JP3425621B2 - O-phase based Ti-22Al-27Nb alloy and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The invention of this application is directed to an O phase group T
The present invention relates to an i-22Al-27Nb alloy and its manufacturing method. More specifically, the invention of this application discloses an O phase group Ti-22A having a highly balanced balance of tensile strength and ductility.
The present invention relates to a 1-27 Nb alloy and a manufacturing method for manufacturing the same.

[0002]

_2. Description of the Related Art Ti ₂ AlNb (Ti-25 mol% Al-25
mol% Nb) is a titanium-based intermetallic compound discovered about 10 years ago. Its crystal structure is orthorhombic and is named O phase. This Ti ₂ AlNb is based on the existing TiAl
Compared with (γ phase) and Ti ₃ Al (α ₂ phase), it is superior in high temperature ductility, creep characteristics and high temperature tensile strength.
It is attracting attention as a new lightweight heat-resistant material that bears iAl. At present, research and development toward practical use are underway, aiming at application to engine members of aircraft, automobiles and the like.

One of them is the high temperature B2 phase (CsCl
There is an attempt to improve room temperature ductility, fracture toughness, etc. by incorporating a (type structure) or β phase (bcc structure) into the metal structure. For example, GE Corp. of the United States of America has a well-balanced mechanical property of (O + B2 / β) type Ti-22Al-27N.
b (Ti-22 mol% Al-27 mol% Nb) alloy has been proposed (RGRowe: Microstructure / Property Relationsh
ips in Titanium Aluminides and Alloys, TMS, (199
1), pp.387-398).

[0004]

However, this O phase group Ti
In order to make -22Al-27Nb alloy a practical material, various characteristic values such as tensile properties at room temperature and high temperature (specifically, tensile strength and ductility), high cycle and low cycle fatigue properties, and creep properties are required. It is required to be expensive. Generally, it is difficult to achieve such improvement of each property with a single metal structure, for example, a so-called lamella structure formed by slow cooling from a high temperature B2 / β single phase region has excellent creep properties. Results have been obtained that lack tensile properties.

On the other hand, with respect to ordinary titanium alloys other than Ti ₂ AlNb, equiaxed α phase and α / β lamella having a quantity ratio (volume ratio) of several to 30% are formed as a metallographic structure balanced with various characteristics. So-called bi-modal consisting of combination with organization
A mixed organization called an organization has been proposed (M. Brun and
G. Shachanova: Titanium'95, The Institute of Mater
ials, (1996), pp.2421-2429).

However, in order to uniformly disperse the equiaxed α phase in a normal titanium alloy, the material is strongly worked in the α + β2 phase temperature range below the β transformation temperature (lower limit temperature of B2 / β single phase range), Next, the α phase must be recrystallized while maintaining it in the α + β2 phase temperature range. It requires a high degree of processing, and it is hard to say that it is practical in terms of workability and economy.

The invention of this application has been made in view of the above circumstances, and in order to use the O-phase based Ti-22Al-27Nb alloy expected as a lightweight heat resistant material as a practical material, the tensile strength and the ductility O with a high balance
An object is to provide a phase base Ti-22Al-27Nb alloy and a manufacturing method for manufacturing the same.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention of the present application aims to provide a lamellar structure in which a needle-shaped O phase is precipitated in a β-phase matrix and a uniform dispersion precipitation in the β-phase matrix. Provided is an O-phase based Ti-22Al-27Nb alloy (claim 1) having a bi-modal structure composed of the equiaxed α ₂ phase.

Further, the invention of this application is characterized in that after rolling in the α ₂ + β 2 phase temperature region below the β transformation temperature, it is held in this temperature region and then gradually cooled at a cooling rate of 1 ° C. per second or less. There is also provided an O-phase based Ti-22Al-27Nb alloy (claim 2) characterized by having a method for producing a Ti-22Al-27Nb alloy.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION
In order to provide the phase-based Ti-22Al-27Nb alloy with a well-balanced tensile strength and ductility, it was attempted to develop a bi-modal structure similar to a normal titanium alloy.

The β-transformation temperature of the Ti-22Al-27Nb alloy depends on the compositional variation, but is set to approximately 1050 to 1075 ° C. In the phase diagram, the temperature range up to about 1000 ° C below the β transformation temperature is α ₂ + β 2 phase region, and the temperature range below this is O 2.
It is considered to be the + β2 phase region. Therefore, the inventors of the invention of this application tried to perform rolling in the α ₂ + β 2 phase temperature range and then hold it in this temperature range. As a result, Ti-22
In the Al-27Nb alloy, the equiaxed α ₂ phase was uniformly and finely dispersed in the β phase matrix. Further, when the material in which the equiaxed α ₂ phase is uniformly and finely dispersed as described above is gradually cooled at a cooling rate of 1 ° C. or less per second, a needle-shaped O phase is precipitated in the β phase matrix to form a so-called lamellar structure. , A bi-modal structure consisting of equiaxed α ₂ phase and its lamellar structure appeared.

