JP3382272B2 - 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.

In a conventional Ti-Al intermetallic compound, the composition ratio of Ti and Al is 49 to 55% in atomic% of Al.
It is known that the structure in the range is mainly a γ single phase (polycrystalline grain structure composed of TiAl). On the other hand, Al
It is also reported that when the atomic% of is less than 49%, a composite structure composed of γ phase and lamella is obtained. A lamella is a layered structure in which TiAl and Ti ₃ Al are mainly alternately laminated.

It is known that the γ single phase structure is lighter in weight and excellent in heat resistance, abrasion resistance and oxidation resistance, but slightly inferior in strength, as compared with a structure mainly composed of lamella. . On the other hand, the structure mainly composed of lamella has high strength, but is slightly inferior in heat resistance, wear resistance and oxidation resistance.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As shown by the alternate long and short dash line in FIG. 1, the Al-based intermetallic compound has an Al content of 48 to 54 at%.
It is known that the strength decreases significantly as the atomic% of increases. The reason is that the γ phase becomes brittle. Therefore, in spite of excellent heat resistance, wear resistance, oxidation resistance, etc., it is the current situation that the above excellent characteristics cannot be fully utilized due to insufficient strength. Further, since the strength is significantly reduced at high temperature, there is a problem in using at high temperature.

Therefore, an object of the present invention is a lightweight Ti-Al system which is lightweight and has both excellent characteristics such as heat resistance, abrasion resistance and oxidation resistance and high strength, and can exhibit excellent characteristics even at high temperatures. To provide an intermetallic compound.

[0007]

The present invention, which was developed to achieve the above object, has a composite structure mainly composed of γ phase and lamella grains, and the grain boundaries of the lamella grains and γ phase are mutually fired. A Ti-Al-based intermetallic compound that is firmly adhered by binding, and is a combination of Ti and Al in the composite structure.
The composition ratio is more than 50% in atomic% of Al and 54%.
The lamella grains are dispersed in the composite structure, the lamella particles in the composite structure have different hardness even when the lamella particles are present independently, and the hardness of the lamella particles in the composite structure is different. Is harder than the γ phase in the composite structure, the ratio of the hardness of the lamella grains to the γ phase (lamella hardness / γ hardness) is larger than 1.15, and the lamella in the composite structure is The adhesive strength of the grain boundary between the grains and the γ phase exceeds the strength of the lamella grains alone. The γ phase is an aggregate of fine crystal grain structures mainly composed of TiAl, and may contain a small amount of Ti ₃ Al, Al ₃ Ti, or the like.

The composite structure of the present invention can be obtained particularly easily by the reaction synthesis method (reaction sintering) of Ti and Al. In this composite structure, the γ-phase and the lamella grains are in a state of being firmly adhered to each other with a bonding force of such a degree that cracks do not occur at grain boundaries of each other or more. In the present invention, even when the composition ratio of Ti and Al is 48 to 54% in atomic% of Al, a structure in which lamella grains are dispersed in the γ phase is obtained by undergoing reaction sintering. In such a composite structure, by setting the ratio of the hardness of the lamella grains to the hardness of the γ phase (lamella hardness / γ hardness) to be larger than 1.15, preferable results can be obtained in order to increase the strength. Moreover, although the volume% of the lamella grains contained in the composite structure is between 8 and 69%, the object of the present invention can be achieved.
More preferable results are obtained when the amount is 29% or more, and more preferably 29 to 36%.

[0009]

The hardness of the γ phase and the lamella grains referred to in the present invention is not the hardness when the γ phase and the lamella grains exist alone, but the hardness in the composite structure is a problem. There is. That is, the composite structure of the present invention is one in which the γ phase and the lamella grains are firmly adhered to each other at their grain boundaries, and for example, the grain boundaries bite into each other in a bay shape and a strong adhesion state is obtained by intermetallic bonding or the like. It is an organized organization. In such a composite structure, when a fracture surface is observed by conducting a bending rupture test or the like, it is observed that the fracture occurs in the grain rather than the crack progresses along the grain boundary. It In such a composite structure, when the γ phase and lamella grains are independent,
The lamella grains may have different hardness even with the same component, and the reason for this is beyond speculation, but it has not yet been elucidated including the difference in thermal expansion between grains during reaction sintering. Factors seem to be involved. Ti-Al
When the Al composition exceeds 50% in intermetallic compounds
When the equilibrium state is reached by heat treatment,
It is known that Therefore, the Al composition is generally 50
% Was the upper limit. However, Ti with Al composition of 50% or more
-Al-based intermetallic compounds can also be
For example, by creating an equilibrium state,
The fine lamellae are more evenly distributed and serve the purpose of the present invention.
It is possible to get an organization.

In the present invention, the composite structure described above is used, while the excellent characteristics of the γ phase (lightness, heat resistance, wear resistance, oxidation resistance, etc.) are utilized, and the weakness of the γ phase in terms of strength is weakened. Overcoming the problem of higher strength, lightweight Ti-
The strength of the Al-based intermetallic compound was remarkably improved.

