JPH089742B2 - Method for producing high strength and high ductility TiAl-based intermetallic compound - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a TiAl-based intermetallic compound having a high level of mechanical strength and ductility.

[0002]

2. Description of the Related Art Since TiAl-based intermetallic compounds are lightweight and have excellent high-temperature strength, they are expected to be useful in fields of application as heat-resistant members such as internal combustion engines. However, this material is not yet in the stage of practical application due to its poor ductility at room temperature and the difficulty in processing which makes the material difficult.

As for the improvement of the room temperature ductility, there have been proposed measures for improving the ductility of TiAl by adding components such as Mn and Cr to the TiAl by the melting method or refining the crystal grains. Among them, the refining of TiAl crystal grains is performed by isothermal forging, but in this case, not only ductility but also TiA
It has been elucidated that the strength characteristics of l also depend on the grain size of the refined crystal [Scripta Metall., 21 (1989) p467].
That is, it is expected that both the ductility and the strength are improved by reducing the crystal grain size of TiAl.

On the other hand, synthesis of a TiAl intermetallic compound by reaction sintering is carried out by mixing Al and Ti powders and densifying by molding as described in Japanese Patent Publication No. 1-30898, and then TiAl. The dense body is subjected to HIP (hot isostatic pressing) treatment at 400 to 1400 ° C. so as to form an intermetallic compound, and according to this method, in a dense mixed state before reaction synthesis, a near n
Since it can be formed into an et shape, it is possible to greatly improve the processability. However, this method has a drawback in that the room temperature ductility of the material is not sufficiently improved.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of multifaceted research on material properties for improving the ductility of TiAl obtained by reaction sintering and manufacturing conditions for obtaining the properties. The purpose is Ti by the reaction sintering method, which has both high strength and high ductility characteristics.
It is to provide a method for producing an Al-based intermetallic compound.

[0006]

A method for producing a high-strength and high-ductility TiAl-based intermetallic compound according to the present invention for achieving the above object is to use a mixed material of Ti and Al in the range of 400 to 1400.
In a method of producing a TiAl-based intermetallic compound by hot isostatic pressing and reaction sintering in a temperature range of ° C, a Ti powder and an Al powder are mixed so that the composition of Al is 40 to 50 at% and the balance is Ti. Then, hot extrusion and cold working with a total working degree of 25 or more are performed to form a dense mixed material, and then the mixed material is subjected to reaction sintering to form a TiAl-based intermetallic compound, and an average A structural feature is that a high-strength and high-ductility TiAl-based intermetallic compound having a crystal grain size of 30 μm or less is obtained.

Generally, a TiAl-based intermetallic compound is Ti
The powder and Al or Al alloy powder are mixed with necessary metal components, compression-molded and degassed, and then hot-pressed using a HIP (hot isostatic pressure) device for reaction sintering. It is synthesized by the method. The TiAl-based intermetallic compound constituting the present invention is a dense mixture of Ti and Al obtained by inserting a means for vacuum-sealing the mixture into an aluminum alloy container after the degassing treatment in the above step and performing hot extrusion and cold working. It is synthesized by forming various mixed materials and subjecting the densified mixed material to reaction sintering. The densified mixed material has a high workability and functions to reduce the crystal grain size after reaction sintering.

The first property requirement of the present invention is to set the average crystal grain size of the TiAl intermetallic compound to 30 μm or less, so that it is not possible to improve strength and ductility at the same time when the average crystal grain size exceeds 30 μm. It will be possible. Thus, in order to adjust the average crystal grain size after reaction sintering to 30 μm or less, the total workability of the dense Ti and Al mixed material is 25
The above is an effective means. In the present invention, the total workability means the extrusion workability (cross-sectional area before extrusion / cross-section after extrusion) and cold workability (cross-sectional area before cold working / cross-sectional area after cold working). ) (Hereinafter the same).

The second property requirement of the present invention is that the composition of the TiAl-based intermetallic compound is Al 40 to 50 at% and the balance is Ti.
It is to consist of. If the Al component is out of the above range, the effect of improving ductility cannot be sufficiently achieved.

