JPH03162532A - Manufacture of ni-ti intermetallic compound - Google Patents

Abstract

PURPOSE:To easily obtain the Ni-Ti intermetallic compound which is thick and broad and having a prescribed compsn. by subjecting Ni-Ti plural layers laminated alternately to homogenizing treatment in vacuum or the like under prescribed conditions such as the temp. range in which a liquid phase is partly formed. CONSTITUTION:Ni-Ti plural layers are alternately laminated to regulate the thickness of each layer respectively into an objective compsn. Next, the Ni-Ti laminated product is subjected to homogenizing treatment in vacuum or in an inert gas atmosphere. This homogenizing treatment is executed in the temp. range where a liquid phase is partly formed, i.e., at 955 to 1015 deg.C for 1 sec to 10 hr or at 1015 to 1110 deg.C for 1sec to 1 hr. Then, the Ni-Ti intermetallic compound having the compsn. of 48 to 55 atomic% Ni can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a NiTi intermetallic compound directly from a laminate of Ni and Ti using reaction diffusion.

[Conventional technology]

Since NiTi-based alloys exhibit various functions depending on their composition, they are being put into practical use as various materials in a wide range of fields.

Conventionally, NiTi-based alloy plates and wire materials have undergone a process of melting, hot rolling, cold rolling, intermediate softening annealing, cold rolling, and final product, just like ordinary metal materials. It was manufactured after.

However, the production by the above method cannot be performed with Ni, which will be described later.
Since this was extremely difficult due to the unique properties of Ti-based alloys, a powder sintering method was developed as an alternative.

In this method, Ni and Ti powders are mixed in a ratio to form a target composition, and this mixed powder is pressed, HIPed, CI
After compacting into the desired product shape or a shape close to it using preforming techniques such as P and cold powder rolling, high-temperature sintering is performed to form a single-phase NiTi-based alloy through the reaction expansion of Ni and Ti. It is an attempt to obtain. According to this method, compared to the method described above which involves melting and cold working, the yield during weight adjustment and intermediate steps is significantly improved.

The two methods mentioned above are the general methods currently used for manufacturing NiTi alloys, but there are other manufacturing methods that solve the problems of these manufacturing methods, such as those described in Japanese Patent Application Laid-Open No. Publication No. 116340 of 1987 discloses that Ni
NiT and Ti are brought into close contact with each other by a film forming method such as pressure welding, plating or vapor deposition, and then heated, and then NiT is formed by reaction diffusion.
A method for obtaining the i-phase has been proposed.

In addition, Japanese Patent Application Laid-Open No. 120467/1983 describes NiT
Regarding the wire material of i-series alloy, the above-mentioned Japanese Patent Application Laid-Open No. 59-11
As an improvement method of the technique disclosed in Japanese Patent No. 6340, a plurality of composite filaments in which the surfaces of Ti core wires are coated with Ni are bundled, and then diameter-reduced, and then NiTi is formed by diffusion treatment.
Methods for generating phases have been proposed. This method is sufficiently practical as a method for producing filament material, and by compressing the filament material obtained, it is possible to
It is also possible to manufacture sheets and strips of about 100 ml.

[Problem to be solved by the invention]

As mentioned above, various manufacturing methods have been proposed for NiTi-based alloys, but all of them leave many problems to be solved, as described below. The main reason for this is that NiTi-based alloys exhibit useful properties because of Ni and Ti.
Although it has a limited composition with an atomic ratio of around 1:1, its cold workability is extremely poor in this composition range compared to ordinary metal materials.

For example, melting, hot rolling, cold rolling, intermediate softening annealing, and cold rolling, which are generally used to obtain plate-shaped NiTi alloys, produce the final product. Unless the intermediate rolling and intermediate softening annealing steps are repeated a considerable number of times, it is not possible to process the product to a predetermined thickness. This repetition of continuous processing and softening annealing can cause edge cracking during rolling, decrease in yield due to oxidation and pickling loss during annealing and pickling, and furthermore, deterioration of the material due to oxidation during annealing. NiTi has poor productivity and is inevitably expensive. In particular, it has been practically impossible to produce temporary products by cold working industrially for some sets in which the Ni content required to exhibit superelasticity at low temperatures is 50 at% or more.

As described above, since NiTi alloys are difficult to process, conventionally, what has been produced in large quantities is mainly wire rods that are relatively easy to process, and the production amount of plate materials is extremely small.

