JPH04143258A - Method for surface reformation of titanium alloy and artificial bone implant made of titanium alloy - Google Patents

Abstract

PURPOSE:To reform the surface of an alpha+beta-type Ti alloy obtd. by powder molding to have excellent fatigue strength with fine metal structure by irradiating the surface of the alloy with a high density energy beam to heat the surface to a specified temp. range and to form a fine metal structure. CONSTITUTION:The surface of an alpha+beta-type Ti alloy obtd. by powder molding or further treated with HIP treatment is irradiated with a high density energy beam such as CO2 laser light, electron beam, etc., to heat the surface to the temp. range between the lower limit of alpha' phase generation and the melting point. Then the alloy is rapidly cooled. The structure of beta phase formed during irradiation changes into a single alpha' or alpha'+alpha phase fine needlelike structure, which gives almost equal fatigue strength to a rolled or forged material. By adopting this method for a Ti-alloy artificial bone implant at the position where tensile stress is repeatedly generated, the optimum material as the artificial bone material can be obtained while maintaining the characteristics of Ti alloy such as high fatigue strength and excellent corrosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for modifying a titanium alloy to improve its surface strength, and to an artificial bone implant made of a titanium alloy with improved surface strength.

BACKGROUND OF THE INVENTION Materials used as implants for artificial bones are required to have corrosion resistance and strength, and α+β type titanium alloys are most suitable in this respect. However, titanium alloys have the disadvantage of poor machinability such as machinability and forgeability, so when manufacturing, the best method is to form them into a semi-finished product that is as close to the finished product as possible to minimize the machining allowance. One such molding method is the powder molding method. In this powder compacting method, the powder is first shaped into the above-mentioned semi-finished product using a cold isostatic pressure press (CIP) or a mold press, and then 1.
S INTE is sintered at a temperature of around 300'C, then heated and pressurized to about 950°C using a hot isostatic press called HIP treatment to remove internal pores, and then slowly aged.
There is a method called the R&HIP method, and a method called the CAPSUL method, in which powder is filled into a suitable vacuum-sealed container and immediately subjected to HIP treatment, thereby performing sintering and HIP simultaneously. The α+β type refers to a state in which the α phase and β phase coexist in the metal structure, but when such sintering or HIP treatment is performed, the α structure expands during aging and the crystal grains increase in general, resulting in tensile and other It has the disadvantage of reduced fatigue strength. In other words, when a titanium alloy is heated to a high temperature, it becomes a β structure above a certain temperature as shown in Figure 7.
Thereafter, as it ages, α crystal grains form and expand, resulting in an overall coarse structure, which has the disadvantage of lower fatigue strength than rolled or forged materials. Recent research has shown that titanium alloys with an equiaxed structure consisting of fine grains have the highest fatigue strength, and titanium alloys with an acicular structure consisting of fine grains also have high fatigue strength.

Therefore, a method that has recently been developed to eliminate these drawbacks of HIP treatment and improve fatigue strength is BU.
There is something called the S method. In this method, a titanium alloy subjected to HIP treatment is quenched from the β single phase region and then heated to the α+β two phase region, thereby obtaining an overall fine two-phase texture. Other processing methods such as TCT processing have also been developed.

Problems to be Solved by the Invention However, such BUS processing and other methods require high vacuum (10-' to 10-'
It is necessary to perform heating and hardening in a chamber of 100 mm or more, which has the disadvantage of increasing costs due to the technical difficulties of equipment and equipment.

The present invention provides a method for modifying the surface of a titanium alloy subjected to HIP treatment, in which a fine metal structure can be obtained and has excellent fatigue strength, and an artificial bone implant that also has excellent fatigue strength. The purpose is to

Means for Solving the Problems In order to solve the above problems, the method of the present invention irradiates the surface of a powder-formed α+β type titanium alloy with a high-density energy beam, and Characterized by heating to a temperature range.

