Manufacturing method for sliding members

Abstract

The objective is to realize a manufacturing method for sliding members with improved wear resistance. [Solution] A method for manufacturing a sliding member according to one aspect of the present disclosure includes the steps of preparing a composite ceramic comprising 65 to 96% by weight of alumina and at least one oxide other than alumina, The process includes a polishing step of polishing the surface of the composite ceramic, and an acid treatment step of treating the surface with a strong acid solution after the polishing step. The acid treatment step is a step of forming recesses on the surface, and the surface roughness Ra of the surface after the acid treatment step is 0.01 μm or less.

Description

Technical Field

[0001] The present disclosure relates to a sliding member and a method for manufacturing the sliding member.

Background Art

[0002] An artificial joint is known that has a pair of joint members constituting a joint, and forms a pair of friction surfaces that relatively slide in contact with each other through a lubricating fluid between the pair of joint members. Further, in a known artificial joint, at least one of the pair of friction surfaces has at least one of groove-shaped and hole-shaped recesses whose width gradually narrows from the surface side to the inside of the friction surface, and a curved surface portion that smoothly connects the surface forming the recess and the surface forming the surface portion of the friction surface.

[0003] Generally, as the surface roughness Ra of the friction surface increases, the wear amount due to cutting increases, and as the surface roughness Ra of the friction surface decreases, the wear amount due to adhesion increases. For this reason, there is a surface roughness Ra at which the sum of the wear amount due to cutting and the wear amount due to adhesion is minimized and the wear resistance is improved.

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object is to realize a method for manufacturing a sliding member with improved wear resistance.

Means for Solving the Problems

[0005] A method for manufacturing a sliding member according to an aspect of the present disclosure includes a step of preparing a composite ceramic containing 65 to 96% by weight of alumina and at least one oxide other than alumina, a polishing step of polishing the surface of the composite ceramic, and an acid treatment step of treating the surface with a strong acid solution after the polishing step. The acid treatment step is a step of forming recesses on the surface, and the surface roughness Ra of the surface after the acid treatment step is 0.01 μm or less.

Effects of the Invention

[0006] According to one aspect of this disclosure, a sliding member with improved wear resistance can be manufactured. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of an artificial hip joint according to one embodiment of the present disclosure. [Figure 2] This is a schematic diagram of a cross-section of a sliding surface according to one embodiment of the present disclosure. [Figure 3] This figure shows the condition of recess formation in a bone head ball according to one embodiment of the present disclosure, depending on the acid immersion time. [Figure 4] This is an enlarged view of the recessed area of ​​the sliding surface of a bone head ball according to one embodiment of the present disclosure, before and after acid immersion (before and after acid cleaning). [Figure 5] This is an enlarged view of the recess of the sliding surface of a bone head ball after acid immersion (acid cleaning) according to one embodiment of the present disclosure. [Figure 6] This figure compares the surface roughness of bone head balls after acid immersion according to one embodiment of the present disclosure. [Figure 7] This figure shows the results of the wear test on femoral head balls after acid immersion. [Modes for carrying out the invention]

[0008] [Embodiment 1] (Overall structure of artificial hip joint 1) Hereinafter, one embodiment of the present disclosure will be described in detail. Figure 1 is a schematic diagram of an artificial hip joint 1 as an artificial joint according to one embodiment of the present disclosure. As shown in Figure 1, the artificial hip joint 1 consists of an acetabular cup 10 fixed to the acetabulum of the pelvic bone 93, a femoral stem 20 fixed to the proximal end of the femur 91, and a femoral head ball 22 that slides with the acetabular cup 10. That is, the acetabular cup 10, the femoral stem 20, and the femoral head ball 22 are components that make up the artificial hip joint 1. However, the artificial joint is not limited to the artificial hip joint 1 according to the present disclosure, and may be, for example, an artificial knee joint, an artificial ankle joint, or an artificial shoulder joint.

[0009] The acetabular cup 10 has a substantially hemispherical acetabular fixing surface 14 and a substantially hemispherical recessed sliding surface 16. A femoral head ball 22 is provided at one end of the femoral stem 20 as a sliding member. In one embodiment of this disclosure, the femoral head ball 22 is fitted into one end of the femoral stem 20.

