JPH0466831B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application and Problems to be Solved by the Invention] The present invention relates to a method for manufacturing a high-density composite sintered body containing aluminum nitride and boron nitride. Specifically, a mixed powder consisting of aluminum nitride powder, boron nitride powder, and a compound consisting of Group A or Group A metals of the periodic table is formed in advance under hydrostatic pressure, and then sintered under pressure and heat. Provided is a method for manufacturing a composite sintered body, characterized by: So-called non-oxide ceramics such as silicon nitride and silicon carbide are ceramics that have recently attracted particular attention as high-temperature, high-strength materials, but once these sintered bodies are sintered, it is difficult to give them an arbitrary shape by post-processing. This has become extremely difficult, and this problem is considered to be one of the major practical difficulties. For this reason, in the field of oxides, glass ceramics in which many fine mica crystals are precipitated in glass, and so-called mica ceramics obtained by hot pressing natural or synthetic mica powder have recently been developed. These ceramics are machinable ceramics that can be cut and ground with ordinary tools, and are useful as ceramics with improved workability. Furthermore, among non-oxidizing ceramics, hexagonal boron nitride has a layered graphite structure, so its sintered bodies can be cut and ground with ordinary tools, and have been in practical use for a long time. However, although the above-mentioned various machinable ceramics have the advantage of being easy to process, they also have fundamental drawbacks such as being "soft" and "weak", so they cannot be widely used as ceramics. I'm not used to it. [Means for Solving the Problems] As a result of intensive research on non-oxide machinable ceramics, the present inventors found that aluminum nitride, boron nitride, and metals selected from group a or group a metals of the periodic table were used. We have already developed and proposed a new composite sintered body consisting of at least one type of metal compound. The composite sintered body is a sintered body in which crystal grains with polygonal mechanical fracture surfaces are closely packed, and thin layered crystal grains are interposed in part or all of the grain interface of the packed particles. It is a revolutionary ceramic that can be cut at high speed with ordinary tools, and has a bending strength of 35 kg/mm ² or more depending on the composition, which is comparable to high-strength ceramics. As a result of intensive research into the manufacturing method of the composite sintered body, the present inventors found that the composite sintered body is made of aluminum nitride powder, boron nitride powder, and at least one metal compound selected from Group A or Group A gold of the periodic table. When sintering the mixed powder, by forming it under hydrostatic pressure before sintering, the resulting sintered body maintains its machinability with ordinary tools, and improves mechanical strength, thermal conductivity, etc. The anisotropy of physical properties becomes smaller,
In particular, the sintered compact obtained by hot press sintering has a higher three-point bending strength when the span is taken in a direction parallel to the hot press axis, compared to the sintered compact obtained by the conventional method of simply hot press sintering mixed powder. The present inventors have discovered that the improvement is about twice or more compared to that of the conventional method, and have completed the present invention. That is, the present invention comprises aluminum nitride powder, boron nitride powder, and a metal compound of group a or group a of the periodic table, and the aluminum nitride powder and boron nitride powder have a total amount of aluminum nitride powder and boron nitride powder. 60 to 95% by weight and 40 to 5% by weight, respectively, and the metal compound is added to the total amount of the aluminum nitride powder and boron nitride powder in terms of the highest valence oxide of the metal. A composite sintered body is produced by forming a composite composition in advance under hydrostatic pressure, and then sintering the formed product under pressure and heat. It's a method. Any type of aluminum nitride powder can be used as the aluminum nitride powder used in the present invention, but in order to obtain a dense composite sintered body, it is necessary to It is preferable that the average particle diameter of aggregated particles measured by CAPA500 or the like is 5 μm or less. Powders with a diameter of 3 μm or less, most preferably 2 μm or less are used. Especially for particles smaller than 3 μm.
Powders containing at least % by volume are suitable. In addition, when obtaining a composite sintered body with high thermal conductivity, the AN content (calculated from the nitrogen content of AN powder) is
Aluminum nitride powder containing 90% by weight or more is preferably used, more preferably 94% by weight or more, and even more preferably 97% by weight or more. The aluminum nitride powder suitably used in the present invention is a powder with an average particle size of 3 μm or less, particularly preferably 2 μm or less, and particles of 3 μm or less are preferred.