In the present invention, in order to improve various characteristics, additional elements such as Si, Nb, Mn, Cr and V, and Ti are used.
_{B 2, Y 2 O 3,} Ti 5 Si 3, ceramics, there is a similar effect plus a fine enhancer of the intermetallic compound.

[0012]

EXAMPLE Ti and Al powders were mixed so as to have four kinds of compositions (No. 1 to No. 4) shown in Table 1 below, and the mixture was compacted and then added. The pressure was maintained for 2 hours at 1350 ° C., and reaction sintering was performed to obtain a member made of a Ti—Al-based intermetallic compound as an example shown in FIG. 3 (photograph). 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. The photograph of FIG. There are 3 organizations.

The manufacturing method utilizing reaction sintering as described above is highly effective because the above-mentioned composite structure is easily obtained, but other methods such as powder of intermetallic compound consisting of TiAl and Ti ₃ Al are used. It is also possible to manufacture by normal sintering or pressure sintering using HIP or the like.

[0014]

[Table 1] Each of the examples in Table 1 is a composite structure mainly composed of the γ phase and lamella grains dispersed in the γ phase, and the lamella is shown as a striped pattern in the photograph of FIG. It is a grain. The γ phase is a structure that appears blacker than the lamella phase in this photograph, is an aggregate of structures having an average particle size of about 20 to 50 μm, and these γ particles are connected throughout the entire member. The amount of Al in the γ phase is about 48 to 57 atomic%.

A member having the composition of each of the above examples (No. 1 to No. 4) was ground into a prismatic shape, and a bending test was conducted in the atmosphere at two kinds of temperatures shown in Table 1 (room temperature and 900 ° C.). Bending strength was determined by carrying out. This bending test was performed with a three-point bending tester as shown in FIG. Also,
The hardness of γ phase and lamella grains is 1 with a micro Vickers hardness tester.
It measured using the weight of 00g, and calculated | required the average hardness.

FIG. 1 shows each example (No. 1 to No. 1) in Table 1.
4) is a plot of the relationship between Al atomic% and bending strength. FIG. 2 is a plot of the relationship between Al atomic% and hardness (hardness of lamella and γ phase) in each of the above examples. Since the absolute value of hardness may change depending on the measurement conditions, the absolute value is also important, but rather the ratio of hardness (ratio of hardness of lamella grains to hardness of γ phase) is more important.

Since the intermetallic compound of the present invention has a complex structure, the adhesion between the lamella grains and the γ phase, which are separate structures, must be good. If the adhesion at the grain boundaries is weak, the cracks proceed along the grain boundaries without reaching the inside of the grains.

Observation of the fracture surface after the bending test for each of the examples in Table 1 revealed that most of the cracks progressed within the γ grains or along the grain boundaries between the γ grains, and the cracks bypassed the lamella grains. From the progress, it was found that the lamella grains of this example had a great effect on increasing the strength. In addition, it was rarely observed that the fracture occurred in the lamella grains, but even in that case, the cracks progressed into the lamella grains and the adhesion strength at the grain boundary between the lamella grains and the γ grains exceeded the strength of the lamella grains alone. It was confirmed.

As described above, the grain boundary of the lamella grain and the γ phase having particularly high adhesion has a small grain boundary distance even if the grain size is small like the lamella grain shown in the upper right of the photograph of FIG. It was also found that it is effective to improve the strength that it is long and has a shape that bites into the lamella grain boundary so as to be recessed inward.

As shown by the solid line in FIG. 1, in the case of this example, when the Al atomic% was increased from 48% to 52%, the strength at room temperature was significantly increased. Further, at a high temperature of 900 ° C., the strength was lower than that at room temperature as indicated by the broken line in the figure, but it was found that the tendency of the strength change was generally similar to that at room temperature. That is, the structure of the present example is intended to have high strength even at high temperatures. On the other hand, in the conventional structure, as shown by the alternate long and short dash line in FIG. 1, the strength tends to gradually decrease as the Al atom% increases.

As shown in FIG. 2, Al atomic% is 48
% To 52% lamella hardness from 283 HV to 3
Increasing to 74 HV also increases the intensity in that range as shown in FIG. That is, there is a correlation between the lamella hardness and the bending strength, and the lamella grains with high hardness are involved in improving the strength. 52% when Al atomic% is 54%
The bending strength is lower than that in the case of No. 1, but this is because the volume% of the lamella is 29% rather than the decrease in the lamella hardness.
It is speculated that this was due to a sharp decrease from 8% to 8% (Table 1).

That is, the lamella volume% is also important, and it is presumed that if the lamella volume% is too small, the effect of improving strength cannot be exhibited. However, also in this case, the strength improvement effect is recognized due to the high hardness of the lamella grains. In addition, the examples have sufficient elongation during the bending test throughout Table 1,
It has high strength and toughness, and was able to overcome brittleness.

