JP2003034584A - Silicon nitride-based composite powder and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride-based composite powder having good mechanical properties in the range from room temperature to a low-to-medium temperature, a low coefficient of friction and good abrasion resistance, and to provide a method for producing the same. SOLUTION: The silicon nitride-based composite powder is a secondary composite-particle powder comprising silicon nitride, a titanium-based compound, and a graphite and/or carbon, all having primary particles having an average particle diameter of 30 nm or less, wherein the surface of these particles are covered by a phase comprising at least titanium and/or silicon, and partly an amorphous phase of carbon. The method for producing the silicon nitride-based composite powder is characterized in mixing and grinding the silicon nitride powder, titanium metal powder, and graphite powder or carbon powder, at a temperature of from room temperature to 250 deg.C and at an acceleration of 10-300 G.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a structural ceramic material having high wear resistance and low friction, which is used for various machine members, cutting tools, sliding members, etc. In addition, the present invention relates to a raw material composite powder of a silicon nitride-based sintered body having a low friction coefficient and a method for producing the same.

[0002]

2. Description of the Related Art Silicon nitride (Si ₃ N ₄ ) is used for strength, toughness,
It is widely used in cutting tools, gas turbines, bearings, etc. because of its excellent corrosion resistance, oxidation resistance, and thermal shock resistance. Furthermore, recently, research has been conducted for use in structural materials such as engine parts, and the required performance levels such as wear resistance and hardness are becoming severe.

For example, when a silicon nitride-based composite material is used for a specific automobile part that requires high wear resistance or a tool for plastic working, cemented carbide (hard particles made of WC and Co, etc. is bonded). It is required to have significantly higher wear resistance than conventional materials such as cermet materials consisting of phases and HSS.

However, the silicon nitride-based composite material is
It is more expensive than these materials and its wear characteristics are
The current situation is that we are not satisfied with the price level.

The term "silicon nitride system" refers to ceramics containing silicon nitride (Si ₃ N ₄ ) and / or sialon as a main crystal phase. Further, the "silicon nitride-based composite material" refers to a material in which a component different from the above is dispersed and composited in a matrix having silicon nitride-based ceramics as a main crystal.

In such a silicon nitride material,
Various studies have been conducted to further improve the characteristics. For example, in JP-A-11-139882 and JP-A-11-139874, fine silicon nitride particles and titanium nitride are obtained by mixing silicon nitride powder and titanium metal powder at high acceleration in a nitrogen atmosphere. It is reported that a composite powder consisting of particles and a titanium nitride particle can suppress grain growth of silicon nitride by using this composite powder, and a high-strength silicon nitride sintered body with a fine crystal structure can be produced. ing.

[0007]

However, although the above-mentioned silicon nitride sintered body exhibits high strength, it has the most expected properties regarding friction as a material for machine structural use, particularly the present tendency of energy saving. Reducing friction under lubrication has not yet been studied.

On the other hand, 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 or graphite in the material is well known. There is. However, the second phase of these solid lubricants can be dispersed only in a size of submicron, so that there is a limit to the reduction of the friction coefficient.

Further, JP-A No. 11-43372 discloses that free carbon is contained in an amount of 0.5% by weight or more and less than 50% by weight, the average minor axis diameter of silicon nitride type crystal grains is 0.5 μm or less, and the conditions under non-lubrication conditions Have proposed silicon nitride ceramics having a friction coefficient of 0.2 or less. However, the combination of silicon nitride and free carbon has a low specific wear amount of 10 ⁻⁷ mm ² / N, and a problem still remains with respect to the wear amount.

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

[0011]

In order to achieve the above object, the present invention has an average primary particle diameter of 30 nm.
A silicon nitride-based composite powder comprising the following silicon nitride, titanium-based compound and graphite and / or carbon, and a secondary composite particle powder composed of a phase covering at least the surface of these particles and containing at least an amorphous material. Is provided. In the above, the amorphous phase is titanium, silicon and partly carbon.

Silicon nitride, titanium-based compound and graphite and // having an average primary particle diameter of 30 nm or less
Or, the carbon is agglomerated with each other to form a composite powder, and the surface thereof is covered with an amorphous metal of titanium and / or silicon and a part of amorphous carbon. The surface oxidation is suppressed more than that of nanopowder, and it can be handled easily. In addition, the average particle size of the secondary composite particle powder that is this agglomerate is 0.3 to
Since it is about 1.0 μm, it can be handled in the same manner as a conventional commercially available powder. The titanium-based compound here is at least one of titanium nitride, titanium carbonitride, and titanium carbide.
More than a seed.