Contains 70% by volume or more, oxygen content is 3.0% by weight or less,
In addition, the aluminum nitride powder contains 0.5% by weight or less of cationic impurities when the aluminum nitride composition is AN. When such aluminum nitride powder is used, it is preferably used in the present invention because it can improve the thermal conductivity of the resulting composite sintered body and suppress a decrease in mechanical strength at high temperatures. In particular, those with an average particle diameter of 3μm or less
Aluminum nitride that is a powder of 2 μm or less, containing 70% by volume or more of particles of 3 μm or less, oxygen content of 1.5% by weight or less, and containing cationic impurities of 0.3% by weight or less when the aluminum nitride composition is AN. When powder is used, it is particularly preferably used in the present invention because it significantly improves the thermal conductivity of the resulting composite sintered body and suppresses the decrease in mechanical strength at high temperatures. The method for producing the aluminum nitride powder used in the present invention is not particularly limited, and any known method can be employed. For example, a method of nitriding metal aluminum in nitrogen and then pulverizing it, a method of reducing and nitriding alumina, a method of arc discharging metal aluminum in nitrogen,
A method by gas phase reaction between AC ₃ and NH ₃ ,
(NH ₄ ) ₃ AF ₆ or a method using thermal decomposition of AC ₃ .NH ₃ or the like can be adopted. The boron nitride powder used in the present invention is not particularly limited, and any powder can be used.
Typical examples that are generally suitably used are as follows. That is, boron nitride powder that is generally preferably used has a boron nitride purity of 99.0% by weight or more and an average particle size of 5 μm or less.
Furthermore, the method for producing the boron nitride powder is not particularly limited, and any known method can be employed. For example, (1) converting H ₃ BO ₃ or Na ₂ B ₄ O ₇ to NH ₃ in the presence of urea.
A method of manufacturing by heating at 500 to 950°C in an atmosphere, (2) A method of manufacturing by reacting BCI ₃ and NH ₃ , (3) A method of manufacturing by heating Fe-B alloy at a temperature of 500 to 1400°C,
After that, a method such as removing Fe by dissolving it with an acid can be adopted. Furthermore, at least one metal or metal compound (hereinafter sometimes simply referred to as a sintering aid) selected from the metals of group a or group a of the periodic table used in the present invention is not particularly limited. Any known material can be used. Typical examples that are particularly preferably used are as follows. Generally, beryllium, calcium, strontium, barium, etc. are suitable as the metal of Group A of the periodic table.
Furthermore, as the metal of group a of the periodic table, yttrium or lanthanum group metal is preferably used,
More specifically, yztrium, lanthanum,
Cerium, praseodymium, neodymium, bromethium, samarium, eurobium, gadolinium,
Terbium, dysprosium, holmium, erpium, thulium, itterpium, lutetium, and especially yttrium, lanthanum, cerium, neodymium, and the like are preferred. These metal compounds belonging to group a or group a of the periodic table are not particularly limited, and the metal compounds known as sintering aids for aluminum nitride powder and/or boron nitride powder can be used. In general, compounds such as nitrates, carbonates, aluminates, halides, and oxides are preferably used. Further, the composition ratio of each component constituting the composite sintered body of the present invention is such that aluminum nitride powder is 60 to 95% by weight, preferably 70 to 90% by weight of the total amount of the aluminum nitride powder and boron nitride powder, and boron nitride is 60 to 95% by weight of the total amount of the aluminum nitride powder and boron nitride powder. 40 to 5% by weight, preferably 30 to 10% by weight, and at least one metal or metal compound selected from Group A or Group A metals of the Periodic Table is added to the aluminum nitride powder and boron nitride. 0.01-10% by weight relative to the total amount with powder, preferably 0.05
It is preferable to select the content within the range of 5% by weight. In the present invention, the above aluminum nitride powder,
A composite composition consisting of boron nitride powder and a sintering aid is previously subjected to isostatic press molding, and then subjected to sintering under pressure and heat. Here, the sintering aid does not necessarily need to be added to the aluminum nitride powder or boron nitride powder, and the sintering aid is not necessarily added to the aluminum nitride powder or boron nitride powder in advance so that the sintering aid is included in the powder. It may be mixed into the manufacturing raw materials. The mixing of the aluminum nitride powder, boron nitride powder, and sintering aid in the present invention is not particularly limited, and may be dry mixing or wet mixing. A particularly preferred embodiment is wet mixing, ie mixing in the wet state using a liquid dispersion medium. The liquid dispersion medium is not particularly limited, and commonly used water, alcohols, hydrocarbons, or mixtures thereof are preferably used. In particular, methanol, ethanol,
Lower alcohols having 4 or less carbon atoms, such as butanol. In addition, the wet mixing device used for the above mixing is not particularly limited and any known device may be used. However, when used for mixing particularly high purity aluminum nitride powder and boron nitride powder, It is preferable to choose one that does not produce any impurity components. For example, the material may be aluminum nitride, a plastic material such as polyethylene, polyurethane, nylon, or a material coated with these materials. The most preferred specific embodiment of the production of the sintered body in the present invention includes the aluminum nitride powder,