[0010] The femoral head ball 22 has a sliding surface 23 that slides against the acetabular cup 10. The sliding surface 23 is slidable against the acetabular cup 10. The femoral head ball 22 functions as a hip joint by sliding against the substantially hemispherical recessed sliding surface 16 of the acetabular cup 10. However, the sliding member in this disclosure is not limited to the femoral head ball 22, but may also be the acetabular cup 10. In this case, the acetabular cup 10 slides against the femoral head ball 22. The surface roughness Ra of the sliding surface 23 is 0.01 μm or less. This reduces the coefficient of friction during sliding between the acetabular cup 10 and the femoral head ball 22.

[0011] The acetabular fixation surface 14 is the outer surface located on the side closer to the acetabulum 94. The sliding surface 16 is also the inner surface or contact surface that comes into contact with the femoral head ball 22.

[0012] In one embodiment of this disclosure, the acetabular cup 10 is made of polyethylene or ultra-high molecular weight polyethylene.

[0013] The femoral head ball 22 comprises a composite ceramic containing alumina and at least one oxide other than alumina. This makes the femoral head ball 22 highly hard and strong. In this embodiment, the femoral head ball 22 is a composite ceramic containing 65-96% by weight of alumina and 4-34.4% by weight of zirconia. As a result, the femoral head ball 22 is stronger and tougher than a ceramic made of alumina alone without zirconia, and is also harder than a ceramic made of zirconia alone.

[0014] The bone head ball 22 may contain 0.20% by mass or more of SiO2, 0.22% by mass or more of TiO2, and 0.12% by mass or more of MgO. This reduces the decrease in the sintering acceleration effect caused by the increased viscosity of the liquid phase formed at the sintering temperature. In this embodiment, the total content of SiO2, TiO2, and MgO in the bone head ball 22 is 0.6 to 4.5% by mass. This provides the effects of high densification and fine-grained structure formation.

[0015] In this embodiment, the artificial joint is an artificial hip joint 1, and the sliding member is the femoral head ball 22 of the artificial hip joint 1. Therefore, wear resistance can be improved in the application of the femoral head ball 22 of the artificial hip joint 1. Wear resistance is evaluated by measuring the weight loss due to wear of the acetabular cup 10 when the femoral head ball 22 and the acetabular cup 10 are repeatedly slid against each other.

[0016] Figure 2 is a schematic cross-sectional view of a sliding surface 23 according to one embodiment of the present disclosure. Each polygon shown in Figure 2 represents an individual crystal grain of a polycrystalline composite ceramic. In one embodiment of the present disclosure, the crystal grains are alumina crystal grains or zirconia crystal grains, but no distinction is made in Figure 2. For convenience, the sliding surface 23 is shown as a plane in Figure 2. As shown in Figure 2, the sliding surface 23 has a plurality of recesses 24 with an aperture diameter L1 of 2 μm or less. Here, the aperture diameter L1 indicates the width of a minute opening present in the sliding surface 23 and does not necessarily indicate the diameter of a circle. The aperture diameter L1 can be determined, for example, by measuring the width of the opening observed in the sliding surface 23 as captured by a scanning electron microscope (SEM). Alternatively, the diameter may be calculated as the diameter when the image of the sliding surface 23 is converted to a circle of the same area by performing binarization processing, circle conversion processing, etc., using image processing software. The sliding surface 23 has multiple recesses 24, which allows it to capture water present in the environment in which the artificial hip joint 1 is applied. As a result, the sliding between the artificial hip joint 1 and the acetabular cup 10 becomes lubricated, thereby improving wear resistance.

[0017] At least some of the plurality of recesses 24 are formed by the absence of some crystal grains of alumina contained in the composite ceramics. For example, the recess 24 can be formed on the sliding surface 23 by the absence of crystal grains of alumina containing additive elements other than aluminum and oxygen. Since the shape of the recess 24 is formed by the absence of some crystal grains of alumina, it has an irregular shape and may have sharp edges. The shape of the recess 24 may be a groove shape or a hole shape in which the width gradually narrows from the surface side to the inner side of the sliding surface 23, or may be a shape in which the width of the recess increases from the opening to a predetermined depth.

[0018] The average crystal grain size of the alumina crystals is 2 μm or less. Thereby, compared with those having an average crystal grain size of 2 μm or more, the plurality of recesses 24 having an opening diameter L1 of 2 μm or less can be increased in the average crystal grain size of the alumina crystals. The average crystal grain size can be obtained by the straight-line cutting method using an enlarged image of the cross section of the composite ceramics photographed by, for example, SEM. In the present embodiment, the individual grain sizes of the alumina crystal grains are in the range of 0.05 to 3 μm. The individual diameters of the recesses formed by the absence of the alumina crystal grains are also 0.05 μm or more.

