JP3419481B2 - Ti-Al intermetallic compound - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Ti-Al suitable for parts of various equipments, refractory structures, high temperature elastic members and the like.
Related to intermetallic compounds.

[0002]

2. Description of the Prior Art Ti-Al intermetallic compounds have excellent properties such as excellent heat resistance, oxidation resistance, wear resistance and the like, and are lightweight, and are therefore regarded as promising materials for various applications. There is. Examples of products using this type of intermetallic compound include outer wall materials used at high temperatures and turbine members,
Engine parts such as pistons and valve systems are being considered.

A lamella-containing structure is known as one aspect of the structure of the Ti-Al intermetallic compound. The lamella is
It has a layered structure in which plate-like phases mainly composed of γ (TiAl) and plate-like phases mainly composed of α ₂ (Ti ₃ Al) are alternately laminated, and one lump thereof is called a lamella grain. Lamella strength is extremely high.

Conventional Ti-Al consisting mainly of lamella
The intermetallic compound is a structure in which a γ phase as another phase is continuously present at the grain boundaries of the lamella grains as shown in the photograph of FIG. The γ phase is mainly composed of TiAl and contains Ti ₃ A
1 and Al ₃ Ti may be contained in a small amount in some cases. Figure 6
The striped pattern is the lamella grains, and the black portion surrounding the lamella grains is the γ phase. FIG. 7 is a photograph in which a part of the intermetallic compound is further enlarged, and the black portion is the γ phase existing in the lamella grain boundary.

The conventional lamella grains shown in FIG. 6 have a small shape anisotropy and have a shape close to a sphere. Also,
At the grain boundaries of conventional lamella grains, the γ phase is generally continuous so as to surround the lamella grains, and the γ phase is present between adjacent lamellas as shown in an enlarged scale in FIG. 7. There are few places where the lamellae come into direct contact with each other and the lamellae dig into each other. 6 and 7 are reflected electron beam composition images. A backscattered electron beam composition image is a type of electron micrograph. Heavy elements appear white and light elements appear black, making it easy to observe the composition distribution.

[0006]

In the Ti-Al intermetallic compound containing the lamella structure, the γ phase of the lamella grain boundary becomes a weak point particularly when it is deformed at a high temperature, and the γ phase of the lamella grain boundary along There were many examples of destruction. FIG. 8 shows the T
2 is a secondary electron beam image of a fractured surface when a bending fracture test was performed at 800 ° C. on a test piece made of an i-Al based intermetallic compound (Ti-44 at% Al). As can be seen from FIG. 8, in the conventional structure, the fracture mainly occurs at the grain boundaries of the lamella grains, and the lamella grain boundaries are weak.

When the fracture occurs at the lamella grain boundary (γ phase) as described above, the excellent properties (high strength properties) of the lamella structure cannot be fully utilized. Further, in order to improve the creep rupture property, it has been proposed to deposit fine precipitates such as Ti ₅ Si _{3 in the} lamellar structure by adding Si, but it is difficult and difficult to obtain a predetermined precipitate. A treatment operation is required, and even in this case, it is inevitable that the γ phase of the lamella grain boundary becomes a weak point.

Therefore, an object of the present invention is to enable the Ti-Al-based intermetallic compound containing a lamella structure to take advantage of the excellent high strength possessed by the lamella structure, and in particular to exhibit excellent properties even at high temperatures. Especially.

[0009]

Means for Solving the Problems The present invention, which was developed to achieve the above object, is a Ti--Al intermetallic compound containing a lamella structure, in which adjacent lamella grains are
Bonded directly at the interface of the lamellas without interposing another continuous phase, the grain boundaries of the lamella grains adjacent to each other form an uneven shape, and the uneven portions bite into each other, and the uneven portion. In the other side, the bite length into the lamella grains on the other side is not less than the lamella layer interval, and in the bite side lamella grains and the bite side lamella grains, both α ₂ phases are directly bound to each other and both γ The phases are directly bonded to each other, and the lamella on the other side in the uneven portion
When the bite length into the grain is more than 3 times the lamella layer spacing
On both sides in the width direction of the convex part of the lamella grain on the biting side.
There is a γ phase in each, and the γ phase is the lame on the side where it is bitten.
Directly binds to the gamma phase of the grit and exists on both sides in the width direction
The α ₂ phase is independently sandwiched inside the pair of γ phases
Or, that the layered structure of α ₂ and γ is sandwiched
It is a feature. These lamella grains three-dimensionally bite into each other at the uneven grain boundaries.

[0010]

The experiments conducted by the present inventors have confirmed that the high temperature strength is remarkably improved by substantially eliminating other phases such as the γ phase in the lamella grain boundaries. That is, by controlling the lamella grain boundaries of the Ti-Al intermetallic compound containing a lamella structure to be in the above state,
It became possible to extremely reduce the breakage at the grain boundary of this kind of intermetallic compound that was often broken at the grain boundary,
By causing the fracture in the lamella grains, the high-strength characteristics of the lamella grains themselves can be sufficiently brought out. In particular, the effect was remarkable at high temperatures, and the performance as a heat-resistant lightweight member could be significantly improved. Also, the creep performance at high temperature is improved.

