JPH03193852A - Production of tial-base alloy consisting of superfine structure - Google Patents

Abstract

PURPOSE:To obtain a Ti-Al alloy consisting of a fine structure and excellent in hot workability and formability while preventing the coarsening of the structure and maintaining sufficient workability by subjecting a Ti-Al alloy having a specific composition to hot working in a specific temp. range related to the gamma-single phase temp. region of the alloy. CONSTITUTION:A Ti-Al alloy having a composition which consists of, by weight, 35.0-38.0% Al and the balance Ti and contains, if necessary, 3-5% Cr and in which O2 as an impurity is limited to <=0.1% and also having a structure in which a gamma-phase comprises >=95% by volume in the equilibrium state at room temp. is hot-worked in vacuum or in an inert-gas atmosphere in a temp. region between the upper-limit temp. in the gamma-single phase temp. region of the alloy and the solidus temp. and in the plural phases coexisting temp. region (a crosshatched part in the figure) of alpha+gamma or beta+gamma and further subjected to secondary working in the gamma-single phase temp. region at 10-90% draft. By this method, the Ti-Al alloy having extremely fine structure and remarkably improved in hot workability and formability as well as in deterioration in ductility at room temp. due to the ordinary coarse structure and acicular structure can be obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention is γi1f! The present invention relates to a method for producing a base alloy.

More specifically, the present invention relates to a method for producing a TiAl-based alloy having an ultrafine structure.

[Conventional technology]

TiA 1 intermetallic compound or TiAlfi-based alloy has extremely low specific gravity and excellent heat resistance compared to general-purpose heat-resistant alloys such as Ni or Co-based superalloys, making it lightweight and heat resistant. It is expected to be used as a key component material for ultra-high-speed aircraft and spacecraft, where improvements in performance are strongly desired, and research into practical application is underway.

However, the γiA single-base alloy has extremely poor ductility at room temperature;
Furthermore, it has not been put into practical use because of its poor hot workability and moldability. The biggest reason for this is that coarse structures and acicular structures that reduce ductility and workability tend to occur. As a countermeasure, we have added innovations to hot processing methods such as constant temperature forging, extrusion with added lateral pressure, Tsujimoto Tokuzo, Materials Science, September 1985, p. 82), and sheath rolling (Japanese Patent Application Laid-open No. 171862/1986). Furthermore, attempts have been made to refine the structure by processing at 1000 to 1250°C and utilizing recrystallization during processing. However, even if these methods are used,
When processed at low temperatures, a non-homogeneous recrystallized structure tends to occur, and in order to obtain a homogeneous recrystallized structure, it is necessary to perform strong processing of 70% or more. Sufficient effects have not been obtained when applied to base alloys. Furthermore, although the processability is improved when processed at high temperatures, the structure becomes coarser, so there is a problem in that the original objective of microstructure refinement is insufficient.

[Problem to be solved by the invention]

The present invention is a TiA film that makes it possible to obtain a fine structure by hot working while preventing the structure from becoming coarse due to an increase in processing temperature and maintaining sufficient workability.
The object of the present invention is to provide a method for producing an l-based alloy.

[Means to solve the problem]

According to the present invention, the above object is to heat a TiAl-based alloy having a composition in which the γ phase accounts for 95% or more by volume in an equilibrium state at room temperature at a temperature above the upper limit temperature of the γ single phase temperature range and below the solidus temperature. A method for producing a TiAl-based alloy having an ultrafine structure characterized by processing at a processing rate of 50% or more and 90% or less at a temperature, or performing the processing by isothermal forging in a vacuum or an inert gas atmosphere. A method for producing a TiAl-based alloy having an ultra-fine structure, or a TiA-based alloy having an ultra-fine structure, further comprising performing secondary processing of 10% or more and 90% or less within the T single-phase temperature range.
12 base alloy manufacturing method, or 35.0 to 38.0
Contains 0.1% by weight of Al and 0.1% of oxygen as an impurity element.
Ti//! consisting of an ultrafine structure characterized by performing the above processing using a binary TiAl intermetallic compound limited to less than % by weight! Manufacturing method of base alloy, or 3-5% by weight
This is achieved by a method for producing a TiA single-base alloy having an ultrafine structure, which is characterized in that the above processing is carried out using a TiAl-base alloy containing Cr.