[0019] The depth L2 to the bottom of the recess 24 is 2 μm or less. Here, the depth L2 to the bottom of the recess 24 means the maximum distance among the distances from the opening of the recess 24 on the sliding surface 23 to the bottom surface of the recess 24. Thereby, the retention of the lubricating liquid between the friction surfaces can be promoted, and the wear of the friction material can be suppressed. The depth L2 can be measured by magnifying and observing a cross section perpendicular to the sliding surface 23 including the recess 24 with SEM or the like. Alternatively, the sliding surface 23 including the recess 24 may be magnified and observed and measured using a confocal laser microscope or the like having a high resolution for shape measurement in the depth direction.

[0020] The sliding surface 23 has 10,000 or more recesses 24 per square millimeter. Thereby, the sliding surface 23 can capture more water present in the environment where the artificial hip joint 1 is applied in the recesses 24 than a sliding surface provided with a sliding surface having less than 10,000 recesses 24 per square millimeter. Although the upper limit of the number of recesses 24 per square millimeter is not particularly defined, if the number of recesses becomes excessive, it affects the surface roughness Ra. When the surface roughness Ra increases, the wear resistance characteristics deteriorate. Therefore, the number of recesses 24 per square millimeter is set in a range where the surface roughness Ra does not exceed 0.01 μm.

[0021] (Manufacturing method) The manufacturing method of the femoral head 22 according to an embodiment of the present disclosure includes a polishing step and an acid treatment step. In the polishing step, the surface (sliding surface 23) of the composite ceramics containing alumina and at least one oxide other than alumina is polished. In the polishing step, the sliding surface 23 is polished so that the surface roughness Ra of the sliding surface 23 becomes 0.01 μm or less. In the present embodiment, at least one oxide other than alumina contains zirconia. Thereby, the femoral head 22 has higher strength and higher toughness than a configuration not containing zirconia. Further, the wear resistance is improved by the polishing step and the acid treatment step.

[0022] In the acid treatment step, the surface of the bone head ball 22 polished in the polishing step is treated with a strong acid solution to form recesses 24 on the surface. In this embodiment, in the acid treatment step, the surface of the bone head ball 22 is brought into contact with the hydrochloric acid solution for 5 to 200 minutes by immersing the bone head ball 22 polished in the polishing step in an aqueous hydrochloric acid solution. In the acid treatment step, the recesses 24 are formed such that the depth L2 from the opening to the bottom of the recess 24 is 2 μm or less. In addition, in the acid treatment step, 10,000 or more recesses 24 are formed on the sliding surface 2 per square millimeter. In the acid treatment step of this embodiment, the method for manufacturing the bone head ball 22 according to one embodiment of this disclosure is simple and cost-effective because the bone head ball 22 can be manufactured simply by immersing it in a strong acid solution after the polishing step. In this specification, the acid treatment step may be referred to as acid immersion or acid washing. In the acid treatment step, it is more preferable to bring the surface polished in the polishing step into contact with the aqueous hydrochloric acid solution for 30 to 150 minutes or more.

[0023] The strong acid solution is, but is not limited to, an aqueous solution of hydrochloric acid, an aqueous solution of sulfuric acid, or an aqueous solution of nitric acid. Furthermore, the strong acid solution may be a mixture of these aqueous solutions. In this embodiment, the strong acid solution is an aqueous solution of hydrochloric acid. This allows for the preparation of the strong acid solution more easily compared to a solution that is, for example, a mixture of an aqueous solution of sulfuric acid and an aqueous solution of nitric acid.

[0024] In one embodiment of the method for manufacturing a bone head ball 22, the surface roughness Ra of the sliding surface 23 after the polishing step and before the acid treatment step is 0.01 μm or less, and the surface roughness Ra of the sliding surface 23 after the acid treatment step is also 0.01 μm or less.

[0025] Furthermore, a method for manufacturing a sliding member according to one embodiment of this disclosure may include a grinding step before the polishing step. In the grinding step, a composite ceramic containing alumina and at least one oxide other than alumina is ground into a predetermined shape (i.e., the shape of a femoral head ball). In the polishing step, the composite ceramic ground into the predetermined shape in the grinding step may be polished. [Examples]

[0026] The following describes in more detail one aspect of the present disclosure based on examples and comparative examples, but the aspects of the present disclosure are not limited thereto. In this example, bone head balls of Example 1, Example 2 and Comparative Examples 1-3 were prepared. The prepared examples and comparative examples were observed by SEM, roughness measurement, and abrasion test.

