JPH0764639B2 - Method for manufacturing silicon nitride sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a silicon nitride sintered body suitable for materials such as high-speed casting cutting.

[Conventional technology]

Since a silicon nitride sintered body has high strength and is excellent in wear resistance and heat resistance, various applications including wear resistant parts are being developed.

As a method for producing such a silicon nitride sintered body, Japanese Patent Publication No.
As described in JP-A-3649, conventionally, α-type silicon nitride (α-Si ₃ N ₄ ) was used as a raw material powder and yttrium oxide (Y ₂ O ₃ ) or aluminum oxide (Al ₂ O ₃ ) was sintered. The method of mixing an auxiliary agent and sintering in a non-oxidizing atmosphere has been taken. In this method, the low-temperature stable α-Si ₃ N ₄ undergoes a phase transformation in the high-temperature stable β-Si ₃ N ₄ during sintering to generate a fibrous structure, and the strength of the resulting sintered body is improved. It is known to improve.

However, α-Si ₃ N ₄ is unstable near the sintering temperature,
It easily dissolves in the sintering aid liquefied during sintering, decomposes and easily scatters out of the sintered body, and pores remain in the sintered body due to recrystallization and crystal grain growth during phase transformation. Therefore, it is difficult to form a uniform and fine structure, which is a cause of deterioration of strength and other properties of the obtained silicon nitride sintered body.

Therefore, pressure sintering such as hot pressing is currently used to reduce the porosity and obtain a dense sintered body, but continuous sintering is difficult and the cost of the product is high. However, it is unsuitable as a sintering means for cutting tool materials and the like which require high production efficiency.

[Problems to be solved by the invention]

In view of the above circumstances, the present invention aims to provide a method for producing a silicon nitride sintered body having excellent characteristics of being dense, having high hardness, and high strength in which pores are unlikely to remain due to sintering. To do.

[Means for solving problems]

The manufacturing method of the silicon nitride sintered body of the present invention is 1 to 15% by weight in total of aluminum oxide and yttrium oxide, β-type is 95% or more, the average particle size is 0.5 μm or less and the particle powder distribution width. Is 2.0 μm or less, and the mixed powder with the remaining silicon nitride is sintered at 1600 to 1900 ° C. in a non-oxidizing atmosphere. Here, the remaining silicon nitride means that the remaining portion of the mixed powder excluding the total amount of other compound powder such as aluminum oxide is silicon nitride.

β-type silicon nitride (β-Si ₃ N ₄ ) is, for example, commercially available α-type silicon nitride in the range of 1700 to 1900 in a nitrogen gas atmosphere of 1 to 10 atm.
It is obtained by heat treatment at a temperature of ° C. Above all, it is preferable to use β-type silicon nitride powder having a small fine particle size distribution width mainly in order to obtain a uniform fine grain structure, and the average particle size range is 0.5 μm or less and the particle size distribution range is 2.0 μm or less. Particularly preferred.

As the sintering aid, yttrium oxide and aluminum oxide may be used, and if necessary, one or more kinds of lanthanide-based rare earth element oxides may be used in combination. The sintering may be pressure sintering using a hot press or the like, or pressureless sintering, but pressureless sintering is preferable because of its high production efficiency. The sintering atmosphere is a non-oxidizing atmosphere, especially 1 atmosphere or more 300
If sintering is performed in a pressurized nitrogen atmosphere at atmospheric pressure or less, a denser and more excellent sintered body can be obtained.

Further, for the purpose of improving the fracture toughness by developing a fibrous structure in the silicon nitride sintered body of the present invention, at least one selected from the IVa, Va, and VIa group elements of the periodic system of elements.
Carbides, nitrides, carbonitrides or borides of certain metallic elements,
Or silicon carbide or silicon carbide whiskers, etc.
It is effective to add 30% by weight. If the addition amount is less than 5% by weight, the above effect is not obtained, and if it exceeds 30% by weight, the density of the sintered body is lowered, which is not suitable.

[Action]

In this method, since high β-type silicon nitride is used, phase transformation does not occur during sintering and mass transfer is reduced. That is, solid solution of silicon nitride does not occur in the sintering aid liquefied during sintering,
There is no decomposition and scattering of components outside the sintered body. Moreover, since silicon nitride powder having a small particle size and a small particle size distribution width is used,
The grain size of the sintered body is fine and the grains grow uniformly throughout the structure.
As a result, it is possible to obtain a silicon nitride sintered body which is dense and has few pores and has a uniform fine structure even at normal pressure sintering, and which has high strength and high hardness at high temperature.

At least one oxide selected from aluminum, yttrium and lanthanide rare earth elements, which is a sintering aid, densifies the grain boundary layer and improves the density of the sintered body,
If the addition amount is less than 1% by weight, the effect of improving the density is insufficient, and if it exceeds 15% by weight, the strength and high temperature hardness of the sintered body are deteriorated.

Since the use of β-type silicon nitride reduces the mass transfer during sintering, it is necessary to prolong the sintering time as compared with the case of using α-type silicon nitride. Even if the amount is reduced, a sufficiently dense sintered body can be obtained. This is effective in reducing grain boundary softening that affects the strength of the sintered body in a high temperature atmosphere and reducing strength deterioration.

