JPH06116690A - Method for producing Ti-Al based intermetallic compound-based alloy - Google Patents

Abstract

(57) [Summary] [Purpose] Room temperature elongation of 2.0% or more, 0.2% at 800 ℃
Ti with a yield strength of 30 kgf / mm ² or more and a fracture toughness value of 50 kgf / mm ^3/2 or more
An Al-based intermetallic compound-based alloy is manufactured. [Structure] A Ti-Al-based intermetallic compound-based alloy is represented by the following formula (1)
After processing 50% or more in the temperature range of T ₁ (° C.), the temperature is maintained in the temperature range of T ₂ (° C.) of the following formula (2) for 1 hour or more, and then air cooling or slow cooling. 1200 ≦ T ₁ <T ₂ ··· (1) T ₂ = {1226 + 37 × (X−46)} ± 25 ··· (2) However, X: Al atom%

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 Ti-Al intermetallic compound base alloy, particularly as a lightweight heat-resistant material, an engine case or compressor blade and vane of a jet engine, an exhaust valve and a piston pin of an automobile engine, and Includes intermetallic compounds of TiAl and Ti ₃ Al, which may be used for space planes, outer skins of supersonic aircraft, heat-resistant tubes of boilers, and turbine blades.
The present invention relates to a method for producing a Ti-Al-based intermetallic compound-based alloy. According to the present invention, the room temperature ductility, strength and toughness are improved by thermomechanical treatment.

[0002]

2. Description of the Related Art A Ti-Al-based intermetallic compound-based alloy contains TiAl (hereinafter referred to as γ phase) and Ti ₃ Al (hereinafter referred to as α ₂ phase) which are intermetallic compounds and, if necessary, Mn. Although it is an alloy containing Mo, V, etc., it is said to have a two-phase structure of α ₂ + γ and is lightweight and excellent in heat resistance. Hereinafter, such Ti-Al-based intermetallic compound-based alloy is
It is called a base alloy.

FIG. 1 is a partially enlarged view of the phase diagram of the Ti-Al alloy. As can be seen from this, in this TiAl-based alloy, the α phase (α-Ti) which is a Ti solid solution at 1130 ° C. or higher. Exists, and the reaction of α → α ₂ + γ occurs as it cools, and it has a two-phase structure of α ₂ + γ at room temperature.

However, in such a TiAl-based alloy, no study has been made on the rate at which the γ phase and the α ₂ phase are precipitated from the α phase, and the mechanical properties have only been investigated with materials having relatively high cooling rate conditions. Not not.

For example, it is said that room temperature ductility appears even in a cast material in the range of 47 to 50 at% Al-Ti by cooling at a relatively high cooling rate of 50 ° C./sec. However, as a result of detailed examination, it has been found that although room temperature ductility appears, its value cannot be said to be sufficient, and rather a high cooling rate has an adverse effect. In other words, such quenching causes strain to remain in the material, which rather reduces ductility. Incidentally, the structure at the time of solidification by casting in such a component, that is, the structure obtained by cooling at a cooling rate of oil cooling, water cooling exhibits a lamellar structure in which the γ phase and the α ₂ phase are layered on the entire surface. , Ductility is insufficient.

On the other hand, little information is available on the technology relating to the processing and heat treatment of TiAl-based alloys. Japanese Unexamined Patent Publication No. 63-171862 discloses a two-step isothermal forging method at 700 to 1100 ° C. In Japanese Patent Laid-Open No. 2-274307, the weight percentage is 34.5%.
A TiAl-based alloy of Al (48.4% Al in atomic%) was hot-extruded at 1200 ° C and then annealed at 1200 ° C for 1 hour. It has been shown to change to a fine grain TiAl-based alloy.

[0007]

However, at the time of solidification by casting,
A material (α ₂ + γ) having a layered lamellar structure of TiAl (γ phase) and Ti ₃ Al (α ₂ phase) has insufficient room temperature ductility and needs to be improved. Further, as described above, it has been reported that the room temperature ductility is improved by obtaining an equiaxed fine grain structure by hot working (JP-A-2-274307), but even with this structure, sufficient fracture toughness and high temperature are obtained. No strength is obtained. From the viewpoint of its practical use, it is desired that the TiAl-based alloy has characteristics such as room temperature elongation of 2.0% or more, 0.2% proof stress at 800 ° C of 30 kgf / mm ² or more, and fracture toughness value of 50 kgf / mm ^3/2 or more.