In addition to this, another major factor that impedes productivity and increases costs is the difficulty in dissolving into an appropriate composition. For example, in shape memory materials, where it is of paramount importance to control their operating temperature on target, NiT
In the case of i-alloys, a change in Nii5 degrees of just 0.1% causes a change in operating temperature of 10 degrees Celsius.

Therefore, accurate adjustment of the composition is essential, but Ti is extremely active at high temperatures and is lost during melting and casting due to oxidation loss and reaction with the mold, so it is extremely difficult to adjust the composition to the target. was difficult.

Therefore, special equipment is required for melting, and this factor has hindered the production of products of constant quality at low cost with a good yield.

Powder sintering was developed as a method to avoid the problems associated with melting and cold working described above, but this method requires the use of Ti powder, which is itself difficult to manufacture and expensive. As a result, product prices had to rise. Therefore, the powder sintering method is
Although it can be said to have certain advantages when applied to the manufacture of parts with complex shapes or small quantities of a wide variety of products, it is not suitable for the manufacture of products such as plate and strip materials that must be supplied in large quantities stably and at low cost. do not have. In addition, with powder sintered materials, the surface of the powder used as a raw material is oxidized to varying degrees, so a considerable amount of oxide remains inside the final product, which poses problems in terms of product quality. was.

Furthermore, JP-A-59-1 was proposed as a method for manufacturing plates and strips based on the same principle as the powder sintering method in that it uses reaction diffusion, but at a lower cost than the Japanese unsintered method.
When the method disclosed in Japanese Patent No. 16340 is suitable for manufacturing actual strips, single-phase NiTi with a thickness of about 0.1 mm is used.
Even when trying to obtain an alloy plate, a long diffusion heat treatment lasting several hundred hours is required.

In addition, if the Ni and Ti layers are thick, defects such as voids will occur frequently inside the material during diffusion heat treatment, impairing the integrity of the structure. The thickness is only about several tens of micrometers at most. Therefore, this method cannot be said to be practical as an industrial manufacturing method either.

Incidentally, there is a method disclosed in Japanese Patent Application Laid-open No. 31938/1983 that is considered to be an extension of the above manufacturing method. Although this method is not particularly limited to NiTi, a plurality of foil-like metal materials are laminated, and then diffusion is caused by heat treatment.

However, in this method, the reaction diffusion is solid phase diffusion,
Reaction diffusion between Ni-Ti, especially Ni layered in a planar manner
- In the case of solid phase reaction diffusion of Ti plates, compared to the case of using powder as a material, specific problems such as those listed below occur, so it is difficult to obtain materials of quality that can withstand practical use, and the time required It's also long. Note that these points have been confirmed through experiments conducted by the present inventors.

(1) The first point is the time required for reaction and diffusion, and when considering the same weight, the area of the interface where diffusion progresses (specific surface area ms''/g) is smaller than that of powder, so the diffusion The problem is that it takes a long time to proceed.

(2) The second point is due to the same cause as mentioned above.
As the absolute number of atoms passing through per unit interface area increases, voids occur frequently due to the Kirkendall effect, a phenomenon specific to interdiffusion. Especially N
In the case of interdiffusion between i and Ti, the diffusion rate of Ni atoms in Ti is 100% higher than that of Ti atoms in Ni.
Since it is more than 0 times larger, there is a strong tendency for Ni atoms to be depleted near the interface, and as a result, the occurrence of Kirkendall voids becomes significant. The generation of voids not only harms the tissue, but interfacial voids in particular become an obstacle to subsequent reaction diffusion and hinder homogenization of the composition, so they must be minimized as much as possible.

The generation of voids is closely related to the reaction-diffusion heat treatment temperature, and in the case of Ni-Ti, although the generation of voids can be suppressed to some extent at a relatively low temperature of about 700°C, the diffusion rate is Because of this slow process, it takes a long time to homogenize the composition, which is not practical. On the other hand, if heat treatment is performed near the upper limit temperature of solid phase reaction of about 900° C. in order to shorten the reaction time, a large amount of voids will be generated.