[For production]

Here, the TiAl-based alloy is a binary TiAl alloy containing 31 to 40% by weight of Al and 60 to 70% by weight of Ti.
It is an intermetallic compound or alloy. Of these, for alloys T
In addition to i, Aj2, and impurity elements that are inevitably present, it further contains one or more third elements. Also, the γ phase is Ll. It is an intermetallic compound phase with a crystal structure of

The reason why the TiAlfi-based alloy to which the present invention is applied is limited to a composition in which the γ phase accounts for 95% or more by volume in an equilibrium state at room temperature is that if the composition has a γ phase of less than 95%, the ductility will significantly decrease. This is because a large amount of deteriorating acicular tissue is generated, so that the effects of the present invention cannot be sufficiently obtained.

The present invention is applied to the most general-purpose T i -A element system equilibrium diagram shown in Fig. 1 (Source: J, L, Murray [rP
haseDiagram of Binary
Titanium A11oysJ ASMInte
This will be explained using pages P12-24 published by rnationa1.

According to this phase diagram, when the Al concentration is 35.0% by weight or more, 95% or more becomes the γ phase at room temperature. Also/l
In the composition range with a concentration of 38.0% by weight or less, the temperature range where multiple phases of α+γ or β+T coexist at temperatures above the upper limit temperature of the γ single-phase temperature range and below the solidus temperature (the hatched part in the figure) ) exists. The present invention aims at microstructural refinement using recrystallization and transformation caused by processing by performing hot working in a temperature range where such multiple phases coexist. In the present invention, the upper limit of the processing temperature is set to the in-plane phase temperature. This is because when the processing temperature exceeds the solidus temperature, a liquid phase occurs and hot processing becomes impossible.

In addition to the unavoidably present impurities, the TiAl-based alloy to which the method of the present invention is applied contains one or more third elements in a total amount for the purpose of improving ductility and workability, or promoting microstructural refinement. It may be added in an amount of 0.5% by weight or more. An example is a TiAlfi-based alloy with 3 to 5% by weight of Cr added. When containing a third element in this way,
Since the γ single-phase temperature range expands to the high-concentration Al side and the low-concentration Af side, the Al concentration range in which the above-mentioned multi-phase coexistence temperature range exists is expanded from that shown in Fig. 1, and is used in the range of 31 to 40% by weight. be able to.

In addition, in order to improve room temperature ductility and hot workability, it is desirable to reduce the oxygen content as much as possible, and especially in binary TiA i and intermetallic compounds, the oxygen content should be reduced to 0.
It is desirable that the amount is 1% or less.

TiAjl with a composition in which the γ phase accounts for 95% or more at room temperature! The base alloy is processed at a processing rate of 50% to 90% at a temperature above the upper limit temperature of the γ single phase temperature range and below the solidus temperature. If the processing rate is less than 50%, an acicular structure that reduces room temperature ductility is likely to be generated, and the effects of the present invention cannot be fully achieved. Moreover, when the processing rate exceeds 90%, the progress of cracking becomes remarkable.

The above-mentioned processing is preferably performed by isothermal forging in a vacuum or an inert gas atmosphere. Constant temperature forging is γiAj
! It has been widely known as a desirable hot working method for materials with poor workability such as base alloys. By performing processing in a vacuum or inert gas, material deterioration and processing cracks due to oxidation can be prevented.

After performing the above-described processing, microstructural refinement can be further promoted by further processing the material by 10% or more and 90% or less at a temperature within the γ single phase temperature range. This second processing may be performed by cooling to room temperature after the first processing and then heating it again to the second processing temperature, or directly after the first processing. Processing may be performed by lowering the temperature to the second processing temperature. If the processing rate is less than 10%, no additional texture refinement will be achieved. Also, the processing rate is 90%
If it exceeds this, the progress of cracking becomes noticeable.

