JPH11139813A - Amorphous silicon nitride powder and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide amorphous Si3 N4 powder and its production for relatively easily producing the amorphous Si3 N4 powder in which finely graining proceeds at the time of sintering as a powdery starting material for an Si3 N4 sintered compact having superior characteristics such as strength in a medium to low temp. range. SOLUTION: A metal such as Ti or B forming nitride under Si3 N4 sintering conditions in the atmosphere of nitrogen forms a solid soln. in amorphous Si3 N4 powder. This amorphous Si3 N4 powder is produced by mixing the amorphous Si3 N4 powder with metal powder at 10-200 G acceleration. The added amt. of the metal powder is preferably 10-50 wt.% of the total amt. and the mixing time is preferably 0.1-10 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body having excellent mechanical properties from room temperature to 1100.degree. C., which is useful as a structural ceramic material used for automobile parts and wear-resistant tools. Raw material powder and a method for producing the same.

[0002]

2. Description of the Related Art Silicon nitride (Si ₃ N ₄ ) is a material that is balanced in strength, fracture toughness, corrosion resistance, abrasion resistance, thermal shock resistance, oxidation resistance, and the like. Etc. are used in a wide range. In particular, recently, it has attracted attention as a structural material for automobile engines and gas turbines.

[0003] As a method for improving the strength of such silicon nitride, the production of a sintered body composed of fine silicon nitride particles has been conventionally attempted. For example, JP-A-6-27
No. 1358 discloses that the average particle size of silicon nitride is 0.3 μm.
m, the three-point bending strength is 17
It is described that a silicon nitride sintered body of 0 kg / mm ² or more can be obtained. However, as is clear from the examples described in the publication, the average particle size of the commercially available Si ₃ N ₄ raw material powder is about 0.7 μm. It is necessary to further reduce the average particle size of this commercially available raw material powder.

[0004] As a method for obtaining fine powder, a CVD method has been conventionally used. For example, Ceramic M
materials & Components for E
As shown in P.70, table II of Nines, a silicon nitride powder having an average particle size of about 20 nm was obtained. However, the CVD method is disadvantageous in that the production cost is high and the mass productivity is poor because it is a synthesis method by a gas phase method. Moreover, since the surface area increases as the particle size of the powder becomes smaller, the properties of the silicon nitride powder are impaired due to surface oxidation, and the powders become more agglomerated, resulting in extremely low moldability. was there.

On the other hand, there is a pulverization method as a method for synthesizing a fine powder excellent in mass productivity. For example, a method of synthesizing a nanocomposite powder of silicon nitride and titanium by mixing silicon nitride and titanium metal at high acceleration is known. However, even when such a nanocomposite powder is used, a phenomenon that crystal grains become coarse due to heating during sintering is inevitable, and it has been difficult to obtain a fine silicon nitride sintered body.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention is relatively easy to produce as a raw material powder of a silicon nitride sintered body having excellent properties such as strength in a low temperature range. It is an object of the present invention to provide a silicon nitride powder in which atomization proceeds during sintering, and a method for producing the same.

[0007]

Means for Solving the Problems In order to achieve the above object, the present invention provides a silicon nitride powder which forms nitride in amorphous silicon nitride under a silicon nitride sintering condition in a nitrogen atmosphere. Amorphous silicon nitride powder characterized in that the metal to be dissolved is in solid solution. As the metal which forms a solid solution in the amorphous silicon nitride, titanium or boron is preferable, and the amount of the solid solution is preferably in the range of 10 to 50% by weight.

Further, the method for producing an amorphous silicon nitride powder according to the present invention comprises the steps of: providing an amorphous silicon nitride powder and a metal powder which forms a nitride under silicon nitride sintering conditions in a nitrogen atmosphere; It is characterized in that a metal is dissolved in amorphous silicon nitride by mixing at an acceleration of 10 to 200 G. The addition amount of the metal powder is preferably 10 to 50% by weight of the whole, and the mixing time is preferably 0.1 to 10 hours.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the amorphous silicon nitride powder of the present invention, a metal that forms a nitride under a normal condition for sintering a silicon nitride powder in a nitrogen atmosphere is dissolved. The solid solution metal becomes a crystal nucleus at the same time as sintering and becomes fine Si ₃ N ₄
Since the particles are precipitated and are precipitated around the silicon nitride particles as fine metal nitrides, grain growth during the sintering process is suppressed, and a fine silicon nitride sintered body can be obtained.