(3) The third point is a phenomenon that is also caused by the difference in mutual diffusion rate between Ni and Ti, and as the diffusion progresses between the Ni and Ti layers, the volume increases and decreases, and as a result, the interface This is because stress is generated and mechanical peeling occurs. To explain this point in more detail, the volume of the Ni layer that preferentially releases atoms naturally tends to decrease relatively, and the way in which the volume decreases in this case is macroscopically determined by the thickness. This appears as a decrease in the layer thickness in the direction. On the other hand, from a macroscopic perspective, the Ti layer on the side that absorbs atoms expands in the plane direction of the layer as the N thickness increases. Therefore, a shearing force acts in the plane direction near the boundary between Ni and TiN, and as a result, mechanical peeling occurs at the interface.

For the reasons mentioned above, the production method disclosed in JP-A-64-31938 cannot be said to be practical on an industrial scale.

Although it can be said that the manufacturing method disclosed in JP-A-62-120467 can be fully used industrially for manufacturing wire material, the dimensions of the temporary wire material obtained by this method are smaller than the original wire material. Since the dimensions of the strips are limited, they have their own limits, and cannot meet diverse dimensional demands such as thick or wide strips.

The present invention advantageously solves the above-mentioned problems and proposes an advantageous manufacturing method for NiTi intermetallic compounds that can be manufactured industrially and inexpensively, even if they are thick or wide. The purpose is to

[Means to solve the problem]

As a result of intensive research to solve the above problem, the inventors of the present invention have found that it is possible to achieve the desired purpose by using liquid phase diffusion rather than solid phase diffusion for reaction diffusion. We have obtained knowledge that this method is extremely effective.

That is, heat treatment was performed by selecting a temperature range that would produce a liquid phase within a specific composition range on the Ni-Ti binary system phase diagram, and a liquid phase was partially generated at the interface between Ni and Ti. However, not only was the reaction completed in a short time, but a material with extremely few defects was also obtained.

In addition, as a method for intervening a liquid phase in a solid phase reaction,
A liquid phase sintering method in powder metallurgy is known, but this method uses only a low melting point binder with a relatively small volume fraction as a liquid phase. , rather than the concept of a binder in liquid phase sintering, the liquid phase generation interface moves as diffusion progresses, and depending on the heat treatment conditions, eventually nearly 100% of the material will form a liquid phase at least once. It is said that the state will be obtained,
It has completely different characteristics from the liquid phase sintering method.

Conventionally, there has been no attempt to utilize a liquid phase in the production of a NiTi intermetallic compound using reaction diffusion, and the present invention is the first to utilize such a liquid phase.

The present invention is based on the above findings.

That is, in the present invention, a plurality of layers of Ni and Ti are alternately laminated,
Then, by diffusion heat treatment, Ni with a composition of 48 to 55 at%
This is a method for producing a NiTi intermetallic compound (first invention), which comprises performing the diffusion heat treatment in a temperature range where a liquid phase partially occurs when producing the Ti intermetallic compound.

In addition, the present invention performs diffusion heat treatment in a vacuum or inert gas atmosphere at a temperature range of 955 to 1015°C for 1 second to
10 hours (second invention), 1 second to 1 hour in a temperature range of 1015 to 1110°C (third invention), 1110 to 124
1 second to 10 minutes in the temperature range of 0°C (fourth invention), and 955 to 1015°C and/or 1015 to 1110°C
℃ for 1 second to 1 minute, and after the liquid phase reaction at that temperature is completed, the reaction is continued at a temperature range of 1110 to 1240℃ for 1 second to 10 minutes (fifth invention). This is a method for producing a NiTi intermetallic compound.

As described in the first invention, the present invention is based on reaction-diffusion in a state where a liquid phase is partially generated.Hereinafter, the second to fifth inventions which define a specific temperature range will be explained.

The second invention is based on a βTi-Ni solid solution and a Ti. Diffusion heat treatment is performed in a temperature range where Ni and the liquid phase coexist (in the figure, Hyo region I). In this temperature range, a liquid phase occurs in the phase on the Ti lynch side, and if the reaction progresses ideally, 83 vol% of the entire material will eventually become a liquid phase, and the entire phase on the Ti lynch side will become Ti2Ni. At that point, the liquid phase reaction ends.

