JPH0344437A - Ti-al intermetallic compound thin sheet and its manufacture - Google Patents

Abstract

PURPOSE:To continuously manufacture the thin sheet in an easy way with high efficiency by continuously feeding Ti-Al series molten metal having speci fied compsn. to the space between a pair of cooling rolls rotating at a prescribed rate and solidifying it at a specified cooling rate. CONSTITUTION:By weight, 35 to 44% Al and the balance Ti are blended, which is melted under heating in an inert gas atmosphere. The molten alloy is continu ously fed to the space between a pair of cooling rolls rotating at 0.1 to 10m/sec circumferential rate through a tundish, which is solidified at 10<2> to 10<5> deg.C/sec cooling rate by a certain supporting force of the twin roll. In this way, the Ti-Al intermetallic compound thin sheet of 0.2 to 3mm sheet thickness in which the solidified structure as cast is constituted of only columnar crystals oriented from both surfaces of the thin sheet to the central part of the sheet thickness or constituted of a mixed structure of the columnar crystals and equiaxed crystals present around the center of the sheet thickness can continuously be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a continuous thin plate of homogeneous TiAl intermetallic compound and a method for producing the same.

[Conventional technology]

TiAl intermetallic compound is generally called TiAl alloy, and has extremely high high temperature strength as a metal material.
Moreover, it is a lightweight material with high corrosion resistance.

Metallurgical Transaction
n, Vol. 68 (1975).

p, 1991, it is reported that a high temperature strength of 40 kg/m- was obtained at 800°C. Taking advantage of these properties, TiAl alloys have been applied to gas turbine axial crystals, automobile engine valves and pistons, high-temperature disks and bearings as axial crystals, aircraft frames, and the exterior of ultra-high-speed passenger planes. It is considered suitable for application to plates, etc.

Ti/V alloys are lightweight, have a high heat resistance, and have high corrosion resistance, so they are suitable for turbine blades used at high temperatures, but their low ductility at room temperature makes it difficult to form the bottom shape by rolling or forging.

In addition, in particular, the thin plate of TiAl intermetallic compound is considered to be applied to the outer panel of an ultra-high-speed passenger aircraft among the above application examples, but in this case, the thickness is about 1 mm and the thickness is 30cra x 30cm.
It is essential to establish a manufacturing method for thin plates with a thickness of about 1.5 m.

Conventionally, thin plates of TiAl intermetallic compounds have been produced by cutting out ingots or by sheathing as shown in Japanese Patent Application Laid-Open No. 61-213361, but long thin plates have not been obtained.

In addition, the yield rate is poor when cutting from ingots,
There is a problem in that it is difficult to obtain a uniform aura due to gravitational segregation and the like. Conventional high-temperature plastic working methods include sheath processing, hydrostatic extrusion, isothermal forging, hot extrusion, and the like. However, it is difficult to apply these processing methods, and TiA! In the case of intermetallic compounds, it was necessary to overcome the problems of high high-temperature strength (200 MPa at 1050'C) and high strain rate dependence. That is, in the above-mentioned Japanese Patent Application Laid-Open No. 61-213361, sheath processing is used to
-1100°C1 using 816Go-based superalloy sheath material
It is said that a rolling speed of 1.5 m/min is required.

Also, Japan Institute of Metals Symposium Proceedings, September 21st, (
1988), p. 24, in isothermal forging, 950
10-2 to 10-” 5ec at a temperature of ~1000°C
-' strain rate is required. Therefore, there were problems in that temperature control was difficult and production speed was slow.

From the above point of view, it is considered virtually impossible to manufacture a thin plate with a thickness of about 30 cm x 30 cm from an ingot or other ingot using the conventional method described above, both from the production speed and equipment standpoint. .

Furthermore, in the method for manufacturing a thin plate according to the above-mentioned conventional technology, the dimensions of the obtained thin plate are small, for example, about 20 mm in length, 10 mm in width, and 10 mm in thickness, and the process is complicated and requires a lot of labor and equipment. The problem was that it was necessary.

