JP3265463B2 - Method for producing Ti sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for manufacturing a Ti component having light weight, high strength and high corrosion resistance, and more particularly to a method for manufacturing a Ti sintered body using Ti powder as a raw material. When sintering a compact made of Ti powder in a carbon furnace, carbides are not generated on the surface of the sintered body, and Ti sintering that enables to obtain a Ti sintered body having excellent room temperature tensile strength and elongation at break It relates to a method for producing a body.

[0002]

2. Description of the Related Art Since Ti has excellent characteristics of light weight, high strength and high corrosion resistance, it is expected to be used in place of iron-based materials in the fields of space and aviation equipment, transportation equipment, and chemical plants. In addition, because of its excellent biocompatibility, it is also being used in the medical field and in the field of ornaments such as watches. Conventionally, the method for producing Ti components has mainly been a melting casting method, but has high activity at high temperatures and has many technical difficulties. Further, since Ti is a difficult-to-process material, it is difficult to manufacture parts by machining.

[0003] In order to overcome the high activity and difficult workability of Ti, research and development of Ti forming technology by powder metallurgy have been advanced. The advantages of the powder metallurgy method are that it is easy to handle because it is sintered at a temperature equal to or lower than the melting point of Ti, so-called near-net shape molding with less post-processing after molding, and that the crystal grains are fine. Therefore, the mechanical properties are excellent. Among powder metallurgy methods, a metal powder injection molding method has recently attracted attention as a technique for mass-producing complicated-shaped parts. In this molding method, an organic binder such as a wax or a thermoplastic resin is added to a metal powder as a raw material in an amount of about 30 to 50% (volume ratio) to produce a compound. It is injected into a mold at high speed and high pressure to obtain a molded body (green body). After removing most of the organic binder contained in the compact by some method, the compact is sintered at a high temperature to obtain a target sintered body.

[0004] In order to obtain a Ti sintered body having good mechanical properties by powder metallurgy, it is necessary to suppress the amount of oxygen contained in Ti. When the oxygen content increases (0.4 wt% or more), a so-called embrittlement phenomenon in which ductility at room temperature decreases is exhibited. In particular, the higher the temperature of Ti, the higher the activity becomes. Even in a vacuum, the tendency of picking up a trace amount of oxygen increases. Therefore, the higher the sintering temperature, the more strictly the sintering atmosphere is desired. . Therefore, as a method for solving this problem, a getter that preferentially picks up oxygen in a sintering container is used.
A method of adding metal and sintering is disclosed (Japanese Unexamined Patent Publication No.
-330105).

Attention must also be paid to the material of the furnace used when sintering Ti powder. If a carbon furnace, which is often used as a vacuum furnace or an atmosphere furnace, is used, the surface of the sintered body may react with carbon to form carbides. Metal materials such as molybdenum and tungsten are often used.

[0006]

SUMMARY OF THE INVENTION In a vacuum sintering furnace using carbon as a furnace body and a heating element, the present invention minimizes the penetration of carbon from the furnace body and the heating element when sintering Ti. It is an object of the present invention to provide a method for producing a Ti sintered body that does not generate carbide on the surface of the sintered body and has excellent mechanical properties.

[0007]

According to the sintering method of the present invention, a compact made of fine Ti powder having an average particle size of 15 μm or less is buried in a ceramic powder, which is inserted into a dense container. Insert into a large, tight container.
In addition, the space between the two containers is filled with ceramic powder.
This double vessel is inserted into a carbon furnace, heated in a vacuum of 1 × 10 ⁻⁴ Torr or less, and sintered at a temperature of 1050 ° C. or less. In a preferred embodiment of the present invention, the above-described method for producing a Ti sintered body in which the ceramic powder is alumina (Al ₂ O ₃ ) and the dense container is an alumina container.

[0008]

In the above invention, the effect of preventing carbon from being mixed in from the heating element and the furnace body can be expected by the dense sintering container, the ceramic powder between them, and the ceramic powder covering the compact. In addition, the ceramic powder covering the molded body is expected to have not only this effect but also an effect of obtaining a sintered body with less deformation by equalizing the heat distribution around the molded body.

