JP2001200302A - METHOD FOR PRODUCING Ni-Al SERIES INTERMETALLIC COMPOUND - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for sintering an Ni-Al series intermetallic compound capable of easily controlling the reacting process. SOLUTION: In the method for producing an intermetallic compound by subjecting a green compact of raw material metal powder to reaction sintering, in the meanwhile in which the green compact is heated to a sintering temperature, the same is isothermally held in a temperature range in which the solid phase reaction between metals occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The invention of this application relates to Ni-A
The present invention relates to a method for producing an l-type intermetallic compound. More specifically, the invention of this application relates to a new method for producing a Ni-Al-based intermetallic compound that can easily control a reaction process at the time of producing a Ni-Al-based intermetallic compound.

[0002]

2. Description of the Related Art Many intermetallic compounds have a complicated crystal structure and are generally hard and brittle, so that they have rarely been used alone as practical materials. However, in recent years, as studies have progressed, specificities that have not been known until now have been found, and intermetallic compounds have become promising as functional materials.

As one of the methods for producing this intermetallic compound, a reaction sintering method has been widely used as a useful method. The reaction sintering method uses two or more metal component powders,
Alternatively, it is a sintering method in which a metal component powder and an atmosphere gas are reacted during a sintering process to form a sintered body. When high heat is applied to the green compact, which is a constituent element, the synthetic reaction proceeds while igniting and generating heat. Generally, the sintering reaction takes 200 seconds in a very short time of several seconds to several tens of seconds.
The process ends when the temperature reaches a high temperature of 0 ° C. or more. For this reason, in the reaction sintering method, it has been generally considered very difficult to control the reaction process.

[0004] Therefore, a method of reaction sintering at a relatively low temperature (JP-A-5-263177, JP-A-9-1997)
3503) has been proposed. However, in practice,
Since it is a sintering reaction at a high temperature of 1000 ° C. or more, a sintering time is as long as tens of hours, or a treatment such as coating inside a clad is required, There is a problem that processing for a long time or special processing is required. Also, these proposed means have not been satisfactory as controlling the reaction process.

However, when a new intermetallic compound is created,
It is necessary to design and execute the optimal composition and process in order to impart further properties as a functional material to the intermetallic compound, so it is easy to control the reaction process during reaction sintering. Was required.

[0006] On the other hand, the inventors of the present application disclose Ni-Al
We have tried to elucidate the thermal behavior in conventional reaction sintering by taking up intermetallic compounds. As a result, Ni-A
In the reaction process of the l-based intermetallic compound, solid phase Ni and solid phase Al
Reaction with Al, melting reaction of Al, solid phase Ni and liquid phase Al
It is evident that three exothermic and endothermic reactions are included in the reaction.
-It was found that the heat generation in the reaction of the liquid phase Al can be controlled by adjusting the particle size of the Al powder.

If it becomes possible to more effectively control the thermal behavior of such an intermetallic compound during the reaction sintering in the reaction sintering process, it is necessary to provide a high heat-resistant facility in the production line of the intermetallic compound. In addition to the practical advantage of not having the same, it also opens the possibility of making the entire reaction system easily controllable, from creating intermetallic compounds that meet the performance required in various fields. Can be expected.

Accordingly, the invention of this application has been made in view of the circumstances described above, and solves the problems of the prior art, and provides a novel method capable of easily controlling the reaction process of reaction sintering. An object of the present invention is to provide a method for producing a Ni-Al-based intermetallic compound.

[0009]

Means for Solving the Problems The invention of this application provides the following inventions to solve the above problems.

That is, first of all, the invention of this application is a method for producing an intermetallic compound by reacting and sintering a green compact of a raw metal powder. Ni-Al based metal is characterized in that the green compact is kept isothermally in a temperature range in which a solid-phase reaction between metals occurs during heating to cause a solid-phase reaction in at least a part of the green compact. A method for producing a compound is provided.

Second, the invention of this application is 430
Thirdly, a method for isothermally holding at any temperature within the temperature range of -470 ° C is provided.

Fourth, the invention of the present application is characterized in that an intermetallic compound capable of near-net shape is obtained by molding a green compact into an arbitrary shape. A method for producing a Ni-Al-based intermetallic compound according to any one of the third aspects is provided.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the features as described above, and embodiments thereof will be described below.