The inclusion of Mn as the third component in the above-mentioned composition has the effect of suppressing the phenomenon of pores occurring during the reaction sintering process. Suitable Mn content is 0.05-10 at
%, If it is less than 0.05 at%, the above-mentioned pore suppressing effect is not effectively exerted, and if it exceeds 10 at%, the ductility is greatly reduced, resulting in an inconvenient result.

[0011]

Since the TiAl-based intermetallic compound according to the present invention has the above-mentioned constitution and function, by using a dense mixed material of Ti and Al as the reaction sintering raw material, the total workability is enhanced and the average crystal grain size is 30 μm. It is refined to the following, and the component composition is Al40
The mechanical properties and ductility of the material can be improved at the same time by the action of the texture property in which the balance is Ti in the range of -50 at%.

[0012]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 A Ti powder having an average particle size of 70 μm and an Al-based powder having an average particle size of 75 μm were mixed so that the composition of Al was 48.5 at% and the balance was Ti, and the mixture was subjected to CIP (cold isostatic pressure) molding and then removed. Qi treatment. Then, the aluminum alloy can was vacuum-sealed, and hot extrusion and cold working were performed as it was to form a dense mixed material. The extrusion processing degree at this time is 15,
The cold workability was 20 and the total workability was 300.

Next, the mixed material is heated to a temperature of 1300 ° C. and a pressure of 152 GP.
A HIP (hot isostatic pressure) treatment was performed under conditions of a time of 2 hrs. and reaction sintering was performed to synthesize a TiAl-based intermetallic compound. The average crystal grain size of the obtained TiAl-based intermetallic compound was measured, and the room temperature tensile strength and elongation properties of the material were also tested. The results are shown in Table 1 in comparison with the component composition.

Example 2 Ti powder having an average particle size of 70 μm, Al-based powder having an average particle size of 75 μm, and Mn powder were mixed so that the composition of Al was 48.5 at%, Mn was 1.5 at%, and the balance was Ti. Otherwise, the same steps and conditions as in Example 1 were applied to Ti
An Al-based intermetallic compound was obtained. In this case, the extrusion workability was 35, the cold workability was 10, and the total workability was 350. The average crystal grain size, normal temperature tensile strength and elongation property of the obtained TiAl intermetallic compound are also shown in Table 1.

Example 3 Ti powder having an average particle size of 50 μm, Al-based powder having an average particle size of 60 μm, and Mn powder were mixed so that the composition of Al was 48.5 at%, Mn was 1.5 at%, and the balance was Ti. Otherwise, the same steps and conditions as in Example 1 were applied to Ti
An Al-based intermetallic compound was obtained. In this case, the extrusion workability was 9, the cold workability was 20, and the total workability was 180. Average crystal grain size of the obtained TiAl-based intermetallic compound,
The normal temperature tensile strength and elongation properties are also shown in Table 1.

Example 4 Ti powder having an average particle size of 40 μm, Al-based powder having an average particle size of 35 μm, and Mn powder were mixed so that the composition of Al was 45.5 at%, Mn was 3.5 at%, and the balance was Ti. Otherwise, the same steps and conditions as in Example 1 were applied to Ti
An Al-based intermetallic compound was obtained. In this case, the extrusion workability was 9, the cold workability was 20, and the total workability was 180. Average crystal grain size of the obtained TiAl-based intermetallic compound,
The normal temperature tensile strength and elongation properties are also shown in Table 1.

Example 5 A Ti powder having an average particle size of 75 μm, an Al-based powder having an average particle size of 72 μm, and a Mn powder were mixed so that the composition of Al was 48.5 at%, Mn was 1.5 at%, and the balance was Ti. Otherwise, the same steps and conditions as in Example 1 were applied to Ti
An Al-based intermetallic compound was obtained. In this case, the extrusion processability was 7, the cold workability was 5, and the total workability was 35. The average crystal grain size, normal temperature tensile strength and elongation property of the obtained TiAl-based intermetallic compound are also shown in Table 1.