That is, in this invention, in a method of forming a titanium alloy material to a state close to a finished product using a powder forming method, the formed titanium alloy material is heated to a temperature higher than the α' phase formation by utilizing the rapid heating and cooling effect of a high-density energy beam. The solution treatment is performed to modify the structure into a fine structure. In this case, specifically, the lower limit temperature for α' phase formation is 800°C. Examples of such a high-density energy beam include a carbon dioxide gas laser electron beam, which is used to irradiate a required portion of the titanium alloy. Since it is a high-density energy beam, the irradiated area is rapidly heated locally and reaches a high temperature, and there is a large temperature difference with the surrounding area, so after the irradiation is stopped, it is rapidly cooled without using cold water. become. As a result of this rapid cooling, the structure that had become a β phase during irradiation becomes a fine acicular structure consisting of a single α′ phase (this is martensite) or an α′+α phase, resulting in a rolled/forged material. Almost the same fatigue strength can be obtained.

In addition, this high-density energy beam irradiation is performed in an inert gas atmosphere such as argon gas or helium gas to prevent surface contamination due to oxidation, but unlike BUS processing, heating and cooling in a vacuum furnace is necessary. Since there is no need to do
It can be easily implemented.

Furthermore, the irradiation with the high-density energy beam is performed after performing the same HIP treatment as in the conventional method, but the α+β type titanium alloy obtained by this HIP treatment has a temperature range above the α' phase formation lower limit temperature and below the melting point. By rapidly heating the material and rapidly cooling it as described above, a fine acicular structure consisting of a single α' phase is obtained, which exhibits excellent fatigue strength. Similarly, high-density energy beam irradiation can be applied to areas where repetitive tensile stress occurs and is at risk of fatigue failure, thereby improving the fatigue strength of those areas and preventing failure. can. From the standpoint of efficiency, it is preferable and possible to perform the treatment locally.

In this invention, the HIP treatment refers to S
This includes those obtained by the R&HIF method and those obtained by filling powder into a vacuum container and immediately HIPing.

Next, the artificial bone implant of the present invention for solving the above-mentioned problems is characterized in that a high-density energy beam is irradiated to a region of the implant where repeated tensile stress occurs.

For example, as shown in FIGS. 1 and 2, in the case of a femoral implant 1 that is repeatedly loaded in the direction of arrow A, the site where this repeated tensile stress occurs may be the outer surface 2 on the intercapsular side. By irradiating a high-density energy beam over a certain range in the vertical direction of this region, an implant material with improved tensile fatigue strength only in the necessary region can be obtained.

Of course, this implant was also subjected to HIP treatment after or at the same time as powder molding as described above.
Implants with such α+β type tissue are rapidly heated by irradiating them with a high-density energy beam in the above temperature range,
By rapid cooling, a fine single α' phase or α'+α phase is formed at the irradiated site, as described above.

In addition, 3 in FIG. 1 is a femur, and the implant 1 of the present invention is inserted and attached to the upper end of the femur, and furthermore,
A femoral head ball 4 for attachment to the hip bone is attached to the upper end of the implant 1, and the above-mentioned repeated load is applied to the top of the femoral head ball 4.

As shown in Fig. 3, the implant 1 thus obtained has a surface layer in the area irradiated with the high-density energy beam that has a fine single α' phase structure or an α'+α phase structure, and the base material (consisting of α+β phase), an α′+α phase structure in which α phase gradually increases is formed.

EXAMPLE An implant having the same shape as shown in Fig. 1 above was manufactured by powder molding, and after being subjected to 5INTER & HIP treatment, it was applied to the above-mentioned region using the apparatus shown in Fig. 4 using a carbon dioxide laser as a high-density energy beam. Irradiation was performed while scanning the area in the vertical direction. At the same time, we compared the actual fatigue strength of three materials: one that had just undergone HIP treatment, a forged material that had been solution-treated (quenched), and one that had been irradiated with the high-density energy beam of this invention.The results are shown in the table below. It was found that the material of the present invention had the best fatigue strength and was at least comparable to forged material. In addition, the fatigue strength evaluation test in this case is based on the ISO proposal (ISO
/TC150/5C4) j: Complied.