The finer the ceramic powder used for filling the compact and the ceramic powder covering the gap between the containers, the greater the effect of blocking carbon, but if it is too fine, it may penetrate into the compact. It is desirable to be within the range. The material of the powder is preferably oxide alumina (Al ₂ O ₃ ), which is stable even at a high temperature and is inexpensive and easily available. In addition, zirconia (Zr
O ₂ ) and yttria (Y ₂ O ₃ ). The sintering container is preferably dense and heat-resistant. Suitable materials for the container include, for example, ceramic materials such as alumina, and high melting point metal materials such as molybdenum and tungsten. Sintering temperature 1
The reason for setting the temperature at 050 ° C. or lower is to prevent the crystal grains of the sintered body from being coarsened by the high-temperature sintering and to avoid the reaction between Ti and the atmosphere gas as much as possible. If it exceeds 1050 ° C., it becomes liable to be contaminated by a decomposition gas from a furnace body deposit or the like or a trace amount of oxygen. T as raw material
Since the i-powder has a low sintering temperature of 1050 ° C. or less, the average particle diameter is set to 15 μm or less in consideration of the improvement in density after sintering. Preferably, the average particle size is 10 μm or less. However, when it is too fine, there is a concern that the amount of oxygen and the amount of the organic binder required due to an increase in the specific surface area of the powder may increase. If it exceeds 15 μm, it will not be sufficiently densified at a sintering temperature of 1050 ° C. or less. The oxygen content of the Ti powder is desirably 0.25 wt% or less. The production method of the Ti powder raw material is not particularly limited, such as gas atomized powder, hydrodehydrogenation (HDH) powder and the like. The molded body made of the fine Ti powder is produced by, for example, a method of producing a green body by injection molding, a CIP method (cold isostatic pressing method), a dry pressing method, or the like. As an organic binder,
A wax-based, thermoplastic resin-based, or a mixture thereof, or a water-based material suitable for a molding method can be used as appropriate. In addition, if a large amount of an organic binder used for molding the Ti powder is present during sintering, carbides are formed inside after sintering, so it is necessary to sufficiently degrease before sintering. . The organic binder is, for example, while flowing Ar gas the molded body at 10 ⁰ Torr stand vacuum and heated to 380 ° C., degreasing, removal. The molded body is buried in ceramic powder, inserted into a dense container, the container is inserted into a larger and dense container, and the space between the two containers is filled with ceramic powder, and the double container (FIG. 1) is inserted into a carbon furnace, but the steps, the form of the double vessel, the amount of ceramic powder, and the like are not particularly limited. As the sintering method,
1 × 10 ⁻⁴ Torr or less, preferably 5 × 10 ⁻⁵ Torr
1050 ° C. or less, preferably 1025 ° C. or less in a vacuum of r or less
A method of heating at a temperature of ９950 ° C. for 1 to 2 hours is employed.

[0010]

Next, the present invention will be specifically described based on embodiments. (Example) To a Ti powder having an average particle diameter of 13 μm (32 μm or less, oxygen content: 0.15 wt%), 9.67 wt% of an organic binder composed of a wax and a thermoplastic resin was added, and a tensile test piece shape (110 mm × 7.5mm × 4m
m) to produce a green body. After removal of 90%, - the grease - the emission body is degreased by heating to 380 ° C. in 10 ⁰ Torr stand vacuum, an organic binder
In the sintering method shown in FIG. 1 of the present invention, alumina (Al ₂ O ₃ ) is used for both the ceramic powder and the container, and the above sample 3 is buried in alumina powder 2 having an average particle size of 30 μm. This alumina container is inserted into a larger alumina container 1, and the gap between the two alumina containers is filled with alumina powder 2, and the double container is inserted into a carbon furnace, and is placed in a vacuum of 10 ^-5 Torr. 1025
Sintered at 2 ° C. for 2 hours. As the evaluation of the obtained sintered body, quantitative analysis of oxygen, analysis of carbide on the surface, measurement of density by a water Archimedes method, and tensile strength test at room temperature were performed.

(Comparative Example 1) A sample was prepared using the same powder and molding method as in the example, and the sample was prepared in a vacuum of 10 ^-5 Torr.
Sintered at 100 ° C. for 2 hours.