With respect to the metal to be solid-dissolved, it is necessary that the metal be a metal that forms a nitride under the sintering condition of silicon nitride in a nitrogen atmosphere due to the action of the metal and its nitride. Titanium or boron is preferable in consideration of the condition that the generated nitride is stable at a high temperature. If the amount of the solid solution of the metal is less than 10% by weight with respect to silicon nitride, it does not precipitate as fine crystal grains at the time of sintering, so that the above-mentioned effects cannot be obtained. Is difficult, the content is preferably in the range of 10 to 50% by weight.

In the production of the amorphous silicon nitride powder of the present invention, the metal is dissolved in the amorphous silicon nitride by a method of mixing the silicon nitride powder and the metal powder at a high acceleration of 10 to 200 G. The reason why the mixing acceleration is in the range of 10 to 200 G is that if the mixing acceleration is less than 10 G, solid solution of the metal in the amorphous silicon nitride does not occur, and if it exceeds 200 G, the metal reacts with the silicon nitride and the metal silicide or the like. Is generated, and the strength of the obtained sintered body is deteriorated.

When the amount of the metal powder added to the silicon nitride powder is less than 10% by weight based on the whole powder, the amount of the formed metal solid solution is too small, so that it does not precipitate as fine crystal grains during the subsequent sintering. If the content exceeds 50% by weight, excess metal which does not form a solid solution remains, so that 10
A range of about 50% by weight is desirable.

Although there is no particular limitation on the mixing time, if the mixing time is less than 0.1 hour, the amount of the solid solution metal decreases irrespective of the mixing acceleration and the amount of the metal powder added. If it exceeds, the impurities are remarkably mixed into the powder from the grinding media and the inner wall of the pot.
Desirably, the time is about 0 hours.

[0014]

EXAMPLE 1 2% by weight of Al ₂ O ₃ powder, 1% by weight of MgO powder and 5% by weight of amorphous Si ₃ N ₄ powder having an average particle size of 0.5 μm as a sintering aid of Y ₂ O ₃ powder were added, and further adding a metal Ti powder having an average particle size of 5μm to 30% by weight relative to the entire powder. This was mixed at an acceleration of 150 G for 4 hours by a planetary ball mill using a SUS304 ball and a pot. The obtained amorphous Si ₃ N ₄ powder was dissolved in sulfuric acid to determine the amount of metal Ti not dissolved in Si ₃ N ₄ .
No undissolved metallic Ti was found, indicating that all Ti was dissolved in the amorphous Si ₃ N ₄ .

Next, the amorphous Si ₃ N ₄ powder in which Ti is dissolved as described above is heated to 500 ° C. for 200 hours.
Press molding was performed in the air at kg / mm ² . The compact was sintered in a nitrogen atmosphere at 1 atm under conditions of 1500 ° C. × 1 hour. After polishing the obtained Si ₃ N ₄ sintered body,
When a thin film specimen was prepared by Ar ion etching and evaluated using a transmission electron microscope, it was mainly composed of matrix Si ₃ N ₄ particles and dispersed TiN particles, and the average particle size of Si ₃ N ₄ particles The diameter is 50 nm and the average particle diameter of the TiN particles is 30 n.
m and very fine.

Also, the obtained Si ₃ N ₄ sintered body is 3 × 4
The specimen was cut out into an eutectoid specimen having a size of × 40 mm, cut and finished with a # 800 diamond grindstone, and the three-point bending strength of 15 test specimens was confirmed in accordance with JIS R1601, and the average strength was 2 GPa. The strength was extremely high.

On the other hand, as a comparative example, an amorphous Si ₃ N ₄ powder was produced in the same manner as above except that the metal Ti powder was not added and mixed for 12 hours, and this powder was molded under the same conditions as above. After sintering, the Si ₃ N ₄ particles in the obtained Si ₃ N ₄ sintered body had a large grain growth of 1 μm, and the sintered body strength evaluated in the same manner as above was 100 kg / mm ² . The strength was low.

Example 2 Example 1 was applied to amorphous Si ₃ N ₄ powder having an average particle size of 0.5 μm.
The same sintering aid, and the metal B powder having an average particle diameter of 5μm was added 5 to 60 weight percent of the total powder, a planetary ball mill using ZrO ₂ balls and the SUS pot and, 5
Mixing was performed at an acceleration of 250 G for 0.05 to 12 hours. In addition, the rotation speed of the ball mill was 500 rpm, and the revolution speed was 200 rpm.

