JPH05277656A - Thin plate of alloy containing ti3al group intermetallic compound and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a technology for preventing product defects (surface crack, porosity) in the direct casting technology of Ti3Al group intermetallic compound material which is a hard-to-work material having a temperature transition point in ductility and brittleness above room temperature. CONSTITUTION:The thin plate of alloy containing the subject intermetallic compound is the Ti3Al group intermetallic compound material containing Al: over 7% to 28% (atomic %, as same heterinafter) and balance of Ti or containing Al: over 7% to 28%, in addition one or two kinds from Mo: 0.5 to 3% and Nb: 0.5-1.8%, and balance of Ti. The material is continuously cast on the thin plate having thickness of 0.25-25mm by means of a double drum continuous casting machine as a device for near net shaping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing surface cracking, which is a problem in the production of thin plates of alloys containing Ti ₃ Al-based intermetallic compounds, and provides a method for producing thin plate materials having excellent surface properties. To do.

[0002]

2. Description of the Related Art TiAl intermetallic compounds, Ti ₃ Al intermetallic compounds, Nb ₃ Al intermetallic compounds, FeAl intermetallic compounds, and Fe ₃ Al intermetallic compounds have been developed as materials for environment-resistant structural materials. There are compounds, Al ₃ Ti intermetallic compounds and the like. Since these materials have excellent high-temperature strength characteristics, they are expected to be developed as future structural materials. However, a common problem with any material is its difficulty in molding. Therefore, a near net shape casting technique, which is close to the final product, is required to manufacture a thin plate.

The thin plate manufacturing technique for forming such a near net shape has been rapidly developed in recent years, and the application to the production of stainless steel / thin plate is progressing especially in the metal material system. As a thin plate manufacturing technique, various casting methods have been proposed. Among them, the twin roll method is suitable for producing a continuous thin plate having a uniform thickness. As an example of applying the above technique to an intermetallic compound material, an example of a nickel-aluminum intermetallic compound (Ni ₃ Al) whose ductility is improved by adding a trace amount of boron is known. An example of this is "Near Net." Held in November 1988.
"Casting of Ne"
ar Net Shape Products ”) (Proceeding)
s offan International Symp
osium of NearNet Shape Pr
products, pages 315-333, The Met
published by allrural Society). A method for manufacturing a TiAl intermetallic compound sheet is described in Japanese Patent Application No.
It is described in Japanese Patent No. 50648.

[0004]

The near net shape forming by the thin plate direct casting technique has advantages such as the omission of steps, but defects (surface cracks, porosity) of the thin plate occur due to rapid cooling after casting. It has the drawback.
In particular, a material having a ductile-brittle transition temperature of room temperature or higher, such as an intermetallic compound material, is apt to crack due to thermal strain, and this problem is remarkable.

Therefore, when a thin plate is produced by directly casting a difficult-to-process material, the removal of surface defects is an important issue for ensuring the soundness of the material.

[0006]

The object of the present invention is to provide a direct casting technique for a Ti ₃ Al-based intermetallic compound material which is a difficult-to-process material having a ductile-brittle temperature transition point above room temperature. It provides technology to prevent product defects (surface cracks, porosity). The alloy containing the intermetallic compound, which is the object of the present invention, is in atomic%: Al: more than 7% to 28% and the balance is Ti
i ₃ Al-based intermetallic compound or ・ Al: more than 7% to 28% and further Mo: 0.5 to
3%, Nb: 0.5 to 18% of one or two kinds, and the balance is made of an alloy material containing a Ti ₃ Al-based intermetallic compound, and is used as a near net shape forming device. It is a thin plate having a thickness of 0.25 to 25 mm cast by using the twin drum type continuous casting machine shown in FIG. 1.

The inventors of the present invention have conducted various studies to achieve the above-mentioned problems, found that it is effective to specify the heat treatment immediately after casting, and completed the present invention. Another object of the present invention is to cast a plate-shaped thin plate slab by injecting the molten metal of the difficult-to-process material into a mold of a twin-drum type continuous casting machine, and then at 500 to 1000 ° C. in the slab immediately after casting. There is a method for producing a sound thin plate material by holding the material for a certain period of time and then slowly cooling it at 200 ° C./hr to prevent the occurrence of strain due to thermal stress and prevent the occurrence of surface cracks. Also, after this
We aim to improve elongation in hot working by reducing porosity by IP treatment. In addition, the characteristics of the material obtained by the above method are the columnar crystals aligned in the surface direction of the thin plate and the equiaxed crystal structure of the central portion, and the compound having the crystallographic correlation between the DO ₁₉ structural phase and the β-Ti phase. That is to have an organization.

[0008]

[Operation] First, the cast structure advantageous for plastic working will be described. The twin-roll cast thin plate of the present invention has a solidification structure as cast only columnar crystals directed from both surfaces of the slab toward the center, or a mixed structure of the columnar crystals and equiaxed crystals existing near the slab center. ing.

