JP2003137655A - Boron carbide-aluminum nitride sintered compact, and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a boron carbide-aluminum nitride sintered compact which has high density and high strength. SOLUTION: In the method of producing a boron carbide-aluminum nitride sintered compact, aluminum nitride powder of 0.5 to 30 mol% is added to boron carbide powder, and, after their mixing, the mixture is sintered in an atmosphere where aluminum nitride is not decomposed. The boron carbide-aluminum nitride sintered compact consists of 99.5 to 70 mol% boron carbide (B4 C) and 0.5 to 30 mol% aluminum nitride (AlN), and has a relative density of >=95%. The boron carbide-aluminum nitride sintered compact also has a four point bending strength of >=600 MP.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a boron carbide (B ₄ C) -aluminum nitride (AlN) sintered body having a high density, a boron carbide-aluminum nitride sintered body having a high bending strength, and a low temperature. The present invention relates to a hot pressing method performed in a range, a hot pressing method performed at a low pressure, and a method for producing a boron carbide-aluminum nitride sintered body by pressureless sintering.

[0002]

2. Description of the Related Art Boron carbide sintered bodies are lightweight, have high hardness, and are excellent in wear resistance and corrosion resistance, and are currently used for sandblast nozzles, wire drawing dies, extrusion dies, etc. . However, since the boron carbide sintered body is difficult to sinter, it is usually produced by the hot pressing method under a high temperature range of 2100 ° C. or higher and a large pressure of 30 MPa or higher. This production method hampers the general application of the boron carbide sintered body because of the high production cost.

On the other hand, JP-A-59-184767
In the publication, Al, Al alloys and Al compounds are added to boron carbide as sintering aids. However, while performing atmospheric pressure sintering in a vacuum or an inert gas atmosphere, Al, A
The 1 alloy and the Al compound are decomposed and evaporated, and these sintering aids remain in the boron carbide sintered body in an amount of 0.2% by weight or less. For this reason, not only the sinterability cannot be improved sufficiently, but also the weight is reduced due to the decomposition and evaporation of the sintering aid.
% Relative densities cannot be obtained.

As described above, since the boron carbide sintered body is difficult to sinter, it is not possible to provide a high density and high strength one at a low cost, and at present, it is applied only to extremely limited uses. It is only being done.

[0005]

That is, an object of the present invention is to provide a boron carbide-aluminum nitride sintered body characterized in that the relative density of the sintered body is 95% or more, and further, it is four MPa of 600 MPa or more. It is to provide a boron carbide-aluminum nitride sintered body having point bending strength at low cost.

[0006]

As a result of various studies to achieve the above-mentioned object, the present inventor has found that the aluminum nitride does not decompose or evaporate in the sintering process in a mixed raw material obtained by adding aluminum nitride to boron carbide powder. As described above, when the mixed raw material is heated while maintaining specific conditions, it is possible to exert the function of the boron carbide contained in the aluminum nitride as a sintering aid, and as a result, it is possible to sinter extremely well. The present invention has been accomplished based on the finding that a high-density, high-strength boron carbide-based sintered body can be obtained.

That is, the present invention relates to boron carbide (B ₄ C) 9
A boron carbide-aluminum nitride sintered body characterized by comprising 9.5 to 70 mol% and aluminum nitride (AlN) of 0.5 to 30 mol% and having a relative density of 95% or more, preferably, The above-mentioned boron carbide-aluminum nitride sintered body having a four-point bending strength of 600 MPa or more.

