JPH01131069A - Complex compact calcined under ordinary pressure - Google Patents

Abstract

PURPOSE:To obtain a complex compact calcined under ordinary pressure, consisting of boron nitride and aluminum nitride, containing AlN and BN at a specific ratio, having a relative density of specific value or above and improved shape restriction and productivity as well as good abrasion resistance and thermal shock resistance. CONSTITUTION:The aimed complex compact calcined under ordinary pressure contains 5-65wt.% AlN and 95-35wt.% BN and has >=70% relative density. The complex compact calcined under ordinary pressure can be obtained e.g., by the following method: AlN powder is blended with BN powder at a prescribed ratio and the blend is pulverized under non-oxidizing atmosphere and then molded and calcined under non-oxidizing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a boron nitride-aluminum nitride composite pressureless sintered body.

<Prior Art> In recent years, various types of ceramics have come to be increasingly used for industrial material parts. This is due to the excellent heat resistance, corrosion resistance, mechanical strength, etc. of ceramics. Recently, among these ceramics, boron nitride (B
A composite material consisting of aluminum nitride (A N), aluminum nitride (A N), and a sintering aid has been developed. The reason for combining AIN with BN is that by adding /IN to BN's corrosion resistance and thermal shock resistance, it improves thermal conductivity, abrasion resistance, and mechanical strength, making it suitable for applications such as heat sinks, break rings, and burner nozzles. The main purpose is to provide

However, since conventional BN-AAN composite materials use sintering aids, they lack the corrosion resistance and thermal shock resistance of BN.
The properties of nN, such as thermal conductivity, abrasion resistance, and mechanical strength, could not be obtained, and there was a drawback that the bending strength, especially at high temperatures, was significantly reduced. In order to obtain such a sintered body, a pressureless sintering method using a sintering aid (Japanese Unexamined Patent Application Publication No. 60-1
95059) and at a temperature of 1,600 to 2,000°C.
A real press method (Japanese Patent Application Laid-Open No. 195060/1983) in which a pressure of 00 to 200 kg/crA is applied is known. The former method uses a sintering aid, so the original characteristics of BN and ANN cannot be obtained, and the latter method has the disadvantage that large-sized or complex-shaped products cannot be obtained and productivity is poor. For these reasons, BN-AI has excellent wear resistance, corrosion resistance, mechanical strength, and thermal shock resistance! It has been desired to provide a pressureless sintered N composite body.

<Problems to be Solved by the Invention> The present invention improves the shape constraints and productivity of the N-AnN composite sintered body, and achieves good wear resistance and thermal shock resistance that could not be obtained conventionally. -An object of the present invention is to provide an AAN composite pressureless sintered body.

<Means for Solving the Problems> That is, the present invention provides a method for solving the problems in which AIN5-65% by weight, BN95
BN containing ~35% and a relative density of 70% or more
-AAN composite pressureless sintered compact.

The present invention will be explained in detail below.

BN-Aj of the present invention! In the N composite pressureless sintered body,
If ApN is less than 5% by weight, the BN content will be relatively large and the thermal shock resistance will improve, but the abrasion resistance and bending strength will decrease. On the other hand, when AIN exceeds 65% by weight, wear resistance and bending strength are improved, but on the other hand, the BN content is relatively reduced and thermal shock resistance and machinability are reduced.

The density of the sintered body is 70% or more in terms of relative density.

A sintered body with a relative density of less than 70% has many pores and is not dense, so bending strength, abrasion resistance, and thermal shock resistance are not improved, and it is not suitable for applications such as high-temperature structural members and break rings. In particular, those having a relative density of 80% or more have significantly improved bending strength, abrasion resistance, and thermal shock resistance, and are therefore expected to be used in fields where high abrasion resistance and thermal shock resistance are required.

To explain the raw material powder used in the present invention, commercially available BN powders can be used, but especially highly crystalline hexagonal B
N powder is good. Since hexagonal BN powder with high crystallinity has excellent plastic deformability during preforming, it is easy to obtain a high-density preform.

