JPH06264203A - Production of ti-al intermetallic compound - Google Patents

Abstract

PURPOSE:To obtain a Ti-Al intermetallic compd. having excellent characteristics by subjecting the compd. to heat treatment to control spaces in lamellar layers. CONSTITUTION:The compd. is subjected to heat treatment to increase spaces in lamellar layers so as to obtain a strong lammellar structure in which the spaces in lamellar layers are controlled to desired spaces and lamellar grains are directly in contact with one another without the presence of other phases on the interfaces of grains. The heat treatment is carried out at temp. lower than the solid phase line and completed by increasing the interlayer spaces by joining lamellas. Preferable result is often obtd. when the heat treatment is carried out in an (alpha+gamma) two-phase region, further in the temp. range from (T-100) to T deg.C temp. T is the temp. where the gamma-phase precipitates when the compd. in the alpha phase or alpha2 phase or their coexistence phase is cooled.

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.
The present invention relates to a method for producing an intermetallic compound.

[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. As examples of products that use this type of intermetallic compound, for example, outer wall materials used at high temperatures, turbine members, engine parts such as pistons and valve systems, and the like are considered.

A lamella-containing structure is known as one aspect of the structure of the Ti-Al intermetallic compound. The lamella is
A plate-like phase mainly consisting of γ and mainly α ₂ (Ti ₃ A
1) is a layered structure in which plate-like phases composed of 1) are generally alternately laminated, and one lump thereof is called a lamella grain. The γ phase is mainly composed of TiAl, but may contain a small amount of Ti ₃ Al, Al ₃ Ti, or the like. The strength of the lamella structure is extremely high.

As a means for controlling the layer spacing of the lamella structure, as described in Japanese Patent Application Laid-Open No. 3-199358, a lamella is formed by heat treatment after producing an α phase (Ti solid solution phase) of 95 area% or more. A manufacturing method for refining the structure has been proposed. However, no method has been found for increasing the layer spacing of the lamella structure. The α phase is a Ti solid solution phase,
The α ₂ phase is a Ti ₃ Al solid solution phase, and the γ phase is a TiAl solid solution phase.

[0005]

With respect to the Ti-Al intermetallic compound containing the lamella structure, the lamella formation process and the growth process are not clear, and an effective method for controlling the lamella structure is known. There wasn't. For example, when a fine lamella is heat-treated in a low temperature range, a disordered layered structure may be formed in the lamella grain boundary, and such a structure has a Ti-structure.
The excellent characteristics of Al-based intermetallic compounds cannot be fully utilized.

According to the research conducted by the present inventors,
Lamellar grains that are adjacent to each other are directly bonded at the lamellar grain boundary without, for example, the γ phase interposed, and the unevenness of the lamellar grain boundary is large, and further, those that three-dimensionally interlock are excellent in strength. However, it was not clear how to obtain such a lamellar structure.

Therefore, an object of the present invention is to control the lamella structure so that the excellent characteristics of the lamella structure in the Ti-Al intermetallic compound containing the lamella structure can be utilized, and the lamella having higher performance can be obtained. Is to

[0008]

As a result of research on the growth process of lamella, the present inventors have found that there are two characteristic growth processes as described below. (1) Growth observed in low temperature region (development of disordered lamellar structure) Growth observed when heat-treating fine lamellas with inter-layer spacing, particularly observed in smooth lamella grain boundaries, and newly observed from lamella grain boundaries. Lamella grains grow. In this case, there is a strong relationship with the direction of the adjacent lamella, and by further being affected by the direction of the lamella in the grain as it grows, a layered structure with disordered regularity in which the direction changes in a complex and continuous manner It is formed. Such growth is likely to occur in a temperature range of (T-100) ° C or lower.

[0009] Incidentally, T ° C., as shown in the example of FIG. 3, is the temperature at which γ is precipitated upon cooling from alpha phase region or alpha ₂ phase region or these coexistence region. This greatly changes depending on the composition, and may change depending on the cooling rate and the added element. As the cooling rate increases, the temperature may shift to the low temperature side. In any case, it is necessary for γ to be precipitated from the α or α ₂ phase region in order to form lamella.

