JPH08238501A - Method for sheathing tial base intermetallic compound - Google Patents

Abstract

PURPOSE: To provide a hot working method by which a TiAl base intermetallic compound is easily taken out of a sheath material after working in the hot- working method of TiAl base intermetallic compound, especially in a sheathing method. CONSTITUTION: In the sheathing method of the TiAl base intermetallic compound, steel is used as a covering material, an oxide 2 is inserted between the steel 1 and the TiAl base intermetallic compound 3, or the oxide is enclosed into the steel after forming those oxides on the surface of this TiAl base intermetallic compound and hot working is execute. The oxide used as a reaction inhibitor may be inserted in a sheet shape or a powdered shape at the time of enclosing the TiAl base intermetallic compound into the sheath material 3 or the oxide may be uniformly on the intermetallic compound. In this way, machining such as cutting and grinding of the sheath material after forming is simplified, so machining time and machining cost are further reduced and also the yield of the TiAl base intermetallic compound is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hot working of a TiAl-based intermetallic compound, and is particularly expected to be used for parts for aircraft, space shuttles, automobile engine parts, etc.
The present invention relates to a method of molding an l-based intermetallic compound by a hot working machine by a sheath working method.

[0002]

2. Description of the Related Art A TiAl-based intermetallic compound is light in weight and has excellent high-temperature strength, and therefore has been attracting attention as a structural material as described above. However, lack of deformability at room temperature and high temperature and difficulty in cutting are problems in the material manufacturing process.

Conventionally, as a hot working method for a TiAl-based intermetallic compound, a constant temperature forging method disclosed in JP-A-63-171862 is known. According to this method, not only the sample but also the processing die is kept at a constant temperature of 800 to 1100 ° C. and then processed at a relatively low strain rate to prevent cracking. Further, in Japanese Unexamined Patent Publication No. 2-224803, a constant temperature of 900 to 1150 ° C. under a vacuum (10 ⁻² Torr or less) or an inert gas atmosphere and a low strain rate of 10 ⁻² to 10 ⁻⁴ / sec. A method using a rolling method is disclosed. In any of the processing methods, since the processing is performed at a high temperature and at a constant temperature, it is necessary to maintain the high temperature, prevent the material from oxidizing, and prevent the reaction between the material and the processing die.
Along with this, a facility for atmosphere control and temperature control is required, so that the entire processing apparatus becomes large.

As an invention for solving these problems, Japanese Patent Application Laid-Open No. 61-213361 discloses a method of performing hot working using a sheath material which covers the periphery of the material. In this method, a Ni-based, Co-based, or Fe-Ni-based heat-resistant alloy is used as a sheath material, and as a result of processing at 1000 ° C. or higher, the material is molded up to a processing rate of about 50% without being oxidized. . Furthermore, JP-A-3-19
Japanese Patent No. 7630 discloses a sheath processing method using a titanium alloy having a deformation resistance close to that of a TiAl-based intermetallic compound as a sheath material. As a result of changing the sheath material to Ti alloy, T
The hot working of the iAl-based intermetallic compound can be performed without cracking up to a working rate of 60% which could not be processed by the above-mentioned sheath material. These sheath processing methods do not require the expensive and large-sized constant temperature forging machine or constant temperature rolling machine just by providing a step of sealing the TiAl-based intermetallic compound with a coating material, and molding using a normal processing process is possible. Became. Further, the processing rate is high, and since it can be molded even under the condition of high strain rate, it is excellent in terms of processing rate.

[0005]

In order to prevent the TiAl-based intermetallic compound, which is a raw material, from being oxidized in sheath processing, when hot working in vacuum or working in air, welding is performed after vacuum sealing. Since it is performed, the inside of the sheath material is degassed in any case. In addition, due to the processing characteristics of the TiAl-based intermetallic compound, the environment for hot working is a high temperature of 1000 ° C. or higher, and the processing conditions are relatively low strain rate and multiple passes, so normal metal working is performed. Processing time is longer than that of. On the other hand, the material to be processed, the intermetallic compound as the sheath material, and the heat-resistant alloy are each composed of a metal element.