In the ordinary titanium alloy, as described above, in order to precipitate the equiaxed phase (that is, the α phase), the material needs to undergo considerable heavy working on the low temperature side, but Ti-22Al-27 is used.
For Nb alloys, the rolling temperature is α ₂ + β ₂ below the β transformation temperature.
As long as it is in the phase temperature region, the equiaxed α ₂ phase is uniformly dispersed even in the rolling with a low workability and a low workability such as reheating at each rolling. Also, the rolling process at this time is approximately 1000 ° C.
Since it is carried out at such a high temperature, the material is in a softened state, and therefore rolling was extremely easy. Furthermore, the obtained bi-modal structure showed good values in both tensile strength and ductility as compared with the lamella structure alone.

The invention of this application has been completed based on the above findings.

In the invention of this application, the rolling temperature,
The holding temperature and the cooling rate are limited to the above ranges for the following reasons. Rolled material in a single phase region above the rolling temperature β transformation temperature, then alpha ₂
+ Be held in .beta.2 phase temperature region not deposited on alpha ₂ phase equiaxed and the rolling temperature is less than alpha ₂ + .beta.2 phase temperature range, it would be O phase precipitates during rolling, bi street of the -No modal organization is available. Holding temperature If the holding temperature is above the β transformation temperature, the α ₂ phase does not precipitate in a sufficient amount, and if it is below the α ₂ + β 2 phase temperature range, the O phase precipitates during holding, and -Can't get modal organization.

The holding time is not particularly limited. In general, it is preferable to maintain the temperature until reaching a tissue that is equilibrium to some extent, and 1 hour or more can be a standard. Cooling rate When the cooling rate exceeds 1 ° C. per second, the O-phase does not precipitate in lamella during cooling, and the bi-modal structure as described above cannot be obtained.

The following will describe the O-phase group Ti-22Al-27Nb alloy of the present invention and the method for producing the same in more detail with reference to the following examples.

[0017]

[Example] Ti-22 produced by gas atomization method
The Al-27Nb alloy powder was formed by hot isostatic pressing, and then hot groove roll rolling was performed at 1000 ° C in the α ₂ + β 2 phase temperature range to produce a square bar. After cooling, the square bar was kept in the α ₂ + β 2 phase temperature range of 1000 to 1050 ° C. for 20 hours.

FIGS. 1A, 1B, 1C are photographs showing the metal structure immediately after the temperature was maintained. That is, FIG.
<a> is the one that was kept at 1050 ° C for 20 hours and then rapidly cooled in ice water. Figure 1 <b> is at 1030 ° C for 20 hours, and Figure 1 <c> is
It was held at 1000 ° C for 20 hours and then rapidly cooled in ice water.

As shown in FIGS. 1 (a), (b), and (c), by maintaining the temperature in the α ₂ + β 2 phase temperature range, β
A metallic structure in which the equiaxed α ₂ phase is uniformly dispersed in the phase matrix is obtained. Also, the equiaxed alpha ₂ phase that amount as the holding temperature increases is reduced, alpha ₂ phase spacing becomes larger.

For comparison, the B2 / β single-phase temperature range of 1150 ° C.
The square rod rolled at 1 is in the α ₂ + β 2 phase temperature range of 1
After holding at 030 ° C. for 20 hours, it was rapidly cooled in ice water. The photograph of FIG. 2 shows the obtained metallographic structure. This Figure 2
As shown in Fig. ₂ , the α ₂ phase was segregated around the pre-β grain boundary, and uniform dispersion was not obtained.

[0021] Then, α ₂ + β2 phase 1 of the temperature range the rolling angular rod fabricated by alpha ₂ + .beta.2 phase temperature range as at 1000 ° C. of
After being kept at 030 ° C. for 20 hours, it was gradually cooled at a cooling rate of 0.1 or 0.03 ° C. per second.

FIGS. 3A and 3B are photographs showing the metal structure after slow cooling. Figure 3 <a> shows the metallographic structure obtained by slow cooling at 0.1 ° C per second, and Figure 3 <b> shows 0.03 per second.
It is a metal structure obtained by slow cooling at ℃.