First, Ni-A provided by the invention of the present application
The method for producing an l-type intermetallic compound is a method by reaction sintering in which a green compact of a raw metal powder is reactively sintered to produce an intermetallic compound, and the green compact is heated to a sintering temperature and heated. During this process, the green compact is kept isothermally in a temperature range in which a solid-phase reaction between the metals occurs, and a solid-phase reaction is caused in at least a part of the green compact.

In this method, the isothermal holding of the green compact within a temperature range in which a solid phase reaction between metals occurs may be set in one step or in multiple steps. The particle size of the raw metal powder is a factor relating to the mixing of the powder and the progress of the solid phase reaction. If a powder having a large particle size is used, the cost is low and the mixture is easy, but the solid-phase reaction between Ni and Al becomes difficult to proceed, so that it is not suitable for use in the method of the present invention. Conversely, if the particle size of the powder is too small, the cost is high and the mixing of the powder becomes difficult, so that the solid phase reaction does not easily proceed, and is not suitable for use in the method of the present invention. Therefore, considering the two factors of the mixing of the powder and the progress of the solid phase reaction, the particle size of the Al raw material powder is 25%.
It is desirable to use a material having a size of about 0 mesh under (average particle size of about 33.6 μm or less).

When the target product is a NiAl intermetallic compound, the raw material powder is 43% from the Ni-Al phase diagram.
-60 at% Ni (63-76 wt% Ni). At this time, for example, a minute amount of an additional element such as Ti, Nb, or Fe may be added for the purpose of improving mechanical characteristics.

The more the green compact is formed, the more easily the solid phase reaction proceeds. Therefore, the conditions for forming the green compact are set in accordance with the equipment capacity, the size and the shape of the green compact.

FIG. 1 is a diagram illustrating the outline of the manufacturing method of the present invention with respect to the one-stage holding and the two-stage holding as a relationship between heating temperature and time. The one-stage hold is illustrated as line (1) in FIG. Also, the two-stage hold is illustrated as line (2). The temperature range (3) in which the solid-phase reaction between metals illustrated in FIG.
1 is a temperature at which solid phase is stable and can diffuse. Specifically, since Al has a lower melting point than Ni, the temperature can be lower than 660 ° C., which is the melting point of Al.
The degree is more appropriate. By keeping the green compact within the temperature range (3) of the solid phase reaction, the diffusion reaction between the solid phase Ni and the solid phase Al forming the green compact proceeds. The amount of the reaction product generated by the solid-phase reaction increases as the retention time (4) in the above temperature range increases,
It takes considerable time to completely react solid phase Ni and solid phase Al in the green compact. For this reason, the holding time (4) of the green compact in the temperature range (3) of the solid phase reaction is set to an appropriate time, and then the reaction is completed by heating to the sintering temperature.

The holding time (4) is important in controlling the calorific value in reaction sintering. In other words, when the holding time (4) is short, a large amount of solid phase Ni and solid phase Al which have not been solid-phase diffused remain in the green compact, and when heated to the sintering temperature, they react with heat generation. I do. That is,
An exothermic reaction occurs between the solid phase Ni and the solid phase Al and between the solid phase Ni and the liquid phase Al. Since this reaction proceeds at an accelerated rate, it cannot be controlled, and the temperature peak due to the heat generation reaches a high temperature similar to the conventional reaction sintering method. Therefore, in the invention of this application, by appropriately adjusting the holding time (4), the amounts of unreacted solid-phase Ni and solid-phase Al remaining in the green compact are controlled. To control the calorific value of the reaction.

The maximum temperature of the green compact due to the reaction heat generated at the sintering temperature, that is, the peak of the exothermic temperature becomes lower as the holding time (4) of the green compact at the solid phase reaction temperature becomes longer. However, it is not practical to make the holding time (4) as long as possible. Therefore, when adjusting the holding time (4), a characteristic relationship between the holding time (4) and the heat generation peak temperature can be considered.