Comparative Example 2 The same organic binder as in Example 1 was added to Ti powder (45 μm or less, oxygen content: 0.12 wt%) having an average particle diameter of 23 μm in an amount of 9.42 wt%, and the same method as in Example was used. A molded body was prepared and sintered at 1025 ° C. for 2 hours in a vacuum of the order of 10 ⁻⁵ Torr in the sintering method shown in FIG.

(Comparative Example 3) A molded body was prepared by the same powder and molding method as in Comparative Example 2, and a thin alumina powder was spread in a dense alumina container (FIG. 2).
It was sintered at 1025 ° C. for 2 hours in a vacuum of the order of 0 ⁻⁵ Torr.

(Comparative Example 4) A compact was prepared by the same powder and molding method as in Comparative Example 2, and the compact was buried in dense alumina powder and placed in a dense alumina container (FIG. 3).
Sintered at 1025 ° C. for 2 hours in a vacuum of ⁻⁵ Torr.

Table 1 shows various characteristics of the Ti sintered bodies according to these examples and comparative examples.

[0016]

[Table 1]

From the results shown in Table 1, the Ti sintered bodies (Examples) sintered by the sintering method of the present invention and Comparative Examples 1 and 2 were observed by X-ray diffraction (XRD). No carbides were observed on the surface, but carbides (TiC) were remarkably observed on the surface of the sintered body of Comparative Example 3 sintered without being embedded in the alumina powder. Also, in the sintered body according to Comparative Example 4, some carbide was generated. Comparative Example 1 in which the sintered body of the example had a small amount of oxygen but was sintered at a higher temperature than the example.
The sintered body of No. 1 has an increased oxygen content and a reduced elongation at break.
The sintered body of Comparative Example 2 using the Ti raw material powder having a larger particle diameter than the example has a low relative density and a low maximum tensile strength. In the Ti sintered body according to the example, the increase in the amount of oxygen was small, and the relative density showed a value (94% or more) sufficient to eliminate through-pores entering from the surface of the sintered body to the inside. In both cases, good values were obtained. In Comparative Example 3 in which sintering was not performed with the alumina powder, arched warpage was observed, but in the sintered body according to the example, deformation such as warpage was hardly observed.

[0018]

According to the present invention, when a Ti compact produced by a metal powder injection molding method or the like is sintered in a carbon furnace, no carbide is generated on the surface of the sintered compact and the tensile strength at room temperature is obtained. And it became possible to obtain the Ti sintered compact excellent in breaking elongation.

[Brief description of the drawings]

FIG. 1 is a schematic view of a sintering method showing one embodiment of the present invention.

FIG. 2 is a schematic view of a sintering method of Comparative Example 3.

FIG. 3 is a schematic view of a sintering method of Comparative Example 4.

FIG. 4 is an X-ray diffraction curve of the surface of a sintered body of an example, comparative examples 3 and 4.

[Explanation of symbols]

 1. Alumina container for sintering 2. 2. Alumina powder for sintering Sample to be sintered

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-21704 (JP, A) JP-A-2-54735 (JP, A) JP-A-6-330105 (JP, A) JP-A-3- 267306 (JP, A) Japanese Utility Model Showa 57-138942 (JP, U)

Claims (2)

(57) [Claims] 1. When a compact made of Ti powder is sintered in a carbon furnace, no carbide is generated on the surface of the sintered body, and a dense Ti sintered body having excellent room-temperature tensile strength and breaking elongation is produced.
A fine Ti having an average particle size of 15 μm or less.
A powder compact is converted to alumina, zirconia or yttria
Embedded in a ceramic powder having an average particle size of 10 to 50 μm selected from a) , inserted into a dense container, inserted this container into a larger and denser container, and placed the ceramic powder in the space between the two containers. After filling, insert the double container into a carbon furnace and place it in a vacuum of 1 × 10 ⁻⁴ Torr or less.
A method for producing a Ti sintered body, comprising sintering at a temperature of 050 ° C. or lower. 2. The ceramic powder is alumina (Al ₂ O).
₃ ), wherein the dense container is an alumina container.
A method for producing a Ti sintered body as described in the above.