JP2002316876A - Silicon nitride based composite powder and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the raw powder of a silicon nitride based sintered compact, which has excellent mechanical properties in the ranges from room temperature to modelate low temperature, further has a low friction coefficient, and has excellent wear resistance, and to provide a production method therefor. SOLUTION: Silicon nitride powder, boron nitride powder and metal titanium powder are mixed at a room temperature to 250 deg.C at an acceleration of 10 to 300 G, so that silicon nitride based composite powder consisting of silicon nitride, titanium nitride, boron nitride and titanium boride in which each average particle size is <=20 nm, and phases at least containing amorphous ones covering the surfaces of the above particles, and having the average particle size of >=0.3 μm is obtained. Desirably, the pressure of a nitrogen atmosphere is 0.05 to 1.0 MPa, the amount of metal titanium powder is 5 to 60 wt.%, the amount of boron nitride powder to be added is 2 to 40 wt.%, and the mixing time is 0.5 to 50 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a silicon nitride having excellent mechanical properties from room temperature to low temperature as a high wear-resistant and low-friction structural ceramic material used for automobile parts and wear-resistant tools. The present invention relates to a raw material powder for a sintered body and a method for producing the same.

[0002]

BACKGROUND ART Silicon nitride (Si 3 _{N 4)} strength, toughness, corrosion resistance, oxidation resistance, because of an excellent material in thermal shock resistance, and cutting tools, gas turbines, is widely used in bearings such I have. More recently, studies have been made on structural materials for automobiles such as engine parts.

[0003] Various studies have been made on such silicon nitride materials in order to further improve their properties. For example, Japanese Patent Application Laid-Open No. 11-139882 discloses that a composite powder composed of fine silicon nitride particles and titanium nitride particles can be obtained by mixing silicon nitride powder and metal titanium powder at high acceleration in a nitrogen atmosphere. Is disclosed. It has been reported that by using this composite powder, titanium nitride particles can suppress the growth of silicon nitride grains and produce a high-strength silicon nitride sintered body having a fine crystal structure.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 11-13 / 1999
In the silicon nitride composite powder described in Japanese Patent No. 9882, titanium nitride particles suppress the growth of silicon nitride particles during sintering, so that a high-strength silicon nitride sintered body having a fine crystal structure can be manufactured.

[0005] However, although the silicon nitride sintered body exhibits high strength, it reduces friction-related properties as a material for machine structure, particularly friction under non-lubrication, which is expected most with respect to the current trend of energy saving. This has not been studied yet.

[0006] As a method generally used for producing a ceramic material having a low coefficient of friction, a method of dispersing a solid lubricant such as boron nitride, molybdenum sulfide, and graphite in the material is well known. However, the second phase of these solid lubricants can only be dispersed in a size of the order of submicron, and therefore, the reduction of the friction coefficient is limited.

The present invention has been made in view of such a conventional situation,
While having excellent mechanical properties from room temperature to low temperature,
An object of the present invention is to provide a raw material powder of a silicon nitride-based sintered body having a low coefficient of friction and excellent wear resistance, and a method for producing the same.

[0008]

In order to achieve the above-mentioned object, the present invention relates to a method for producing silicon nitride, titanium nitride, boron nitride and titanium boride having an average particle diameter of not more than 20 nm, and a method for forming the surface of these particles. An object of the present invention is to provide a silicon nitride-based composite powder comprising an overlying amorphous phase and having an average particle size of 0.3 μm or more.

The method for producing a silicon nitride-based composite powder according to the present invention comprises the steps of: mixing silicon nitride powder, boron nitride powder and metal titanium powder in a nitrogen atmosphere at room temperature to 250
It is characterized by mixing at a temperature of ° C. and an acceleration of 10 to 300 G.

In the method for producing a silicon nitride-based composite powder according to the present invention, the pressure in the nitrogen atmosphere is 0.05 to 1.0M.
Pa, the addition amount of the metal titanium powder is 5 to 60% by weight, the addition amount of the boron nitride powder is 2 to 40% by weight, and the mixing time is 0.5 to 50 hours. Is desirable.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the silicon nitride composite powder of the present invention, fine silicon nitride (Si ₃ N ₄ ) particles having an average particle diameter of 20 nm or less and titanium nitride (T
iN), boron nitride (BN), titanium boride (Ti
Since the fine particles of B ₂ ) are dispersed, it is possible to suppress the grain growth of Si ₃ N _{4 and} the grain growth of the dispersed particles themselves during sintering. Moreover, since boron nitride is extremely finely and uniformly dispersed in the silicon nitride-based composite powder, a silicon nitride-based sintered body having a low friction coefficient and excellent wear resistance can be obtained.

