 70% or more. On the other hand, considering the fact that the upper limit of N content in ASTM F75-07 is defined as 0.25% by mass from the viewpoint of securing the strength / ductility balance, as described later, the volume fraction of the fcc phase is The upper limit is about 85%.

  In the present invention, as described above, the ratio of the fcc phase in the base material structure may be 50% or more. In the present invention, there are other structures that may inevitably remain in the manufacturing process of the base material. It may include the case where it exists. Specifically, the hcp phase, precipitates such as carbides, nitrides, carbonitrides, and intermetallic compounds may be included.

  Next, the present inventor examined a specific method for obtaining a structure in which the fcc phase accounts for 50% or more. As described above, it is possible to make the structure uniform by performing a heat treatment at a high temperature. However, in the present invention, since the carbides disappear and the wear resistance of the base material is deteriorated, The investigation was conducted with a particular focus on the component composition rather than the production conditions.

  First, as shown in Table 3 of Examples described later, a cobalt-chromium based alloy cast base material having various component compositions is prepared, and the proportion of the fcc phase in the metal structure of each base material is shown in the Examples described later. The relationship between each component element and the ratio of the fcc phase was examined. As a result, it has been found that among various component elements, the N content is correlated with the proportion of the fcc phase.

  FIG. 6 is a graph obtained by rearranging the N content (nitrogen content) and the volume fraction of the fcc phase of the cobalt-chromium base alloy cast base material (note that the additional numbers in the graph are those described later) No. in Table 3 of the example is shown, and the same applies to FIGS. From FIG. 6, there is a correlation between the amount of N in the base material and the volume fraction of the fcc phase. When the amount of N is small, the fcc phase is extremely reduced, and N is contained by 0.1 mass% or more. As a result, it was found that 50% or more of the fcc phase can be stably secured.

  For reference, a graph showing the relationship between the content of C (carbon content) as a component other than N and the volume fraction of the fcc phase is shown in FIG. As is apparent from FIG. 7, it can be seen that there is no correlation between the C content of the base material and the volume fraction of the fcc phase.

  In the present invention, by setting the N content in the cobalt-chromium base alloy cast base material to 0.1% or more in this way, even in the as-cast state (as-cast state), the cobalt-chromium base alloy casting is performed. The ratio of two types of fcc phase and hcp phase, which are typical crystal structures constituting the base material, can be controlled to a stable structure of fcc phase: 50% or more. As a result, diffusion hardening such as carburizing treatment It is characterized in that a cured layer with high reproducibility and uniform hardness can be obtained when the treatment is performed.

  In order to increase the volume fraction of the fcc phase in the metal structure, preferably 60% or more as described above, and to obtain a hardened layer having a more uniform hardness by diffusion hardening treatment, the N amount is 0.15% by mass or more. It is preferable to do. Further, in order to increase the volume fraction of the fcc phase, more preferably 70% or more and to obtain a hardened layer having a more uniform hardness by diffusion hardening treatment, the N content is more preferably 0.20% by mass or more. .

  Although Patent Document 1 and Patent Document 2 describe that the N amount is specified, the effect is limited to improvement in strength, ductility and corrosion resistance, or plastic workability. There is no knowledge that homogenization was achieved.

  In the present invention, in the component composition, it is necessary to make the amount of N not less than a certain value as described above. However, the upper limit of the amount of N and the contents of other elements are conventionally used for biomedical cobalt / chromium. It may be within the range of the base alloy. For example, as specified in ASTM F75-07, the upper limit of the N amount is set to 0.25% by mass, and the content of other elements is determined. Specifically, Cr: 27.00 to 30.00 mass%, Mo: 5.00 to 7.00 mass%, Ni: 0.50 mass% or less, Fe: 0.75 mass% or less, C: 0 .35% by mass or less, N: 0.1 to 0.25% by mass, Si: 1.00% by mass or less, and Mn: 1.00% by mass or less, including the balance Co and inevitable impurities. It is done. In addition, it is preferable that the minimum of the said C amount shall be 0.15 mass% from a viewpoint of forming a carbide | carbonized_material in a base material.