As can be seen from Table 1 and FIGS. 1 and 2, No. 1 in which the ratio of the hardness of the lamella grains to the γ phase (lamella hardness / γ hardness) is larger than 1.15. 1-No. In No. 4, a sufficient strength is obtained as compared with the conventional structure. In these examples, composite structures having different hardness of lamella grains were obtained, but the reason why the hardness becomes different is not clear. Since there is no correlation between the composition analysis results of lamella grains and hardness, some action due to the composite structure, such as difference in structure change or thermal expansion during reaction sintering, difference in adhesion between grains, etc. It is considered that, due to factors such as the above, differences in hardness occurred even with the same component. In addition, as shown in FIGS. 1 and 2, Al
If the composition exceeds 50%, the bending strength and hardness will be further improved.
is doing.

In the above embodiment, Al atomic% is 52%
At that time, when the hardness ratio is 1.4 or more and the lamella volume% is 29% or more, the strength has a peak, and a particularly large effect is recognized in the range of 51% to 53 atom%. A yield strength of 35 kgf / mm ² or more was realized at temperatures from room temperature to 900 ° C. Such a composite structure is particularly effective as a high temperature elastic member. Further, a composition having an Al composition of 50 to 54 atomic% and a lamella volume% of 8 to 36 volume% is obtained, and particularly when the hardness ratio is 1.3 or more, these effects are exhibited.

Particle size ratio of lamella grains to γ phase (lamella grain size / γ
No. in Table 1 regarding the particle size). 1 like 7.5
Even if it is large, it is effective, and conversely No. Even when it is smaller than 1 as in 4, the effect of improving the strength is recognized because the lamella is finely dispersed in the grain boundary of γ. It is also possible to control the particle size ratio to improve various characteristics.

Among the conventional members made of Ti-Al intermetallic compounds, the composition of the entire member is Al in the composition ratio of Ti: Al.
In the range of 49 to 55 atomic%, it is considered to be unusable due to its brittleness, though it is a structure mainly composed of γ single phase and is lightweight and excellent in oxidation resistance. However, according to the present invention, high strength and toughness were achieved while making use of the above characteristics, and the member became usable. The structures of the above-mentioned respective examples have the same characteristics even after being used at 1000 ° C., and do not decompose during use.

Although the effect is particularly large in the above composition range, the present invention has a composite structure mainly composed of γ phase and lamella grains and the grain boundaries of the lamella grains and γ phase are firmly adhered to each other. It is a Ti-Al intermetallic compound, and the effect is exerted on all of the Ti-Al intermetallic compounds in which the hardness of the lamella grains in the composite structure is harder than the γ phase in the composite structure.

[0028]

According to the present invention, Ti and A in the composite structure are
The composition ratio of 1 is more than 50% and 54% in atomic% of Al.
The lamella grains dispersed in the composite structure,
The above lamella grains in the tissue have lamella grains alone
The hardness is different from that when
The hardness of mellar grains is higher than that of the γ phase in this composite structure.
It is hard and the ratio of hardness of the lamella grains and the γ phase is more than 1.15.
Large and with the lamella grains and γ phase in the composite structure
The adhesion strength of the grain boundaries of the lamellae exceeds that of the lamella grains alone.
As a result, it is possible to obtain a Ti—Al-based intermetallic compound that can exhibit excellent characteristics such as heat resistance, oxidation resistance, and abrasion resistance and that has high strength.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the atomic percentage of Al in a Ti—Al-based intermetallic compound and bending strength.

FIG. 2 is a diagram showing the relationship between the atomic percentage of Al and hardness of a Ti—Al-based intermetallic compound.

FIG. 3 is a micrograph showing a metal structure of an intermetallic compound showing one example of the present invention at 400 times magnification.

FIG. 4 is a diagram showing an outline of an apparatus for performing a bending test.

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Claims (2)

(57) [Claims] 1. A Ti-Al-based intermetallic compound having a composite structure mainly composed of γ-phase and lamella grains, and the grain boundaries of the lamella grains and γ-phase are firmly adhered to each other by sintering. And the composition ratio of Ti and Al in the composite structure is A
The atomic percentage of 1 is more than 50% and 54%,
The lamella grains are dispersed in the weave, the lamella grains in the composite structure have a hardness different from that when the lamella grains are present alone, and the hardness of the lamella grains in the composite structure is in the composite structure. Is harder than the γ phase, and the hardness ratio of the lamella grains to the γ phase (lamella hardness / γ hardness) is 1.1.
A Ti-Al-based intermetallic compound having a adhesion strength of the grain boundary between the lamella grains and the γ phase in the composite structure is larger than that of the lamella grains alone. 2. The Ti—Al based intermetallic compound according to claim 1, wherein the lamella grains contained in the composite structure have a volume% of 8 to 69%.