JPH06340955A - Production of ti-al series intermetallic compound base alloy - Google Patents

Abstract

(57) [Summary] [Structure] Al: 38-53 atom%, balance Ti: Ti-Al binary alloy is processed in the high temperature α-Ti single phase region to be fine-grained, and then to room temperature. When cooling at a rate of 1 to 10 ° C./s or less, or when cooling at a rate of 1 to 10 ° C./s or more, a lamella forming treatment is performed, which is an aging treatment. [Effect] Ti-Al with room temperature ductility of 1.5% or more, 0.2% proof stress at 800 ° C of 30 kgf / mm ² or more, fracture toughness value of 60 kgf / mm ² or more.
An intermetallic compound based alloy is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is intended to improve room temperature ductility, strength and toughness of alloys containing intermetallic compounds TiAl and Ti ₃ Al, which are expected to be used as lightweight heat resistant materials for jet engines and automobile parts. The present invention relates to a method for producing a Ti-Al-based intermetallic compound-based alloy which is subjected to the thermomechanical treatment.

[0002]

2. Description of the Related Art In a Ti-Al binary alloy, from the Ti side
TiAl and Ti ₃ Al as intermetallic compounds up to around 70 atomic% Al
Is known to exist. TiAl has almost the same number of atoms
An intermetallic compound composed of Ti and Al atoms, with a specific gravity
It has a L1o (tetragonal) crystal structure at 3.8. Ti ₃ Al is an intermetallic compound composed of a Ti: Al atomic ratio of about 3: 1 and has a DO ₁₉ (hexagonal) crystal structure with a specific gravity of 4.2.

Both of these are intermetallic compounds and are lightweight and excellent in heat resistance. While TiAl is stable just below the melting point (about 1500 ° C), Ti ₃ Al transforms into the β-Ti phase at about 1200 ° C or higher, and therefore its heat resistance is inferior to that of the TiAl phase. TiAl
In alloys based on Al, the problem of room temperature ductility tends to appear when the composition is on the low Al side, and the composition at the time of solidification in such composition is a lamella that is a layered structure of TiAl phase and Ti ₃ Al phase. It has an organization. However, in this structure, the room temperature ductility is not so high and needs to be improved. (See Shoji Yamaguchi, "Titanium Aluminide" Metal, July 1990, p.34).

FIG. 1 shows Ti-Al which is also disclosed in the above-mentioned document.
Binary phase diagram (C. McCullough et al., Scripta Metallu
gica Vol.22 (1988), p.1131 to 1136), the region relevant to the present invention is shown. It is a recent recognition that the state diagram shown by the thin dotted line in this figure is correct. In other words, the recent recognition is that the αTi phase equilibrates with the liquid phase in the high temperature range of 50 atomic% Al. There is little information on the technology related to the processing and heat treatment of TiAl-based alloys. Japanese Unexamined Patent Publication (Kokai) No. 63-171862 discloses a two-step isothermal forging method as a manufacturing method, but it mainly relates to strength improvement, and room temperature ductility is not improved at all.
Further, in Japanese Patent Laid-Open No. 2-274307, a hot-working process is used to obtain a structure composed of equiaxed fine grains of TiAl to improve the room temperature ductility, but this structure provides sufficient fracture toughness (high temperature strength). Absent.

[0005]

An alloy mainly composed of TiAl or Ti ₃ Al is an intermetallic compound, but it is very brittle and it is difficult to obtain room temperature ductility. Further, the fact that the fracture toughness is at a low level limits the practical application. The cast structure of such an alloy is a lamellar (layered) coarse-grained structure composed of TiAl and Ti ₃ Al. On the other hand, for example, a component close to TiAl tends to have a fine equiaxed grain structure when processed. When it is heated, it becomes an equiaxed coarse grain structure. In this way, as the structure changes drastically, the mechanical properties also change drastically. Summarizing these, the correlation between the structure and mechanical properties is as shown in the table below.

[0006]

[Table 1]

As can be seen from this table, balanced characteristics are not obtained. An object of the present invention, in the alloy of which based on TiAl and Ti ₃ Al is TiAl-based intermetallic compound,
It is an object of the present invention to provide a method for producing a Ti-Al intermetallic compound-based alloy having an improved balance of properties such as room temperature ductility, high temperature strength and fracture toughness. A more specific object of the present invention is room temperature ductility 1.
5% 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 intermetallic compound-based alloy having characteristics of a fracture toughness value of 60 kgf / mm ² or more.

[0008]

The inventors of the present invention have found that it is difficult to obtain room temperature ductility in the lamella grain structure of a polycrystalline body, but the fracture toughness,
Excellent high temperature strength. On the other hand, it was noted that the equiaxed fine-grained structure has excellent ductility at room temperature but low fracture toughness and high-temperature strength. Therefore, by creating a structure consisting of fine lamella grains, we believe that a Ti-Al intermetallic compound-based alloy with an excellent balance of properties such as room temperature ductility, high temperature strength, and fracture toughness can be obtained. The present invention has been completed based on the following findings regarding the method of forming a fine grain structure.