The present invention will be explained in more detail below using Examples.

[Example] AI on the blind screen! A TiAl-based alloy (binary TiAl intermetallic compound) containing 35.6 wt. % of was manufactured. A test piece with a height of 120 mm and a diameter of 100 mm was cut out from this ingot.
It was subjected to a hot working test.

The upper limit temperature of the γ single phase temperature range in the above composition is 1340°
The C1 solidus temperature is 1480°C, and between this temperature there is a β+T two-phase structure.

The hot working was performed in vacuum (I Xl0-'Torr) by constant temperature forging. The above test piece was placed in a graphite mold and upset forged at an initial strain rate of 5 x 10-'' per second.At this time, to prevent reaction between the test piece and the mold, a thickness of 300 aa was placed between the two. Tantalum foil was inserted as a spacer.Table 1 shows the test results conducted by varying the processing temperature and processing rate.

Table 1 (Note) * The value in parentheses is the grain size. The value in parentheses is the thickness ***1
Coarse grains of 100u or more.

Example 1゜2 where processing was performed at a processing temperature (1340-1480°C) and processing rate (50% or more) within the range of the present invention
and No. 3, the proportion of equiaxed structure with good ductility and workability is extremely high at 90% or more, and the crystal grain size is equiaxed structure of 0.
5-1-1 Even if there is a small amount (10% or less) of needle-like tissue, 1
A fine structure with ~2 lines was obtained, and no unrecrystallized coarse elongated grains remained.

Furthermore, despite the high processing rate of 55 to 80%, cracks during processing were extremely slight (depth of 0.5 to Im) and caused no problems at all.

On the other hand, in Conventional Example 1 and Comparative Example 1, in which the processing temperature is lower than that of the present invention, there are considerably many unrecrystallized coarse elongated grains, and the grain size of the equiaxed structure is 50 to 80.
The corners were extremely rough. Furthermore, in Conventional Example 1 where the processing temperature was particularly low, the cracks progressed to a depth of 15 mm, resulting in a large decrease in yield.

In addition, in Comparative Example 2, although the processing temperature was within the range of the present invention, the processing rate was below the range of the present invention, so the proportion of acicular structure that reduces ductility and workability was as high as 20%.
Fine equiaxing was insufficient.

Further, in Comparative Example 3, the processing temperature was within the range of the present invention, but the processing rate was above the range of the present invention, so cracks progressed to a depth of 8M, resulting in a large decrease in yield.

Test amount'' - Next, the test piece processed in Example 2 of Test 1 was once cooled to room temperature, and minor cracks (1 m or less in depth) on the surface layer were removed by grinding. It was heated again to a temperature in the γ single-phase region, and processed by isothermal forging in the same manner as in Test 1 while changing the processing rate. The results are shown in Table 2.

Table 2 (Note) * The value in parentheses is the particle size. The value in parentheses is the thickness ***1
Coarse grains with OOura.

In Example 4 (comparative example in Claim 3), processing was performed at a processing rate smaller than the desired processing rate (10% or more) of the present invention, so additional refinement was not achieved compared to Example 2. , rather it has become coarser.

Examples 5 and 6 are cases where processing was performed at the desired processing rate of the present invention, and both achieved further refinement compared to Example 2.

In addition, in Example 6, no cracks were observed despite processing at a processing rate of 70%, and workability was significantly improved compared to Conventional Example 1 in Table 1, which was processed at the same temperature and processing rate. .

Further, in Comparative Example 4, since the processing rate was above the range of the present invention, cracks progressed to a depth of 8 mm, resulting in a large decrease in yield.