FIG. 2 shows the retention time at the solid phase reaction temperature (4).
And the outline of the relationship between the peak temperature and the exothermic peak temperature. In the case where the line (A) is held in one stage, the line (B)
Exemplifies the case of two-stage holding.

As shown in FIG. 2, generally, when the holding time (4) at the solid-state reaction temperature reaches a certain time, that is, near the critical holding time (5), the exothermic temperature peak at the sintering temperature rapidly increases. To decline. Therefore, the holding time (4)
It can be seen that the time should be longer than the critical retention time (5). From the viewpoint of lowering the exothermic peak temperature, it is sufficient that the temperature is not less than the critical retention time (5).

Here, the critical holding time (5) is shown in FIG. 2 as an intermediate point between the start point and the end point of the decrease in the exothermic peak temperature. Depending on the situation of the reaction sintering, the critical holding time (5) may indicate the completion point of the decrease.

In consideration of the above, in the invention of this application, generally, the holding time (4) at the solid phase reaction temperature can be set to several hours or less. In the case of the single-stage holding exemplified by the line (1) in FIG. 1, the solid-phase reaction temperature is, for example, 430 ° C. to 470 ° C., more specifically, about 44 ° C.
At 0 ° C., for example, 440 ± 5 ° C., the holding time (4) may be from 120 minutes to 180 minutes (2 to 3 hours).

When the solid-phase reaction is performed in two stages as shown by the line (2) in FIG. 1, the line B in FIG.
As shown in the above, the critical holding time (5) can be shortened. That is, the critical holding time (5) can be shortened by combining the holding time (4) at the first temperature and the holding time (4) at the second temperature in FIG. It is. Specifically, as a more preferable example,
The process of isothermal holding is, for example, 430 ° C. to 470 ° C., more specifically about 440 ° C., for example, at 440 ± 5 ° C. for 60 to 90 minutes, and about 460 ° C., for example, 460 ± 5 ° C. for 3 hours.
It is exemplified that the process is performed in two stages of holding for 0 minute.

The temperature range at each stage is about 44
It is appropriate to hold isothermally at a relatively low temperature, such as 0 ° C. and about 460 ° C., and then hold isothermally at a temperature higher than the above temperature. In this case, the temperature difference may be about several to several tens of degrees Celsius, and a preferable example is about 10 to 30 degrees Celsius.

For the step of heating to the sintering temperature,
This can be achieved by heating to a temperature higher than the melting point of Al. However, in order to maintain the shape of the green compact after sintering, it is necessary to lower the melting point of Ni (1455 ° C.) or less.
It is also considered that the higher the final sintering temperature is, the more easily a single intermetallic compound is generated. Therefore, the final sintering temperature can be shown to be about 700 ° C. to 1400 ° C., more preferably 1000 ° C. to 1300 ° C.
It is desirable to be about.

In the method of the present invention, the higher the heating speed of the green compact, the more efficient it is.
The heating rate is 10 to 20 ° C / min. Desirably.

By this operation, diffusion between Al and Ni is sufficiently advanced, and the mechanical properties of the obtained Al-Ni metal compound are further improved. Thereby, Al-
In the production of the Ni-based intermetallic compound, it is possible to control the reaction process.

Of course, the method of the present invention is not limited to the above-described one-stage or two-stage holding, but may be an isothermal holding in more stages. It is appropriate that the isothermal holding is performed in a vacuum reduced pressure atmosphere. An inert gas atmosphere such as a rare gas may be used.

Further, according to the invention of this application, an intermetallic compound capable of near net shape can be obtained by molding a green compact of a raw material powder into an arbitrary shape. The green compact of the raw material powder may have a complicated shape or a simple shape, and can be formed into an arbitrary shape. The molding method can be performed by any conventionally known method such as mold molding, CIP molding or HIP molding.

The intermetallic compound obtained by the method of the invention of the present application does not dissolve because the reaction process of sintering is controlled, and maintains its shape. If the method of the present invention is applied to an intermetallic compound that is hard and brittle and has difficulty in processing, an intermetallic compound having an arbitrary shape can be obtained, so that it is not necessary to perform plastic working or the like, thereby greatly reducing costs. Can be done. In addition, the intermetallic compound can be put to practical use in various fields as parts and the like, and an effect of promoting the use of the intermetallic compound can be expected.

The embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0034]

EXAMPLE A green compact of Ni-50 at% Al was reaction-sintered using a solid-phase reaction. <1> Production of a green compact was performed as follows.

As the raw material powder, commercially available Al powder (average particle size)
Diameter: 32.7 μm, purity: about 99.5%) and Ni powder
Powder (average particle size: 22.6 μm, purity: about 99.8%)
Using. This powder is made to be Ni-50 at% Al.
And mixed well by milling. Mirin
First, the powder and the diameter are put in a pot mill.
10 mm and 5 mm alumina balls
0 g each, and 40 ml of acetone, put the rotation speed
Perform wet milling at 80 rpm for 7200 seconds
Was. After that, the acetone was evaporated, and this time was dried in a dry manner for 72 hours.
Milling was performed for 00 seconds. Put this mixed powder in a mold
Filled and preformed at 80 MPa for 300 seconds
Then, compression molding is performed at 800 MPa for 900 seconds,
20mm, 3mm thick cylindrical Ni-50at% Al
A green compact was obtained. <2> As illustrated in FIG. 3, this green compact (6) is made of quartz.
After setting in glass tube (7), quartz glass tube
The inside of (7) is 2.67 × 10 by a vacuum pump (11). ^-3P
With the vacuum above a, the reaction sintering is performed using the electric furnace (9).
went. A CA thermocouple (8) is inserted into the green compact (6).
By measuring the center temperature of the green compact (6),
The temperature was recorded on a temperature recorder (10). <3> Reactive sintering of green compacts
Performed in each process of Example 1 and Example 2. What
The heating rate in all methods is 10 ° C./min.
It is. For the obtained sintered body,
Surface observation, analysis of reaction products by X-ray diffraction, and
Physical properties such as Vickers hardness (Hv) were measured. Bit
Curse hardness (Hv) is the average of the results of five measurements.
And a load of 100 gf was applied for 15 seconds for measurement. (Comparative example) As a comparative example, a green compact was heated to 440 ° C.
At 440 ° C., a: 60 minutes, b: 90 minutes,
Hold at each time of c: 180 minutes and d: 240 minutes,
Cooled to room temperature. That is, after holding at 440 ° C.
Was not heated to a higher temperature.

Each of the obtained four samples was designated as Sample 1
-A to 1-d, various measurements were made, and the results are shown in Table 1.

[0037]

[Table 1]

As a result of analyzing the reaction product by X-ray diffraction,
It was confirmed that an Al ₃ Ni intermetallic compound was generated in the sample by holding the Ni-50 at% Al compact at 440 ° C. and performing a solid phase reaction. At that time, Al ₃
The production amount of the Ni intermetallic compound increases as the retention time increases, but it was also confirmed that a large amount of unreacted Al and Ni remained.

The Vickers hardness of a compact (Hv = 6)
0) did not change much. From these results, Ni
By keeping the -50 at% Al compact at the solid-state reaction temperature, an Al ₃ Ni intermetallic compound is generated.
It was confirmed that it was difficult to use a Ni-based intermetallic compound. (Example 1) Ni-50at as one-step holding reaction sintering
% Al compact was heated to 440 ° C., and at this 440 ° C., a: 90 minutes, b: 105 minutes, c: 120 minutes, d:
After holding each time for 180 minutes, each was heated to 700 ° C. and cooled to room temperature.

The four types of samples obtained by the one-step holding reaction sintering were designated as Samples 2-a to 2-d, and the results of various measurements are shown in Table 2. FIG. 4 shows the center temperatures of Samples 2-b and 2-c during sintering. FIG. 5 shows the results of the obtained X-ray diffraction.

[0041]

[Table 2]

As shown in FIG. 4, both Samples 2-b and 2-c undergo an exothermic reaction when heated to the sintering temperature. However, a large difference was observed in the exothermic peak temperature (Tp), and the Tp of Sample 2-c was 1083 ° C.
On the other hand, it was confirmed that the Tp of the sample 2-b became unmeasurable at 1370 ° C. or more, which is the upper limit temperature of measurement of the CA thermocouple, and reached a considerably high temperature.