In the present invention, additive elements such as Si, Nb, Mn, Cr, V and Pb, and T are added in order to improve various characteristics.
_{iB 2, Y 2 O 3,} Ti 5 Si 3 or the like ceramics, or the addition of a fine enhancer of the intermetallic compound, in Ti-Al system intermetallic compound comprising lamellar structure that has been modified by, for example, to deposit effective. Composition width in which lamella is formed by adding the above-mentioned additional elements (35 to 50 at% Al)
Can vary, but in short it is effective against all tissues where lamella is predominantly present.

The composition width in the present invention is Ti and Al.
It is effective because a lamella is formed in the composition ratio of the two elements of 35 to 50 at% Al. However, especially 45 to 47
In the range of at% Al, a heat resistant member made of a Ti—Al based intermetallic compound having particularly high strength can be obtained.

[0013]

EXAMPLE Ti and Al powders were mixed in a dry ball mill so as to have a composition of Ti-46 at% Al, the mixture was compacted by a rotary shaving machine, and then pressed with PHIP. (For example, 350kgf / cm
² ) While raising the temperature to 1350 ° C., holding in a vacuum atmosphere for 2 hours to cause reaction sintering, and then gas cooling to about room temperature, as shown in the reflected electron beam composition image of FIG. A member made of a Ti-Al-based intermetallic compound was obtained.

PHIP is a pseudo isotropic press using a pressure medium such as alumina powder. The reaction sintering (self-propagating high temperature synthesis method) causes a reaction of a part of the mixed powder by heating the mixed powder of Ti and Al or the like above the reaction temperature, and the reaction heat generated at that time causes the reaction to occur one after another. Is a method of propagating. Although the above structure can be easily obtained by the manufacturing method utilizing reaction sintering, other methods such as Ti are used.
A method of producing a powder of an intermetallic compound consisting of Al and Ti ₃ Al by normal sintering or pressure sintering using HIP, or by forging a molten material into a fine structure to obtain a recrystallization temperature. It can also be manufactured by holding.

The structure of the above embodiment is mainly composed of lamella grains. A lump having a striped pattern in the same direction in FIG. 2 is one lamella grain. In the figure, the black stripes are the plate-like phase mainly consisting of γ, and the white stripes are the plate-like phase mainly consisting of α ₂ . The lamella grains have large shape anisotropy and tend to be slightly longer in the direction along the lamella stripes. As shown in the enlarged view of FIG. 3, the lamellas adjacent to each other are directly bonded at the grain boundary,
There are many places where the grain boundaries of lamellae dig into each other greatly. Therefore, the γ-phase, which is a phase other than lamella grains, is rarely continuous to the lamella grain boundary, and the lamella grains are in direct contact with each other and the lamella grains bite into each other in a three-dimensional complex manner. Matching.

The features of the structure of the above embodiment are as follows. [Characteristic 1] There is substantially no other phase in the lamella grain boundary,
The lamellas are in direct contact with each other, and the tips of the stripes are large and uneven. As for the degree of the unevenness, as shown in FIG. 1, there are many places where the biting length H in the uneven portion is three times or more the layer interval d of the lamella. [Characteristic 2] Lamella comrades are almost completely integrated at the grain boundary. That is, α ₂ (the part that looks white) is directly bonded, and the plate-like crystal grains of α ₂ are directly metal-bonded via the grain boundary. That is, the bond form is the same as that of the crystal grain boundaries of the same type of crystal grains, and the bond form is extremely strong. In such a structure, another phase is not observed even when magnified about 2000 times with a microscope. Even if another phase is observed at 2000 times or more, there is practically no problem in terms of strength. [Characteristic 3] In the convex part where one lamella bites into the other lamella at the lamella grain boundary, the γ phase (black stripes) is always present on both sides in the width direction of the convex part, and inside the pair of γ phases. The α ₂ phase (the part that looks white) is sandwiched by itself, or the layered structure of α ₂ and γ is sandwiched inside the pair of γ phases. In any case, the γ phase exists on both sides of the convex portion of the grain boundary where large irregularities are seen.

The structure of the above example was processed into a columnar bending test piece, and a bending test was conducted at 800 ° C. in the atmosphere.
It broke at 103.8 kgf / mm ² . As shown in the secondary electron beam image of FIG. 4, most of the fracture surfaces of this test piece fractured within the lamella grains, and the fracture surface had sharp and fine irregularities. It turns out that is strong.