A mixed powder containing boron nitride powder and a sintering aid is molded using a hydrostatic press, and after further molding processing is performed as necessary, it is placed in a graphite mold and placed in an inert atmosphere, for example under a nitrogen gas atmosphere. This is a method in which sintering is performed while applying mechanical pressure. The hydrostatic press molding employed in the present invention is not particularly limited, and any known method can be used. For example, a method of filling a mixed powder of the composite composition into a rubber mold and pressurizing it in water is used. The pressurization is generally preferably in the range of 200 to 5000 Kg/cm ² , more preferably in the range of 500 to 3000 Kg/cm ² . If the above-mentioned pressure is too low, the density of the obtained compact will not increase sufficiently, the strength of the compact will be low and it will be difficult to handle, or the amount of shrinkage during sintering will increase and the boron nitride particles will become oriented. In some cases, the isotropic sintered body, which is the object of the present invention, cannot be obtained. On the other hand, if the pressure is too high, there is no negative effect on the molded product, but even if the pressure is increased more than necessary, the density of the molded product will not change much, and it will also be accompanied by equipment difficulties, so there is an upper limit on an economical basis. All you have to do is decide on the pressure. The molded body obtained by the above-mentioned hydrostatic press is then subjected to sintering under pressure and heat. In general, a hot press sintering method is preferably employed; in this case, the molded body is placed in a hot press mold, such as a graphite mold, and the molded body is preferably selected so that the outside dimensions of the molded body and the inside dimensions of the graphite mold match as much as possible. Therefore, it is common to predict the dimensions of the molded body in advance and manufacture a mold for hydrostatic press molding, but the dimensions can also be adjusted by processing the outer shape of the molded body. Further, the inner surface of the mold is preferably coated with boron nitride in order to prevent a reaction between the sintered body and the material of the mold, such as graphite. Furthermore, the atmosphere during sintering is generally an inert atmosphere, such as a nitrogen gas atmosphere. The hot press sintering method is generally suitably employed for the sintering under pressure and heat in the present invention, and it is usually sufficient to carry out the sintering at a temperature range of 1500 to 2100°C and a pressure range of 20 to 500 kg/cm ² . In addition, the temperature increase rate needs to be changed depending on the volume and shape of the sintered body, and also depends on the type of sintering aid, but in general, the smaller the specific surface area of the sintered body, the slower the temperature increase rate. This is effective in obtaining a homogeneous sintered body. [Effects of the Invention] The composite sintered body obtained by the manufacturing method of the present invention has less anisotropy in physical properties, but this means that the amount of shrinkage during sintering is smaller than when simply sintering. This is thought to be because the boron nitride particles are prevented from being oriented in a direction perpendicular to the pressurizing axis. As a result, when the composite sintered body obtained by the present invention is used, for example, as a mechanical part, there is no need to consider strength anisotropy, and reliability is improved, etc., and the industrial value of the present invention is It is extremely large. [Examples] Hereinafter, the present invention will be specifically illustrated by Examples, but the present invention is not limited to these Examples. Example 1 Particles with an average particle size of 1.31 μm and 3 μm or less accounted for 90% by volume, and 80 parts by weight of aluminum nitride powder had the composition shown in Table 1, and the ratio of particles with an average particle size of 2.5 μm and 5 μm or less was 95% by weight. 20 parts by weight of hexagonal boron nitride powder with a purity of 99.5% by volume and 0.5 parts by weight of calcium aluminate (3CaO・A ₂ O ₃ ),
Using a nylon pot and a nylon-coated ball, the mixture was uniformly mixed in a ball mill using ethanol as a dispersion medium. After drying the obtained mixed powder, approximately 600g was filled into a rubber mold and 2000g
Hydrostatic pressing was performed at a pressure of Kg/cm ² to form a cylindrical molded product with an outer diameter of approximately 50 mm and a length of approximately 170 mm. This molded body,
Hexagonal boron nitride powder was placed in a graphite mold with an inner diameter of 50 mm and the inner wall was coated, and hot press firing was performed at a temperature of 1900°C for 12 hours while applying uniaxial pressure at 200 kg/cm ² . In addition, the heating rate from room temperature to 1400℃ is 5
The heating rate from 1400°C to 1900°C was 1°C/min, and the atmosphere was nitrogen gas at about 1 atmosphere. The density of the obtained white sintered body is 2.97
g/ ^cm3 . From this sintered body, a columnar test piece of about 3 mm square was cut out so that the span could be taken in the direction perpendicular and parallel to the hot press axis, and it was finished with 1500 grit sandpaper and set at a crosshead speed of 0.5 mm/min. Three-point bending strength with a span of 20 mm was measured. As a result, the average strength when the span is taken in the direction perpendicular to the hot press axis is 36 kg/mm ² ,
The average strength when the span was taken in a direction parallel to the hot press axis was 32 kg/mm ² . In addition, from the same sintered body, a diameter of approximately 10 mm and a thickness of 2.5 mm can be obtained.