As a conventional technique using a rapid cooling method for TiAl intermetallic compounds, as shown in Japanese Patent Application Laid-Open No. 62-256902, molten metal is cooled using a rapid solidification process such as a single roll method or a twin roll method. There is a method of obtaining a flake-like solidified product by rapid solidification at a cooling rate of 10'°C/sec or higher, but there is no report of obtaining a continuous thin plate.

[Problem to be solved by the invention]

As mentioned above, with the conventional technology, it was impossible to manufacture a thin plate of Ti7V all 7V compound with a thickness of about 1 mm and a size of about 30 cm x 30 cm, but the present invention solves this problem and produces a continuous thin plate of TiAZ intermetallic compound. The object of the present invention is to provide an easy and efficient manufacturing method for the same thin plate.

[Means to solve the problem]

The twin roll method can process a thin plate several meters thick x several tens of centimeters wide at several m/s.
It is generally known as a method for continuous production at a speed of EC, and is considered to be an ideal process for producing Ti/V intermetallic compound thin plates from the viewpoint of the dimensions of the thin plates mentioned above. In addition, compared to conventional techniques, the process up to the production of thin plates is extremely simple, and additional effects such as process savings, equipment savings, and labor savings are also possible.

Other processes that cast sheet metal directly from molten metal include
There are methods such as the twin belt method, single belt method, and single roll method.

However, in the method using a belt, the thickness of the obtained thin plate is several centimeters, which is too thick compared to the thickness of the final product, so there is not much difference in the amount of labor required in the post-process with the conventional method. On the other hand, in the case of the single-roll method, the thickness of the thin plate obtained is as thin as several 100 μm, and the shell strength is weak, making it difficult to form a continuous thin plate.Also, the single-roll method has one-sided cooling, which can lead to uneven solidification. This tends to cause cracks to occur, as will be described later.

From the above, it is considered that it is possible to manufacture a continuous thin plate with a thickness of several mm only by the twin roll method.

The gist of the invention is as follows.

That is, in the present invention, A435 to 44 wt%, the balance Ti
and unavoidable impurities, and the solidified structure as cast is either columnar crystals extending from both surfaces of the thin plate toward the center of the thickness, or a mixed structure of the columnar crystals and equiaxed crystals existing near the center of the plate thickness. Continuous TiAj with thickness 032~3mm
An intermetallic compound thin plate, the manufacturing method of which is IV35
44 wt% and the remaining Ti are heated and melted in an inert gas atmosphere, and the molten metal is rolled at a peripheral speed of 0.1 to 10 m.
It is continuously supplied between a pair of cooling rolls rotating at a speed of 102 to 10'° (:/
It is characterized by solidifying at a cooling rate of sec.

In addition, although there are different casting types such as vertical type, inclined type, and different diameter type as the twin roll method, the present invention is applicable to any of them.

[For production]

The present invention will be explained in detail below along with its operation.

The reason why the composition range of M is limited to 35 to 44 wt% is that only in this range, it consists of a mixed phase of Ti/V intermetallic compound and a small amount of other phases (for example, Ti3/V), and is homogeneous with a micro Vickers hardness of about 350 Hv. This is because it is easy to obtain TiA1.

The board thickness is 0.2~31! The reason for limiting it to III+ is 0.
This is because if the thickness is less than 2 mm, the thin plate is likely to break during casting and subsequent transportation due to insufficient strength of the thin plate or deformability of the material.In order to stably obtain a continuous thin plate, the thickness of the plate must be 0.2 mm. Even if it is 2 mm or more, it is preferable to make it thicker. Furthermore, if the thickness is greater than 3M, voids are likely to form inside.

FIG. 1 shows a cross-sectional structure in the casting direction of a thin plate obtained by the present invention. The as-cast solidified structure consists of only columnar crystals extending from both surfaces of the thin plate toward the center of the plate thickness, or a mixed structure of the columnar crystals and equiaxed crystals existing near the center of the plate thickness.

