JP2949936B2 - Method for producing silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a silicon nitride sintered body.

[0002]

2. Description of the Related Art Silicon nitride has high strength and high toughness, and is the material that has received the most attention as a structural material. But,
Since silicon nitride is difficult to sinter, Y ₂ O ₃ , Al ₂ O
₃ , Add a sintering aid such as MgO,
Sintered at 00 ° C. Further, a pressure sintering method is adopted for further increasing the strength and densification.

[0003]

As described above, since silicon nitride is difficult to sinter, 1700
The temperature must be as high as 1 ° C. to 1800 ° C., and there are inconveniences such as using a closed furnace for maintaining the temperature and using a heater material that can withstand the high temperature. In addition, when the firing temperature is increased for densification, there is a problem that grain growth occurs and the strength of the sintered body decreases.

Accordingly, an object of the present invention is to provide a method for producing a silicon nitride sintered body which is fired at a low temperature using a simple furnace and which is dense and has high strength at a high temperature.

[0005]

According to the present invention, in order to achieve the above object, Y ₂ O ₃ and MgAl ₂ O ₄ are added as sintering aids to a silicon nitride powder having an average particle size of 0.5 μm or less. 5% to 15% by weight in total, Y ₂ O ₃ and the weight ratio of _{MgAl 2 O 4 (Y 2 O} 3 / MgAl 2 O 4) were mixed in a range of 0.3 to 10, in a molding after a nitrogen atmosphere 1500 to 15
A method for producing a silicon nitride sintered body characterized by sintering at a temperature of 50 ° C.

The starting material silicon nitride powder has a particle size of 0.5 μm.
m, preferably 0.1 to 0.4 μm
You. Due to the small particle size of silicon nitride powder,
Performance and the fine structure of the sintered body
High strength sintered body can be obtained by sintering at temperature
Become. Y as sintering aid_TwoO_ThreeAnd MgAl_TwoO_Fouruse
To use. This combination has the best sinterability up to the low temperature range.
And a dense sintered body can be obtained. Y_TwoO_ThreeAnd MgAl_TwoO
_FourIs 5 to 15% by weight in total. These baked
If the amount of binder added is small, densification does not occur, and therefore strength is also improved.
Don't go up. On the other hand, when the amount of the sintering aid increases,
Although the grain boundary glass phase increases and the strength decreases,
is there. Also, Y _TwoO_ThreeAnd MgAl_TwoO_FourWeight ratio (Y_Two
O_Three/ MgAl_TwoO_Four) Is in the range of 0.3 to 10.
You. Outside this range, it does not sinter densely.

It is preferable to use Si ₃ N ₄ having a total amount of metal impurities of 100 ppm or less and a sintering aid having a purity of 99.9% or more. If there are too many impurities, it will not be sintered densely. In the present invention, sintering at a lower temperature than before and sintering at a lower temperature are made possible by specifying the particle size of the starting material, the type and the mixing ratio of the sintering aid. Thus, the growth of the crystal grains of the sintered body is suppressed, and the strength can be increased.

More specifically, the silicon nitride sintered body of the present invention
Sinter at 1500-1550C. Sintering temperature is 15
Since the temperature is as low as 00 ° C. to 1550 ° C., the structure and material of the furnace can be greatly different from those of the conventional high temperature furnace, and the cost reduction effect is great.

Sintering in the temperature range of 1400 ° C. to 1650 ° C.
However, room temperature strength of 800 MPa to 1500 MPa was obtained.
Requires a sintering temperature between 1700 ° C and 1800 ° C
It was the strength that I had. However, the sintering temperature range of the present invention is 1500 ° C. to 1550 ° C., and in this range, the strength also shows the highest value (1200 MPa to 1300 MPa or more). This strength value is a high strength almost comparable to the highest strength level sintered at a conventional high temperature, and is obtained at a lower temperature in the present invention. It densifies even at temperatures below 1500 ° C, but α →
Strength is reduced due to insufficient β transition. 155
When the temperature is set to 0 ° C. or higher, the grain size of the sintered body structure becomes coarse, and the strength decreases. However, at a sintering temperature of 1400 ° C, 8
There has been no example in which an intensity value of 00 MPa or more has been developed. This strength value is much higher than that of an oxide such as alumina (about 400 MPa) sintered in the same 1400 ° C. range.

The sintering atmosphere is an N ₂ atmosphere. A dense and high-strength sintered body can be obtained even at normal sintering pressure.
Sintering under high pressure further improves the strength.

[0011]

[Function] By specifying the types, characteristics, and compounding ratios of the starting materials and the sintering aid, sintering at a low temperature, which has not been conventionally performed, becomes possible, and a sintered body having finer particles is obtained. Was done. By obtaining a dense sintered body with fine particles, a high strength value of 800 MPa to 1500 MPa is exhibited at room temperature.

[0012]

EXAMPLE The thermal decomposition method of silicon diimide or metal silicide
Si produced by the direct nitriding method of concrete_ThreeN_FourPowder (flat
Sintered to a uniform particle size of 0.5 μm or less, pregelatinized 92% to 97%
Y as auxiliary_TwoO_ThreePowder (average particle size 0.3 μm, purity 9
9.9%), MgAl_TwoO _FourPowder (average particle size 0.3μ
m, purity 99.9%) with the composition shown in Table 1.
Various powders mixed (silicon nitride ball mill) are mixed with 200
kg / cm^TwoPressure molding with the pressure of
3000kg / cm by CIP after vacuum sealing^TwoPressurized with pressure
Thereafter, the molded body was subjected to N 2 under the conditions shown in Tables 1 and 2._TwoIn the atmosphere
In a furnace. Heating rate is 1 ℃ / min, maximum temperature
Was 4 hours.

[0013] The room temperature four-point bending strength (JI
Table 1 shows the average intensities of ten SR 1601). The relative density of the sintered body is a value obtained by dividing the bulk density obtained by the n-butanol substitution method by the theoretical density. For comparison, the starting material and the sintering aid were changed, and molded in the same manner as in the example.
Sintering was performed in a furnace in _two atmospheres, and the results in Table 3 were obtained.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

According to the present invention, the following effects can be obtained. 1) Sintering at a very low temperature of 1500 ° C. , similar to oxides such as alumina, exhibits a high strength value of about 1200 MPa or more , far exceeding the strength of oxides. Moreover, it was realized not only by gas pressure sintering but also by normal pressure sintering. 2) When sintering at a level of 1500 to 1550 ° C. , sintering in a firing furnace that is less expensive than conventional sintering at a high temperature becomes possible. Therefore, the ripple effect on manufacturing cost reduction such as furnace durability and maintenance cost is enormous.

2) When sintering at the level of 1400 ° C., sintering in an inexpensive sintering furnace becomes possible as compared with conventional sintering at a high temperature. Therefore, the ripple effect on manufacturing cost reduction such as furnace durability and maintenance cost is enormous.

Claims (1)

(57) [Claims] 1. A silicon nitride powder having an average particle size of 0.5 μm or less, Y ₂ O ₃ and MgAl ₂ O ₄ as sintering aids in a total amount of 5 to 15% by weight, Y ₂ O ₃ and MgAl ₂ O ₄
Weight ratio (Y ₂ O ₃ / MgAl ₂ O ₄ ) of 0.3 to 10
After molding, from 1500 ° C in a nitrogen atmosphere after molding
A method for producing a silicon nitride sintered body, comprising sintering at a temperature of 1550 ° C.