The main content of the wiper is 33.2% by weight of Al, 4.1% by weight of Cr, and 0% of oxygen.
．． 12% by weight of TiAl, the remainder consisting essentially of Ti
The base alloy was melted by plasma arc melting, and an ingot was cast. A test piece having the same dimensions as Test 1 was cut out from this ingot and subjected to a hot working test. In addition, the upper limit temperature of the γ single phase temperature range in the above composition is 1330°C5
The solidus temperature is 1430°C, and between this temperature γ+
It is a β two-phase structure (or a T+β+α three-phase structure).

Using this test piece, a hot working test using constant temperature forging similar to Test 1 was conducted. The results are shown in Table 3.

Table 3 below (Note) *The numbers in parentheses are particle diameters The numbers in parentheses are thickness ***1
Coarse particles of 00 flies or more.

Example 7゜8 where processing was carried out at a processing temperature (1330-1430°C) and processing rate (50% or more) within the range of the present invention.
, and 9 have an extremely high proportion of equiaxed structure with good ductility and workability of 90% or more, and the crystal grain size is 0 in equiaxed structure.
．． 2 to 0.5 s, even if a small amount (10% or less) of the acicular structure was present, a fine structure of 0.5 to 1 strand was obtained, and no unrecrystallized coarse elongated grains remained at all. Furthermore, despite the high processing rate of 55 to 80%, cracks during processing were extremely slight (less than 0.3 to 0.5 m deep) and caused no problems at all. In addition, Example 1 of Test 1 in which Cr was not added.
Compared to 2 and 3, the crystal grain size is finer, and C
Refinement was further promoted by the addition of r.

In contrast, conventional example 2 has a lower processing temperature than the present invention.
In Comparative Example 5, there were quite a lot of unrecrystallized stretched grains, and the grain size of the equiaxed structure was as large as 30 to 50. In addition, especially in conventional example 2 where the processing temperature is low, 1
Cracks had progressed to a depth of 0 m, resulting in a large decrease in yield.

In addition, in Comparative Example 6, although the processing temperature was within the range of the present invention, the processing rate was below the range of the present invention, so the proportion of acicular structure that reduces ductility and workability was as high as 15%.
Fine equiaxing was insufficient.

In addition, in Comparative Example 7, the processing temperature was within the range of the present invention, but the processing rate was above the range of the present invention, so cracks progressed to a depth of 7 mm, resulting in a large decrease in yield.

Weight % Az [Effects of the Invention] As explained above, according to the present invention, the processing temperature can be reduced by performing hot working in a temperature range above the upper limit temperature of the γ single phase temperature range and below the solidus temperature. TiA II has a fine structure that prevents coarsening of the structure due to rise and maintains sufficient workability.

Base alloys can be produced.

[Brief explanation of drawings]

FIG. 1 shows an equilibrium phase diagram of the γi-AN binary system. Figure 1 L...Liquid phase

Claims (1)

[Claims] 1. A TiAl-based alloy having a composition in which the γ phase accounts for 95% or more by volume in an equilibrium state at room temperature is heated in a temperature range above the upper limit temperature of the γ single phase temperature range and below the solidus temperature range. , 50% or more9
A method for producing a TiAl-based alloy having an ultrafine structure, characterized by processing at a processing rate of 0% or less. 2. The method for producing a TiAl-based alloy having an ultrafine structure according to claim 1, wherein the processing is performed by isothermal forging in a vacuum or an inert gas atmosphere. 3. Furthermore, a second temperature of 10% or more and 90% or less within the γ single phase temperature range
3. A method for producing a TiAl-based alloy having an ultrafine structure according to claim 1 or 2, which comprises performing a subsequent processing. 4. Binary system T containing 35.0 to 38.0% by weight of Al and limiting oxygen as an impurity element to 0.1% by weight or less
A method for producing a TiAl-based alloy having an ultrafine structure according to any one of claims 1 to 3, characterized in that an iAl intermetallic compound is used. 5. A method for producing a TiAl-based alloy having an ultrafine structure according to any one of claims 1 to 3, characterized in that a TiAl-based alloy containing 3 to 5% by weight of Cr is used.