In reality, some Ti diffuses into the Ni side, which is the solid phase, due to solid phase diffusion, so the liquid phase rate is 83vo 1%.
less than After the liquid phase reaction is completed, the reaction transitions to solid phase diffusion within this temperature range, and the reaction diffusion progresses until the entire material has a uniform composition. At this time, Ti. Since the solid phase diffusion between Ni and Ni is rate-determining, compared to the third to fifth inventions described later in which reaction and diffusion are performed in a temperature range above this temperature range where the liquid phase biovolume is larger, NiTi becomes a single phase. The reaction time for this reaction is somewhat longer (more than 1 second, especially about 10 hours when stacking 20 μm of Ni and Ti), but the solid phase on the Ni-rich side that supports the liquid phase in a sandwich-like manner is relatively thick. for,
This is advantageous in suppressing to a low level distortion and deformation of the material that normally occurs with reaction-diffusion.

The third invention is based on the phase diagram shown in FIG.
Heat treatment is performed in a temperature range (region II in the figure) in which no liquid phase is generated on the Ni-rich side than iNi. In this temperature range, a liquid phase occurs in the phase on the Ti-rich side, and if the reaction progresses ideally, the final 99 vol of the entire material
About 1% becomes a liquid phase, and the Ti-rich phase is all 48a.
A combination of t%Ni-52at%Ti (TiN on the phase diagram)
The liquid phase reaction is completed at the point when the boundary line of the liquid phase coexistence region of i and TiNi is reached. The actual liquid phase formation rate varies depending on the ratio of Ni and Ti in the stacked state and the temperature, and the boundaries between the two regions of the phase diagram, NiTi and NiTi + liquid phase, are not completely determined, so at present cannot be clearly defined.

In this temperature range, since almost the entire amount of the material passes through a liquid phase state at least once, the reaction to form a NiTi single phase is completed in a short time (about 1 second to 1 hour). It is thought that the rate-limiting reaction is the diffusion of Ni into the solid solution to cause melting of the βTi-Ni solid solution, or the melting reaction at the interface between the βTi-Ni solid solution and the liquid phase, but neither of these poses much of a problem. It's not that slow of a reaction. In addition, during the progress of this reaction, it is mainly the Ni phase in the solid phase that retains the liquid phase portion, and the TiNi. and TiNi phase.

The fourth invention of Xingdo Hatsutsui is that on the phase diagram of FIG.
On the rich side, βTi-Ni solid solution and TiNi coexist with the liquid phase, and on the Ni-rich side than NiTi, TiN
i. The heat treatment is performed for a shorter time in a temperature range where TiNi and the liquid phase coexist (region ■ in the figure).

In this temperature range, as the reaction progresses, the entire amount of the material will eventually pass through the liquid phase at least once. Therefore, the reaction time for the entire material to become a TiNi single phase is extremely short (approximately 1 second to 10 minutes), and depending on the thickness of each layer, it actually takes a few seconds to a few minutes to turn the entire material into a TiNi single phase. Become.

What must be particularly noted when carrying out reaction-diffusion in this temperature range is that as the reaction progresses, there is a process in which all parts of the material become a liquid phase or a solid-liquid coexistence phase.

In this respect, in the second and third inventions, even during the progress of the reaction, a part of the Ni phase and the TtNix produced by the reaction are always present.
Since TiNi and TiNi exist in a solid state, this part plays a role in maintaining a liquid phase or a solid-liquid coexistence phase. On the other hand, in the temperature range of the fourth invention, there is no part that always maintains a solid state before and after the reaction, so the material itself has almost no ability to firmly maintain its shape during the reaction.

Therefore, in order to carry out reaction diffusion in this temperature range,
It is necessary to use a support that holds the shape of the material from the outside, such as a mold made of ceramics or a heat-resistant alloy. However, even in this case, all the materials do not become liquid phase at the same time (TiNiz, β
Since the Ti--Ni solid solution and the liquid phase coexist, the shape retention ability exists due to the interfacial tension between the liquid phase and the solid phase, capillary phenomenon, and the like. Therefore, unlike a complete liquid, there is no fear that the shape will collapse indefinitely.

Comparison 15 The fifth invention is a heat treatment method that allows the entire amount of the material to pass through a liquid phase at least once, and that a portion always remains in a solid phase during reaction and diffusion, thereby maintaining the shape retention ability of the material itself. be. In this method, the reaction progresses first in the second or third invention.
Proceeds in the same manner as described in the invention (955-1050℃
Alternatively, heat treatment is performed at 10I5 to 1110°C for 1 second to 1 minute), and the liquid phase reaction is completed with a small amount of Ni phase and/or Ni3Ti phase generated by the solid phase spreading reaction remaining. Next, the temperature range and time (1
By heat treatment at 110°C to 1240°C for 1 second to 10 minutes), the remaining Ni phase that had remained in a solid state as well as TiNi3 and TiN recovered by the reaction were removed.
The reaction ends when a part of i becomes a liquid phase and the whole becomes a TiNijit phase.

