JP2002363675A - Co BASED ALLOY FOR LIVING BODY AND PRODUCTION METHOD THEREFOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a Co based alloy which has excellent wear resistance, and is suitable as a prosthetic material for artificial coxae, or the like. SOLUTION: The Co based alloy for the living body has a composition containing, by mass, 26 to 30% Cr, 6 to 12% Mo and 0 to 0.3% C, and the balance substantially Co, and has a structure in which a granular second phase is finely dispersed into a matrix consisting of crystal grains having the average crystal grain size of <=50 μm. The alloy is produced by subjecting a Co based alloy having a prescribed composition to rapid cooling casting by using a water cooled mold made of copper, and subjecting the obtained ingot to forging at 1,000 to 1,300 deg.C. In this way, its structure is controlled to the one where a granular second phase is finely dispersed into a fine structure, so that the alloy exhibits exceedingly excellent wear resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biomedical C which is excellent in corrosion resistance, abrasion resistance and workability and is suitable as a prosthetic material for artificial aggregate.
The present invention relates to an o-based alloy and a method for producing the same.

[0002]

2. Description of the Related Art Co-Cr based alloys for casting (HS-21) and processing (HS-25) such as Vitallium and Co-Ni
-Cr-Mo alloy (MP35N) is known, but Vitalliu has high clinical data and experience in use and high stability.
m is frequently used. Vitallium was developed as a dental alloy, but its use has been expanded to the orthopedic field through subsequent improvements. Other products include Alivium, Endcast, Orthochrom
e, Orthochrome plus, Protasul, Zimaloy and many other trade names. Vitallium was put into practical use in 1937, 10 years later than stainless steel. However, since it has better corrosion resistance than stainless steel, and has both sufficient strength and toughness, prosthetic materials for artificial hip joints such as heads and stems Has been used as

Vitallium for casting (HS-21) is a high Cr (30% by mass) -Co alloy containing 5 to 7% by mass of Mo, and is the most excellent in corrosion resistance among Vitalliums, and has pitting corrosion, crevice corrosion, and granularity. Interfacial corrosion, stress corrosion cracking, and the like hardly cause problems in practical use. However, internal defects such as sink marks, bubbles, and segregation are likely to occur, and low fatigue strength (250 MPa) is a disadvantage. Vitallium (HS-25) for processing is an alloy that contains W instead of Mo and has been improved to eliminate sink marks and segregation, which are defects of cast materials, by replacing a part of Cr with Ni. is there. Vitallium (HS-25) for processing is given more ductility than solution-annealed stainless steel by solution treatment,
Cold working provides the same strength as stainless steel for working. Although corrosion resistance is superior to stainless steel, it is not sufficient for long-term implants, so it is used for short-term fixing of bone plates, wires, and the like.

[0004]

[Problems to be Solved by the Invention] M of Vitallium for processing
When the o content is increased, corrosion resistance and abrasion resistance are improved. In fact, high Mo-Vi with Mo increased to 10% by mass
Tallium is known to exhibit superior corrosion and abrasion resistance as compared to alloys of the original composition. But Mo
Since the plastic workability of Vitallium decreases with an increase in the amount, the fine structure of high Mo-Vitallium is difficult to control by the plastic working method.

[0005] In Vitallium for casting, it has been studied to eliminate internal defects by adjusting the thermal history. Generally, sinkholes and bubbles generated in a cast alloy are crushed by forging, the dendrite structure is also destroyed, and a uniform structure is obtained by subsequent recrystallization annealing. But Vitalliu
In m, although there is numerical data on the improvement of the mechanical properties, sufficient knowledge has not been obtained on the relationship between the thermal history and the structure and the change in the mechanical properties associated with it. Therefore, despite the fact that Vitallium is a material that combines the advantages of both stainless steel with excellent workability and titanium alloy with excellent properties such as strength and corrosion resistance, the demand is only about 20% of the total. Low and not yet widely used.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem. The present invention provides high corrosion resistance and high resistance by increasing the amount of Mo and adjusting the structure by plastic working. An object of the present invention is to provide a bio-based Co-based alloy exhibiting abrasion properties.

