JP4892726B2 - Implant material for living body - Google Patents

Description

  The present invention relates to a biomedical implant material made of a Co-Cr-Mo-based alloy suitable for use in a living body such as an artificial hip joint, and in particular, intends to advantageously improve its strength. .

Since the implant material for living body is used by being embedded in a living body, it is required to be excellent in corrosion resistance and cytocompatibility. Furthermore, it is required to have excellent strength and wear resistance in an application such as an artificial hip joint that requires a large applied load and requires slidability.
Co-Cr-Mo type casting alloys defined in ASTM F-75 and Co-Cr-Mo type alloys as described in Patent Document 1 are known as satisfying such requirements.
JP 2004-269994 A

By the way, in recent years, such implant materials have strict demands for longer life, and accordingly, higher strength is required for Co-Cr-Mo alloys.
As a technique for increasing the strength of a Co—Cr—Mo alloy, there is known a method of controlling a structure by subjecting a cast material to warm or hot processing or applying heat treatment.

However, performing warm and hot processing, and further heat treatment such as heat treatment not only complicates the process, but also has a disadvantage in terms of manufacturing cost.
Therefore, it has been desired to develop an implant material that reduces such heat treatment and preferably has high strength as cast.

In addition, the above-mentioned ASTM F-75 standard contains a little Ni to improve its castability, but recently there has been concern about Ni allergies, so there has been a Ni-free biomaterial. It is requested.
However, in the alloy composition corresponding to the ASTM F-75 standard, when Ni-free is performed, the stacking fault energy decreases, the strength decreases significantly, and a large amount of martensite phase is introduced at room temperature. It also caused a significant decrease in ductility.

  The present invention has been developed in view of the above situation, and is made of a Co-Cr-Mo alloy that is Ni-free, does not require a complicated work heat treatment process, and has greatly improved strength over conventional materials. The object is to propose a biomedical implant material.

Now, in order to achieve the above object, the inventors have made a Co-Cr-Mo system corresponding to a Co-Cr-Mo casting alloy defined in ASTM F-75, which has been conventionally recognized as a biomedical implant material. A new alloy design was attempted for the alloy.
As a result, by adding an appropriate amount of B to the Co—Cr—Mo alloy, the cast structure can be refined, and the martensite amount can be suppressed to an appropriate range. We have found that the objective is achieved advantageously.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. Co—Cr—Mo—B alloy containing Cr: 20 to 34% by mass, Mo: 1 to 10% by mass and B : 0.05 to 0.5% by mass with the balance being Co, and the structure of the alloy The bioimplant material is characterized in that it contains 50 to 90% by volume of the γ phase and 10 to 50% by volume of the ε phase, and the ratio of the σ phase is suppressed to 0.6% or less in terms of area ratio .

According to the present invention, it is needless to say that the corrosion resistance and cell compatibility are excellent, and a Co—Cr—Mo alloy having high strength and good wear resistance can be obtained.
As a result, it is possible to provide a biomedical implant material that is safe for the living body and has a long service life, and is particularly effective when applied to medical devices such as an artificial hip joint and an artificial knee joint.

Hereinafter, the present invention will be specifically described.
In the present invention, a basic composition is a Co—Cr—Mo ternary alloy.
Here, the proper content of each element in this ternary alloy is as follows.
Cr: 20 to 34% by mass
Cr is an essential element for ensuring corrosion resistance. However, if the content is less than 20% by mass, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 34% by mass, it becomes brittle. It was limited to a range of ˜34% by mass. In order to reduce the magnetic susceptibility and suppress the occurrence of distortion (artifact) during MRI image diagnosis, the Cr content is preferably 30% by mass or more.

Mo: 1 to 10% by mass
Mo contributes effectively to the improvement of corrosion resistance and wear resistance. However, if the content is less than 1% by mass, the effect of addition is poor. On the other hand, if it exceeds 10% by mass, the workability is deteriorated. Was limited to the range of 1 to 10% by mass.

Now, in this invention, with respect to the Co—Cr—Mo ternary alloy having the above composition, B is contained in the range of 0.05 to 0.5 mass% to improve strength and ductility.
Here, if the amount of B is less than 0.05% by mass, sufficient strength and ductility improvement effects cannot be obtained. On the other hand, if it exceeds 0.5% by mass, the ductility is rather deteriorated and the implant material for living body is hindered. Is contained in the range of 0.05 to 0.5% by mass.

