JPS5895647A - Manufacture of silicon nitride/boron nitride composite material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicon nitride ceramic composite material containing boron nitride fibers, which is suitable as a high-temperature material with rich lubricity.

As is well known, silicon nitride-based ceramic materials have recently become widely used due to their good heat resistance and high strength, and boron nitride is known as a lubricating material. Therefore, recently, a composite material of silicon nitride and boron nitride has been attracting attention as a high-temperature material with excellent lubricity.

As the boron nitride/silicon nitride composite material mentioned above, it has been proposed that boron nitride fibers are embedded in a silicon nitride matrix with their axes aligned in a certain direction. , boron nitride fibers are placed in silicon nitride powder and heated to high temperature. However, in this manufacturing method, silicon nitride is not uniformly interposed between each boron nitride fiber, and adjacent boron nitride fibers often come into contact with each other, so each boron nitride fiber is not uniformly dispersed. Products that are not aligned are often obtained, and such products have uneven friction coefficients and uneven wear rates, resulting in unstable lubrication performance and lack of durability. There is a problem.

This invention was made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a boron nitride/silicon nitride composite material in which boron nitride fibers are uniformly dispersed and arranged in a silicon nitride matrix. It is.

That is, the manufacturing method of the present invention involves exposing boron nitride fibers to an atmosphere containing vapor of an organic liquid typified by di-n-butyl phthalate, causing the organic liquid to adhere to the surface of the nitrided boron fibers in the form of a film, and then A first mixed powder consisting mainly of silicon nitride and uniformly mixed with a small amount of a sintering aid such as spinel is uniformly adhered to the surface of the boron nitride fiber via the organic liquid film, and then Similarly to the above, the second mixed powder is made by uniformly mixing silicon nitride with a small amount of sintering aid such as spinel,
The fibers are arranged with their axes aligned in one direction so that the volume ratio is 20 to 50 with respect to the second mixed powder, and then a pressing force is applied in a direction perpendicular to the fiber axis direction. Hot press at high temperature to sinter the powder particles, and also sinter and integrate the fibers and powder particles to obtain a composite material in which boron nitride fibers are uniformly dispersed and arranged in the silicon nitride matrix. It is something.

The method of the present invention will be explained in more detail below.

In carrying out the method of the present invention, boron nitride (BN) fibers are first exposed to an atmosphere containing vapor of an organic liquid, so that the organic liquid is deposited in a film on the surface of the boron nitride fibers. The organic liquid should have good wettability to the boron nitride fibers and be able to adhere to the surface of the boron nitride fibers in the form of a film;
However, it is necessary to have a viscosity to the extent that the mixed powder described below can be uniformly adhered to it.From these points, it is most desirable to use di-n-butyl phthalate. Octyl phthalate, hydro-furfuryl, triethyl phosphate, butylphate, talyl butyl glycolate, etc. can also be used, and a liquid mixture thereof can also be used.

Next, as described above, a first mixed powder mainly composed of silicon nitride (5t5N4) is applied to the surface of the boron nitride fibers to which a film of an organic liquid such as di-n-butyl phthalate is attached via the organic liquid film. Apply it evenly with a uniform thickness.

This first mixed powder is mainly composed of silicon nitride, and sintering aid powder such as spinel, ittria, alumina, etc.
A small amount of zirconia, magnesia, or a mixed powder thereof, preferably 3 to 15 weight, is uniformly added and mixed. Use particles having a small and fine particle size, preferably particles having a particle size of 0.3 μm or less. If the particle size of this first mixed powder is too coarse, there is a risk that the mixed powder will not adhere uniformly to the surface of the boron nitride fibers and will peel off.
．． By setting the thickness to 3 μm or less, the mixed powder can be uniformly adhered in a good condition. In addition, by uniformly adhering the fine mixed powder to the surface of the boron nitride fibers, the sinterability especially around the fibers is improved.
The bond between the boron nitride fiber and the surrounding silicon nitride sinter base can be strengthened. Note that the means for adhering the first mixed powder to the fiber surface may be, for example, spraying the first mixed powder from around the fibers, or placing the fibers on the powder surface of the first mixed powder and then applying further powder on top of the first mixed powder. 1st
In this way, the first mixed powder is deposited with a uniform thickness due to the viscosity of the organic liquid film on the fiber surface.