[0027] For the femoral head ball in Example 1, zirconia-reinforced alumina (manufactured by Kyocera Corporation) conforming to ISO 6474-2 was used as the material. Specifically, a material containing 79.3% by weight of alumina and 18.2% by weight of zirconia was used.

[0028] For the femoral head ball in Example 2, zirconia-reinforced alumina (manufactured by Kyocera Medical Corporation) conforming to ISO 6474-2 was used as the material. Specifically, a material containing 79% by weight of alumina and 19% by weight of zirconia was used.

[0029] For Comparative Example 1, a commercially available zirconia-reinforced alumina conforming to ISO 6474-2 of the same size as that used in Examples 1 and 2 was used as the material for the femoral head ball. This zirconia-reinforced alumina contains approximately 75% by weight of alumina and approximately 25% by weight of zirconia. For Comparative Example 2, high-purity alumina was used as the material for the femoral head ball. This high-purity alumina contains 99.5% by weight or more of alumina. For Comparative Example 3, a Co-Cr-Mo alloy (compliant with ASTM F1537) was used as the material for the femoral head ball.

[0030] (Observation by SEM) The surface of each femoral head ball 22 was coated with platinum, and the surface of the femoral head ball 22 was observed using a scanning electron microscope (SEM). Secondary electron images were acquired at magnifications ranging from 1,000x to 30,000x.

[0031] Figure 3 shows the formation of depressions when the immersion time of the femoral head ball in the hydrochloric acid solution of Example 1 is varied. As shown in Figure 3, the sliding surface 23 of the femoral head ball after 5 minutes of acid immersion was rougher than before acid immersion, indicating the formation of depressions 24. The sliding surface 23 of the femoral head ball 22 after 30 minutes of acid immersion had more depressions formed compared to the sliding surface 23 of the femoral head ball 22 after 5 minutes of acid immersion. The sliding surface 23 of the femoral head ball after 150 minutes of acid immersion had more depressions formed compared to the sliding surface 23 of the femoral head ball 22 after 30 minutes of acid immersion. This indicates that depressions 24 can be formed on the surface of the sliding surface 23 by contacting the surface of the composite ceramic with the hydrochloric acid solution for 5 minutes or more.

[0032] Figure 4 is a magnified view of the recesses on the sliding surface of the femoral head ball of Example 1 before and after acid immersion (before and after acid cleaning). Figure 5 is a magnified view of the recesses on the sliding surface of the femoral head ball of Example 1 after acid immersion (after acid cleaning). As shown in Figures 4 and 5, before acid immersion, when the magnification was set to 5000 times, fine irregularities were formed on the surface of the sliding surface. This corresponds to the surface roughness of the sliding surface of the femoral head ball before acid immersion. As shown in Figure 4, after acid immersion, when the magnification was set to 1000 times, recesses were formed on the sliding surface. Furthermore, after acid immersion, when the magnification was set to 5000 times, black spots appeared on the sliding surface. These black spots were formed by the absence of some of the alumina crystals contained in the composite ceramics.

[0033] (Laser microscope observation) The surface of each femoral head ball was observed at 100x magnification using an Olympus confocal laser microscope. Figure 6 compares the surface roughness of the sliding surface of the femoral head ball of Example 1 after acid immersion with that of Comparative Example 1, which was not acid immersed. The scale length in the lower right of each photograph is 15 μm. As shown in Figure 6, the surface of Example 1 had many more depressions formed compared to the surface of Comparative Example 1.

[0034] (Roughness measurement) In accordance with JIS B 0601, a contact-type roughness meter (Mitutoyo Corporation, SV-3100SA) was used to obtain roughness curves at the apex of each femoral head ball with a reference length of 0.08 mm and 5 intervals. The arithmetic mean roughness Ra was measured by cutting off with a Gaussian filter with λc: 0.08 mm and λs: 0.0008 mm. [Table 1] Table 1 shows the surface roughness of the femoral head balls of Example 1 and Example 2, and the surface roughness of the femoral head ball of Comparative Example 1, which was not acid-soaked, after acid immersion. In Table 1, n is the sample number for each example and comparative example. As shown in Table 1, the average surface roughness of the femoral head balls 22 after acid immersion was 0.0034 for Example 1, 0.0033 for Example 2, and 0.0032 for Comparative Example 1. In other words, the average surface roughness of the femoral head balls 22 after acid immersion was approximately the same for all three: Example 1, Example 2, and Comparative Example 1. From these results, it was shown that in this example, the recesses formed on the femoral head balls had little effect on the surface roughness of the femoral head balls. Furthermore, it was confirmed that the surface roughness Ra of the femoral head balls of Comparative Examples 2 and 3 was also equivalent, and all were 0.01 μm or less.