(1) In a TiAl alloy with Al: 38 to 53 atomic% and the balance Ti, recrystallization occurs when the cast structure consisting of coarse lamella grains is processed in the two-phase region of Ti ₃ Al + TiAl at about 1120 ° C. or less in FIG. As a result, a structure composed of equiaxed TiAl phase and Ti ₃ Al phase or a deformed structure of the original lamella is not obtained, and an equiaxed fine lamella grain structure cannot be obtained. (2) Processing the alloy in the above composition range in the α single phase region of high temperature range,
The target lamella fine particles are formed by refining the crystal grains of the α grains themselves and generating the γ phase by aging treatment during cooling or after processing and at the same time transforming the α phase into the α ₂ (Ti ₃ Al) phase. The organization is obtained.

The gist of the present invention is as follows.
l: 38-53 atomic%, Ti-Al binary alloy with the balance Ti or a part of Ti for the purpose of improving room temperature ductility, hot workability, high temperature strength and oxidation resistance, Mo, Mn, V, A Ti-Al binary alloy obtained by substituting at least one element selected from the group consisting of Cr, Nb, W and Si up to a total of 5 atomic% was processed in a high temperature α-Ti single phase region to form a fine alloy. Along with granulation, then, characterized by performing a lamella forming treatment to generate a lamella of TiAl and Ti ₃ Al inside the obtained fine crystal grains to form a fine lamella grain structure, ductility, high temperature strength, This is a method for producing a Ti-Al-based intermetallic compound-based alloy having excellent properties of toughness balance.

According to a preferred embodiment of the present invention, the high temperature α
The processing in the single-phase region is to carry out processing with a working ratio of 30% or more in terms of cross-sectional area ratio or height ratio one or more times, and the lamella forming treatment is determined by chemical components up to room temperature after processing 1 It is to cool at a rate equal to or lower than the critical cooling rate within the range of up to 10 ° C / s. Further, according to another preferred embodiment of the present invention, the processing in the high temperature α single phase region is performed once or more by a processing degree of 30% or more in terms of cross-sectional area ratio or height ratio, And the lamella forming treatment, after processing, after cooling at room temperature to a room temperature of 1-10 ℃ / s determined by chemical components at a critical cooling rate or higher, or without cooling to room temperature
It is to heat to the temperature of the coexisting region of Ti ₃ Al and TiAl phase.

[0012]

The present invention will now be described in more detail with reference to the accompanying drawings. The reason for defining the alloy composition and the processing conditions as described above in the present invention is as follows. (1) Chemical composition: Al: 38-53 atom% (24-38wt%),
Alloy consisting of balance Ti: According to the production method of the present invention, it is necessary to work in the α single phase region at high temperature, and it is necessary to include TiAl phase in the composition range of the region. If they fall outside these ranges, they cannot be realized.

Further, no difference is observed in the change behavior of the microstructure even if other elements, alone or in combination, are added in place of a part of Ti and added up to a total of 5 atom%. Such additional elements include Mo, Mn, V, Cr, Nb, W and Si.

(2) High temperature α single phase region: In order to obtain fine crystals, it is necessary to process in the α single phase region, and the temperature range in which the α single phase region can be obtained is as shown in FIG. It depends on Ti-40% Al, but it is sufficient if it is in the range of 1100 to 1300 ° C. (3) When the workability is 30% or more and less than 30%, it is difficult to make the structure finer throughout, and 50% or more is desirable from the viewpoint of homogeneity. Here, the workability is obtained by the cross-sectional area ratio or height ratio. The processing means is not particularly limited even if it is rolling, forging or other extrusion, and powder processing or the like may be applied.

(4) Lamella forming treatment: Cooling at a cooling rate below the critical cooling rate within the range of 1 to 10 ° C./s: for example, Ti
With -40% Al, the above critical cooling rate is 1 ℃ / s and 1 ℃ / s
With the above cooling rate, and with Ti-48% Al, this critical cooling rate is 10 ° C / s, and at cooling rates of 10 ° C / s or more, the cooling rate is too fast and sufficient time cannot be ensured during cooling. Ti
No lamella structure is obtained because no Al phase is generated.

(5) Lamella forming treatment: Cooling at a critical cooling rate or higher within a range of 1 to 10 ° C./s and aging: up to a temperature range close to room temperature by suppressing α-grain growth in (4) above Holds the α-phase fine particles (transforms to Ti ₃ Al during cooling) and precipitates the TiAl phase by aging treatment. In this case, the range of 1 to 10 ° C / s is determined by the chemical composition as described above. It is necessary to cool at above the critical cooling rate. In this case, the material may be cooled to room temperature and then heated again, or may be directly cooled to the temperature at the above-mentioned rate and held after processing. The holding time is not particularly limited, but may be any time necessary and sufficient for the precipitation of the TiAl phase to occur, usually 15 minutes or more.