Further, the present invention is a method for producing a boron carbide-aluminum nitride sintered body having a relative density of 95% or more, wherein the boron carbide powder is 0.5% aluminum nitride powder.
A method for producing a boron carbide-aluminum nitride sintered body, which comprises adding 30 mol% to 30 mol% and mixing, and then sintering the mixture in an atmosphere in which decomposition of aluminum nitride does not occur, preferably 1600 ° C. or higher, 2200 The method for producing a boron carbide-aluminum nitride sintered body described above, which comprises performing hot press sintering at a pressure of more than 20 MPa and less than 60 MPa in a temperature range of 0 ° C. or less, more preferably an average grain size. The diameter (D ₅₀ ) is 1 μm or less, the maximum particle size is 5 μm or less, and the specific surface area is 15 m ² /
Production of the above-mentioned boron carbide-aluminum nitride sintered body, characterized in that hot pressing sintering is carried out using a boron carbide powder of g or more to produce a sintered body having a four-point bending strength of 600 MPa or more. Is the way.

[0009] In addition, the present invention, 1900 ℃ or more, 22
A method for producing the above-mentioned boron carbide-aluminum nitride sintered body, which comprises performing hot press sintering at a pressure of 20 MPa or less in a temperature range of 00 ° C or less, or
The method for producing a boron carbide-aluminum nitride sintered body is characterized by performing atmospheric pressure sintering in a temperature range of 1900 ° C. or higher and 2200 ° C. or lower.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below.

As described above, the present invention has conducted various experiments to obtain a high-density and high-strength boron carbide sintered body, and as a result, the present invention has revealed that a mixed raw material obtained by adding aluminum nitride to boron carbide powder. With respect to the above, when the mixed raw material is heated while maintaining specific conditions so that the aluminum nitride does not decompose or evaporate in the sintering process, the aluminum nitride has a function as a sintering aid of boron carbide. It is based on the new finding that a boron carbide based sintered body having a high density and a high strength can be obtained as a result.

That is, in order to improve the sinterability of the boron carbide powder, 0.5 to 3 of aluminum nitride powder is added as a sintering aid.
Add 0 mol% to decompose aluminum nitride during sintering.
When sintering is performed in an atmosphere that does not evaporate, a part of the surface of the aluminum nitride powder reacts with the boron carbide powder to form a grain boundary reaction phase, which activates diffusion during sintering, which results in sintering. Can be promoted. However, in the conventionally known technique, aluminum nitride is decomposed (2AlN) because it is sintered in a vacuum or in an inert atmosphere.
→ 2Al + N ₂ ), and not only the effect as an auxiliary agent is not sufficiently exhibited, but also the Al content is evaporated together with N ₂ to cause a large weight reduction, and a sufficiently dense sintered body cannot be obtained.

In the present invention, the N ₂ gas is introduced into the inert gas so that the decomposition temperature of the aluminum nitride becomes equal to or higher than the N ₂ pressure at the sintering temperature, so that the aluminum nitride contained in the raw material powder in the sintering process. Can be prevented from decomposing and evaporating, and as a result, a high-density and high-strength boron carbide-based sintered body can be provided with high reproducibility and thus can be stably provided.

That is, the sintered body of the present invention comprises boron carbide (B ₄
C) 99.5 to 70 mol% and aluminum nitride (Al
N) in an amount of 0.5 to 30 mol% and a relative density of 9
It is a boron carbide-aluminum nitride sintered body characterized by being 5% or more. Here, aluminum nitride (Al
The reason for defining the amount of N) in the sintered body within the above range is 0.
If it is less than 5 mol%, it may not be sufficient to exert the effect as a sintering aid in a practical sintering schedule, and if it exceeds 30 mol%, the obtained sintered body may have a boron carbide firing property. This is because it is difficult to maintain the properties of the bound body that are light weight, high hardness, excellent in wear resistance and corrosion resistance, and particularly high elasticity. Further, when the relative density is less than 95%, the strength is low, and the application is limited when it is put to practical use.

Furthermore, since the sintered body of the present invention has a four-point bending strength of 600 MPa or more in a preferred embodiment, it is suitable for conventionally known applications such as sandblast nozzles, wire drawing dies and extrusion dies. It can be applied to applications other than the above applications.

The sintered body of the present invention can be stably obtained with high reproducibility according to the production method of the present invention described below, but if the above requirements are satisfied, the production method is required to be limited to the above production method. There is no.