It is therefore an object of the present invention, an alloy containing a TiAl and Ti ₃ Al is TiAl-based intermetallic compound (TiAl
(Base alloy), a method for producing a Ti—Al-based intermetallic compound-based alloy having an improved balance of room temperature ductility, high temperature strength, and fracture toughness.

A more specific object of the present invention is room temperature elongation 2.
0% or more, 0.2% proof stress at 800 ℃ 30kgf / mm ² or more,
It is an object of the present invention to provide a method for producing a Ti-Al-based intermetallic compound-based alloy having a fracture toughness value of 50 kgf / mm ^3/2 or more.

[0010]

DISCLOSURE OF THE INVENTION The inventors of the present invention believe that a microstructure composed of lamella grains and equiaxed γ grains has an excellent balance of room temperature ductility, high temperature strength and fracture toughness. We proposed a method for producing a Ti-Al-based intermetallic compound-based alloy, which is characterized by processing in a temperature range of (α + γ) two-phase region of 1200 ° C or higher, and then cooling from a temperature below the critical temperature (Japanese Patent Application No. (Head 3-233151).

However, although this method can obtain a mixed structure of the fine lamella grains and the fine equiaxed γ grains, the lamella grains and the equiaxed γ grains are not uniformly dispersed, and the aggregate of the lamella grains, etc. A non-uniform structure in which aggregates of axial γ grains are mixed,
The balance between room temperature ductility, high temperature strength and fracture toughness has not been sufficiently improved.

Therefore, as a result of further studies, the inventors of the present invention conducted a thermomechanical treatment in which machining and heat treatment were combined, and at that time, the temperature difference between the machining temperature and the heat treatment temperature was reduced and the heat treatment was performed. It was found that the lamella grains and the equiaxed γ grains can be dispersed extremely uniformly by carrying out at a temperature at which the amount ratio of the α phase and the γ phase in the (α + γ) two-phase region becomes equal to each other for a predetermined time or longer, and thus the present invention was completed. It was

Here, the gist of the present invention is, in atomic%, Al:
46-51%, balance Ti-Al-based intermetallic compound-based alloy, or one or more of Mo, Mn, V, Cr, Nb, W, Si and Ta in a total amount of 5% Below, Al: 46-51%,
For the balance Ti-Al based intermetallic compound based alloy, the following formula
After processing 50% or more in the temperature range of T ₁ (° C) of (1), hold it in the temperature range of T ₂ (° C) of the following formula (2) for 1 hour or more, and then perform air cooling or slow cooling. Ti−
It is a method for producing an Al-based intermetallic compound alloy.

1200 ≦ T ₁ <T ₂ (1) T ₂ = {1226 + 37 × (X−46)} ± 25 (2) However, X: Al atom% According to the present invention , Unlike the lamellar structure in which the α ₂ phase and the γ phase are layered as seen in the conventional cast solidification structure,
Alternatively, as in the above-mentioned prior application, the aggregate of lamella grains and the equiaxial γ
Unlike a non-uniform structure in which aggregates of grains are mixed, a structure in which lamella grains and equiaxed γ grains are uniformly dispersed is obtained, and as a result,
Good balance of room temperature toughness, high temperature strength and fracture toughness.

[0015]

The present invention will now be further described with reference to the accompanying drawings. 2 (a) and 2 (b) are diagrams showing the heat patterns (Pattern I and Pattern II) of the method of the present invention, respectively, in which the Ti--Al based intermetallic compound-based alloy having a predetermined structure is
After processing 50% or more in the temperature range T ₁ specified by the above formula (1), in the case of pattern I, once cooled to 1200 ° C or less, for example, room temperature and then heated again, or the pattern
In the case of II, after processing, heating is performed, heat treatment is performed for 1 hour or more in the temperature range of T ₂ defined by the formula (2), and air cooling or slow cooling is performed. Note that “slow cooling” also includes furnace cooling. The workability is indicated by the reduction rate or the area reduction rate.

Now, the reason why the alloy composition, working conditions and heat treatment conditions are limited as described above in the present invention will be explained. In the present specification, “%” is “atomic%” unless otherwise specified. In the present invention, the object is Al: 46 to 51 atomic% (approximately 32.4 to 37.0% by weight).
%), And the balance Ti is a Ti-Al binary intermetallic compound base alloy.