FIG. 2 is a diagram showing a heat pattern of the thermomechanical treatment according to the present invention, in which the material is worked to a predetermined working degree in a high temperature α single phase region and then cooled at a cooling rate of 1 ° C./s or less. The case where a lamella formation process is performed is shown. FIG. 3 shows an example of a heat pattern in the case where the lamella forming treatment by the aging treatment is performed after performing the processing of a predetermined working degree in the high temperature α single phase region. After cooling for more than s, it is heated again in the α ₂ + γ region, that is, the region where Ti ₃ Al and TiAl phase coexist, and the aging treatment is performed to precipitate the TiAl phase and form a lamellar structure.

FIG. 4 is a diagram showing a heat pattern of another example in the case where the lamella forming treatment by the aging treatment is carried out after the working of the predetermined working degree is carried out in the high temperature α single phase region. Without cooling to room temperature, the α ₂ + γ region is cooled at 1 ° C./s or more and then kept at that temperature for aging treatment.

[0019]

EXAMPLE Ti-40 atomic% Al (alloy A), Ti-40 atomic% Al-1 atomic% Mo (alloy B) and Ti-48.4 atomic% Al-0.6 melted by the consumable Ar arc melting method Atomic% Mo (alloy C)
A block of 40 × 40 × 80 (mm) was cut out from each of the ingots, and several sheath materials for each alloy were produced by enclosing and enclosing the block with a plate made of Ti-6Al-4V alloy having a thickness of 10 mm.

The sheath material prepared in this manner is used at 1300 ° C.
After homogenizing at 1, the sample was cooled with water and then subjected to isothermal forging using a ceramic mold. Table 2 shows the constant temperature forging conditions, normal temperature tensile elongation of the forged material, 0.2% proof stress at 800 ° C, and normal temperature fracture toughness. In the table, α ₂ represents Ti ₃ Al, α represents α-Ti, and γ represents TiAl. In addition, the degree of processing is TiAl that does not include the sheath material.
This is a value only for + Ti ₃ Al based alloy, and the cooling rate was adjusted by furnace cooling, air cooling, blast cooling, oil cooling, water cooling, etc.

Other test conditions were as follows.

Tensile Test: A tensile test was conducted on a round bar having a diameter of 4 mm at a room temperature and a test temperature of 800 ° C. at a strain rate of ε = 10 ^-3 S ^-1 . Fracture toughness test: CT test pieces (half size) were used. Also from the results shown in Table 2, according to the present invention, room temperature tensile elongation
It can be seen that 1.5% or more, 0.2% proof stress at 800 ° C of 30 kgf / mm ² or more, and room temperature fracture toughness of 60 kgf / mm ² or more can be obtained. Figure 5
Is a metallographic micrograph of the comparative material of Test No. 17,
FIG. 6 is a similar metallographic micrograph of the alloy produced by the method of Test No. 3 according to the present invention. According to the present invention, it can be seen that a fine lamella structure is generated.

[0023]

[Table 2]

[0024]

Industrial Applicability According to the present invention, it becomes possible to produce a Ti--Al based intermetallic compound-based alloy that achieves the desired mechanical properties, and the field of industrial application of this alloy expands.

[Brief description of drawings]

FIG. 1 is a partial view of a binary phase diagram of Ti—Al.

FIG. 2 is a diagram showing a heat treatment heat pattern in the present invention.

FIG. 3 is a diagram showing another heat treatment heat pattern according to the present invention.

FIG. 4 is a diagram showing still another heat treatment heat pattern in the present invention.

FIG. 5 is an optical metallographic micrograph of a comparative material in Example.

FIG. 6 is an optical metallographic micrograph of an example of the present invention in Examples.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 19, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

FIG. 5 is an optical micrograph of a metal structure of a comparative material in an example.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

FIG. 6 is an optical micrograph of a metal structure of an example of the present invention in Examples.

Claims (3)

[Claims] 1. A Ti-Al binary alloy with Al: 38 to 53 atomic% and the balance Ti, or at least one portion of this Ti selected from the group consisting of Mo, Mn, V, Cr, Nb, W and Si. Of the Ti-Al binary alloy obtained by substituting up to 5 atomic% of the elements in the above was processed in the high temperature α-Ti single-phase region to be fine-grained, and thereafter, inside the obtained fine crystal grains. A Ti-Al intermetallic compound with excellent properties of ductility, high temperature strength, and toughness, characterized by performing a lamella forming treatment that produces a lamella of TiAl and Ti ₃ Al to form a fine lamella grain structure. Base alloy manufacturing method. 2. The processing in the high temperature α single-phase region is performed by performing processing with a processing degree of 30% or more in terms of cross-sectional area ratio or height ratio one or more times, and the lamella forming treatment is performed after processing. The method according to claim 1, wherein the cooling is performed to a room temperature at a rate not higher than the critical cooling rate within the range of 1 to 10 ° C / s determined by the chemical composition. 3. The processing in the high temperature α single-phase region is performed by performing processing with a processing degree of 30% or more in terms of cross-sectional area ratio or height ratio one or more times, and the lamella forming treatment is performed after processing. , The temperature of the coexistence region of Ti ₃ Al and TiAl phase after cooling to room temperature at a rate higher than the critical cooling rate within the range of 1 to 10 ° C / s determined by the chemical composition or without cooling to room temperature The method according to claim 1, which comprises cooling and then heating to that temperature.