The manufacturing method of the present invention is a method for manufacturing a boron carbide-aluminum nitride sintered body having a relative density of 95% or more, in which 0.5 to 30 mol% of aluminum nitride powder is added to boron carbide powder, It is characterized in that after mixing, sintering is performed in an atmosphere in which decomposition of aluminum nitride does not occur. Here, the compounding amount of the aluminum nitride powder is as described in the present invention regarding the sintered body. As an atmosphere in which decomposition of aluminum nitride does not occur, a nitrogen-containing gas such as nitrogen or ammonia is usually used, and at the sintering temperature, the nitrogen partial pressure may be higher than the decomposition pressure of aluminum nitride, In order to avoid adverse effects such as reaction with the materials that make up the furnace at high temperatures when excessive nitrogen pressure is applied,
A method of adding nitrogen or ammonia to an inert gas such as argon or helium is used.

The boron carbide powder used in the present invention has an average particle diameter (D ₅₀ ) measured by a laser diffraction / scattering analyzer (Microtrac): 10 μm or less. When the average particle diameter (D ₅₀ ) is larger than 10 μm, the sinterability is poor and a dense sintered body may not be obtained. In addition, the specific surface area (BE
Regarding T), it is possible to use a boron carbide powder of 2 m ² / g or more.

In the present invention, the first embodiment is 16
The second embodiment is characterized in that hot press sintering is performed at a pressure of more than 20 MPa and less than 60 MPa in a temperature range of 00 ° C. or more and 2200 ° C. or less.
The present invention is characterized in that hot press sintering is performed at a pressure of 20 MPa or less in a temperature range of 200 ° C. or lower, and the third embodiment is characterized by performing normal pressure sintering in a temperature range of 1900 ° C. or higher and 2200 ° C. or lower. There is.

First, the first embodiment is a method of sintering while maintaining a high pressing force, and is characterized in that a sintered body having characteristics of high density and high strength can be stably obtained. Furthermore,
In this case, when selecting a raw material boron carbide powder having an average particle diameter (D ₅₀ ) of 1 μm or less, a maximum particle diameter of 5 μm or less, and a specific surface area of 15 m ² / g or more, A sintered body having a four-point bending strength of 600 MPa or more can be stably obtained.

The second embodiment is characterized by sintering under a low pressure of 20 MPa or less,
A relatively high density sintered body can be obtained without requiring an excessive pressurizing device. Further, when applying a conventional hot press device, it is possible to avoid the problem that the product shape is restricted because a large pressing force is required, and it is possible to obtain a large size product by using the conventional device as it is. There is a feature that can be done.

The third embodiment is a method of sintering a powder or a molded product obtained by molding the powder by a conventionally known technique such as pressing, extrusion and injection molding without pressurizing. There is a feature that a large amount of sintered bodies can be provided at a lower cost than in the embodiment. Further, since no pressure is applied during the sintering process, the raw material is made into a complicated product shape or a shape close to it in advance, and then only the sintering is performed, or a post-treatment such as some processing is performed to obtain a product having a complicated shape. There are features that can be obtained.

In the present invention, the sintering temperature range is 1
600 ° C. or more and 2200 ° C. or less are selected. 1600 ° C
If the temperature is less than the above, it is difficult to obtain a dense sintered body because the sintering does not proceed sufficiently, and if the temperature exceeds 2200 ° C, it is difficult to suppress the grain growth of boron carbide in the obtained sintered body and the decomposition of aluminum nitride. There will be problems such as

Further, in the present invention, the present inventor has found that the physical properties of the obtained sintered body are influenced by the sintering method, the sintering temperature, and the grain size of the raw material, based on the results of the experimental study. That is, in the first case, as described above, the raw material boron carbide powder has an average particle diameter (D ₅₀ ) of 1 μm.
In the following, when selecting a material having a maximum particle size of 5 μm or less and a specific surface area of 15 m ² / g or more, a sintered body having a four-point bending strength of four-point bending strength of 600 MPa or more is stable. In order to obtain the above-mentioned high-strength sintered body, the sintering temperature is preferably in the range of 1600 ° C. to 2000 ° C. in order to suppress the crystal growth of boron carbide. In the case of the second and third embodiments, that is, when sintering is performed while maintaining the applied pressure at 20 MPa or less, the sintering temperature is preferably 1900 to 2200 ° C.