The Al content is limited to 46 to 51 atomic%, because when the method of the present invention is applied and the Al content is less than 46% or more than 51%, the amount of α ₂ phase or γ phase when cooled is small. This is because the amount becomes excessive and the intended characteristics of the present invention cannot be obtained. A part of Ti may be replaced by one kind or two or more kinds of Mo, Mn, V, Cr, Nb, W, Si, and Ta up to a total amount of 5 atom%, but the total amount of these is 5 If it exceeds atomic percent, the machinability of the resulting alloy deteriorates.

The Ti-Al-based intermetallic compound-based alloy thus prepared is processed within the temperature range restricted by the above formula (1). This is because the recrystallized grains are finely equiaxed and uniformly mixed. 12
The recrystallized grains of γ phase and α phase are fine equiaxed grains even when processed at less than 00 ° C, but when performing heat treatment, the difference between the processing temperature and the heat treatment temperature is too large, and the equilibrium occurs at the processing temperature. γ / α
Ratio and the γ / α ratio that equilibrates at the heat treatment temperature become too large,
Α grains grow in the cooling process after the heat treatment, and the transformed lamella grain size generated during cooling becomes coarse, resulting in a non-uniform structure. Therefore, the lower limit of processing temperature was set to 1200 ℃.

The upper limit of the processing temperature is set to be lower than the subsequent heat treatment temperature because the driving temperature is equal to or higher than the heat treatment temperature, and the driving is for uniformly mixing the α phase and the γ phase, which is a function of the heat treatment. This is because the power will disappear. Therefore,
The upper limit of the processing temperature was lower than the heat treatment temperature. The processing temperature is preferably closer to the subsequent heat treatment temperature from the viewpoint of obtaining a uniform fine mixed structure.

The processing in the (α + γ) 2 phase region at this time is as follows.
This is because the workability is 50% or more, but if it is less than 50%, it is not recrystallized uniformly. The workability at this time is represented by the reduction rate or the area reduction rate. The degree of processing is the total amount, but it is preferable to achieve a reduction rate or surface reduction rate of 30% or more in one processing. In addition, the higher the degree of processing, the finer the recrystallized grain size after heat treatment and the more excellent the ductility. Specifically, the workability is preferably 80% or more for room temperature ductility.

The processing means is not particularly limited, but for example, conventional isothermal forging may be performed. Alternatively,
Sheath forging, isothermal rolling, pack rolling, sheath rolling, normal forging and rolling with the surface coated with an antioxidant,
Forging materials, plate materials, pipe materials and the like can be manufactured by extrusion and the like.

Even after the material is once cooled as shown in the pattern I shown in FIG. 2 (a) after the processing but before the heat treatment, the material shown in FIG.
As in the pattern II shown in (1), the heat treatment may be carried out by raising the temperature as it is, and in any case, a uniform fine mixed structure can be obtained. The heat treatment temperature (T ₂ ) was set within the range of 25 ° C. above and below the critical temperature represented by the following equation.

Critical temperature: T = 1226 + 37 (X−46) (X: Al atomic%) (3) This is because the volume amounts of the α phase and the γ phase equilibrated during the heat treatment are almost equal to each other, and the mutual growth of crystal grains is caused. This is to suppress and prevent the formation of locally coarse α ₂ grains and γ grains during cooling.
As a result, according to the present invention, a uniform fine mixed structure can be obtained. When the heat treatment temperature (T ₂ ) is out of the range of the critical temperature T ± 25 ° C., the volume ratio of the γ phase and the α phase deviates greatly from 1, and the homogeneity of the structure is lost. It is desirable that the heat treatment temperature be as close to the critical temperature (T) as possible (T = T ₂ ).

Thus, in the present invention, the range of the heat treatment temperature T ₂ is defined by the above equation (2). If the heat treatment time is less than 1 hour, a uniform fine mixed structure (equiaxed grains + lamella grains) cannot be obtained. Therefore, the lower limit of heat treatment time is 1
It was time. Within the temperature range defined by the above equation (2), since the heat treatment time is close to γ / α = 1 even at the longest time, almost no grain growth is observed, and there is no problem in the characteristics. However, 24 hours is sufficient from the viewpoint of productivity.