(2) Growth observed in a high temperature range (coalescence of lamellas and growth in the layer direction) Mainly because layer structures are coalesced (or aggregated) within the same lamella grain to increase the layer interval. , This lamella coalescing (mainly layered α ₂ coalescing) is
This lamellar structure grows in the direction parallel to the lamella plate surface at the same time as the layer spacing increases due to coalescence, although it can be seen both near and within the lamella grain boundaries. By this growth, the disordered layered structure as seen in (1) above is not generated, and the initial layer direction is maintained.

In some cases, new lamella grains may grow from the grain boundaries or within the grains. Even in this case, the layer spacing of the new lamella grains increases, so that the lamella grains preferentially grow. The layered structure is hardly disturbed and grows while maintaining the layer direction.

Due to the growth of the lamella, the grain boundaries of the lamella become large and uneven, and the lamella grains become a structure in which they largely dig into each other. Also,
After cooling, the γ phase does not continuously exist in the lamella grain boundaries, and a high-strength lamella grain boundary in which the lamella grains (especially α ₂ and γ) are directly bonded is obtained. Therefore, the method (2) is suitable for achieving the object of the present invention.

There are roughly two methods for achieving the above-mentioned growth (2). The first method is to cool from the α phase region at a relatively high cooling rate to form a lamella structure, and then to a predetermined temperature region, for example, (T-100) ° C to T ° C.
How to keep in the temperature range. In order to maintain this temperature range, for example, it may be cooled to room temperature and reheated as shown in FIG. 4, or may be held for a certain period of time in a continuous cooling process as shown in FIG. .

In the second method, as shown in FIG. 6, after cooling from the α phase region at a relatively slow rate to form a lamella structure, a temperature range of (T-100) ° C. to T ° C. is continuously applied. A method of maintaining substantially this temperature range by controlling the cooling rate. The cooling rate from the α phase region in this method is
For example, at 45 at% Al or more, 10 ° C / min to 300 ° C /
If it is less than 45 at% Al, it is recommended to set it to 1 ° C / min to 30 ° C / min. If it is faster than that, the lamella grain boundary becomes a structure with less irregularities. If it is slower than that, γ grains may be separated and precipitated.

This second method is particularly suitable when there is a difference in the temperature (T ° C.) at which the γ phase precipitates due to uneven composition in the member. That is, T in the same member
Continuous cooling is convenient when there are parts with different temperatures.

When the above heat treatment is carried out in the (α + γ) two-phase region, lamella coalescence may easily occur. It is assumed that the reason is that the diffusion rate of α, which is a solid solution of Ti, is high. By the combination of this lamella,
The lamellar layer spacing is much more likely to occur. In addition,
If the deviation from the equilibrium state is large due to the rapid cooling, lamella with a disordered direction is likely to occur.
Good results may be obtained by heat treatment at 200 ° C. or higher.

Further, after the temperature is kept at T ° C. or higher, if the cooling rate at the time of cooling to T ° C. or lower is relatively slow, lamella growth is likely to proceed, so that the temperature of (T-50) ° C. to T ° C. It may be good to set it as the area. In the temperature range of T ° C or higher, lamella does not exist and becomes α or α ₂ phase, so that lamella coalescence cannot occur at T ° C or higher. (T-100) ° C
In the following, particularly, the growth of lamella having a disordered direction from the lamella grain boundary is likely to occur, and it may be difficult to obtain a lamella structure that meets the object of the present invention.

Therefore, the present invention for achieving the above object is characterized in that, in the method for producing a Ti-Al intermetallic compound containing a lamella structure, the heat treatment for increasing the lamella layer spacing is performed at a temperature below the solidus temperature. And The lamella structure obtained by the present invention is a structure in which adjacent lamella grains are directly bonded at the interface of the lamellas without interposing another continuous phase. In this intermetallic compound, the grain boundaries of the lamella grains that are adjacent to each other form an irregular shape, and the lamellae are mutually three-dimensionally bite into each other in the irregular portion.

The composition of the intermetallic compound of the present invention may be in the composition range capable of forming a lamella, but in the case of a binary system of Ti and Al, the range of 35 to 50 at% Al is suitable.
Furthermore, it is possible to have a (α + γ) 2 phase region 4
A range of 1 to 50 at% Al is suitable. In addition, in order to improve various characteristics, additive elements such as Si, Nb, Mn, Cr, V, and Pb, ceramics such as TiB ₂ , Y ₂ O ₃ , and Ti ₅ Si ₃ and micro-reinforced compounds of intermetallic compounds. T containing a lamella structure modified by adding or precipitating
It is also effective for i-Al intermetallic compounds and is effective for all tissues in which lamellae exist.