A disk-shaped sample was cut out, and the thermal conductivity at room temperature was determined using the laser flash method.The thermal conductivity in the direction perpendicular to the hot press axis was 94 W/m・k, and in the direction parallel to the hot press axis was 91 W/m・k. Ta. Furthermore, when the workability of the composite sintered body obtained in this example was investigated, it was found that it was easy to perform both drilling with a carbide drill and high-speed cutting with a carbide cutting tool, and was found to be free-cutting.

【table】

[Table] Comparative Example 1 The same procedure as in Example 1 was carried out except that the hydrostatic pressing step was omitted and the dried mixed powder was directly filled into a graphite mold and hot pressed. The density of the obtained white sintered body is 2.96
g/ ^cm3 . A test piece was cut out from this sintered body in the same manner as in Example 1, and its three-point bending strength was measured.The average strength when the span was taken in the direction perpendicular to the hot press axis was 39 kg/mm2, and when the span was taken in the direction perpendicular to the hot press axis, the average strength was 39 kg/mm ² . The average strength when spanned in the same direction was 18 kg/mm ² . Further, when the thermal conductivity was measured, it was 102 W/m·k in the direction perpendicular to the hot press axis and 86 W/m·k in the direction parallel to the hot press axis. Furthermore, when the workability of the composite sintered body obtained in this comparative example was examined, it was found that it had free machinability as in Example 1. Example 2 72 parts by weight of aluminum nitride powder similar to those used in Example 1, 28 parts by weight of hexagonal boron nitride powder, and calcium aluminate (3CaO・A ₂ O ₃ )
0.2 parts by weight were mixed in the same manner as in Example 1. After drying the obtained mixed powder, about 920 g was filled into a rubber mold and hydrostatically pressed at a pressure of 2000 Kg/cm ² to form a cylindrical molded body with an outer diameter of about 100 mm and a length of about 71 mm. This molded body was placed in a graphite mold with an inner diameter of 100 mm whose inner wall was coated with hexagonal aluminum nitride powder, and while being uniaxially pressed at a pressure of 200 kg/cm ² ,
It was baked at a temperature of 2000℃ for 18 hours. Furthermore, from room temperature
The temperature increase rate up to 1400℃ is 5℃/min, from 1400℃
The temperature increase rate up to 2000°C was 1°C/min. The atmosphere was nitrogen gas at about 1 atm. The density of the obtained white sintered body was 2.85 g/cm ³ . When the physical properties of this sintered body were examined in the same manner as in Example 1, the average strength was 32 kg/cm 2 when the span was taken in the direction perpendicular to the hot press axis, and the average strength was 32 kg/cm ² when the span was taken in the direction parallel to the hot press axis. The average strength in this case was 29Kg/ ^cm2 . Further, the thermal conductivity in the direction perpendicular to the hot press axis was 81 W/m·k, and the thermal conductivity in the direction parallel to the hot press axis was 77 W/m·k. Furthermore, it was found that the workability was similar to that obtained in Example 1, and that it was free-cutting. Examples 3 to 5 In Example 1, the types and amounts of sintering aids are shown in Table 2.
A composite sintered body was obtained in the same manner as in Example 1 except for the following changes. The physical properties of each composite sintered body were measured in the same manner as in Example 1, and the results are shown in Table 2.

【table】

【table】

Claims (1)

[Claims] 1. Consisting of aluminum nitride powder, boron nitride powder, and a metal compound of group a or group a of the periodic table, and the aluminum nitride powder and boron nitride powder are the sum of aluminum nitride powder and boron nitride powder. 60-95% and 40-5% by weight of the amount, respectively.
In addition, the metal compound is 0.01 to 10% of the total amount of the aluminum nitride powder and boron nitride powder in terms of the highest valence oxide of the metal.
1. A method for producing a composite sintered body, which comprises molding composite compositions in advance under hydrostatic pressure, each of which is blended in a weight percentage, and then sintering the molded product under pressure and heat. 2. The method for producing a composite sintered body according to claim 1, wherein the hydrostatic pressure is 200 to 5000 Kg/cm ² . 3 Pressure heating is 20~500Kg/ ^cm2 pressure and 1500~
The method for producing a composite sintered body according to claim 1, wherein the temperature is 2100°C.