As the method for producing the above-mentioned silicon nitride-based composite powder, commercially available silicon nitride powder is added with metallic titanium powder and graphite powder and / or carbon powder, and the temperature is from room temperature to 250 ° C. in a nitrogen atmosphere. So 10-30
Mix at high acceleration of 0G. As a mixing means, it is preferable to use a planetary ball mill or an attritor that involves grinding. It should be noted that graphite and carbon are effective not only in the form of powder but also in the form of phenol resin or the like.

It is considered that the titanium metal and graphite cause the following reactions by the mixing at such a high acceleration, and the silicon nitride is miniaturized. Si ₃ N ₄ + 4Ti → 4TiN + 3Si 2Ti + N ₂ → 2TiN Ti + C → TiC In addition, TiCN is also partially generated.

Here, the reason why the acceleration is limited to 10 to 300 G is that if it is less than 10 G, it is difficult for the powder to be made uniform and the crystal grain size of the sintered body when finally made into a sintered body is not uniform. This is because Also, if the acceleration during mixing exceeds 300 G, impurities are mixed due to wear of the pots and balls.

The temperature for mixing and pulverizing with high acceleration is room temperature to 250 ° C, more preferably 50 ° C to 200 ° C.
℃. The reaction is promoted in this temperature range,
The target secondary composite powder can be obtained in a short time.
Regarding the mixing time, if the time is less than 0.5 hours, the miniaturization accompanying the reaction does not proceed, and if the time exceeds 50 hours, impurities are mixed, so that the mixing time is preferably 0.5 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.

Further, a nitrogen atmosphere is required to cause the above reaction, and the pressure of the nitrogen atmosphere is 0.05 to.
The range of 1.0 MPa is preferable, and 0.08 to 0.15 M
The range of Pa is more preferable. The pressure of the nitrogen atmosphere is 0.
If it is less than 05 MPa, it is difficult to control the reaction, 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 titanium metal added is not particularly limited,
If it is less than 5% by weight, the amount of Ti that reacts is too small, and therefore silicon nitride cannot be made fine. Further, if the addition amount of titanium metal powder exceeds 60% by weight,
This is not preferable because the amount of Ti that reacts increases and color unevenness or the like occurs in the sintered body. Therefore, the addition amount of the titanium metal powder is preferably in the range of 5 to 60% by weight.

The addition amount of graphite and / or carbon is 0.5 to 20% by weight. If the amount is less than 0.5% by weight, sufficient friction characteristics cannot be obtained when a sintered body is formed. Further, the powder adheres to the wall surface of the container at the time of mixing, but the adhered amount increases, and the powder recovery rate decreases. Addition amount of graphite and / or carbon is 20
If it exceeds 5% by weight, it will not be densified when it is made into a sintered body and the material properties will deteriorate.

A silicon nitride-based composite sintered body produced using such a silicon nitride-based composite powder of the present invention is Si ₃
N ₄ , titanium compounds, SiC, and C have a crystal structure controlled by a fine grain size, have a low friction coefficient, and have excellent high wear resistance.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below based on Examples.

Example 1 2.5 wt% Y ₂ O ₃ powder and 1 wt% Al ₂ O ₃ as a sintering aid were added to a commercially available Si ₃ N ₄ powder having an average particle size of 0.5 μm.
Powder was added, and metal Ti powder with an average particle size of 10 μm was added to 4
0 wt%, 5 wt% graphite powder with an average particle size of 5 μm
%, And added in a nitrogen atmosphere of 0.1 MPa to 50
Under a temperature condition of ° C, they were mixed for 16 hours at an acceleration of 150 G by a planetary ball mill using Si ₃ N ₄ balls.

Qualitative analysis of the obtained secondary composite particle powder by XRD revealed that Si ₃ N ₄ , TiN, TiC (T
iCN) and C broad peaks could be confirmed. In addition, as a result of observing this secondary composite particle powder with a transmission electron microscope, the average particle diameter of each constituent particle is 30 n.
m or less, and their particles are amorphous Ti and S
i Furthermore, it was found that the structure was partially covered with C. The average particle size of the obtained secondary composite particle powder was 0.3 μm.