Cooling after the heat treatment is performed by air cooling or slow cooling (including furnace cooling and slow cooling performed by wrapping in a heat insulating material). This is because the γ phase and the α ₂ phase are sufficiently precipitated during cooling from the α phase, which is a high temperature solid solution phase, to form (α ₂ + γ) transformed lamellar grains. Thus, according to the invention,
A Ti-Al-based intermetallic compound-based alloy having excellent balance of room temperature ductility, high temperature strength and fracture toughness is manufactured. Next, the present invention will be described more specifically by way of examples.

[0026]

Example Each alloy having the components shown in Table 1 was melted by a consumable Ar arc skull melting method. 40 × 40 × 80 (m from each ingot
A block of m) was cut out and wrapped with a plate made of Ti-6Al-4V alloy having a thickness of 10 mm, and several sheath materials were produced for each alloy and sealed.

The sheath material thus prepared was subjected to isothermal forging using a ceramic mold to be processed.

Tables 2 to 4 collectively show the isothermal forging conditions at this time, the room temperature tensile elongation of the obtained forged material, the 0.2% proof stress at 800 ° C., and the room temperature fracture toughness value. The workability is a value indicated by the rolling reduction of only TiAl + Ti ₃ Al based alloy containing no sheath material, and the cooling rate was adjusted by furnace cooling, air cooling, wrapping with a heat insulating material, or the like. The other test conditions were as follows.

Tensile test: A plate test piece having a plate thickness of 0.5 mm, a plate width of 2 mm and a parallel part length of 5 mm was subjected to a tensile test at a strain rate of ε = 10 ⁻⁴ 1 / S at room temperature and a test temperature of 800 ° C. .

Fracture toughness test: CT test pieces (half size) were used. From the results shown in Tables 2 to 3, according to the present invention, the properties such as room temperature tensile elongation of 2.0% or more, 0.2 proof stress at 800 ° C of 30 kgf / mm ² or more, and room temperature fracture toughness of 50 kgf / mm ^3/2 or more can be obtained in a well-balanced manner. You can see that

FIG. 3 is a metallographic micrograph of the material obtained in Test No. 11 (comparative example), showing a non-uniform mixed microstructure (equiaxed grains,
(Transformed lamella grains). On the other hand, FIG. 4 is a similar metallographic micrograph of the alloy produced by the method according to the present invention of Test No. 13. According to the present invention a uniform fine mixed structure
It can be seen that (equiaxed grains and transformed lamellar grains) are generated.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

Industrial Applicability According to the present invention, it becomes possible to produce a Ti-Al-based intermetallic compound base alloy which can obtain desired mechanical properties in a well-balanced manner, and the industrial application field of the Ti-Al-based alloy is expanded.

[Brief description of drawings]

FIG. 1 is a binary system state diagram of Ti—Al showing a processing temperature range in a shaded area.

FIG. 2 (a) and FIG. 2 (b) are diagrams showing a heat treatment heat pattern in the present invention.

FIG. 3 is an optical metallographic micrograph of a comparative material in an example.

FIG. 4 is an optical metallographic micrograph of an alloy material produced by the method of the present invention in Examples.

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[Procedure amendment]

[Submission date] July 6, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

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[Correction method] Change

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[Procedure Amendment 2]

[Document name to be corrected] Drawing

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[Correction method] Change

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 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Yamaguchi 24-403 Kita-Shirakawa-Kamibetsuto-cho, Sakyo-ku, Kyoto

Claims (1)

[Claims] 1. An atomic percentage of Al: 46 to 51%, the balance of Ti-
Al-based intermetallic compound-based alloy, or Mo, Mn, V, Cr, N
b, W, Si and Ta, one or two or more of which are contained in a total amount of 5% or less, Al: 46 to 51%, and the balance Ti is based on the following formula (1) After processing 50% or more in the temperature range of T ₁ (° C), hold for 1 hour or more in the temperature range of T ₂ (° C) in the formula (2) below, and then perform air cooling or slow cooling. A method for producing a Ti-Al-based intermetallic compound-based alloy, which is characterized. 1200 ≦ T ₁ <T ₂ ··· (1) T ₂ = {1226 + 37 × (X−46)} ± 25 ··· (2) However, X: Al atom%