[0035] (Abrasion test) Femoral head balls with an outer diameter of 40 mm were fabricated using zirconia-reinforced alumina material, and wear simulation tests were conducted in accordance with ISO 14242-1 and ISO 14242-2. The sliding mating surface was a gas-plasma sterilized cross-linked ultra-high molecular weight polyethylene liner (cup). The tests were conducted with n=3 samples for each example and comparative example. Wear was determined by measuring the weight change of the liner every 500,000 cycles and measuring the difference between the weight decrease from the start of the test and the load soak. Wear was measured every 500,000 cycles up to 5,000,000 cycles, and the average wear amount for n=3 was calculated for each cycle.

[0036] Figure 7 shows the results of an abrasion test of a femoral head ball after acid immersion. The vertical axis in Figure 7 represents the amount of wear in milligrams of the liner slid against the femoral head ball. The horizontal axis in Figure 7 represents the number of sliding cycles. For example, a value of 5 on the horizontal axis in Figure 7 represents 5 million cycles.

[0037] As shown in Figure 7, the wear amount of Examples 1 and 2 after 5 million cycles was approximately 8 mg. In contrast, the wear amounts of Comparative Examples 1, 2, and 3 after 5 million cycles were approximately 12 mg, 13.5 mg, and 17.5 mg, respectively. The wear amount of Examples 1 and 2, which had recesses formed, was lower than that of Comparative Examples 1, 2, and 3. Therefore, it was shown that the formation of multiple recesses improved wear resistance.

[0038] The inventions described in this disclosure have been explained above based on the drawings and embodiments. However, the inventions described in this disclosure are not limited to the embodiments described above. That is, the inventions described in this disclosure can be modified in various ways within the scope shown in this disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the inventions described in this disclosure. In other words, it should be noted that it is easy for those skilled in the art to make various modifications or alterations based on this disclosure. Furthermore, it should be noted that these modifications or alterations are included in the scope of this disclosure. [Explanation of Symbols]

[0039] 1. Artificial hip joint (artificial joint) 10. Acetabular cup (sliding member) 16, 23 Sliding surface 22. Femoral head ball (sliding member) 24 recesses L1 opening diameter Depth to the bottom of the L2 recess

Claims

1. A step of preparing a composite ceramic containing 65-96% by weight of alumina and at least one oxide other than alumina, A polishing step for polishing the surface of the composite ceramic, The process includes an acid treatment step in which the surface is treated with a strong acid solution after the polishing step, The acid treatment step is a step of forming a recess on the surface, A method for manufacturing a sliding member, wherein the surface roughness Ra of the surface after the acid treatment step is 0.01 μm or less.

2. The method for manufacturing a sliding member according to claim 1, wherein the composite ceramic comprises 4 to 34.4% by weight of zirconia.

3. The method for manufacturing a sliding member according to claim 1, wherein the recess formed by the acid treatment step has a depth of 2 μm or less from the opening to the bottom.

4. The method for manufacturing a sliding member according to claim 1, wherein the acid treatment step is a step of forming recesses on the surface by causing the absence of alumina crystal grains.

5. A method for manufacturing a sliding member according to any one of claims 1 to 4, wherein the surface roughness Ra of the surface after the polishing step and before the acid treatment step is 0.01 μm or less.

6. The method for manufacturing a sliding member according to any one of claims 1 to 5, wherein the strong acid solution is an aqueous hydrochloric acid solution, an aqueous sulfuric acid solution, or an aqueous nitric acid solution.

7. The method for manufacturing a sliding member according to claim 6, wherein in the acid treatment step, the surface is brought into contact with the hydrochloric acid aqueous solution for 30 minutes or more.

8. The aforementioned composite ceramics are SiO ２ 0.20 mass% or more of TiO ２ A method for manufacturing a sliding member according to any one of claims 1 to 7, comprising 0.22% by mass or more of and 0.12% by mass or more of MgO.

9. The aforementioned composite ceramics are SiO ２ , TiO ２ A method for manufacturing a sliding member according to any one of claims 1 to 7, wherein the total content of the and MgO is 0.6 to 4.5% by mass.

10. A method for manufacturing a sliding member according to any one of claims 1 to 9, comprising a grinding step of grinding the composite ceramics before the polishing step.

11. The method for manufacturing a sliding member according to claim 10, wherein the grinding step is a step of grinding the composite ceramic into the shape of a femoral head ball.

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