Under the above processing conditions and the structure of the sheath material, both materials will be pressure bonded after processing, or bonding will occur due to solid phase diffusion of the respective constituent atoms. Therefore, in order to take out the TiAl-based intermetallic compound after molding, it is necessary to perform machining such as cutting and grinding of the sheath material, which increases the number of steps in the process. Furthermore, all of the above-mentioned sheath materials are difficult-to-cut materials, and there is a problem that processing costs are high. Further, since the material and the sheath material are bonded to each other, the surface of the material has to be ground, and a reduction in the yield of the material is unavoidable.

The present invention relates to a hot working method of a TiAl-based intermetallic compound, and particularly, in the sheath working method, it is possible to prevent the reaction between the sheath material and the TiAl-based intermetallic compound and to facilitate the TiAl-based intermetallic compound after the working. The purpose is to provide a method of taking out the same.

[0008]

The gist of the present invention is as follows. That is, when performing hot working using a sheath material that coats a material to be processed, an oxide having a low reactivity with the TiAl-based intermetallic compound between the sheath material to be coated and the internal TiAl-based intermetallic compound. A hot working method for a TiAl-based intermetallic compound, characterized in that The hot working method for a TiAl-based intermetallic compound as described above, wherein a sheet-shaped oxide is inserted between the sheath material to be coated and the TiAl-based intermetallic compound inside. The hot working method of a TiAl-based intermetallic compound as described above, wherein a powdery oxide is inserted between the sheath material to be coated and the TiAl-based intermetallic compound inside. During hot working using a sheath material that covers the workpiece, the TiAl-based intermetallic compound is formed on the surface of the TiAl-based intermetallic compound.
After forming an oxide with low reactivity with the base intermetallic compound,
A hot working method of a TiAl-based intermetallic compound by enclosing it in a sheath material.

The present invention will be described in detail below. First,
The TiAl-based intermetallic compound used for processing is of course composed of Ti and Al, and of course, Cr, V, Mn,
Materials including Nb added are also included. The layer formed between the TiAl-based intermetallic compound and the sheath material must be thermally and chemically stable in view of processing conditions.
It is preferable to use a substance that has low chemical reactivity with the base intermetallic compound and is opposite to the preferable conditions for bonding, that is, a substance whose physical properties such as a thermal expansion coefficient are far from those of both materials. Ceramics are known as a group of thermally and chemically stable materials. Among them, oxides such as Al ₂ O ₃ and CaO are also used in crucibles for high-frequency melting of TiAl-based intermetallic compounds. It can be said that it is thermally stable and has low reactivity with the TiAl-based intermetallic compound. In addition, it has been reported that when performing metal-to-metal bonding in a hot air atmosphere in titanium-clad steel composed of titanium and steel, no bonding occurs due to the formation of oxides. There are advantages. Furthermore, since oxide has a lower thermal conductivity than metal, it is also excellent in that it has a heat insulating effect of preventing a temperature drop from the surface during sheath processing.

In the oxide, the processing environment is 10
Considering the high temperature of 00 ℃ or more, it is thermally stable,
That is, Al ₂ O ₃ and CaO, which have low free energy of formation
Is preferred. In particular, Al ₂ O ₃ is TiA
It has been confirmed that it is effective as an oxidation resistant protective film for an l-based intermetallic compound. The reason is that it can be formed more densely than TiO ₂ or the like and suppresses the diffusion of metal atoms and oxygen.

In the case where the reaction preventive layer as in the present invention is not provided, it is necessary to cut in order to take out the TiAl-based intermetallic compound from the sheath material after processing, and the portion that has reacted with the sheath material must be ground. I have to. But T
Since the iAl-based intermetallic compound is a difficult-to-cut material, many cracks are easily generated in the surface layer region of the cut finish surface, and it is expected that the toughness value will be low when it is put into practical use as a product.
On the other hand, if a stable oxide is formed as the reaction-preventing layer, after removing the TiAl-based intermetallic compound from the sheath material, T
It is not necessary to grind the surface layer of the iAl-based intermetallic compound. If a thermally and chemically stable oxide is used, TiAl
This is because even if an oxide is formed on the surface of the base intermetallic compound, the characteristics of the TiAl base intermetallic compound are not impaired in the environment of use. Rather, when Al ₂ O ₃ is used, it is advantageous because it can be expected to have characteristics as a protective film due to its oxidation resistance.