In order to achieve the object, the Co-based alloy for living body of the present invention has a Cr content of 26 to 30% by mass and a Mo content of 6-1.
2% by mass, C: 0 to 0.3% by mass, the balance being substantially Co
And a structure in which a granular second phase is finely dispersed in a matrix composed of crystal grains having an average crystal grain size of 50 μm or less.

This Co-base alloy is quenched by casting a Co-base alloy having a predetermined composition using a water-cooled copper mold.
It is manufactured by forging at 000 to 1300 ° C.

[0009]

According to the present invention, by increasing the amount of Mo and adjusting the structure,
Improves the corrosion and abrasion resistance of Vitallium. The effect of Mo on corrosion resistance and abrasion resistance is Mo: 6% by mass.
Although it becomes remarkable above, it is saturated at 12% by mass and an excess amount of M
The o content adversely affects plastic workability. Cr is required to be 26% by mass or more to ensure corrosion resistance, but an excess amount exceeding 30% by mass adversely affects plastic workability. The C content added as necessary is regulated to 0.3% by mass or less from the viewpoint of abrasion resistance and plastic working.

In the microstructure adjustment, the growth of precipitates is suppressed by rapid cooling casting using a water-cooled copper mold, and the precipitates and the second phase such as intermetallic compounds are finely dispersed by plastic working such as high-temperature forging. I have. The effect of rapid cooling during casting on growth suppression of precipitates becomes significant when the temperature range from the casting temperature to 400 ° C. is cooled at a cooling rate of 1000 ° C./min or more. Further, the casting structure such as dendrite is destroyed by the high-temperature forging, and a matrix composed of equiaxed crystal grains refined to 50 μm or less is formed. Refinement of the matrix is also effective in improving abrasion resistance. However, if the Mo content is simply increased to 6% by mass or more, plastic workability such as forging is lost, so that a high Mo-Vitallium forged alloy cannot be produced.

High Mo-Vitall containing 6% by mass or more of Mo
In ium, a brittle intermetallic compound phase (σ phase) is generated from a temperature region around 700 ° C. to a low temperature side. Therefore, in the present invention, generation of the σ phase is prevented by selecting the heat treatment method and the processing temperature. Specifically, the Mo content is set to 6-1.
In the present system set to 2% by mass, the high temperature forging temperature is set in the range of 1100 to 1400 ° C. Even when bringing the high Mo-Vitallium forged at high temperature to room temperature, the σ phase is prevented by adopting rapid cooling such as water cooling, and the second phase does not grow and the matrix as a granular precipitate or crystallized substance is formed. Finely dispersed.

[0012]

Example 1 600 g of a Co-based alloy having the composition shown in Table 1 was melted in a high-frequency vacuum melting furnace, a molten metal at 15500 ° C. was poured into a water-cooled copper mold, and a cooling rate at which the temperature became 400 ° C. or less in 30 seconds ( (2300 ° C./min). Figure 1 shows the tensile properties of each as-cast material at room temperature.
Shown in In the Co-Cr-Mo ternary alloy, the elongation is improved as the amount of Mo added is increased. Nos. 4 and 5 to which Ni was added exhibited high elongation and ductility.

[0013]

FIG. 2 shows the result of investigation on the effect of heat treatment on the elongation and ductility of the alloy of Sample No. 1 which showed the smallest elongation and ductility in the as-cast state. 1 for comparison
The effect of heat treatment on the elongation and ductility of the same sample No. 1 whose structure was adjusted by high-temperature forging at 100 ° C. is also shown. As is clear from FIG. 2, the as-cast material and the as-quenched material (after aging at 1050 ° C. for 2 hours and then water-quenched) exhibited low elongation and ductility in the as-cast material without forging. Above all, the furnace cold material cooled after the aging treatment at 1050 ° C. showed extremely low elongation. Elongation was significantly improved by hot forging.