If the composition of the intermetallic compound is uneven, the growth rate of the lamella tends to vary.
Suitable are a sintering method using as a raw material a powder, foil, or the like for which fine unevenness can be easily controlled, or a production method by a reaction synthesis method (reactive sintering method) that can easily obtain a finer structure.

[0021]

The coalescence of lamellae (increased layer spacing) described above and the growth of lamellas at the lamella grain boundaries are closely related to each other, and it is considered that these proceed simultaneously. The reason is presumed to be as follows. Lamella is γ and α
Since it has an interface of (or α ₂ ), it becomes energetically more stable if the interface is reduced by coalescence. At the same time, in the lamella grain boundary, the layered structure having a large layer spacing grows in the direction parallel to the layer by dissolution and re-precipitation from the layered structure having a small layer spacing to a larger layer structure that is energetically more stable.

Since the lamella coalescence proceeds even within the grains, the layer spacing varies within the lamella grains during the coalescence process, which causes a difference in the growth rate at the lamella grain boundary on a layer-by-layer basis. As a result, large unevenness is generated in the layer unit, and one lamella grain largely digs into the other lamella grain at the grain boundary. Large ruggedness is likely to occur due to such lamella coalescence and growth at the grain boundary simultaneously, and this growth is (T-100).
It has been found by the study of the present inventors that this phenomenon is likely to occur between 0 ° C and T ° C.

In the lamella structure in which the lamella grows in the direction parallel to the plate-like body surface as described above, the adjacent lamella grains are adjacent to each other in the lamella grain boundary portion. Instead, they are directly bonded at the interfaces of the lamellas, and the grain boundaries have an irregular shape, and the irregularities bite into each other, and the length of biting into the mating lamella grains in the irregularities is the lamella. There is more than the layer interval. Furthermore, the lamella grain boundary comrades dig into each other in three dimensions. Such a state of grain boundaries is referred to as grain boundary form A in this specification.

The above-mentioned lamellae coalescence forms a fine lamella by cooling from the α region, and the subsequent heat treatment is performed in the (α + γ) two-phase region and at a temperature of (T-100) ° C to T ° C for a certain period of time. This is an example in which the control of the lamella grain boundary is achieved by maintaining the temperature. It was also found that in order to combine the lamellae, it is important to maintain a certain temperature range during the heat treatment, and it is not directly related to the cooling rate after the retention. Therefore, the cooling after the heat treatment may be rapid cooling such as gas quenching. By controlling the lamella layer spacing in this way, it becomes possible to control the characteristics (strength, hardness, heat resistance, impact resistance, etc.) according to the purpose.
-Higher performance of the Al-based intermetallic compound can be achieved.

[0025]

[Examples] Table 1 below shows N with different compositions and heat treatment conditions.
o. 1-No. 17 shows data with controlled layer spacing. In Table 1, the grain boundary morphology is A or A + B
The following is a tissue suitable for the purpose of the present invention in which an increase in the layer spacing is achieved. A grain boundary morphology of B or C does not meet the purpose of the present invention.

In Table 1, the grain boundary morphology is A or A + B.
In all of the above, an increase in lamella layer spacing (for example, an increase in layer spacing as shown in FIG. 1) due to lamella coalescence was observed. From this result, it was found that the lamella layer spacing and the grain boundary morphology A were achieved by the coalescence of the lamellas.

[0027]

[Table 1]

[No. 8, No. 9] (Example) Ti and Al powders were weighed and mixed so as to have a composition of Ti-46 at% Al, and this mixture was compacted into a predetermined shape, and then each was pseudo-HIP (pseudo-HIP). ), The reaction sintering (reaction synthesis) was caused while pressurizing, and a Ti-Al-based intermetallic compound was obtained. Furthermore, in a vacuum atmosphere, 1350 ° C
The mixture was heated to (α phase region), and gas was rapidly cooled to room temperature. The cooling was performed in the range of (T-100) ° C to T ° C at a cooling rate of 300 ° C per minute. Through the above steps, a TiAl + Ti ₃ Al member composed of a fine lamella (average layer spacing 0.4 μm) was obtained. However, the grain boundary unevenness was small (grain boundary form B) and the γ phase was formed in the grain boundary. Because there are consecutive
Not the desired organization. Therefore, this member was reheated to 1300 ° C. in an Ar atmosphere and cooled at 30 ° C. per minute, so that No. 8 lamella structure (layer spacing 1.0 μm)
Got

Pseudo HIP 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 a fine structure can be easily obtained by the manufacturing method using reaction sintering, other methods such as T
A method of producing a powder of an intermetallic compound composed of iAl and Ti ₃ Al by ordinary 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.