When the fracture surface was observed, it was found that a part of the grain boundaries of the lamellae, where the irregularities were shallow, was rarely separated at the grain boundaries. When this portion was further magnified and observed in detail, it was found that as shown in the secondary electron beam image of FIG. 5, the irregularities were arranged in rows in two directions (diagonal direction of the photograph), and in this example, It was confirmed that the meshing of the lamella grain boundaries was three-dimensional. In the case of mere two-dimensional meshing, the irregularities should be arranged in one direction, but in the organization of this example, no such example is seen.
It was found that the three-dimensional meshing of the lamella grain boundaries as described above improves the strength of the lamella grain boundaries and further enhances the effect in obtaining the above-described high-strength structure.

In the structures of the above-mentioned examples, it is desirable that the bite length H in the uneven portion of the grain boundary is larger than the layer interval d, and further more preferable results are obtained if H is 3 times or more of d. In a portion where the unevenness is shallow (for example, H is about the same as d), it is rare that the structure of the above-mentioned embodiment is peeled off at a part of the grain boundary. No peeling example was observed at a place with a large unevenness, and it was confirmed that the effect of increasing the unevenness of the grain boundary was great. As described above, in the structure of this example, the lamella grain boundary was strengthened, so that the high strength of the lamella structure could be sufficiently brought out, and the high strength was achieved even at a high temperature.

On the other hand, the comparative example is Ti-44 at% Al.
After compacting the mixture mixed so as to have the composition shown in FIG.
The structure shown in Fig. 4 was obtained, but the structure is such that the γ phase is generally continuous in the lamella grain boundaries. When this comparative example was subjected to a bending rupture test at 800 ° C. in the same manner as the above-mentioned examples, it broke under a load (82.4 kgf / mm ² ) much lower than that of the examples. As shown in FIG. 8, the fracture surface after rupture of the comparative example was mostly fractured along the grain boundary, and the fracture surface was rough and uneven, and the lamella grain boundary was a weak structure. I understand. Therefore, the structure of the comparative example cannot sufficiently bring out the characteristics of the lamella structure having high strength.

The present invention is not limited to the composition of the above-mentioned embodiment, and in short, the effect is exerted even in a structure in which lamellae are mainly present, or in a structure in which lamellae particles are dispersed in the matrix and lamellae particles are in contact with each other. To be done. Further, in the comparative example, the γ phase has been continuously formed at the grain boundaries of the lamella grains, but even with the same composition as the comparative example, a structure suitable for the present invention is obtained by changing the heat treatment conditions. It is possible to do so.

[0022]

According to the present invention, lamella crystal grains are
It is possible to obtain a Ti-Al-based intermetallic compound that can be bonded extremely strongly without the interposition of another phase and can exhibit the excellent properties of the lamella, and that exhibits particularly excellent strength at high temperatures.

[Brief description of drawings]

FIG. 1 is an enlarged view of a part of a lamellar structure of a Ti—Al-based intermetallic compound showing an example of the present invention.

FIG. 2 is a micrograph showing a metal structure of a Ti—Al-based intermetallic compound, showing one embodiment of the present invention, magnified 300 times.

FIG. 3 is a micrograph showing a part of the metal structure shown in FIG. 2 at a magnification of 2000 times.

FIG. 4 is a micrograph showing a fractured surface of the metal structure shown in FIG. 2 after a fracture test, magnified 85 times.

FIG. 5 shows fractured portions at the grain boundaries of the metallographic structure shown in FIG.
A micrograph showing a magnification of 000.

FIG. 6 is a micrograph showing a metal structure showing a comparative example at 300 times magnification.

FIG. 7 is a micrograph showing a part of the metal structure shown in FIG. 6 at a magnification of 2000 times.

FIG. 8 is a micrograph showing a fractured surface of the metal structure shown in FIG. 6 after a fracture test, magnified 85 times.

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Claims (2)

(57) [Claims] 1. In a Ti—Al-based intermetallic compound containing a lamella structure, adjacent lamella grains are directly bonded to each other at the interface of the lamellas without interposing another continuous phase, and are adjacent to each other. The grain boundaries of lamella grains have an irregular shape, and the irregularities bite into each other,
And, the biting length to the lamella grains on the other side in the uneven portion is a lamella layer interval or more, and between the lamella grains on the biting side and the lamella grains on the biting side, both α ₂ phases are directly bonded to each other. And the γ phases of both are directly bonded to each other, and the bite length into the mating lamella grain in the above-mentioned uneven portion
Is the bite side at a location where the lamella layer spacing is three times or more.
Γ phases exist on both sides in the width direction of the convex part of the lamella grains of
However, the γ-phase directly interacts with the γ-phase of the lamella grains on the bite side.
Of a pair of γ-phases that are bonded and that are present on both sides in the width direction
Or inside alpha ₂ phase is sandwiched alone or in alpha ₂ and
Ti-A characterized in that the layered structure of γ is sandwiched
l-based intermetallic compound. 2. The T according to claim 1, wherein the grain boundaries of the lamella grains adjacent to each other are three-dimensionally engaged with each other.
i-Al-based intermetallic compound.