The reaction preventing layer made of an oxide may be inserted in a sheet form or a powder form when the TiAl-based intermetallic compound is sealed in the sheath material, but various coatings such as plasma spraying and molecular control sol-gel method are also available. Ti by technology
It may be formed uniformly on the Al-based intermetallic compound. It is also possible to form an oxide on the surface of the TiAl-based intermetallic compound by modifying the TiAl-based intermetallic compound itself. For example, a method of forming an oxide film on the surface by performing heat treatment in a low oxygen partial pressure atmosphere as is done by Yoshiwara et al. Of Yokohama National University to improve the oxidation resistance of TiAl-based intermetallic compounds may be used. .

By the method described above, it is possible to form a chemically stable oxide between the TiAl-based intermetallic compound and the sheath material, which hardly reacts with the TiAl-based intermetallic compound. As the sheath material at that time, not only conventionally used heat-resistant alloys such as Ni and Ti alloys but also steel materials such as stainless steel can be used.

On the other hand, as hot working, hot forging, hot rolling, hot extrusion and the like are possible, but in the end all of them have a high working rate, so both the sheath material and the TiAl-based intermetallic compound can be obtained. Deforms considerably. Therefore, the reaction preventive layer is
It is necessary to secure a certain thickness so that the iAl-based intermetallic compound and the sheath material do not bond.

[0015]

The present invention will be further described below with reference to Examples and Comparative Examples. 33.4% by weight of Al as material, Cr
4.2 wt% (hereinafter, wt% unless otherwise noted) balance T
A TiAl-based intermetallic compound consisting of i and unavoidable impurities was cast into an ingot by plasma arc melting, and the structure was controlled by a constant temperature forging method at a temperature of 1000 ° C. or higher in order to improve high-temperature deformation characteristics. From this, a plate material having a size of 50 × 50 × 5 mm was cut out as a test material and used for the test.

As a sheath material, T is excellent in hot working characteristics.
i alloy, that is, Ti-15% V-3% Al-3% C
Two types of r-3% Sn and SUS304 were prepared.

As shown in FIG. 1, the lid 80 × 200
The sample 2 is enclosed between the sheath material 1 having a size of 10 mm and the sheath material 3 having a cavity having a size capable of enclosing the sample 2. As a reaction-preventing material between the sheath material and the test material, one covered with an Al ₂ O ₃ sheet, a method of inserting CaO powder between the sheath material and the sample, and a sol-gel method directly on the surface of the TiAl-based intermetallic compound A total of 3 coatings of Al ₂ O ₃ were prepared and sealed. As a comparative example, a test material that was not processed and enclosed as it was was also prepared.

After encapsulation, the side surfaces of the sheath materials 1 and 3 were joined in a vacuum by electron beam welding, and the sample was sealed to obtain a rolled sample. After heating to the specified temperature in an atmospheric furnace, 60
After holding for a minute, rolling was performed under the conditions shown in Table 1. Table 1
The processing rate in the table is the processing rate of the TiAl-based intermetallic compound obtained after rolling.

[0019]

[Table 1]

Example 1 A sheet of Al ₂ O ₃ was used as a reaction inhibitor. When SUS304 is used for the sheath material, the furnace temperature is 1
It carried out at two levels of 250 degreeC and 1050 degreeC. When a Ti alloy was used, it was held at 1250 ° C. and then rolled under the conditions shown in Table 1. After rolling, the boundary between the TiAl-based intermetallic compound and the sheath material was cut at two locations in the rolling direction and at two locations perpendicular to it, and it was evaluated whether the TiAl-based intermetallic compound could be separated from the sheath material. The thickness of the TiAl-based intermetallic compound was measured to obtain the processing rate.

Regardless of the type of sheath material, TiAl inside the sheath material can be easily formed after cutting under any rolling condition.
The base intermetallic compound could be peeled off, and a sound product was obtained without cracking.

The surface of the obtained TiAl-based intermetallic compound was analyzed when SUS304 was used as a sheath material and rolled under the conditions of a furnace temperature of 1250 ° C. and a roll speed of 1 m / min. The result is shown in FIG. According to FIG. 2, although Al ₂ O ₃ was partly adhered by rolling, no diffusion of metal atoms from the sheath material was detected and it was confirmed that the material was sound rolled.