No. An intermetallic compound having the same composition as that of No. 8 was obtained by the above-mentioned reaction synthesis, then heated to 1350 ° C. and then rapidly cooled to room temperature to refine the structure, and then reheated to 1300 ° C. in a vacuum atmosphere, and further gas quenched. No. Lamellar structure of 9 (layer spacing: 0.8μ
m) was obtained.

These No. 8 and No. 9 is α
By cooling from the region, a fine lamella is formed, and the heat treatment to be performed thereafter is held in the (α + γ) two-phase region and at a temperature of (T-50) ° C to T ° C for a certain period of time so that the lamella coalesces. However, an increase in lamella layer spacing and control of lamella grain boundaries (conversion of grain boundary form B to A) were achieved. As shown in Fig. 2, in lamella grains with grain boundary morphology A, adjacent lamellae are directly bonded to each other at grain boundaries, and there are many places where the lamellae's grain boundaries largely dig into each other. To be

Therefore, the γ phase, which is a phase other than the lamella grains, is rarely continuous at the lamella grain boundaries, and the lamella grains are in direct contact with each other. Moreover, the relationship between the lamella layer spacing d and the biting length H into other lamella grains was found to be many in which H / d> 3. Such a large bite of H / d> 3 was often observed in the grain boundary form A. In addition, No. 8 and No. From the comparison of No. 9, it was found that it is important for the lamella coalescence to be kept in a certain temperature range during the heat treatment, and it is not related to the cooling rate after the holding.

The lamella coalescence is as shown in FIG. That is, the α ₂ phases are bonded to each other and integrated, and the number of stripes is reduced at the ends of the lamella grains. And the γ phase (hatched portion) exists between α ₂ . In this figure, the number of layers on the upper side in the figure is smaller than that on the lower side in the figure due to uniting. Such coalescence, by carrying out the present invention, not only near the lamella grain boundary,
It is also found inside lamella grains.

[No. 3-5, 10-12, 15-1
7] No. A lamella was formed through the same steps as in Example 8, but the composition and the heat treatment temperature or the cooling rate were changed. No. 5 and No. No. 12 was heat treated in a temperature range other than the (α + γ) 2 phase region, and the grain boundary morphology was B or C, so that the grain boundary evaluation was “x (poor)”.
Is. Therefore, it is preferable to perform the heat treatment in the (α + γ) 2 phase region.

With 46 at% Al, (T-100)
Grain boundary evaluation is all “○” by heat treatment in the temperature range of ℃ to T ℃.
(Good), but with 44,48 at% Al, (T-
50) "○ (good)" in the temperature range of ℃ ~ T ℃, (T-10
In the temperature range of 0) ° C to (T-50) ° C, it was “Δ (somewhat good)”.

In this way, even if the composition changes (T-10
It can be said that if the heat treatment is carried out in the temperature range of 0) ° C. to T ° C., there is no grain boundary evaluation “x”. However, all of the grain boundary evaluations are “◯” (T-50) ° C. It can be said that this range is more preferable because the temperature range is from to T ° C. It was found that this temperature range is influenced more by the layer spacing of the fine lamella formed first and the degree of supersaturation by quenching rather than the composition, but it was found that holding in this temperature range generally succeeds.

[No. 1, 2, 6, 7, 14, 15] These are all examples in which the continuous cooling step (FIG. 6) is performed from α. The temperature range that controls the cooling rate is (T
-100) ° C to T ° C, and in some cases (T-5
0) ° C-T ° C may be sufficient.