[0015] In order to investigate the reason why the elongation ductility differs between the As cast material and the furnace cold material, the respective metal structures were observed with an optical microscope. The As cast material (FIG. 3) had a metal structure in which Mo-rich bcc phase was precipitated in a granular form, while the σ phase grew linearly in the furnace cooling material (FIG. 4). Since the σ phase is a fragile precipitate that acts as a starting point of fracture, it is presumed that the σ phase is a cause of exhibiting low elongation and ductility in a tensile test. Further, in the high-temperature forged material exhibiting high elongation and ductility, the linear σ phase was not detected, and had a structure in which the granular bcc phase was finely dispersed.

From the relationship between the elongation and ductility and the metal structure, the increase of Mo is not a direct cause of impairing the high-temperature forgeability of the Co—Cr—Mo ternary alloy, but suppresses the precipitation of the σ phase.
When a forging temperature is set at 0 ° C. or higher (preferably 1100 ° C. or higher) and high temperature forging is performed, Co that exhibits excellent elongation and ductility is obtained.
It can be seen that a base alloy is obtained. Further, as the forging material, a material which is rapidly cooled and cast using a water-cooled copper mold to suppress precipitation of the σ phase is preferable. From the above results, it was confirmed that a Co-Cr-Mo ternary alloy having good elongation and ductility, in other words, good workability, can be obtained by controlling the casting conditions and the forging conditions. Therefore, Co-C shown in Table 2
An r-Mo ternary alloy was melted, and the effects of rapid casting and high temperature forging were investigated.

[0017]

Alloy Nos. 1 and 2 are 40
After quenching at a cooling rate of 0 ° C. or less, the ingot was heated to 1100 ° C. and forged at a high temperature. When the metal structures after forging were observed, it was found that each of them had an equiaxed crystal structure (FIGS. 5 and 6). Alloy No. No. 1 has an average crystal grain size of about 100 μm, 2 has an average crystal grain size of about 5
It was 0 μm. As a result of observing the structure of alloy No. 2, alloy N
In o.1, the second phase not detected was precipitated or crystallized along the grain boundaries. The precipitate or the crystallized product is considered to be a Mo-enriched phase having a crystal structure of bcc from the results of Thermo-Calc calculation phase diagram and EDS analysis. For alloy Nos. 3 and 4,
The heat treatment was performed at 1100 ° C. × 4 hours without forging the ingot. When the metal structure after the heat treatment was observed, a dendrite-like solidified structure was observed in each case (FIGS. 7 and 8).

Each alloy No. The surfaces of the test pieces cut out from Nos. 1 to 4 were finally polished and finished with a No. 4000 wrapping film, and then subjected to an abrasion test. In the abrasion test, a pin-on-flat type reciprocating motion abrasion tester using an alumina ball was used, and the atmosphere, the amplitude was 10 mm, and the sliding distance was 200,000 m.
m, the sliding speed was 8.33 Hz. As can be seen from the test results in FIG. 9, alloys Nos. 2 to 4 equivalent to Vitallium were much more excellent in wear resistance than alloy No. 1 equivalent to MP35N. From this, it can be said that adding Ni at a high concentration to the Co—Cr—Mo ternary composition is effective in terms of elongation and ductility, but is not advisable in securing high abrasion resistance.

FIG. 10 shows the results of a detailed investigation of the amount of wear of Vitallium equivalent alloys Nos. 2 to 4. Alloy No.4
Has the least amount of wear because it remains a solidified structure containing the largest amount of Mo. On the other hand, alloy No. 2 is Mo
Alloy No. 4 despite being the material with the lowest content
The amount of wear was almost the same as the above. Good abrasion resistance is the result of the fine structure of Alloy No. 2 being adjusted by high-temperature forging. That is, it is found that the wear resistance is improved by increasing the amount of Mo, but is further improved by finely adjusting the structure. Next, the crystal grain size of the forged material is changed by forging a Co-Cr-Mo ternary alloy at a high temperature under various forging conditions such as a forging temperature and a reduction ratio, and the crystal grain size is reduced by the amount of wear. The effects were investigated. FIG.
As a result, the wear resistance was improved by the refinement of the crystal grains, and the wear amount was remarkably reduced when the crystal grain size was 15 μm or less.