After attaching the first mixed powder to the surface of the boron nitride fibers as described above, a large number of the boron nitride fibers are arranged at equal intervals in the second mixed powder with their axes aligned in one direction. do. As with the first mixed powder, this second mixed powder mainly contains silicon nitride, and spinel and silicon nitride.
An emotional auxiliary agent such as ictoria, alumina, magnesia, or a mixed powder thereof is desirably added and mixed in an amount of 3 to 15% by weight uniformly. Also this second
It is desirable to use a mixed powder with a particle diameter of 1.0 μm or less, and the ratio of boron nitride fiber to the second mixed powder is such that the volume ratio of boron nitride fiber is 2.
It is necessary to set it so that it occupies 0 to 50%. In other words, the smaller the proportion of boron nitride fibers, the lower the temperature and pressure in the next hot press step, but 2
If the volume is less than 0, the lubricity of the sintered body (product) will decrease and it will be unsuitable as a high-temperature lubricant material.On the other hand, if the volume exceeds 50, the sintered body (product) will be hot-pressed at considerably high temperatures and pressures.・Next, as mentioned above, with the boron nitride fibers arranged in one direction in the No. 20 mixed powder, the whole is heated at high temperature and high pressure in a nitrogen atmosphere or an argon gas atmosphere. The pressing force in this hot pressing is applied in a direction perpendicular to the fiber axis. By hot pressing in this way, the particles of the first and second mixed powders are sintered and bonded, and at the same time, the surface of the boron nitride fiber and the surrounding mixed powder particles are sintered and bonded, and the whole A strongly and densely bonded sintered body (product) is obtained. here,
Since the mixed powder is attached to the surface of the boron nitride fibers in advance via the organic liquid film, the mixed powder is always present between adjacent boron nitride fibers, so even if hot pressing is performed, the boron nitride The fibers are prevented from coming into contact with each other, and as a result, a sintered body in which the boron nitride fibers are uniformly dispersed and arranged can be obtained.

Note that the temperature in the hot press mentioned above is 1600 to 18
The temperature is preferably about 00°C, and the pressure is 100 to 400°C.
A value of approximately kII/C11 is desirable.

If the temperature is lower than 1600℃, apply pressure to 400 klil/d.
Even if the temperature exceeds 1800°C, sufficient densification is not achieved.On the other hand, at 1800°C, a sufficient density is reached with a pressing force of about 100 kYcd, but if the temperature exceeds 1800°C, grain growth occurs, which is undesirable.

Examples of this invention are described below.

Example: Boron nitride fibers (manufactured by Carbora/Dam) with a diameter of 5 to 10 μm were exposed to air containing about 2 s of di-n-butyl phthalate in the vapor phase and substantially free of moisture.
Di-n-butyl phthalate was deposited in a film form on the surface of the boron nitride fibers, and then a first mixed powder with a particle size of 0.3 μm or less consisting of 8% by weight spinel and the balance silicon nitride was applied to the surface of the boron nitride fibers. It was deposited at a uniform thickness. Next, a grain size of 1.0 consisting of spinel 8% by weight and the remainder silicon nitride.
Spreading a second mixed powder of µm or less on the bottom of a hot press graphite mold, arranging the boron nitride fibers at equal intervals in one direction on top of it, and further scattering the second mixed powder on top of it; This arrangement and scattering was repeated several times to arrange the boron nitride fibers in the second mixed powder at a ratio of 35 volumes. Next, hot pressing was carried out in a nitrogen atmosphere at 1700° C. by applying a pressure of 250 wail in a direction perpendicular to the fiber axis direction to obtain a sintered body (in which the mixed powder and fibers were integrated).
Composite material) was obtained.