FIG. 1 shows the stress-strain of various alloys obtained by adding B in various proportions to a Co-29Cr-6Mo (Cr: 29 mass%, Mo: 6 mass%, Co: bal) alloy and melting and casting it. The results of examining the diagram are shown with the yield stress (MPa) on the vertical axis and the strain rate (%) on the horizontal axis.
As shown in the figure, it can be seen that the tensile strength is significantly improved by containing B by 0.05 mass% or more.

The reason why the strength and ductility are improved by adding an appropriate amount of B to the Co—Cr—Mo ternary alloy according to the present invention is considered as follows.
When a cast structure of a Co-29Cr-6Mo alloy containing no B and a Co-29Cr-6Mo-0.5B alloy containing 0.5% by mass of B was investigated, coarse dendrite was formed in the Co-29Cr-6Mo alloy. On the other hand, in the Co-29Cr-6Mo-0.5B alloy, the dendrite was refined by the formation of precipitates at the dendrite interface.
Further, when the alloy structure was investigated, in the Co-29Cr-6Mo alloy, the ε phase had a dominant (γ + ε) structure and the σ phase was dispersed, whereas the Co-29Cr-6Mo-0.1B The alloy has an increased proportion of γ phase.
Therefore, it is considered that the effect of improving the strength and ductility by the addition of B is achieved through the refinement of the structure and the reduction of the σ phase.

Moreover, the effect of this invention can be show | played by reducing (sigma) phase to 0.6% or less by area ratio by said process.
In this alloy, the γ phase and the ε phase other than the above-mentioned σ phase are γ phase and ε phase, and the phase ratio is γ phase: 50 to 90% by volume and ε phase: 10 to 50 % by volume .

As described above, the essential components in the present invention have been described, but in the present invention, in addition to the above-described elements, the following elements can be appropriately contained as necessary.
C: 0.2% by mass or less C is an element useful for improving the yield strength and elongation. However, if the content exceeds 0.2% by mass, the elongation decreases, so C is contained at 0.2% by mass or less. It is preferable.

Fe: 10% by mass or less
Fe is an element useful for improving the yield strength and elongation, but if the content exceeds 10% by mass, disadvantages such as an increase in the σ phase and a decrease in ductility occur, so Fe is 10% by mass. It is preferable to make it contain below.

Ni: 0.05% by mass or less Since the present invention is a Co—Cr—Mo alloy used for biomedical implants, Ni may be inevitably mixed, but if it is 0.05% by mass or less, there is a problem. Absent.

Next, preferred production conditions for the alloy of the present invention will be described.
In order to produce the alloy of the present invention, it is important to rapidly cool after heating to 1500-1600 ° C. If the heating temperature is less than 1500 ° C. (lower limit value), it cannot be dissolved uniformly. On the other hand, when the temperature exceeds 1600 ° C. (upper limit), there is a problem that the composition changes due to evaporation of the alloy elements.

Example 1
A Co-Cr-Mo-B alloy in which B is added in various proportions shown in Table 1 in a Co-Cr-Mo alloy having a basic composition of Co-29Cr-6Mo is heated to 1500 ° C and then rapidly cooled. A biomedical implant material was produced.
The results of examining the mechanical properties (0.2% yield strength, maximum tensile stress, plastic elongation) of the implant material thus obtained are also shown in Table 1.

The mechanical properties were investigated as follows.
That is, a plate-shaped tensile test piece (thickness: 1.0 mm, gauge length: 14 mm) was cut out from each alloy material, a tensile test was performed at a strain rate of 6.0 × 10 ⁻⁴ s ⁻¹ , and mechanical properties were obtained. (0.2% yield strength, maximum tensile stress, plastic elongation) was determined.

  As shown in the table, by containing B by 0.05% by mass or more, the 0.2% proof stress and the maximum tensile stress are remarkably improved. Also, the plastic elongation is greatly improved by containing B by 0.05% by mass or more. However, when the B content exceeds 0.5% by mass, the elongation tends to deteriorate.

It is a stress-strain diagram which shows the addition effect of B on the tensile property of a Co-Cr-Mo type alloy.

Claims (1)

Co—Cr—Mo—B alloy containing Cr: 20 to 34% by mass, Mo: 1 to 10% by mass and B : 0.05 to 0.5% by mass with the balance being Co, and the structure of the alloy The bioimplant material is characterized in that it contains 50 to 90% by volume of the γ phase and 10 to 50% by volume of the ε phase, and the ratio of the σ phase is suppressed to 0.6% or less in terms of area ratio .

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