Comparative Example 1 Under the conditions shown in Comparative Example 1 of Table 1, no reaction inhibitor was used,
The TiAl-based intermetallic compound was directly enclosed in the sheath material and rolled. As a result of cutting the four places after rolling, the TiAl-based intermetallic compound itself was rolled, but the TiAl-based intermetallic compound could not be peeled from the sheath material under any conditions. This is because heat treatment is performed at a high temperature necessary for processing and rolling is performed, so that a reaction occurs due to the diffusion of metal atoms between the sheath material and the TiAl-based intermetallic compound, resulting in bonding.

FIG. 3 shows an optical micrograph of a cross section of a rolled material obtained by rolling a Ti alloy as a sheath material under the conditions of a furnace temperature of 1250 ° C. and a roll speed of 1 m / min. T
As a result of a line analysis by EPMA at the interface between the iAl-based intermetallic compound and the Ti alloy that is the sheath material, it was found that each constituent atom diffuses, and the reaction layer thereof reaches up to about 400 μm. This is SUS as a sheath material
Even when 304 was used, a reaction layer was similarly produced.

[0025]Example 2  CaO powder was used as a reaction inhibitor. Al after processing₂
O₃TiAl-based intermetallic compound as in the case of using a sheet
Objects can be taken out easily, and they are uniform and sound without cracks.
The wood was obtained. CaO is Al₂O₃Freedom compared to
Low energy, applicable at lower temperature than Example 2
is there. Also, the form of the reaction inhibitor may be powder.
Is clear from this result.

Example 3 The surface of a TiAl-based intermetallic compound was directly coated with Al ₂ O ₃ by a sol-gel method and sealed in a sheath material. In the case of a high workability, some coating layers were damaged, but the surface of the TiAl-based intermetallic compound was not exposed. As in the above two examples, the sheath material could be easily peeled off and the rolled material was sound. From this, it was found that even if an oxide was formed on the surface of the TiAl-based intermetallic compound, the TiAl-based intermetallic compound could be easily taken out after the processing and had no effect on the processing.

[0027]

As described above, according to the present invention, when the TiAl-based intermetallic compound is hot-worked by using the sheath material that covers the workpiece, the sheath material and the TiAl-based intermetallic compound are used. Intercalation between TiAl-based intermetallic compounds and chemically stable oxides such as Al ₂ O ₃ and CaO are inserted, or these oxides are formed on the surface of TiAl-based intermetallic compounds. As a result, the TiAl-based intermetallic compound can be easily taken out after the hot working.

[Brief description of drawings]

FIG. 1 is a perspective view showing configurations of a sample and a sheath material according to the present invention.

FIG. 2 shows Al ₂ O ₃ as a reaction inhibitor according to the present invention.
3 is an optical micrograph of a cross section of a rolled material obtained by rolling the sheet of No. 1 and using SUS340 as a sheath material.

FIG. 3 is an optical micrograph of a cross section of a rolled material obtained by rolling a Ti alloy as a sheath material without using the reaction preventing material according to the comparative example.

[Explanation of symbols]

 1,3 Sheath material 2 samples

Claims (4)

[Claims] 1. When performing hot working using a sheath material for coating a material to be processed, the reactivity of the TiAl-based intermetallic compound between the sheath material to be coated and the internal TiAl-based intermetallic compound is improved. T, characterized by inserting a low oxide
Hot working method of iAl-based intermetallic compound. 2. The hot working method for a TiAl-based intermetallic compound according to claim 1, wherein a sheet-shaped oxide is inserted between the sheath material for coating and the TiAl-based intermetallic compound inside. 3. The hot working method for a TiAl-based intermetallic compound according to claim 1, wherein the oxide to be inserted between the sheath material to be coated and the TiAl-based intermetallic compound inside is in the form of powder. 4. An oxide having a low reactivity with the TiAl-based intermetallic compound is formed on the surface of the TiAl-based intermetallic compound during hot working using a sheath material that covers the workpiece. , T is characterized by being enclosed in a sheath material.
Hot working method of iAl-based intermetallic compound.