No. 1 in which the grain boundary morphology is A. 6 was processed into a columnar bending test piece, and a bending test was performed at 800 ° C. in the atmosphere. As a result, 103.8 kg / mm ² It broke at. It can be seen that most of the fracture surfaces of this test piece are fractured within the lamella grains, and the fracture surfaces are sharp and fine, and the lamella grain boundaries are strong.

On the other hand, N in which the grain boundary morphology is B
o. No. 2 When a bending test was conducted under the same conditions as No. 6, No. Load much lower than 6 (82.4kg / mm ² )
It was destroyed by. No. It can be seen that most of the fracture surfaces after fracture of No. 2 fracture along the grain boundaries, and the fracture surfaces are rough and uneven, and the lamella grain boundaries are weak. With such a structure, it is not possible to sufficiently bring out the characteristics of a lamellar structure having high strength.

When the content is 45 at% Al or more, for example, No. 7
As described above, when a composition of 46 at% Al is cooled at 300 ° C./min [(T-100) ° C. to T ° C.], almost no structure of form A is found in the grain boundaries, and the grain boundary evaluation is “ X ”. Furthermore, No. When a composition having a composition of 48 at% Al, such as No. 15, was cooled at 300 [deg.] C./min [(T-100) [deg.] C.-T [deg.] C.], a structure other than morphology A was observed in a part of the grain boundary. The field evaluation was "△ (somewhat good)".

No. When the member was large even under the same conditions as in No. 7, the cooling rate of the central portion was slightly slower than that of the peripheral portion, so that the grain boundary evaluation might be “Δ”. Therefore, in this composition range, by cooling at a rate slower than 300 ° C. per minute, the structure of grain boundary evaluation “◯” is obtained. 10 ° C
If it is slower than every minute, equiaxed γ other than lamella may be precipitated, so it is preferable to set the temperature to 10 ° C. per minute or more. Further, if it is slower than 1 ° C. per minute, the volume ratio of γ becomes 39% or more, and the heat resistance strength may be lowered. Therefore, it may be desirable to be faster than this.

When the composition is less than 45 at% Al, for example, No. The composition of 44at% Al like 2 is 30 ℃
When cooled at [(T-100) ° C. to T ° C.] per minute, the grain boundary evaluation was “x”. In addition, No. 44 like 1
At% Al composition is 10 ° C / min [(T-100) ° C
.About.T ° C.)], the grain boundary evaluation was “◯”. Further, for the same reason as when it is 45 at% Al or more, it is preferable that the cooling rate is slower than 30 ° C. per minute, faster than 1 ° C. per minute, and further faster than 0.1 ° C. per minute.

[0043]

According to the present invention, the excellent characteristics of the lamella can be exhibited by the heat treatment, and the Ti-Al intermetallic compound exhibiting excellent strength and the like can be obtained.

[Brief description of drawings]

FIG. 1 is an enlarged view of a part of lamella tissue obtained according to an embodiment of the present invention.

FIG. 2 is an enlarged view of lamella grain boundaries obtained according to an example of the present invention.

FIG. 3 is an equilibrium diagram of Ti—Al.

FIG. 4 is a diagram showing an example of a relationship between time and temperature in a heat treatment / cooling process.

FIG. 5 is a diagram showing another example of the relationship between time and temperature in the heat treatment / cooling step.

FIG. 6 is a diagram showing yet another example of the relationship between time and temperature in the heat treatment / cooling step.

Claims (5)

[Claims] 1. A method for producing a Ti—Al-based intermetallic compound, characterized in that in the production of a Ti—Al-based intermetallic compound containing a lamella structure, a heat treatment for increasing the lamella layer spacing is performed at a solidus temperature or lower. . 2. The manufacturing method according to claim 1, wherein the increase in the layer spacing is performed by a heat treatment that causes coalescence of lamellas. 3. The method according to claim 1, wherein the heat treatment is performed in a (α + γ) 2 phase region. 4. When the temperature at which the γ phase precipitates when cooled from the α phase region or α ₂ phase region or a coexistence region thereof is T ° C., the heat treatment is performed at a temperature of (T-100) ° C. to T ° C. The manufacturing method according to claim 1, which is carried out within a range. 5. A lamella structure is formed after maintaining a temperature range of T ° C. or higher and then cooling to T ° C. or lower (T-10).
The method according to claim 1 or 2, wherein the temperature is substantially maintained in the temperature range of 0) ° C to T ° C.