From this, the critical holding time when the Ni-50 at% Al compact is subjected to the solid-phase reaction at 440 ° C. may be between the holding times of sample 2-b and sample 2-c. Understand. Then, it is understood that the reaction temperature during the reaction sintering can be controlled by adjusting the holding time.

From FIG. 5, it was confirmed that all the sintered bodies were AlNi intermetallic compounds. However, for sample 2-d, which had the longest retention time, A
lNi ₃ and Ni were also present.

As for Hv, all the samples are higher than the unsintered green compact, but the longer the holding time at the solid-state reaction temperature is, the lower the Hv is. Indicated. In particular, there was a large difference in the Hv value between sample 2-b and sample 2-c having a large difference in Tp.

Further, all the samples kept their shapes at the time of molding. These results indicate that it is possible to control the reaction temperature during reaction sintering by the method of the present invention. It was also found that an intermetallic compound capable of near net shape could be obtained. (Example 2) Ni-50at was used as the two-step holding reaction sintering.
The% Al compact was kept isothermally at two stages of 440 ° C. and 460 ° C., then heated to 700 ° C. and cooled to room temperature. The retention time at each temperature is
a: 30 minutes, 30 minutes total 60 minutes, b: 45 minutes, 30 minutes total 75 minutes, c: 60 minutes, 30 minutes total 90 minutes, d: 90
Minutes and 30 minutes for a total of 120 minutes.

The four samples obtained by the two-stage holding reaction sintering were designated as samples 3-a to 3-d, respectively, and Hv was measured. The results are shown in Table 3.

[0048]

[Table 3]

Samples 3-a and 3-b, which had a short holding time, melted during the exothermic reaction and did not retain the shape of the green compact. On the other hand, the Tp of sample 3-c and sample 3-d were held down to 806 ° C. and 737 ° C., respectively, and maintained their shapes.

It was confirmed that all the samples were Al-Ni intermetallic compounds, and that the longer the holding time, the more various compositions such as AlNi ₃ and Ni ₅ Al ₃ were formed. .

From the above, it can be seen that the reaction process can be controlled by the method of performing the isothermal holding during the reaction sintering in two stages according to the invention of the present application, and the process time can be further reduced. Indicated.

Of course, the present invention is not limited to the above-described example, and it goes without saying that various embodiments are possible in detail.

[0053]

As described in detail above, according to the present invention, the reaction process can be easily controlled by effectively applying the solid-phase reaction to the reaction sintering method for producing an intermetallic compound. A method for producing a Ni-Al-based intermetallic compound is provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an outline of temperature control in a sintering method of the invention of the present application.

FIG. 2 is a diagram exemplifying a relationship between an isothermal holding time at a solid-state reaction temperature and an exothermic peak temperature when heated to a sintering temperature. B: two-stage holding reaction sintering.)

FIG. 3 is a diagram exemplifying an outline of an apparatus when a green compact of a Ni—Al-based mixed powder is subjected to reaction sintering.

FIG. 4 is a diagram exemplifying a center temperature of a sintered body obtained by one-step holding reaction sintering.

FIG. 5 is a diagram illustrating the results of X-ray diffraction of a sintered body obtained by one-step holding reaction sintering.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 1-stage holding reaction sintering 2 2-stage holding reaction sintering 3 Temperature range in which solid phase reaction occurs 4 holding time 5 critical holding time 6 green compact 7 quartz glass tube 8 CA thermocouple 9 electric furnace 10 temperature recorder 11 vacuum pump

Claims (4)

[Claims] 1. A method for producing an intermetallic compound by reacting and sintering a green compact of a raw metal powder, wherein a solid phase reaction between the metals is performed while the green compact is heated to a sintering temperature. A method for producing a Ni-Al-based intermetallic compound, characterized in that a green compact is kept isothermally in a temperature range in which a solid phase reaction is caused in at least a part of the green compact. 2. The method according to claim 1, wherein the temperature is kept isothermally at any temperature in the range of 430 to 470 ° C. 3. The method according to claim 1, wherein the temperature is maintained in multiple stages.
Manufacturing method. 4. The method according to claim 1, wherein an intermetallic compound capable of near-net shape is obtained by molding a green compact.