According to this two-stage heat treatment, although the entire amount of the material passes through the liquid phase state once, part of the Ni phase remains in the first stage, while part of the TiNi phase recovered by the reaction remains in the solid state in the second half stage. Therefore, the material will not melt and become unable to hold its shape.

[For production]

In the present invention, N of the NiTi intermetallic compound to be produced is
The reason why the i-containing content was limited to the range of 48 to 55 at% is as follows.

That is, the reason why the lower limit of the Ni content is 48 at % is because below this value, a shape memory alloy or a superelastic alloy with advantageous properties cannot be obtained. On the other hand, the amount is 5
This is because if it exceeds 5 at%, the material becomes brittle and is not suitable for practical use in terms of fatigue strength.

Further, in the present invention, as the form or method of alternately laminating Ni-Ti, any conventionally known method is suitable, including a method of alternately stacking foils, and a vapor phase deposition method such as spa sottering or CVD method. At this time, the thickness of each phase is preferably as thin as possible in consideration of processing time, but there is no problem in practice if the thickness is about 20 μm or less. The key point is to strictly control the total thickness of each of the Ni and Ti layers so that they meet the desired thickness.

Furthermore, after lamination, it is advantageous to apply light pressure or to perform preheat treatment as necessary. This is because, if air bubbles are present at the lamination interface, such air bubbles can be removed by applying light pressure, thereby avoiding product quality deterioration.

In addition, the purpose of the preliminary heat treatment is that the reaction in which NiTi is produced from Ni and ↑i is an exothermic reaction, so if the laminate is heated rapidly, the reaction will proceed too much and melt beyond the melting point due to self-heating. The goal is to prevent this from happening. By this preliminary heat treatment, TiNi. YaTi
Ni, Ti. Ni, etc. are generated, and these are Ni and Ti.
acts as a barrier to prevent the direct reaction of
Dissolution due to self-heating reactions is advantageously prevented.

In the present invention, the treatment time during the diffusion heat treatment was set over a wide range of times.
This is because it changes depending on the thickness of each layer in the laminate. However, at the time when the liquid phase reaction is completed, especially in the second invention, the TiNi single phase is not formed.
>50at%, TiJi4, TiJi4,
Precipitation of TizNi3 or TiNiz phase is observed. Also under other conditions, TiNiO&lIt on the phase diagram
Since there is some non-uniformity in the composition corresponding to the c width, in order to make the entire material uniform, homogenization annealing for several to tens of hours after the liquid phase reaction is completed, that is, NiTi single phase Separately from the diffusion heat treatment to achieve this, it is desirable to perform a treatment to even out the temperature variations in the obtained NiTi single phase.

Note that the temperature range in the present invention is based on the currently known Ni-
This was derived from the Ti binary system phase diagram (Figure 1), and although the absolute value of the temperature may change with future research into a more detailed and accurate phase diagram, the essence of the present invention is that the Ni- Ti binary system. If the temperature is in the phase change region on the phase diagram and the absolute value of the temperature is corrected, the appropriate temperature range of the present invention is changed based on the corrected value. A similar change in the absolute value of temperature is caused by a third element (<
20% Cu, etc.) may be considered in the same way.

〔Example〕

In order to produce a NiTi intermetallic compound according to the method of the present invention, a material was first produced as follows.

In order to set the atomic ratio of Ni to Ti to 50.5 7 49.5, pure Ni foil and pure Ti foil whose thickness was adjusted to have a thickness ratio of 38.8:61.2 were alternately coated with Ni. After laminating 25 sheets of foil as the outer layer and rolling until the total thickness was 0.2 mm, the foil was rolled at 750°C for 4 hours, then at 900°C.
A preliminary heat treatment was performed at ℃ for 1 hour to obtain a material.

The above material was heated from room temperature to 60℃ in a vacuum atmosphere.
The temperature was raised to 1000°C at a heating rate of in, and at this temperature
After holding for a period of time, it was cooled in the furnace. Note that the heat treatment was performed with the material placed flat on a flat plate of zirconia ceramics.