Next, a method of casting the plate-shaped thin cast piece will be described. Generally, a drum type continuous casting machine (hereinafter referred to as a continuous casting machine) has two cooling drums arranged so as to rotate in parallel and in opposite directions, and a side dam is provided outside the cooling drums to form a molten metal pool. A (mold) is configured and a thin plate cast is manufactured while cooling the molten metal in the molten metal pool by rotating the cooling drum.

In the present invention, molten metal of various intermetallic compounds is injected into the pool to manufacture a thin cast slab. However, since the intermetallic compound material is a material having low ductility, the slab is cracked during cooling. Therefore, it is necessary to suppress the formation of oxides in the meniscus portion, which easily causes uneven solidification. Therefore, it is necessary to melt and cast in an inert gas (Ar, He, etc.).

Although direct casting by the above-mentioned method is a conventional method, the above-mentioned method alone causes a rapid cooling accompanying the direct casting, especially in the case of an intermetallic compound having a high ductile-brittle transition temperature.
The rapid thermal strain causes a crack at the time when the ductile-brittle transition temperature is passed, which causes a fine surface crack.
The removal of this surface crack is the object of the present invention. As a solution to this problem, it is desirable that the cast slab after demolding is gradually cooled to 200 ° C. or less at a cooling rate of 200 ° C./hr or less in order to avoid rapid cooling. However, as a gradual cooling method, the slab immediately after solidification is held in the temperature range of 500 to 1000 ° C. for a certain period of time and then cooled in the furnace to obtain 200 ° C./h.
Cooling rates slower than r may be achieved. This holding temperature is a temperature for preventing the occurrence of cracks due to thermal stress.

By the above method, the columnar crystals aligned in the sample surface direction and the equiaxed crystal structure of the central portion, which are the characteristics of the material, and the compound having the crystallographic correlation between the DO ₁₉ structural phase and the β-Ti phase are obtained. The organization is obtained. Next, HIP processing is performed for the purpose of crushing the porosity (void portion) of the cast material. As the HIP processing condition, the slab is held in a temperature range of 1000 to 1400 ° C. (melting temperature or lower) in an atmosphere of 1000 atm or higher for 10 minutes to 1 hour.

By the above method, it is possible to manufacture a thin plate of an alloy containing an intermetallic compound, which is excellent in surface quality and has no porosity.

[0014]

EXAMPLE Aluminum ingot, titanium sponge, and other elements (Mo, Nb) were mixed in the composition shown in Table 1, and this was melted by a plasma arc to refine a mother alloy. Next, each of the master alloys was poured into the casting machine shown in FIG. 1 to cast a thin cast piece. The casting machine has the following structure. In the figure, a tundish 2 for uniformly supplying a molten metal is arranged below a crucible 1 for melting an intermetallic compound, and a molten metal pool 5 (mold) composed of a cooling drum 3 and a side dam 4 is provided immediately below the tundish 2. These are arranged in the atmosphere adjusting container 7. Reference numeral 8 is an inert gas introducing mechanism, and 9 is an discharging mechanism.

Each of the mother alloys shown in Table 1 is 2000-3500.
After being put in the crucible in a weight range of g, melted by heating in an Ar atmosphere, and once adjusted to a temperature of 1700 ° C., a width of 4 m
It was poured into the pool 5 through a tundish having an opening of m and a length of 95 mm. The cooling drum 3 which constitutes the pool 5 is made of a pair of copper alloys having a diameter of 300 mm and a width of 100 mm and is internally cooled. This cooling drum 3 holds the molten metal at a constant drum supporting force and at 10 ³ ° C / se.
It was rapidly solidified according to the cooling rate of c, and the results are shown in Table 1 (No. 1,
A continuous plate-shaped slab having the thickness shown in 2) was produced.

The slab 6 sent out from the cooling drum 3 is gradually cooled in the atmosphere adjusting container 7 at a cooling rate of 1 ° C./sec and then inserted into the heating furnace for the transport system. In the furnace, the secondary cooling shown in Table 1 is carried out. Treated with conditions. Then, the power of the furnace was stopped and the temperature was cooled to 200 ° C or lower. Table 1 (No. 3 to 8)
As shown in (3), the gentle cooling treatment prevented surface cracks and improved the surface properties.

Regarding the sectional structure in the casting direction of the obtained slab, the as-cast solidification structure exists only in the columnar crystals extending from both surfaces of the slab toward the center, or in the vicinity of the columnar crystal and the slab center. It is composed of a mixed structure with equiaxed crystals.
The microstructure of the cast slab obtained by the method of the present invention is β-centered around the structure in which the <0001> crystal direction of the DO ₁₉ type structure in the Ti ₃ Al-based intermetallic compound is preferentially oriented in the cast slab thickness direction. The structure including the Ti phase has a fine layered composite structure, but the layered structure is extremely fine due to the addition of the third element such as Mo and Nb, and the width of one layer is It was 1000 nm. In a normal solidified structure that is cast without adding the third element, this width is 10,000 nm, which is a coarse structure.