In addition, by adding the compound of the IVa, Va, and VIa group elements, a fibrous structure develops in the sintered body, and as a result, toughness is improved.

Thus, the structure of the silicon nitride sintered body obtained by this method is uniformly refined and densified even under normal pressure sintering, the number of pores is significantly reduced, and the characteristics of the sintered body such as hardness and its uniformity are improved. However, since the strength and hardness at high temperatures are not significantly deteriorated, it is particularly suitable as a material for cutting tools. Also, IV a, V a, V
The sintered body whose toughness is improved by adding the group Ia element compound is also effective as a structural material.

〔Example〕

Example 1 A commercially available Si ₃ N ₄ powder having an average particle size of 0.5 μm was heat-treated at 1800 ° C. for 3 hours in an N ₂ atmosphere at 10 atm. Obtained Si ₃ N
₄ Powder A had an average particle size of 0.5 μm and a particle size distribution width of 2.0 μm, and was found by X-ray diffraction to be 100% β-type Si ₃ N ₄ .

As a comparative example, α-Si ₃ having a commercially available average particle size of 1.5 μm is used.
The N ₄ powder was heat-treated at 1800 ° C. for 3 hours in a N ₂ atmosphere at 10 atm. The obtained Si ₃ N ₄ powder B of the comparative example has an average particle size of 1.5.
It was found to be 100% β type Si ₃ N ₄ by X-ray diffraction with a particle size distribution width of 3.1 μm.

These β-Si ₃ N ₄ powders A and B were separately mixed with Al ₂ O ₃ powder (average particle size 0.5 μm) and Y ₂ O ₃ powder (average particle size 0.5 μm) in the composition shown in Table 1 below. After adding a molding binder, the mixed powder was press molded into a JIS SNG 432 grade slow away chip at a pressure of 1.5 ton / cm ² . The compact was sintered at 1850 ° C. for 3 hours in a N ₂ atmosphere at 10 atm.

(Note) Sample Nos. 4, 5, 6, and 7 are comparative examples.

Each sintered body samples obtained by grinding in the slow Au H. class tap, the results of cutting tests having conducted the following cutting conditions, the as well as the relative density of each sintered body sample (%) and hardness (H _R A) The results are shown in Table 2.

Work: FC25 Width 180 x Length 300mm Machine: NC lathe Cutting conditions: Cutting speed 600m / min Cutting depth 2mm Feed 0.36mm / rev. Life judgment: V _B = 0.3mm Also according to JIS R1601, in room temperature atmosphere The three-point bending strength test was conducted at 1300 ° C. and the three-point bending strength test was conducted at 1300 ° C. in air.

Example 2 Using the same β-type Si ₃ N ₄ powder A, Al ₂ O ₃ powder and Y ₂ O ₃ powder as in Example 1, and TiC powder and SiC powder having an average particle size of 0.5 μm, the following Table 3 is used. A powder mixed with the composition shown was sintered by the same method as in Example 1, a JIS R1601 test piece was cut out from the sintered body, the same characteristic evaluation as in Example 1 was performed, and the fracture toughness value was obtained. These results are also shown in Table 4.

[Effects of the Invention] According to the present invention, production can be performed by pressureless sintering with good production efficiency, has a fine and fine structure with few remaining pores, and has high strength and high hardness and wear resistance. It is possible to produce a silicon nitride sintered body which is excellent, has little deterioration in strength and hardness at high temperatures, and is particularly suitable as a cutting tool material.

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location 102 M 102 Q 102 R (72) Inventor Matsuo Higuchi 1-1-1 Kunyokita, Itami City, Hyogo Sumitomo Electric Industries Itami Seisakusho Co., Ltd. (56) Reference JP-A-59-107908 (JP, A) JP-A-58-151371 (JP, A) JP-B 57-8046 (JP, B2) JP-B 61-43311 ( JP, B2)

Claims (3)

[Claims] 1. A total of 1 to 15% by weight of aluminum oxide and yttrium oxide, β-type is 95% or more, and the balance of the average particle size is 0.5 μm or less and the particle size distribution width is 2.0 μm or less. A method for producing a silicon nitride sintered body, which comprises sintering a mixed powder with silicon nitride at 1600 to 1900 ° C in a non-oxidizing atmosphere. 2. The method for producing a silicon nitride sintered body according to claim 1, wherein the sintering is performed in a pressurized nitrogen atmosphere of 1 atm to 300 atm. 3. A total of 1 to 15% by weight of aluminum oxide and yttrium oxide, and IVa, Va, VIa of the periodic table of elements.
5 to 30% by weight of carbide, nitride, carbonitride or boride of at least one metal element selected from the group elements, or silicon carbide or silicon carbide whiskers, and β type is 95
% Or more and an average particle size of 0.5 μm or less and a particle size distribution width of 2.0 μm or less, the mixed powder with the rest of silicon nitride is sintered at 1600 to 1900 ° C. in a non-oxidizing atmosphere. A method for producing a silicon nitride sintered body, which is characterized.