The method for producing the cobalt-chromium based alloy cast base material is not particularly limited. For example, after melting a component of the cobalt-chromium based alloy, for example, near net shape casting, that is, for example, a bone head type of an artificial joint Pour into a mold to obtain a base material as cast (as cast). As described above, in order to increase the amount of N in the cobalt-chromium based alloy cast base material, nitrogen gas is introduced at the time of melting, or nitrides such as Cr ₂ N, CrN, FeCrN, Si ₃ N ₄ , MnN, etc. And the like. After casting, the surface may be somewhat ground to remove surface defects and roughness.

  By subjecting the as-cast cobalt-chromium base alloy cast base material to diffusion hardening treatment without heat treatment after forging, it can be maintained without losing carbides in the metal structure, and as a result, excellent wear resistance can be secured. . If the base material is subjected to heat treatment (particularly heating at a temperature of 1000 ° C. or more), the carbides are lost, which is not preferable.

  A living body sliding alloy member constituting an artificial joint or the like can be obtained by subjecting the as-cast cobalt-chromium base alloy cast base material to diffusion hardening treatment. Examples of the diffusion hardening treatment include nitriding treatment, boriding treatment, oxidation treatment, and the like in addition to the above carburizing treatment. In any treatment, the same effect as the carburizing treatment can be obtained. For example, a base material (or a base material subjected to activation treatment as described later) is placed in a processing furnace, and a mixed gas containing a carbon source, a nitrogen source, etc. is introduced into the furnace, and is generally adopted. The treatment can be performed at a certain temperature.

  For example, as a carburizing method, performing on the following conditions is mentioned. That is, the carburizing treatment may be performed at a base material temperature (carburizing temperature) of 450 to 550 ° C. Within this temperature range, carbon is preferable because it forms a solid solution on the surface of the substrate but hardly forms chromium carbide. When the carburizing temperature is less than 450 ° C., carbon does not progress in solid solution, and a solid solution layer having a desired surface hardness is not formed. Moreover, since the production | generation of chromium carbide is accelerated | stimulated as it is temperature higher than 550 degreeC, it is unpreferable.

As the carbon source in the carburizing treatment, for example, one or more of CO, CO ₂ , CH ₄ , C ₂ H ₆ , C ₃ H ₈ , and C ₄ H ₁₀ can be used. For example, a mixed gas of the carbon source and, for example, H ₂ is diluted with an inert gas and introduced into the processing furnace. N ₂ , Ar, and He can be used as the inert gas. The time for the carburizing treatment can be adjusted according to the relationship between the treatment temperature and the thickness of the solid solution layer, but it is usually performed for 1 to 50 hours, and most commonly for 10 to 35 hours.

  Before the diffusion hardening treatment, an activation treatment may be performed in order to remove the passive film formed on the substrate surface. Chromium in the substrate reacts with oxygen in the air to form a passive film. This passive film tends to inhibit the penetration of carbon into the substrate surface when carburizing. Therefore, carburization can be sufficiently performed by removing the passive film by the activation treatment. The activation treatment can be performed by a method using gas or a method using liquid.

  Examples of the activation treatment using gas include fluorination treatment. In the fluorination treatment, a cobalt-chromium-base alloy cast base material is placed in a furnace for heat treatment, heated to 200 ° C. to 500 ° C. in a fluorine-based gas atmosphere, and the temperature is set for 10 minutes to 180 minutes. Hold. Thereby, chromium oxide on the surface is replaced with chromium fluoride.

The fluorine-based gases suitable for this fluorination _treatment, there is a _{NF 3, BF 3, CF 4} , HF, SF 6, C 2 F 6, WF 6, CHF 3, SiF 4, ClF 3 or the like. These fluorine-based gases are used alone or in combination of two or more. Usually, these fluorine-based gases are diluted with an inert gas such as N ₂ gas.