[0025]

[Example] [Example 1]

A boron carbide powder A having the physical properties shown in Table 1 was mixed with 10 mol% of an aluminum nitride powder having an average particle diameter (D ₅₀ ) of 0.7 μm, and a methanol solvent was used to make a silicon carbide (SiC) planetary ball mill. Rotation speed: 185r
After mixing pm for 30 minutes, the mixture was dried by an evaporator, further dried at 150 ° C. for 24 hours, and then passed through a sieve having openings of 250 μm to prepare a boron carbide-aluminum nitride mixed powder.

[0027]

[Table 1] A graphite die was filled with a boron carbide-aluminum nitride mixed powder, molded at 7.5 MPa, and then mounted in a firing furnace. While pressurizing to 10 MPa, heating at a temperature rising rate of 40 ° C./min while evacuating to a pressure of 2.0 × 10 ^{−1 to} 2.0 × 10 ⁻² Pa using a diffusion pump. I went. When the temperature reached 1000 ° C., the evacuation was terminated and Ar gas was introduced at a flow rate of 2 liter / min. 17
At 00 ° C., the decomposition pressure (N ₂ partial pressure) of aluminum nitride is 6.2 × 10 ⁻⁶ MPa, so the N ₂ partial pressure in the firing furnace should be 3.1 × 10 ⁻⁴ MPa. , N ₂ gas was introduced at a flow rate of 0.006 liter / min to create an atmosphere of gas pressure: 0.103 MPa and heated to 1500 ° C. 10 ℃ / m from 1500 ℃ to 1700 ℃
It heated at the temperature rising rate of in. After reaching 1700 ° C., the applied pressure was raised to 50 MPa and the pressure was maintained for 1 hour for sintering to produce a boron carbide-aluminum nitride sintered body.

The four-point bending strength of the boron carbide-aluminum nitride sintered body was measured according to JIS R1601. The surface of the test piece was finished with a surface grinder No. 400. Moreover, the density of the test piece was measured by the Archimedes method, and the relative density was calculated. After lapping the surface of the test piece and performing etching treatment, SEM observation was performed to find the size of the largest particles of boron carbide. Further, the crystal phase in the sintered body was identified by the X-ray diffraction method. The results are shown in Table 2.

[0029]

[Table 2] As a result of the evaluation, the produced boron carbide-aluminum nitride sintered body had a density of 2.50 g / cm ³ , a relative density of 98.0%, and a maximum particle size of 2.7 μm.
A four-point bending strength of MPa was obtained. As the crystal phase, an aluminum nitride phase was detected in addition to the boron carbide phase. [Examples 2 to 3]

A boron carbide-aluminum nitride mixed powder was prepared by the same procedure as in Example 1 except that the boron carbide powders B and C having the physical properties shown in Table 1 were used and the aluminum nitride powder was blended in an amount of 7 mol%. . Heating was performed to 1000 ° C. in the same procedure as in Example 1, and Ar gas was introduced. At 2000 ° C., the decomposition pressure (N ₂ partial pressure) of aluminum nitride is 0.0013 MPa,
As N ₂ partial pressure in the sintering furnace is 0.0040MPa, N ₂
Gas was introduced at a flow rate of 0.08 liter / min.
Hot pressing temperature: 2000 ° C., pressing force during sintering: 10
Sintering was performed by the same procedure as in Example 1 except for MPa,
A boron carbide-aluminum nitride sintered body was prepared, and Example 1 was prepared.
The sintered body density was measured and the crystal phase was identified by the same procedure as described above. The evaluation results are shown in Table 2. Both examples are 95
The aluminum nitride phase was detected with a high density of at least%. [Comparative Example 1]