Table 2 shows the mechanical properties (breaking stress of three-point bending) at room temperature of the thus obtained slab. The present invention example shows a high value. The surface texture of the slowly cooled slab and the surface texture of the slab left to cool after leaving the cooling drum are shown in FIGS. 2 (A) and 2 (B), respectively. Almost no cracks were found on the surface of the slowly cooled slab, but fine surface cracks were observed on the surface of the slab that was allowed to cool.

Table 1 shows the surface texture of each sample after furnace cooling. The examples of the present invention were all good. Also, 20
The rupture stress of the slab that had been furnace-cooled to 0 ° C. or lower and subjected to the HIP treatment of holding at 1000 ° C. and 1500 atm for 1 hour was examined. The results are shown in Table 2. It was confirmed that the inventive example had a larger breaking stress than the comparative example, and that the breaking stress was remarkably increased by the HIP treatment.

In order to examine the porosity removing effect of the HIP treatment, HIP treatment at 1250 ° C., 1500 atm for 1 hour was performed, and it was found that most of the porosity before the HIP treatment was removed. Also, Mo
Degree of hot working (800 ℃, 5 × 1
The strain rate of 0 ⁻⁴ sec ⁻¹ ) was investigated, and it was possible to obtain 100% elongation after the HIP treatment, and the difference from the sample of the comparative example was obvious.

As described above, according to the present invention, the mechanical properties of the obtained slab or treated thin plate are remarkably improved. This is mainly because the texture of the Ti ₃ Al intermetallic compound was refined by the addition of the third element,
This is considered to be the result of HIP processing.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

As is apparent from the above examples, the rapidly solidified thin cast piece or the treated thin plate produced by the present invention has mechanical properties and surface properties superior to those of conventional thin cast pieces. Since it provides a new method for producing a difficult-to-process material, it is extremely useful industrially.

[Brief description of drawings]

1 is a cross-sectional side view showing the outline of an apparatus for carrying out the present invention.

FIG. 2 (A) is a photograph showing the surface state of the material of the present invention after cooling after casting, and FIG. 2 (B) is a photograph showing the surface state of the material of the present invention after cooling after casting.

[Explanation of symbols]

 1 crucible 2 tundish 3, 3 cooling drum 4 side dam 5 molten metal pool 6 cast slab 7 atmosphere control container 8 inert gas introduction mechanism 9 exhaust mechanism

Claims (6)

[Claims] 1. Al in atomic%: more than 7 atomic% to 28 atomic%
Alloy material containing Ti ₃ Al-based intermetallic compound containing Ti and the balance being Ti or Al: more than 7 atomic% to 28 atomic%, further Mo: 0.5 to 3 atomic%, Nb:
It is made of an alloy material containing 0.5 to 18 atomic% of one or two kinds and the balance is a Ti ₃ Al-based intermetallic compound composed of Ti, and the as-cast solidification structure is on both surfaces of a plate-shaped thin cast piece. Ti having a columnar crystal structure extending from the center to the center, and the thickness of the slab is 0.25 to 2.5 mm.
₃ Thin alloy plate containing Al-based intermetallic compound. 2. The Ti ₃ A composition according to claim 1, wherein the as-cast solidification structure is a mixed structure of a columnar crystal structure extending from both surfaces of the slab toward the center and an equiaxed crystal existing near the center of the slab.
An alloy thin plate containing an l-based intermetallic compound. 3. The method according to claim 1 or 2, wherein the columnar crystal structure is DO ₁₉ in a direction from both surfaces of the cast slab toward the center.
A thin plate of an alloy containing a Ti ₃ Al-based intermetallic compound which is preferentially oriented in the <0001> direction of the structure and which has a β-Ti phase and a fine composite structure of a DO ₁₉ structure. 4. Al in atomic%: more than 7 atomic% to 28 atomic%
Alloy material containing Ti ₃ Al-based intermetallic compound containing Ti and the balance being Ti or Al: more than 7 atomic% to 28 atomic%, further Mo: 0.5 to 3 atomic%, Nb:
Mold of twin-drum type continuous casting machine containing molten alloy material containing 0.5 to 18 atomic% of 1 or 2 and the balance of Ti ₃ Al based intermetallic compound consisting of Ti in an inert gas atmosphere 0.25 to 0.25
A 2.5 mm plate-shaped thin cast piece is cast, and the obtained cast piece is cooled to 200 ° C. or less at a cooling rate of 200 ° C./hr or less immediately after being separated from the twin drum.
A method for manufacturing a thin plate of an alloy containing an i ₃ Al-based intermetallic compound. 5. The Ti ₃ Al according to claim 4, wherein the slab cooled to 200 ° C. or lower is subjected to a reduction treatment by high temperature hydrostatic pressure in a temperature of 1000 ° C. or higher and an atmosphere of 1000 atmospheric pressure or higher. A method for manufacturing a thin plate of an alloy containing a base intermetallic compound. 6. The method according to claim 4, wherein the slab is separated from the twin drum, and immediately after the cast slab is separated from the twin drum, the temperature range of 500 to 1000.degree.
A method for producing a thin plate of an alloy containing a Ti ₃ Al-based intermetallic compound, which is maintained for 20 minutes and then cooled to room temperature at a cooling rate of 200 ° C./hr or less.