  Examples of the activation treatment using a liquid include a method of immersing in an acidic solution. As the acidic solution, a solution in which one kind or a mixture of two or more kinds of hydrochloric acid, nitric acid, hydrogen peroxide, sulfuric acid and hydrofluoric acid can be used. In particular, hydrochloric acid and nitric acid, hydrochloric acid, nitric acid and hydrogen peroxide are used. Alternatively, a solution in which hydrochloric acid and hydrogen peroxide are mixed is preferable, and the passive film of chromium oxide on the surface can be dissolved in a short time.

  After the diffusion treatment, post treatment is performed depending on the surface condition. As the post-treatment, there are acid treatment for removing soot (in the case of carburizing treatment) adhering to the surface, surface polishing such as mirror polishing, and the like.

  The living body sliding alloy member obtained by performing the diffusion hardening treatment or the like is suitably used as a sliding member of an artificial joint such as an artificial hip joint, an artificial knee joint, or an artificial elbow joint. In particular, the two sliding members constituting the sliding surface are artificial joints made of a cobalt-chromium based alloy sliding member, and at least one of the cobalt-chromium based alloy sliding members (e.g., head and / or If the living body sliding alloy member of the present invention is employed for the stem, it is preferable because the effects of the present invention are fully exhibited.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  Eleven types of cobalt-chromium-base alloy castings (bars having a diameter of 15 mm and a length of 150 mm) shown in Table 3 were produced. The N and C amounts of the cast material were controlled by the partial pressure of nitrogen during melting and the amount of graphite added. After casting, the obtained bar was cut into a disk shape having a thickness of about 2 mm, and then wet-polished using SiC paper to obtain a cobalt-chromium based alloy cast base material.

  The amount of N (nitrogen) in the cobalt-chromium-based alloy cast base material thus obtained was measured using an inert gas melting method. Further, the C (carbon) amount was measured by a combustion infrared absorption method, the Si amount was measured by an absorptiometry, and the contents of other components shown in Table 3 were measured by an ICP analysis method. In addition, in order to confirm the average crystal grain size of the cobalt-chromium-base alloy cast base material (the average value of the equivalent circle diameter of crystal grains in an arbitrary field of view), the observation surface is mirror-finished by wet polishing. Etching was performed in an acid solution, and the macro structure was observed. A typical macro structure photograph (No. 7 macro structure photograph in Table 3) is shown in FIG. It was confirmed that all of the produced cast base materials had an average crystal grain size of 1000 μm or more as shown in FIG.

<Measurement of volume fraction of fcc phase of cobalt-chromium base alloy cast base material (before carburizing treatment)>
Using the substrate, the volume fraction of the fcc phase was determined by X-ray diffraction. That is, using an X-ray diffractometer (Rigaku RINT1500), rotating and shaking the sample under the conditions of rotational speed: 60 rpm, peristaltic angle / period: -45 ° to 45 ° / 4 sec, target: Cu, target output: The range of 2θ = 45 ° to 53 ° was measured under the conditions of 40 kV-200 mA, slit system: light reception 0.3 mm, length 2 mm, sampling step: 0.02 °, measurement time: 8 sec / step. Among the obtained diffraction peaks, the integrated intensity of the peak shown in the following calculation formula (1) was obtained, and the volume fraction Vγ of the fcc phase (γ phase) was calculated from the following calculation formula (1). Table 3 shows the volume fraction (volume%) of the fcc phase of each substrate.

Next, activation treatment and carburization treatment were sequentially performed on the substrate. Specifically, the substrate is subjected to activation treatment with a fluorinated gas (held in an NF ₃ gas atmosphere at 350 ° C. for 2 hours), and then a gas carburizing treatment (in a CO + H ₂ mixed gas atmosphere). , Held at 500 ° C. for 32 hours).

<About hardness variation in the same plane>
The Vickers hardness at a plurality of locations was measured in the same plane of each sample after the carburizing treatment. Vickers hardness was measured with a load of 50 gf using a Vickers hardness measuring device.