The fine particles of silicon nitride, titanium nitride, boron nitride, and titanium boride having an average particle diameter of 20 nm or less are aggregated with each other to form a composite powder, and the surface is mainly composed of silicon and titanium. Since it is covered with the amorphous metal of titanium, the surface oxidation is suppressed more than in the case of ordinary non-oxide nanopowder, so that it can be handled easily. The average particle size of the composite powder, which is the aggregate, is 0.1.
Since it is about 3 to 1.0 μm, it can be handled in the same manner as a conventional commercially available powder.

As a method for producing the above silicon nitride-based composite powder, boron nitride powder and metal titanium powder are added to commercially available silicon nitride powder, and the mixture is added at room temperature to 25% in a nitrogen atmosphere.
Mix at a temperature of 0 <0> C with a high acceleration of 10-300G.
In addition, as a mixing means, it is preferable to use a ball mill or an attritor with pulverization.

It is considered that the mixing at such a high acceleration causes the titanium metal to cause each reaction represented by the following chemical formula 1 to refine boron nitride and silicon nitride. Here, the reason why the acceleration is limited to 10 to 300 G is that if the acceleration is less than 10 G, uniform powder refinement is unlikely to occur, and the crystal grain size of the final sintered body becomes non-uniform. Further, when the acceleration during mixing exceeds 300 G, impurities are mixed in due to wear of the pot and the ball.

[0015]

Embedded image 2BN + Ti → TiB₂+ N₂  Si₃N₄+ 4Ti → 4TiN + 3Si 2Ti + N₂→ 2TiN

The temperature at the time of the high acceleration mixing is as follows:
Room temperature to 250 ° C, preferably 50 ° C to 200 ° C.
In this temperature range, the above reaction is promoted, and the desired composite powder can be obtained in a short time. With respect to the mixing time, if the mixing time is less than 0.5 hour, the fineness accompanying the reaction does not progress, and if the mixing time is more than 50 hours, impurities are mixed.
It is desirable to set it to 50 hours. In addition, it is necessary to appropriately control the acceleration, temperature and mixing time during mixing depending on the conditions of the powder to be produced.

In order to cause the above reaction, a nitrogen atmosphere is required.
The range of 1.0 MPa is preferable, and 0.08 to 0.15 MPa
The range of a is more preferable. Nitrogen atmosphere pressure is 0.05
If it is less than MPa, it is difficult to control, and if it exceeds 1.0 MPa, a special container such as a pressure-resistant container is required, which is not preferable.

The amount of the metal titanium powder added is not particularly limited, but if it is less than 5% by weight, the amount of reactive Ti is too small, so that boron nitride and silicon nitride cannot be miniaturized. On the other hand, if the addition amount exceeds 60% by weight, the amount of Ti to react with increases, and color unevenness of the sintered body occurs, which is not preferable. Therefore, the addition amount of the metal titanium powder is preferably in the range of 5 to 60% by weight.

The amount of boron nitride powder to be added is not particularly limited, but boron nitride of 2% by weight or more is required to obtain a sufficiently low friction property. Is preferably 40% by weight or less in order to maintain the above, the range of 2 to 40% by weight is preferable.

The silicon nitride composite sintered body produced using the silicon nitride composite powder of the present invention is Si
₃ N ₄ , TiN, TiB ₂ , and BN have a controlled crystal structure with a fine grain size, and have high strength in a temperature range from room temperature to medium to low temperature, and boron nitride is extremely finely and uniformly dispersed. Therefore, it has a low coefficient of friction and excellent high wear resistance.

[0021]

【Example】Example 1  Commercially available Si having an average particle size of 0.5 μm₃N₄Sintering aid for powder
2.5 wt% Y as an agent₂O₃Powder and 1 wt% Al
₂O₃Add powder, and further add metal Ti powder with an average particle size of 10 μm
40 wt% powder, 10 wt% BN powder with an average particle size of 5 μm
% In a nitrogen atmosphere of 0.1 MPa.
Under the temperature condition of ℃, Si₃N₄Planetary bow using ball made of
The mixture was mixed for 16 hours at 150 G by a mill.