AAN powder may be a commercially available product, but preferably has a purity of 9.
9% or more, and the average particle diameter/I is 4 μm or less.

If the grain size of A4N is equal to or finer than that of BN powder, the density and strength of the sintered body will be improved.

When mixing the above raw materials, mix BN and A7! so that the final product composition is achieved. A method of mixing N with a vibrating ball mill, etc., a method of mixing finely ground BN and Al1N with a ball mill, etc. until the specific surface area is more than twice that of the original surface area, or a method of mixing a mixture of BN and AIN with an attritor, etc. A method is used in which the material is pulverized so that the surface area is more than twice its original size.

In molding these powders, well-known molding machines such as generally well-known mold molding machines and cold isostatic pressing machines (CIP) can be used. Regarding the molding pressure, we use highly crystalline macrogonal BN powder or amorphous B
When N powder is used as it is, it is 5 ton/c+J or more, preferably 7 torl/c+J or more. 5ton/
At a molding pressure lower than CIA, it is difficult to obtain a pressureless sintered body with a relative density of 70% or more. On the other hand, finely ground BN
When using powder or powder obtained by mixing BN and AfN and then finely pulverizing the mixture, the same effect as described above can be obtained at 2 ton/cn or more.

As a crushing device, a commonly known crusher such as a ball mill, a vibrating ball mill, an attritor, a Raikai machine, etc. can be used.

When pulverizing is performed, it is performed until the specific surface area of the powder becomes at least twice, preferably at least 10 times, the specific surface area of the original powder. If the pulverization is less than twice, it becomes difficult to obtain a pressureless sintered body with a relative density of 70% or more.

If pulverization is carried out in an oxidizing atmosphere, oxides will be produced, and if sintered as is, not only will the high temperature strength and thermal shock resistance deteriorate significantly, but also cracks will occur in the sintered body. Therefore, for example, Ar
, Nz, etc., in a non-oxidizing atmosphere. The reason why it is possible to obtain a pressureless sintered body that has high strength and excellent wear resistance and thermal shock resistance is that the pulverization process is caused by the progress of crystal lattice misalignment and partial amorphization. This is thought to be because newly formed particle surfaces appeared and activated powder was obtained due to the so-called mechanochemical effect.

Firing is performed in a non-oxidizing atmosphere at 1200 to 2100°C. When the firing temperature is less than 1200°C, BN grains and BN
Since the grains and the AIN grains are difficult to bond directly, a high-strength pressureless sintered body cannot be obtained. Also, when it exceeds 2100'C, BN,
AnN undergoes thermal decomposition and loses its original properties. 1300 to obtain a sintered body with particularly high wear resistance and thermal shock resistance.
It is preferable to perform the firing in a non-oxidizing atmosphere at a temperature of ~1800°C.

The non-oxidizing atmosphere is an inert atmosphere such as He, Ar%N2, or vacuum, but preferably B
N,/M! A N2 atmosphere is preferred since it has the effect of suppressing the decomposition of N. When fired in an oxidizing atmosphere, not only the corrosion resistance, thermal shock resistance, and abrasion resistance are significantly reduced, but also cracks occur in the sintered body. As the firing device, a Tammann furnace, a high frequency furnace, or a resistance heating furnace is used.

<Examples> The present invention will be explained in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these in any way.

Example I BN powder (hexagonal crystal, purity 99%, specific surface area 6ml/g)
40 parts by weight/IN powder (purity 99%, specific surface area 4rr)
After adding 60 parts by weight (r/g), the mixture was mixed in a vibrating ball mill to obtain a mixed powder for molding.

After this mixed powder was cold isostatically pressed at a pressure of 5 tow+/cJ, it was embedded in a graphite container containing the BN powder and fired in a high frequency furnace at 1700° C. for 160 minutes in an N2 atmosphere. The measurement results of the composition, relative density, bending strength, Shore hardness, thermal conductivity, and thermal shock resistance of the obtained sintered body are shown in the table.