The microstructure of the thin plate obtained by the present invention is shown in Figure 3 (A
). In the same figure, the microstructure consists of three phases: Ti/ij, trace amounts of Ti3Aj, and Al z Ti, but it is also possible to obtain one close to a TiIV single phase by changing the composition. In addition, for comparison, the microstructure of the ingot obtained by the arc melt method was
Shown in Figure (B). Note that the average crystal grain size of the thin plate obtained by the present invention is about 100-.

Metals, January issue, (1989), p. 49, states that mechanical properties such as ductility and strength are expected to improve by increasing the absolute amount of lamellar structure and decreasing the lamellar spacing by rapid cooling. It has been reported. Therefore, the twin roll method is considered to be a very effective means for improving mechanical properties.

Next, a method for manufacturing the above-mentioned thin plate will be explained.

Blend AI and Ti to a composition of 35 to 44 wt%M and heat at 1500 to 1600°C in an inert gas atmosphere.
The molten alloy is heated and melted to a temperature of 1,400 to 1,500"C. Then, the molten alloy is rolled at a peripheral speed of 0.1 to 10 m.
102 to 10'''' (:
/sec to produce a continuous TiAl intermetallic thin plate. Here, in order to promote the reaction between M and Ti to form an intermetallic compound and obtain a uniform molten state, it is preferable to raise the melting temperature to 1500 to 1600°C.

In order to make the plate thickness 0.2 to 3 mm, the peripheral speed of the rolls needs to be 10 to 0.1 m/sec, and the cooling rate of the slab at that time is 10' to 102° (:/sec). Equivalent to.

Therefore, the roll circumferential speed is 0.1 to 10 m/se
c and the cooling rate was limited to 102-105°C/sec.

The biggest problem with the TiAZ intermetallic compound is that the material has low ductility. This also applies to coagulation and
This is a very important problem related to cracking of slabs during cooling. Uneven cooling and solidification in the width direction is thought to be the main cause of cracking due to lack of ductility. Therefore, in order to reduce the cracking of slabs, it is necessary to eliminate as much as possible the heat transfer resistance between the rolls and the metal, such as non-uniform pouring flow and oxide films on the meniscus surface, which cause non-uniform solidification. In order to make the pouring flow uniform, it is desirable to use a slit-shaped pouring nozzle. Furthermore, in order to suppress the formation of an oxide film on the meniscus surface, melting and casting in an inert gas is necessary. The inert gas may be Ar, He, or the like.

As a method for reducing cracks in the slab, it is desirable to perform casting in which the unsolidified portion of the center of the slab at the point closest to the rolls is minimized. To that end, CAMP-ISIJ
, 1 (1988), p. 186, the rolls are supported by sprinks, etc., and the rolls are not fixed, but the solidified shells are pressed with a constant force, and the rolls open naturally as the shells grow. It is necessary to have a structure like this.

In addition to improving the non-uniformity of solidification, it is necessary to completely eliminate flash at the ends of the slab, which causes restraint when the solidified shell contracts in the width direction. In order to reduce the insertion of molten metal between the sides, the pressing force of the side weirs must be controlled.

FIG. 2 schematically shows the apparatus used in the method of the present invention, and 1 is a crucible for melting and supplying the intermetallic compound TtjV. In order to make the supply between the rolls uniform in the width direction, the molten metal passes through a refractory tundish 2 and is supplied between a pair of rotating rolls 3.3'. 4 is a side weir made of refractory material, which is used to form a pool of molten metal between the rolls. Reference numeral 5 denotes an atmosphere control container in which a protective atmosphere is created using an inert gas. 6 is the manufactured thin plate. 7 is an inert gas introduction mechanism into the container 5;
8 is an exhaust mechanism.

〔Example〕

Examples of the present invention are shown below.

Aluminum base metal and sponge titanium are A136wt%,
8kg of Ti blended to obtain a composition of 64wt%
was placed in a crucible and heated at 1600°C in an Ar atmosphere.
It was heated and melted to form an alloy. Next, -1500°C
After adjusting the temperature to
A tundish with a diameter of 300 mm and a width of 100 mm rotates at various roll circumferential speeds through a tundish with an opening of 95 mm in length.
The material was fed between a pair of rolls made of a prepared alloy of mm, and solidified at a cooling rate of 102 to 105 °C/sec under a constant roll supporting force to obtain a continuous thin plate having the thickness shown in Table 1. Ta.