The density of the sintered body obtained in the above example was measured and it was confirmed that the density reached 99% of the theoretically calculated density. In addition, the friction coefficient of the plane parallel to the axial direction of the fibers of the sintered body obtained in the example was determined to be 400% in a nitrogen atmosphere.
When measured at °C, the friction coefficient was 0.16. For comparison, we measured the friction coefficient of a sintered body that does not contain boron nitride fibers, and in that case the friction coefficient was 0.58. It is clear that In this friction coefficient measurement test, the outer peripheral surface of a cylinder made of chromium molybdenum steel was finished to a surface roughness of 0.03 to 0.05 μm, and a sintered body with a surface roughness of 0.1 to 0.2 μm was attached to the outer peripheral surface of the cylinder. Measurements were made with the length direction of the cylinder in contact with the outer peripheral surface of the cylinder.

Furthermore, the sintered body obtained in the example was used in the bearing part of a rotary heat exchanger for a ceramic gas turbine, and for comparison, a sintered body that did not contain boron nitride fiber was used in the same bearing part. It was confirmed that when the sintered body obtained in the example was used, the energy required for rotation could be reduced by about 30% compared to the case where a sintered body that did not contain boron nitride fibers was used. .

As is clear from the above explanation, in the manufacturing method of the present invention, a first mixed powder mainly composed of silicon nitride powder is attached in advance to the surface of boron nitride fibers via an organic liquid film such as di-n-butyl 7-talate. This is then placed in a second mixed powder, which is also mainly composed of silicon nitride powder, and hot-pressed.Thereby, a sintered body in which the silicon nitride fibers are uniformly dispersed and arranged can be obtained. . Therefore, according to the manufacturing method of the present invention, it is possible to obtain a fragile sintered body optimal for high-temperature lubricating materials with a uniform coefficient of friction and a uniform wear rate.

Claims (9)

[Claims] (1) A boron nitride fiber is exposed to an atmosphere containing the vapor of an organic liquid, so that the organic liquid is deposited on the surface of the boron nitride fiber in the form of a film, and then the boron nitride fiber is made mainly of silicon nitride and a small amount of a sintering aid is added thereto. A first mixed powder formed by uniformly mixing is adhered to the surface of the boron nitride fiber via the organic liquid film, and then a powder mainly composed of silicon nitride and a small amount of a sintering aid is uniformly mixed therein. The fibers are placed in a second mixed powder with their axes aligned in one direction so that the volume ratio is 20 to 50, and then a pressing force is applied in a direction perpendicular to the fiber axis direction. A method for producing a silicon nitride/boron nitride composite material, which is characterized by hot pressing at a high temperature. (2) As the organic liquid, one or more selected from di-n-butyl phthalate, octyl phthalate, hydrofurfuryl, triethyl phosphate, and butylphthalyl butyl glycolate is used. The manufacturing method according to claim 11@l. (3) The above-mentioned mixed powders each contain 3-1% of silicon nitride.
The manufacturing method according to claim 1, wherein a 5 weight weight performance aid is blended. (4) The manufacturing method according to claim 1, wherein the sintering aid is one or more selected from spinel, ittria, aluminum, zirconia, and magnesia. (5) The first mixed powder has an average particle size of a second powder.
The manufacturing method according to the claims, which uses a mixed powder having a small size. (6) The manufacturing method according to claim 5, wherein the first mixed powder has a particle size of 0.3 μm or less. (7) The manufacturing method according to claim 5, wherein the second mixed powder has a particle size of 1.0 μm or less. (8) Pressure force in the hot press is 100~
400- The manufacturing method according to claim 1. (9) The heating temperature in the hot press is 1600~
The manufacturing method according to claim 1, wherein the temperature is 1800°C.