For each of the obtained amorphous Si ₃ N ₄ powders,
The concentration of solid solution B and the concentration of impurity ZrO ₂
It was determined by the CP method and is shown in Table 1 below together with the amount of B added, the mixing acceleration and the mixing time during the production of the powder. Further, each amorphous Si ₃ N ₄ powder was molded and sintered in the same manner as in Example 1, and the average of Si ₃ N ₄ particles was obtained for each of the obtained Si ₃ N ₄ sintered bodies in the same manner as in Example 1. The particle size and strength were measured, and the results are shown in Table 1 below.

[0020]

[Table 1] Mixing conditions Characteristics of Si ₃ N ₄ powder Characteristic B addition amount of sintered body Acceleration time ZrO ₂ concentration B concentration Si ₃ N ₄ particle size Strength sample (wt%) (G) (hr) (wt% ) (wt%) (nm) (MPa) 1 * − 150 2 0.2 − 1000 800 2 20 150 2 0.2 20 10 1500 3 * 20 5 2 0.2 − 30 700 4 20 15 2 0.5 20 20 1600 5 20 180 2 0.7 20 10 2000 6 * 20 250 2 2.5 − 1000 800 7 5 150 2 1.0 5 50 1200 8 40 150 2 1.5 40 15 1600 9 60 150 2 2.0 50 10 1200 10 20 150 0.05 0.1 10 80 1200 11 20 150 7 2.0 20 40 1800 12 20 150 12 6.0 20 20 1400 (Note) Samples marked with * in the table are comparative examples.

As can be seen from the results shown in Table 1, metal B
In sample 1 of the comparative example mixed without adding the powder and in sample 3 of the comparative example mixed at a low acceleration, BN did not precipitate as fine crystal grains during sintering because B was not dissolved in the powder. ,
The strength of the sintered body is very low. Sample 6 of the comparative example has a large mixing acceleration, and reacts with Si ₃ N ₄ to form BN before B forms a solid solution in the powder during mixing.
i ₃ N ₄ did not form fine grains, and the strength of the sintered body was extremely low.

On the other hand, in each of the samples of the examples, Si ₃ N ₄ in the sintered body was formed into fine crystal grains, and extremely high strength of the sintered body was obtained. However, since the amount of B added in Sample 7 was small, the amount of B solid solution was small, and the amount of Si _{3 in} the sintered body was small.
The degree of atomization of N ₄ was small, and the strength was slightly reduced. On the contrary, in Sample 9, since the amount of B added was large, B that did not form a solid solution remained, and the strength of the sintered body was slightly reduced. Further, since the mixing time of the sample 10 is short, the amount of B dissolved in the powder becomes small,
Since the degree of fine crystallization was small, the strength of the sintered body was slightly reduced. In Sample 12, since the mixing time was long, the amount of ZrO ₂ mixed in the pulverized media was large, and the strength of the sintered body was also slightly reduced.

[0023]

According to the present invention, there is provided, as a raw material powder for a silicon nitride sintered body, an amorphous silicon nitride powder which is relatively easy to produce and which can promote the refinement of crystal grains during sintering. can do. By using this amorphous silicon nitride powder, a silicon nitride sintered body excellent in both strength and fracture toughness can be manufactured in a medium to low temperature range from room temperature to 1100 ° C., and an automobile engine requiring high reliability It is extremely useful as a raw material powder for structural ceramic materials such as members and wear-resistant tools.

Claims (6)

[Claims] 1. An amorphous silicon nitride powder characterized in that a metal that forms a nitride under a silicon nitride sintering condition in a nitrogen atmosphere is dissolved in the amorphous silicon nitride. 2. The method according to claim 1, wherein the amount of the solid solution of the metal in the amorphous silicon nitride is 10 to 50% by weight.
Amorphous silicon nitride powder described in 1. 3. The amorphous silicon nitride powder according to claim 1, wherein the metal is titanium or boron. 4. An amorphous silicon nitride powder and a metal powder that forms a nitride under silicon nitride sintering conditions in a nitrogen atmosphere are mixed at an acceleration of 10 to 200 G,
A method for producing an amorphous silicon nitride powder, comprising dissolving a metal in amorphous silicon nitride. 5. The addition amount of said metal powder is 10 to 5 in total.
The method for producing an amorphous silicon nitride powder according to claim 4, wherein the amount is 0% by weight. 6. The method for producing an amorphous silicon nitride powder according to claim 4, wherein the mixing time is 0.1 to 10 hours.