The length of the slats was approximately 3 m to 10 m. The height of the pool of molten steel formed between the rolls was approximately 80M.

An example of the cross-sectional Mi weave in the casting direction of the obtained thin plate is shown in FIG. The as-cast solidified structure consists of only columnar crystals extending from both surfaces of the thin plate toward the center of the plate thickness, or a mixed structure of the columnar crystals and equiaxed crystals existing near the center of the plate thickness.

As mentioned above, the ξ-chromatic structure of the thin plate obtained by the twin roll method in Figure 3 (A) shows TiA/ and trace amounts of Ti3/V and A.
Although it consists of three phases of iz Ti, it is also possible to obtain something close to TiA/single phase by changing the composition.

Note that the average grain size at this time is approximately 1 in the case of the twin roll method.
00n, it was about 115 compared to the arc melt method.

Furthermore, the micro-Vickers hardness of the as-cast material was 35011v, which was almost the same as the value obtained by the ingot method, etc., regardless of the measurement location of the thin plate.

Table 1 [Effects of the invention] By using the manufacturing method of the present invention, 0.2 to 3 mm
Intermetallic compound TiA with continuous thickness! The production of thin plates becomes easier. Therefore, unlike the usual powder metallurgy method, cutting from an ingot, or high-temperature plastic processing method, it is possible to significantly reduce the labor and equipment burden associated with the complexity of the process, and to produce a homogeneous thin plate of intermetallic compound TiA1. It is extremely effective for mass production at low cost.

[Brief explanation of drawings]

Fig. 1 is a photographic diagram showing the cross-sectional metal structure in the casting direction of a thin plate obtained by the present invention, Fig. 2 is an explanatory diagram showing an outline of the apparatus for carrying out the present invention, and Figs. 3 (A) and (B). are metallurgical micrographs showing as-cast microstructures of thin plates obtained by the twin roll method and the arc melt method, respectively. l...crucible, 2...tandine, 3,3'.
... Roll, 4... Side weir, 5... Atmosphere control container, 6... Thin plate, 7... Inert gas introduction mechanism, 8...
・Exhaust mechanism. No. 509 Ree 6; 'JT? ,l'' Figure 2 ゛zur3choden! A) '>00y* Procedural support document (method) % formula % Display of the case 1990 Patent Application No. 50307 Name of the invention TiAl intermetallic compound thin plate and its manufacturing method 3, relationship with the amendment person case Patent Applicant 2-6-3 Otemachi, Chiyoda-ku, Tokyo (665) Nippon Steel Corporation Representative Zen Yamamoto 4゜Embedment 〒100 2-4-1-5 Marunouchi, Chiyoda-ku, Tokyo Amended Date of order: March 26, 2008 (Date of dispatch) (1) Changed "This is a metallographic micrograph showing a microstructure." to "This is a microscopic photo showing a metallographic structure." on page 14 of the specification, lines 10-11. to correct.

Claims (2)

[Claims] (1) Consisting of 35 to 44 wt% Al, balance Ti and unavoidable impurities, the solidified structure as cast is present only in columnar crystals extending from both surfaces of the thin plate toward the center of the plate thickness, or in the presence of the columnar crystals and near the center of the plate thickness. A continuous TiAl intermetallic compound thin plate having a thickness of 0.2 to 3 mm and consisting of a mixed structure with equiaxed crystals. (2) 35 to 44 wt% Al and the remainder Ti are heated and melted in an inert gas atmosphere, and the molten metal is rolled at a peripheral speed of 0.
Continuously supplied between a pair of cooling rolls rotating at a speed of 1 to 10 m/sec, and under a constant roll supporting force, 10^2 to 1
A method for producing a continuous TiAl intermetallic compound thin plate, characterized by solidifying at a cooling rate of 0^5°C/sec.