A boron carbide sintered body was prepared and evaluated in the same procedure as in Example 2 except that the aluminum nitride powder was not added. The results are shown in Table 2. The sintered body of Comparative Example 1 had a low density of 77.0%. [Example 4]

A boron carbide-aluminum nitride mixed powder was prepared in the same procedure as in Example 1. After mold molding at 20 MPa, CIP molding at 200 MPa was performed to produce a molded body. The molded body was placed in a graphite container and subjected to 100% by the same procedure as in Example 1 under normal pressure without applying pressure.
It heated up to 0 degreeC and introduced Ar gas. At the sintering temperature of 2000 ° C., the decomposition pressure of aluminum nitride (N ₂
Since the partial pressure) is 0.0013 MPa, N ₂ gas was introduced at a flow rate of 0.08 liter / min so that the N ₂ partial pressure in the firing furnace would be 0.0040 MPa. In the same procedure as in Example 1, the temperature was raised to 2000 ° C. and pressureless sintering was performed to produce a boron carbide-aluminum nitride sintered body. In the same procedure as in Example 1, the sintered body density was obtained. Was measured and the crystal phase was identified. Table 3 shows the evaluation results. The example has a high density of 95% or more, and the aluminum nitride phase was detected.

[0033]

[Table 3] [Comparative Example 2]

A boron carbide sintered body was prepared and evaluated by the same procedure as in Example 4 except that N ₂ gas was not introduced during sintering. The results are shown in Table 3. The relative density of the sintered body of Comparative Example 2 was as low as 92.9%, and the aluminum nitride phase was not detected.

[0035]

INDUSTRIAL APPLICABILITY The boron carbide-aluminum nitride sintered body of the present invention can be manufactured by an inexpensive process as compared with the prior art, and has various applications such as sliding parts, cutting tools and new wear resistant parts. And is industrially useful.

Continued front page    F-term (reference) 4G001 BA23 BA36 BB23 BB36 BC13                       BC42 BC52 BC54 BC55 BC56                       BD11 BD12 BD14

Claims (7)

[Claims] 1. Boron carbide (B ₄ C) 99.5 to 70 mol
% And aluminum nitride (AlN) 0.5 to 30 mol
%, And a relative density of 95% or more, a boron carbide-aluminum nitride sintered body. 2. The boron carbide-aluminum nitride sintered body according to claim 1, which has a four-point bending strength of 600 MPa or more. 3. Boron carbide having a relative density of 95% or more
A method for producing an aluminum nitride sintered body, which comprises adding 0.5 to 30 mol% of aluminum nitride powder to boron carbide powder, mixing them, and then sintering in an atmosphere in which decomposition of aluminum nitride does not occur. A method of manufacturing a boron carbide-aluminum nitride sintered body. 4. The boron carbide-aluminum nitride sintering according to claim 3, wherein hot press sintering is performed in a temperature range of 1600 ° C. or higher and 2200 ° C. or lower at a pressure of more than 20 MPa and 60 MPa or less. Body manufacturing method. 5. An average particle diameter (D ₅₀ ) of 1 μm or less, a maximum particle diameter of 5 μm or less, and a specific surface area of 15 m ² /
5. A boron carbide-aluminum nitride sintered body according to claim 4, wherein a boron carbide powder of g or more is used to perform hot press sintering to produce a sintered body having a four-point bending strength of 600 MPa or more. Body manufacturing method. 6. The method for producing a boron carbide-aluminum nitride sintered body according to claim 3, wherein hot press sintering is performed at a pressure of 20 MPa or less in a temperature range of 1900 ° C. or more and 2200 ° C. or less. . 7. The method for producing a boron carbide-aluminum nitride sintered body according to claim 3, wherein the pressureless sintering is performed in a temperature range of 1900 ° C. or higher and 2200 ° C. or lower.