Comparative Example 1 Ti powder having an average particle size of 50 μm, Al-based powder having an average particle size of 60 μm, and Mn powder were mixed so that the composition of Al was 48.5 at%, Mn was 1.5 at%, and the balance was Ti. This mixture was subjected to reaction sintering under the same conditions as in Example 1 to obtain a TiAl-based intermetallic compound. In this case, the extrusion workability was 5, the cold workability was 2, and the total workability was 10. The average crystal grain size, normal temperature tensile strength and elongation property of the obtained TiAl-based intermetallic compound are also shown in Table 1.

Comparative Example 2 Ti powder having an average particle size of 70 μm, Al-based powder having an average particle size of 75 μm, and Mn powder were mixed so that the composition of Al was 38.0 at%, Mn was 1.0 at%, and the balance was Ti. Otherwise, the same steps and conditions as in Example 1 were applied to Ti
An Al-based intermetallic compound was obtained. In this case, the extrusion processing degree is 1
5, the cold workability was 20, and the total workability was 300.
The average crystal grain size, normal temperature tensile strength and elongation property of the obtained TiAl intermetallic compound are also shown in Table 1.

Comparative Example 3 Ti powder having an average particle size of 70 μm, Al-based powder having an average particle size of 75 μm, and Mn powder were mixed so that the composition was 52.0 at% Al, 2.5 at% Mn, and the balance Ti. Otherwise, the same steps and conditions as in Example 1 were applied to Ti
An Al-based intermetallic compound was obtained. The extrusion processability in this case is 3
5, the cold workability was 10, and the total workability was 350.
Table 1 shows the average crystal grain size, normal temperature tensile strength and elongation properties of the obtained TiAl-based intermetallic compound.

Comparative Example 4 Ti powder having an average particle size of 60 μm and Al having an average particle size of 65 μm so as to have a composition of Al 48.0 at%, Mn 12.5 at% and the balance Ti.
The system powder and the Mn powder were mixed. Otherwise, the same steps and conditions as in Example 1 were applied to obtain a TiAl-based intermetallic compound. Table 1 shows the average crystal grain size, normal temperature tensile strength and elongation properties of the obtained TiAl-based intermetallic compound.

[0022]

From the results shown in Table 1, it is recognized that all the examples satisfying the property requirements of the present invention have high tensile strength and elongation, and have both high strength and high ductility. On the other hand, in Comparative Example 1 in which the average crystal grain size exceeds 30 μm because the mixture material raw material is not densified, Al
Comparative Example 2 in which the component is less than 40 at% and Comparative Example 3 in which the Al component exceeds 50 at% have low tensile strength and elongation properties. Further, it is found that in Comparative Example 4 in which the added content of Mn exceeds 10 at%, the strength and the elongation are reduced.

[0024]

As described above, the TiAl-based intermetallic compound of the reaction sintering method provided by the present invention has effectively improved ductility while maintaining excellent mechanical strength. Therefore, T with high strength and high ductility, which is useful as a heat resistant member
Since it is extremely advantageous to produce and supply the iAl-based intermetallic compound by using the reaction sintering method, a high industrial advantage is brought about.

Claims (2)

[Claims] 1. A mixed material of Ti and Al is 400 to 1400.
In a method of producing a TiAl-based intermetallic compound by hot isostatic pressing and reaction sintering in a temperature range of ° C, a Ti powder and an Al powder are mixed so that the composition of Al is 40 to 50 at% and the balance is Ti. Then, hot extrusion and cold working with a total working degree of 25 or more are performed to form a dense mixed material, and the mixed material is reacted and sintered so as to form a TiAl-based intermetallic compound, and then averaged. A high-strength and high-ductility TiAl-based intermetallic compound having a crystal grain size of 30 μm or less is obtained. However, the total workability is the product of the extrusion workability (cross-sectional area before extrusion / cross-section after extrusion) and cold workability (cross-sectional area before cold working / cross-sectional area after cold working). Say. 2. The high strength and high ductility TiA according to claim 1, wherein the mixed material contains Mn 0.05 to 10 at%.
Method for producing l-based intermetallic compound.