The metal structure after gradual cooling is a bi-modal structure consisting of an equiaxed α ₂ phase precipitated during temperature maintenance and a lamellar structure in which a needle-shaped O phase is precipitated in the β phase matrix during gradual cooling. became. From the comparison of FIGS. 3A and 3B, it is confirmed that the O / β phase becomes finer when the cooling rate is higher, that is, when the cooling rate is 0.1 ° C./sec.

In addition, for the O-phase based Ti-22Al-27Nb alloy having the bi-modal structure after the slow cooling, the room temperature to 80
Tensile tests were performed in vacuum up to 0 ° C. The result is shown in the graph of FIG. In the graph of Figure 4,
After rolling at 1150 ℃ in the B2 / β single-phase temperature range, holding at 1150 ℃ in the B2 / β single-phase temperature range for 1 hour, and then slowly cooling the Ti-22Al-27Nb alloy at a cooling rate of 0.03 ℃ per second The test results are also shown. The metal structure of the latter Ti-22Al-27Nb alloy was only the lamella structure as shown in FIG.

As can be seen in FIG. 4, the O-phase based Ti-22Al-27Nb alloy having a bi-modal structure has room temperature to 650 ° C as compared with the Ti-22Al-27Nb alloy having only a lamellar structure.
In the temperature range up to ° C, 0.2% proof stress (white mark in Fig. 4) and tensile strength (black mark in Fig. 4) show good values. In addition, in the O-phase based Ti-22Al-27Nb alloy having a bi-modal structure, a bi-modal structure having a finer O / β phase (faster cooling rate) exhibits higher tensile properties. As for ductility, the O-phase based Ti-22Al-27Nb alloy having a bi-modal structure has a lamellar structure of Ti only.
Compared with the -22Al-27Nb alloy, it shows a high value up to 800 ° C, which is much higher especially at high temperatures.

From the above results, O having a bi-modal structure
It is understood that the phase-based Ti-22Al-27Nb alloy has a highly balanced combination of tensile strength and ductility.

Of course, the invention of this application is not limited to the above embodiments. It goes without saying that various aspects are possible in details such as alloy composition, rolling method and conditions, holding temperature and holding time.

The invention of this application is not limited to the above-mentioned ternary Ti-Al-Nb alloy, but Ti-Al-Nb alloy.
It is considered that the method is equally applicable to quaternary alloys such as Mo.

[0029]

As described in detail above, according to the invention of this application, an O-phase based Ti-22Al-27Nb alloy having a highly balanced balance of tensile strength and ductility is realized.
This is extremely effective for practical use of Ti-22Al-27Nb alloy.

[Brief description of drawings]

[1] <a><b><c> are each, showed metal structure of Ti-22Al-27Nb alloy immediately after holding the alpha ₂ + .beta.2 phase temperature region after rolling with alpha ₂ + .beta.2 phase temperature range It is a photograph replacing a drawing.

FIG. 2 is a photograph, instead of a drawing, showing the metal structure of a Ti-22Al-27Nb alloy immediately after rolling in a B2 / β single-phase temperature range and then holding it in an α ₂ + β2 phase temperature range.

[Figure 3] <a><b><c> are each held in alpha ₂ + .beta.2 phase temperature region after rolling with alpha ₂ + .beta.2 phase temperature range, and then slowly cooled at per 1 ℃ less cooling rate Ti-22Al-27
It is a photograph substituted for the drawing which showed the metal structure of Nb alloy.

FIG. 4 is a graph showing the results of a tensile test in vacuum of a Ti-22Al-27Nb alloy having only a bi-modal structure and a lamella structure as a metal structure from room temperature to 800 ° C.

FIG. 5: Rolling in the B2 / β single-phase temperature range, holding in the B2 / β single-phase temperature range, and then slow cooling at a cooling rate of 0.03 ° C. per second
It is a photograph replacing a drawing showing a metallographic structure of an i-22Al-27Nb alloy.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI C22F 1/00 683 C22F 1/00 683 692 692A 693 693A 694 694B (56) Reference JP-A 2001-152269 (JP, A) JP-A-11 -241131 (JP, A) JP 5-214470 (JP, A) JP 2-247345 (JP, A) JP 11-80866 (JP, A) JP 11-61298 (JP, A) ) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 14/00 C22F 1/00-3/02

Claims (2)

(57) [Claims] 1. A bimodal structure in which an acicular O-phase has a lamella structure precipitated in a β-phase matrix and an equiaxed α ₂ phase uniformly dispersed in the β-phase matrix. O-phase based Ti-22Al-27Nb alloy. 2. An O phase group Ti-22 characterized by being rolled in the α ₂ + β 2 phase temperature range below the β transformation temperature, held in this temperature range, and then gradually cooled at a cooling rate of 1 ° C. or less per second.
Manufacturing method of Al-27Nb alloy.