When the obtained powder was subjected to qualitative analysis by XRD, peaks of Si ₃ N ₄ , TiN, TiB ₂ and BN could be confirmed. Also, as a result of observing this composite powder with a transmission electron microscope, it was found that Si ₃ N ₄ , Ti
Each of the particles of N, TiB ₂ , and BN has an average particle diameter of 20 nm or less, and the particles have an amorphous T
It was found that the structure was covered with i and Si.
The average particle size of the obtained composite powder was 0.5 μm.

After the composite powder is filled in a carbon die, it is heated to 1300 ° C. using a discharge plasma sintering machine (SPS).
Sintered. After the obtained sintered body was subjected to grinding and lapping treatment, the wear resistance was evaluated using a ball-on-disk tester. As a result, the obtained sintered body had a coefficient of friction of 0.1.
2 and a low coefficient of friction, and the specific wear amount is 2.0 × 10 ⁻⁸ m
It exhibited high abrasion resistance of m ² / N. Further, after polishing this sintered body, a thin film test piece was prepared by Ar ion etching, and Si ₃ N ₄ , TiN,
BN, a result of evaluating the particle size of the TiB _2, each of the particles 5
It was very fine, 0 nm or less.

For comparison, instead of a planetary ball mill,
A composite powder was prepared in the same manner as in Example 1 except that the raw material powder was subjected to ultrasonic mixing, and sintered similarly using the composite powder. TiN particles and BN particles having a size of several μm were observed in the obtained sintered body of the comparative example, the friction coefficient was as high as about 0.5, and the specific wear amount was 7.0 × 10 ⁻⁷ mm. ² /
N.

[0025]Example 2  Commercially available Si having an average particle size of 0.5 μm₃N₄Example on powder
Add the same sintering aid as in 1 and add a metal
The following table shows the Ti powder and the BN powder having an average particle size of 5 μm, respectively.
1 was added.

[0026]

[Table 1]

The raw material powder of each sample in Table 1 was mixed with a planetary ball mill in the same manner as in Example 1 under the conditions A to H shown in Table 2 below for each mixing condition of atmosphere, pressure, temperature, acceleration, and mixing time. And mixed.

[0028]

[Table 2]

With respect to each of the obtained composite powders, the average particle diameter of each of Si ₃ N ₄ , TiN, BN, and TiB ₂ particles was determined in the same manner as in Example 1. The results are shown in Table 3 below.

[0030]

[Table 3]

From the above results, fine selection of the addition amounts of the metal Ti powder and the BN powder and the respective mixing conditions of the atmosphere, pressure, temperature, acceleration, and mixing time within the scope of the present invention can provide finer powder. It can be seen that a composite powder composed of particles is obtained. In addition, even when a mixing device other than a planetary ball mill, an attritor, or the like is used, 10 to 300 G
Almost the same result could be obtained by mixing at an acceleration of.

[0032]

According to the present invention, as a raw material powder for a silicon nitride-based sintered body, it is relatively easy to produce, can suppress grain growth during sintering, and is composed of fine particles. A silicon nitride-based composite powder can be provided.

Further, by using the silicon nitride-based composite powder of the present invention, the silicon nitride-based composite powder having excellent mechanical properties from room temperature to medium to low temperature, a low friction coefficient, and excellent wear resistance. You can get union.

Claims (6)

[Claims] Claims: 1. A silicon nitride, titanium nitride, boron nitride or titanium boride having an average particle diameter of 20 nm or less, and a phase containing at least an amorphous phase covering the surface of these particles. A silicon nitride-based composite powder having a size of 0.3 μm or more. 2. A method for preparing a silicon nitride powder, a boron nitride powder, and a metal titanium powder in a nitrogen atmosphere at room temperature to 250 ° C.
A method for producing a silicon nitride-based composite powder, wherein mixing is carried out at a temperature of 10 to 300 G. 3. The pressure of a nitrogen atmosphere is 0.05 to 1.0 MPa.
3. The method for producing a silicon nitride-based composite powder according to claim 2, wherein a. 4. The method for producing a silicon nitride-based composite powder according to claim 2, wherein the amount of the metal titanium powder added is 5 to 60% by weight. 5. The method for producing a silicon nitride-based composite powder according to claim 2, wherein the addition amount of the boron nitride powder is 2 to 40% by weight. 6. The method for producing a silicon nitride-based composite powder according to claim 2, wherein the mixing time is 0.5 to 50 hours.