Example 2 Using the mixed powder for molding obtained in Example 1, the molding pressure was 7t.
It was carried out in the same manner as in Example 1 except that the on/cn and firing temperature were set to 1400°C.

Example 3 Boric acid and melamine were mixed at a weight ratio of 1:1 and heated in an ammonia gas stream at 1200°C for 4 hours to obtain a BN purity of 90% and a specific surface area of 50 nm. /g of BN powder was obtained. As a result of X-ray diffraction of this powder, it was found that it was amorphous BN. Add 40 parts by weight of AIN powder to 60 parts by weight of this powder.
After adding parts by weight, they were mixed in a ball mill to obtain a mixed powder for molding. It was carried out in the same manner as in Example 1 except that this mixed powder was used and the firing temperature was 1600°C.

Example 4 The specific surface area of the BN powder used in Example 1 was 5On using a dry triter. /g under N2 atmosphere until BNI
A powder was obtained. The specific surface area was measured by the BET method. 20 parts by weight of iN powder was added to 80 parts by weight of this powder and mixed in a ball mill to obtain a mixed powder for molding.

The same method as in Example 1 was carried out except that this mixed powder was used.

Implementation Ml Using the mixed powder for molding obtained in Example 4, it was mixed at 2 tons/
The same method as in Example 1 was carried out except for the cJ molding.

Example 6 10 parts by weight of AnN powder was added to 90 parts by weight of the BN powder used in Example 1.
After adding parts by weight, the specific surface area is 60r with attritor.
The mixture was ground in an Ar atmosphere until it reached rr/g to obtain a mixed powder for molding. Example 1 except that this mixed powder was used
It was carried out in the same manner as.

Sufu 1ff91J7 Using the molding powder mixture obtained in Example 6, 2 tons/
It was carried out in the same manner as in Example 1 except that it was carried out using the c+d molds.

Comparative Example 1 A7! was added to 97 parts by weight of the BN powder used in Example 1. N powder 3
After adding parts by weight, they were mixed in a vibrating ball mill to obtain a mixed powder for molding. Using this mixed powder, 2toa'/c+a
It was carried out in the same manner as in Example 1 except for the molding performed in Example 1.

Comparative Example 2 47 parts by weight of ApN powder was added to 50 parts by weight of BN powder used in Example 1.
．． After adding 5 parts by weight and 2.5 parts by weight of Y20, they were mixed in a vibrating ball mill to obtain a mixed powder for molding. It was carried out in the same manner as in Example 1 except that this mixed powder was used and the molding pressure was 5 tos/cra.

Comparative Example 3 Used in Example 1. 70 parts by weight of IN powder and 30 parts by weight of BN powder
After adding parts by weight, they were mixed in a vibrating ball mill to obtain a mixed powder for molding. The same method as in Example 1 was carried out except that this mixed powder was used.

In addition, each physical property described in the table was measured by the following method.

+l) Relative density - Find the volume from the dimensions of the sintered body,
After calculating the density from its weight, calculate the relative density (%) - density (
g/c+J)/theoretical density (g/cJ) x 100(7
) was calculated using the formula.

(2) Room temperature bending strength - Measured in accordance with JIS R1601.

(3) Shore hardness - Measured in accordance with JIS Z2246.

(4) Thermal conductivity - by laser flash method.

(5) Thermal shock resistance - After heating and holding a sample cut from a sintered body at a constant temperature, the sample is rapidly cooled in water at 20°C to apply thermal shock, and the bending strength of the sample after rapidly cooling is measured. The critical temperature difference ΔT at which a sudden decrease in bending strength begins was determined and defined as thermal shock resistance.

<Effect of the invention> BN-A7 according to the invention! The N composite pressureless sintered compact has excellent thermal conductivity, abrasion resistance, bending strength, and thermal shock resistance, so it can be used for applications such as heat sinks, break rings, burners, and nozzles.

Patent applicant Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A pressureless sintered boron nitride-aluminum nitride composite body having a relative density of 70% or more and containing 5 to 65% by weight of AlN and 95 to 35% by weight of BN.