  As a result, no. 1, 3 and 4, the above No. As in the case of No. 2, the hardness was varied within the same plane, whereas no. In Nos. 5, 6, and 8 to 11, the above-mentioned No. 5 is used. Similar to 7, the hardness in the same plane was almost constant regardless of the measurement location.

<Dispersion of carbon profile of carburized layer>
In order to confirm whether a uniform hardened layer was stably obtained by the carburizing treatment, the carbon concentration distribution after carburizing treatment of each sample was measured. Specifically, it was measured by glow discharge emission spectroscopy (GDS). For glow discharge emission analysis, a JY5000RF-PSS type GDS apparatus manufactured by Jobin Ybon was used, and measurement was performed in a low voltage mode (40 W) under a vacuum of Ar pressure of 775 Pa.

  The carbon concentration distribution of the carburized layer is shown as an example (comparative example) in the region (region A) where the N content is less than 0.1% by mass and the proportion of the fcc phase is less than 50% in FIG. FIG. 9 shows an example (invention example) in the region (region B) in which the N amount is 0.1% by mass or more and the ratio of the fcc phase is 50% or more.

  From FIG. 9, it can be seen that any of the cobalt-chromium based alloy cast base materials shows a profile with a high carbon concentration from the surface to about 20 μm. Next, comparing the details of the profiles, No. In the profiles 1 to 4, large variations were observed between samples. This is probably because the hardness varies between samples as a result of variations in hardness depending on the measurement location in the same plane of one sample. On the other hand, No. 5 to 11 show that the carbon profiles in the vicinity of the surface layer are almost the same regardless of the component composition and are in a uniform solid solution distribution state.

1 is a Vickers impression photograph of the surface of a base material (No. 2 in Examples) after carburizing treatment. FIG. 2 is a Vickers impression photograph of the surface of the base material (No. 7 in the example) after the carburizing treatment. FIG. 3 is a photograph showing a crystal orientation analysis result by electron beam backscatter diffraction (EBSP) method of a base material (No. 2 in the example) before carburizing treatment. FIG. 4 is a photograph showing a crystal orientation analysis result by an electron beam backscatter diffraction (EBSP) method of a base material (No. 7 in the example) before carburizing treatment. 5 is a Vickers impression photograph of the surface of the base material (No. 2 and No. 7 in the example) before carburizing treatment. FIG. 6 is a graph showing the relationship between the nitrogen content of the substrate and the volume fraction of the fcc phase. FIG. 7 is a graph showing the relationship between the carbon content of the substrate and the volume fraction of the fcc phase. FIG. 8 is a representative macrostructure photograph of the cobalt-chromium based alloy cast base material of the present invention. FIG. 9 is a diagram showing the carbon concentration distribution of the carburized layer divided into an example in the region A and an example in the region B.

Claims (6)

  A casting base for living bodies made of a cobalt-chromium alloy, containing 0.1% by mass or more of nitrogen (N) and having a volume fraction of fcc (face-centered cubic lattice) phase in the metal structure of 50% or more. A bio-cobalt / chromium-base alloy cast base material excellent in diffusion hardening processability characterized by being.   2. The biomedical device according to claim 1, wherein the upper limit of the N content of the cobalt-chromium-based alloy is 0.25 mass%, and the content of elements other than N is within the range specified in ASTM F75-07. Cobalt-chromium base alloy casting base material.   3. The biomedical cobalt-chromium based alloy casting base material according to claim 1, wherein an average crystal grain size of the metal structure is 1000 μm or more.   A sliding alloy member for a living body obtained by subjecting the as-cast cobalt-chromium alloy cast base material according to any one of claims 1 to 3 to a diffusion hardening treatment.   The living body sliding alloy member according to claim 4, wherein the diffusion hardening process is a carburizing process.   The two sliding members constituting the sliding surface are artificial joints made of a cobalt-chromium based alloy sliding member, and at least one of the cobalt-chromium based alloy sliding members is according to claim 4 or 5. An artificial joint which is a sliding alloy member for a living body.