Note that the irradiation conditions of the carbon dioxide laser are as follows.

Optical system used: Two-line beam irradiation power: 690 W (irradiation position) Scanning speed:
0.15ca+/s Irradiation distance: 657mm (second mirror) Assist gas:
High purity argon (35J,/rnin) coating material: colloidal graphite irradiation beam shape (width 1x
Thickness b): 18.6mm x 1.6mm Figure 5 shows:
This is a 200x microscopic photograph of the relevant part after high-density energy beam irradiation obtained in the above example, and is the 6th! ! I is a 100x micrograph after SINTER&HIP treatment. As can be seen from these figures, the material that has only been subjected to HIP treatment has a coarse acicular structure with black β phase interposed between the bamboo-like α phase, but the material of the present invention has a coarse acicular structure with black β phase interposed between the bamboo-like α phase. It can be seen that the metal structure is one-α′ phase gold.

Effects of the Invention As described above, according to the present invention, even an acicular structure can be modified into a fine single α′ phase or α′+α phase structure by irradiation with a high-density energy beam. This has the effect of producing a titanium alloy material with excellent fatigue strength that is almost comparable to forged material. Moreover, unlike BUS processing, expensive large-scale equipment such as vacuum hardening IIIWl is not required, and the process can be carried out at low cost. Furthermore, the implant of this invention makes use of the characteristics of titanium alloy, which has high fatigue strength and excellent corrosion resistance, and is optimal as an artificial bone material, and furthermore, strength can be improved only in the necessary areas. Therefore, the most preferable material can be selected depending on the purpose, and since there is no need to perform treatment on the entire area, irradiation time can be saved and implementation can be carried out at lower cost.

[Brief explanation of drawings]

1111! I is a side view of the implant of this invention, Fig. 2 is a cross-sectional view, and Fig. 31! I is an enlarged cross-sectional view of the beam irradiation area, FIG. 4 is a perspective view of the laser irradiation device used in the example, and FIG. Micrograph, Figure 6 shows 100% of the implant after HIP treatment.
7th magnification micrograph! ! I is a schematic diagram of titanium alloy Ml! It is I. 1... Implant, 2... Tensile stress generation site, 3
...femur. Patent Applicant Yanmar Diesel Co., Ltd. Agent Patent Attorney Hisashi Tarumoto Figure 2 Figure 3 - c /,') Procedural amendment (method) % formula % Relationship with the title of invention case

Claims (5)

[Claims] 1. A method for surface modification of a titanium alloy, which comprises irradiating the surface of a powder-molded α+β type titanium alloy with a high-density energy beam and heating it to a temperature range above the α′ phase formation minimum temperature and below the melting point. 2. A high-density energy beam is irradiated onto the surface of an α+β type titanium alloy that has been HIP-treated after powder compaction or simultaneously with compaction, and is heated to a temperature range above the α′ phase generation lower limit temperature and below the melting point to form fine single particles. A method for surface modification of titanium alloy, characterized by forming an α' phase or an α'+α phase. 3. An artificial bone implant made of a powder-molded α+β type titanium alloy, characterized in that a high-density energy beam is irradiated to a region where repeated tensile stress occurs. 4. α HIP treated after powder molding or at the same time as molding
A titanium alloy artificial bone implant for a femur made of a +β-type titanium alloy, characterized in that a high-density energy beam is irradiated on the outer surface of the opposite groin side where repeated tensile stress occurs. 5. An artificial bone implant for a femur made of an α+β type titanium alloy subjected to HIP treatment after powder molding,
A high-density energy beam is irradiated on the outer surface of the opposite groin side where repeated tensile stress occurs, and a fine single α′ phase or α
A titanium alloy artificial bone implant characterized by forming a '+α phase.