Next, a sintered body was manufactured using this silicon nitride composite powder of the present invention. After filling the secondary composite particle powder in a carbon die, a spark plasma sintered body (SP
S) is used to raise the temperature at 100 ° C./min and the holding time is 5
Min, sintered at 1400 ° C. About the obtained sintered body,
After grinding and lapping, abrasion resistance was evaluated by a ball-on-disk tester. As a result, the obtained sintered body had a low friction coefficient of 0.12 and a high specific wear amount of 5 × 10 ⁻⁹ mm ² / N. After polishing the sintered body, a thin film test piece was prepared by Ar ion etching and evaluated using a transmission electron microscope. As a result, very fine particles of 50 nm or less were formed.

Comparative Example 1 For comparison, a composite powder was prepared in the same manner as in Example 1 except that the raw material powder was ultrasonically mixed instead of the planetary ball mill, and the composite powder was similarly burned. Tied up. In the obtained sintered body of Comparative Example 1, TiC having a size of several μm was used.
N particles were observed, and the friction coefficient was as high as about 0.5,
A material having a low wear resistance with a specific wear amount of 5.0 × 10 ⁻⁸ mm ² / N was also obtained.

Example 2 and Comparative Example 2 The same sintering additive as in Example 1 was added to Si ₃ N ₄ powder having an average particle size of 0.5 μm, and Ti of 10 μm and an average particle size of 5 μm were added.
Graphite powder of m was added as shown in Table 1, and secondary composite particles were obtained in the same manner as in Example 1 in the atmosphere, temperature, acceleration and time shown in Table 2. Regarding the obtained secondary composite particles X
Qualitative analysis by RD revealed that the average particle diameters of Si ₃ N ₄ , titanium compounds (TiN, TiC, TiCN) and C are as shown in Table 3.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

According to the present invention, fine dispersed particles containing a metal nitride as a main component are dispersed in a fine matrix containing Si ₃ N ₄ as a main component, and a raw material in a manufacturing process thereof and By devising the mixing and pulverizing method, it is possible to provide a silicon nitride composite powder capable of easily obtaining a sintered body having excellent characteristics even by ordinary handling.

Continued front page    F-term (reference) 4G001 BA03 BA09 BA25 BA32 BA38                       BA57 BA60 BA61 BB03 BB25                       BB32 BB38 BB57 BB60 BC01                       BC02 BC21                 4G030 AA12 AA36 AA45 AA49 AA52                       AA60 AA61 BA18 BA19 GA03                       GA04 GA07

Claims (9)

[Claims] 1. The average particle size of primary particles is 30 nm in all cases.
A silicon nitride-based composite, which is a secondary composite particle powder comprising the following silicon nitride, a titanium-based compound, graphite and / or carbon, and a phase covering at least the surface of these particles and containing at least an amorphous material. Powder. 2. The silicon nitride-based composite powder according to claim 1, wherein the amorphous phase is titanium and / or silicon and a part of carbon. 3. The silicon nitride-based composite powder according to claim 1, wherein the titanium-based compound is at least one selected from titanium nitride, titanium carbonitride, and titanium carbide. 4. A silicon nitride system characterized by mixing and pulverizing silicon nitride powder, metallic titanium powder and graphite powder and / or carbon powder at a temperature of room temperature to 250 ° C. at an acceleration of 10 to 300 G. Method for producing composite powder. 5. A nitrogen atmosphere pressure of 0.05 MPa to 1.
The method for producing a silicon nitride-based composite powder according to claim 4, wherein the pressure is 0 MPa. 6. The total amount of titanium metal powder added is 5-6.
The method for producing a silicon nitride-based composite powder according to claim 4, wherein the content is 0% by weight. 7. The amount of graphite or carbon powder added is 0.5 to 20% by weight of the total weight.
A method for producing the silicon nitride-based composite powder described. 8. The method for producing a silicon nitride-based composite powder according to claim 4, wherein the mixing time is 0.5 hours to 50 hours. 9. The method for producing a silicon nitride-based composite powder according to claim 4, wherein the mixed pulverization is performed by a planetary ball mill or an attritor.