After deforming the test piece thus obtained at room temperature, 90
When immersed in warm water at ℃, it immediately returned to its original shape. Furthermore, when the cross section of this test piece was observed under a microscope, the layered structure that existed before the diffusion heat treatment disappeared, and a complete Ni
It was in a Ti single phase state.

Back construction 1 The above material was heated from room temperature to 60°C/m under a vacuum atmosphere.
The temperature was raised to 1050°C at a heating rate of
After holding for 0 minutes, the mixture was cooled in the furnace. The mounting condition of the material during heat treatment was the same as in Example 1. The obtained test piece was deformed at room temperature and then immersed in warm water at 90°C, and immediately restored to its original shape. Further, the cross section of the test piece was in a complete NiTi single phase state.

The above material was heated from room temperature to 60℃/mi under a vacuum atmosphere.
The temperature was raised to 1150° C. at a heating rate of n, held at this temperature for 5 minutes, and then cooled in the furnace. Note that the mounting state of the material during the heat treatment is the same as in Example 1.

The obtained test piece was deformed at room temperature and then immersed in hot water at 90°C, and immediately restored to its original shape. Moreover, the structure was in a complete NiTi single phase state.

Carved 1 liter of the above material in a vacuum atmosphere from room temperature to 60℃/mi.
The temperature was raised to 1150°C at a heating rate of n, and IO was added to this temperature.
After holding for a minute, the temperature was raised to 1150° C. at the same heating rate of <60° C/min, held at this temperature for 5 minutes, and then cooled in the furnace. Note that the mounting state of the material during the heat treatment is the same as in Example 1.

The obtained test piece was deformed at room temperature and then immersed in hot water at 90°C, and immediately restored to its original shape. Also m
The weave was in a complete NiTi single phase state.

Tenshaji 41 Heat treatment was performed under the same conditions as in Example 4, except that the material was made into a cylindrical shape and placed in an upright state in the furnace.

After the heat treatment, the shape of the test specimen remained almost the same, although some deformation was observed.

For comparison, heat treatment was carried out under the same conditions as in Example 3, and the specimen was so significantly deformed that it was impossible to open the cylinder and return it to a flat plate shape.

Comparative Example 1 20 μm thick Ni and Ti foils were laminated alternately to make the whole 0.5 m thick, and then cold
0% rolling was performed, and then diffusion annealing was performed at 950° C. for 5 hours.

When the cross section of the obtained sample was observed under a microscope, it was found that many voids were formed in a layered manner, and therefore it was found that industrially it would be difficult to manufacture a thick and wide sample.

〔Effect of the invention〕

Thus, according to the present invention, even thick-walled, wide-width NiTi intermetallic compounds, which have conventionally been virtually impossible to manufacture on an industrial scale, can be manufactured in a short time and at low cost with high quality. Can be done.

[Brief explanation of the drawing]

Figure 1 shows It is a Ni-Ti binary system phase diagram.

Claims (1)

[Claims] 1. When producing a NiTi intermetallic compound having a Ni composition of 48 to 55 at% by laminating a plurality of layers of Ni and Ti alternately and then performing diffusion heat treatment, the diffusion heat treatment is performed at a temperature at which a portion of the liquid phase occurs. 1. A method for producing a NiTi intermetallic compound, characterized in that the production method is carried out within a range. 2. The manufacturing method according to claim 1, wherein the diffusion heat treatment is performed in a vacuum or in an inert gas atmosphere at a temperature range of 955 to 1015°C for 1 second to 10 hours. 3. The manufacturing method according to claim 1, wherein the diffusion heat treatment is performed in a vacuum or in an inert gas atmosphere at a temperature range of 1015 to 1110°C for 1 second to 1 hour. 4. The manufacturing method according to claim 1, wherein the diffusion heat treatment is performed in a vacuum or in an inert gas atmosphere at a temperature range of 1110 to 1240°C for 1 second to 10 minutes. 5. Performing diffusion heat treatment at a temperature range of 955 to 1050°C and/or 1015 to 1110°C for 1 second to 1 minute,
After the liquid phase generation reaction at that temperature is completed, 111
The manufacturing method according to claim 1, wherein the manufacturing method is carried out at a temperature range of 0 to 1240°C for 1 second to 10 minutes.