[0021]

Example 2 600 g of a Co-based alloy having the composition of alloy No. 3 in Table 2 was melted in a high-frequency vacuum melting furnace, and a molten metal at 1550 ° C. was poured into a water-cooled copper mold, and the cooling rate was the same as in Example 1. Quenched casting. The obtained ingot was clad with a hollow rod of SUS316L stainless steel, and 1100 to 1400
The structure was adjusted by high-temperature forging at ℃. By cladding with stainless steel, direct contact between the forging tool and the ingot was avoided, and the ingot during forging could be maintained at a high temperature of 1100 ° C. or higher. As a result, the precipitation of the σ phase during the high-temperature forging was prevented. High-temperature forging-1250 ° C. annealing was repeated until the wall thickness became 20 mm including the clad material, and finally water quenching was performed after annealing at 1250 ° C. × 2 hours.

Next, the forged material is cold-rolled to a thickness of 5 mm.
Was obtained. By immersing the cold-rolled material in a mixed acid of concentrated hydrochloric acid: concentrated nitric acid = 3: 1 (volume ratio), stainless steel on the surface of the cold-rolled material was removed by etching. 1250 ° C
After annealing for 1 hour and water quenching, a sheet material having a thickness of 50 μm was manufactured by cold rolling again. From the manufacturing results, the Co-based alloy of the present invention makes use of good workability,
It turns out that it can be molded into a shape suitable for various artificial aggregates.

[0023]

As described above, the Co-based alloy for living body according to the present invention has a high Mo content of 6 to 12% by mass, and a fine phase dispersion of the second phase by quenching casting.
The crystal structure is refined by high-temperature forging that suppresses the formation of phases. This further improves wear resistance, and Vitall
It is used as a material for living organisms utilizing the original excellent properties of ium.

[Brief description of the drawings]

FIG. 1 is a graph showing strain-stress curves of various Co-based alloys.

FIG. 2 is a graph showing the effect of manufacturing conditions on the strain-stress curve of a Co-based alloy.

FIG. 3 is a photograph showing the metal structure of a Co-based alloy as cast material.

FIG. 4 is a photograph showing a metal structure of a cold material of a Co-based alloy furnace.

FIG. 5 is a photograph showing the metal structure of alloy No. 1 high-temperature forged material used in the examples.

FIG. 6 is a photograph showing the metallographic structure of alloy No. 2 high-temperature forged material used in Examples.

FIG. 7 is a photograph showing the metallographic structure of the heat-treated alloy No. 3 used in the examples.

FIG. 8 is a photograph showing a metal structure of a heat-treated alloy No. 4 used in Examples.

FIG. 9 is a graph showing wear characteristics of various Co-based alloys.

FIG. 10 is a graph showing wear characteristics of various Co-based alloys.

FIG. 11 is a graph showing the effect of the crystal grain size on the wear resistance of a Co-based alloy forged material.

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Claims (2)

[Claims] 1. Cr: 26 to 30% by mass, Mo: 6-1.
2% by mass, C: 0 to 0.3% by mass, the balance being substantially Co
A Co-based alloy for a living body, characterized by having a structure in which a granular second phase is finely dispersed in a matrix composed of crystal grains having an average crystal grain size of 50 μm or less. 2. A Co-based alloy having the composition according to claim 1 is rapidly quenched and cast using a water-cooled copper mold.
Production of a Co-based alloy for a living body characterized in that by forging at 00 to 1300 ° C., a structure in which a granular second phase is finely dispersed in a matrix having an average crystal grain size of 50 μm or less is finely dispersed. Method.