JPS5918347B2 - Manufacturing method of silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicon nitride sintered body having excellent high-temperature properties.

Silicon nitride has been attracting attention in recent years as a material for high-temperature structural materials such as gas turbine parts because it has excellent mechanical strength, heat resistance, thermal shock resistance, and corrosion resistance.

However, silicon nitride is a substance that is extremely difficult to sinter, and it is difficult to obtain a high-density sintered body by sintering it alone.

Therefore, a method has been proposed in which oxide powders such as magnesia, alumina, and ittria are added to silicon nitride powder as sintering aids, and the resulting mixture is sintered under normal pressure or pressure to produce a high-density sintered body. has been done.

In the sintered body obtained by the proposed method, the metal in the oxide added as a sintering aid reacts with silicon nitride to form a silicate, and this silicate constitutes the sintered body. A glass phase is formed at the grain boundaries of silicon nitride particles, and when the sintered body is used at high temperatures, the glass phase softens and the mechanical strength is significantly reduced, so it is undesirable as a high-temperature structural material.

The present invention eliminates the drawbacks of the proposed method and provides a method for producing a silicon nitride sintered body in which mechanical strength decreases little at high temperatures.

That is, the present invention provides a silicon nitride powder which is characterized by sintering silicon powder containing yttrium nitride powder with a weight coefficient of 2 to 15 at a temperature in the range of 1500 to 1900° C. under a pressure of 200 kg/d or more. This is a method for producing a raw material sintered body.

According to the present invention, an excellent effect is achieved in that a high-density silicon nitride sintered body whose mechanical strength decreases little even at high temperatures of 1000° C. or higher is obtained.

The proportion of yttrium nitride used as a sintering aid is 2 to 15% by weight or 5 to 10% by weight relative to the total amount of yttrium nitride and silicon nitride.

If the proportion of yttrium nitride used is too small, a sintered body with high mechanical strength at high temperatures cannot be obtained, and if the proportion of yttrium nitride used is too large, the resulting sintered body will contain many grain boundary phases. Its mechanical strength decreases.

There are no particular restrictions on the method for preparing silicon nitride powder containing yttrium nitride powder in the present invention, and for example, the following method may be employed.

(1) A method in which yttrium nitride powder and silicon nitride powder prepared in advance are mixed in an organic solvent such as acetone, benzene, or toluene, and then the organic solvent is distilled off.

Since yttrium nitride in the present invention is susceptible to hydrolysis, it is desirable to carry out the above method under a dry inert gas atmosphere.

(2) After mixing yttrium powder and silicon nitride powder,
A method of nitriding yttrium by heating it to a temperature in the range of 750 to 1100°C in a nitrogen gas atmosphere.

In this method, prior to heating in a nitrogen gas atmosphere, the powder mixture is preferably heated to a temperature in the range of 550 to 900° C. under hydrogen flow to remove oxygen mixed in the raw material powder.

In the present invention, the silicon nitride powder containing yttrium nitride may be molded in advance and then sintered, or molding and sintering may be performed simultaneously.

In the present invention, a silicon nitride sintered body is obtained by heating a silicon nitride powder containing yttrium nitride or a molded body thereof under pressure.

The sintering pressure is 200 ky/cyit or more.

If the sintering pressure is lower than this, it will be difficult to obtain a sintered body with high mechanical strength.

The sintering temperature is 1500 to 1900°C, preferably 16
00-1800°C.

If the sintering temperature is lower than the lower limit, a sintered body with high mechanical strength cannot be obtained, and if the sintering temperature is higher than the upper limit, silicon nitride itself will decompose.

Next, Examples and Comparative Examples will be shown.

In Examples and Comparative Examples, the density of the sintered body was measured by the Archimedes method, and its micro Vickers hardness (
The hardness (hereinafter simply referred to as hardness) was measured using a QM high temperature micro hardness meter manufactured by Nippon Kogaku Co., Ltd.

The bending strength of the sintered body was determined by cutting out a 3 x 3 x 40 mm test piece from the sintered body, polishing the surface, and performing a three-point bending test under the conditions of a span of 20 m and a crosshead speed of 0.5 mm for 1 minute. Ta.

In the following description, all references to "person in charge" refer to "person in charge of weight."

Examples 1 and 2 Silicon nitride powder (nitrogen content 38
．． 0%, silicon content 60.0%, oxygen content 1.8
%, specific surface area: 4.2 m/g), a total amount of 10 g of yttrium nitride, and 10 d of acetone were charged into an alumina ball mill, and wet milled at room temperature under a nitrogen atmosphere for 16 hours.

The ground mixture was dried under nitrogen atmosphere to remove acetone and obtain a powder mixture.

0.5 g of the powder mixture was heated to a diameter of 7 at a pressure of 1.5 ton/i.
After molding into a cylinder with a length of 8 mm and a length of 8 mm, it was placed in a capsule made of boron nitride, and this capsule was vacuum sealed in quartz glass.

Then, the quartz glass encapsulated molded product was vacuum sealed in Pyrex.

The double-encapsulated molded product obtained in this way was
Hot isostatic sintering was carried out for 30 minutes at the temperature shown in Table 1 under a pressure of kg/i to obtain a silicon nitride sintered body.

Table 1 shows the density and hardness of the sintered body.

Comparative Examples 1 and 2 Example 1 was repeated, except that yttrium nitride was replaced by yttrium in the amounts listed in Table 1.

The results are shown in Table 1. Example 3 Silicon nitride powder (nitrogen content 35.0i%, silicon content 59.3%, oxygen content 2.7, specific surface area 11.4)
60 g of a mixture consisting of 93% m/g) and 7.0% yttrium nitride powder and 60 d of acetone were placed in an alumina ball mill and wet milled at room temperature under a nitrogen atmosphere for 16 hours.

The ground mixture was dried under nitrogen atmosphere to remove acetone and obtain a powder mixture.

Fill the powder mixture into a 40 x 20 mm graphite die,
The powder mixture was molded and sintered simultaneously by hot pressing at 1780°C under a nitrogen atmosphere for 1 hour under a pressure of 480 kg/i.

The density of the sintered body is 3.089/cyit, and its bending strength is 88 kg/m4 at 25°C. 75kg/at 1200℃
It was in ma.

Comparative Example 3 Example 3 was repeated except that yttrium 7.0 was used in the mixture in place of the yttrium nitride powder.

The density of the obtained sintered body was 3.129/i, and its bending strength was 78 kg/ryal at 25°C and 6 at 1200°C.
It was 1 kg/mm.

Example 4 Silicon nitride powder (nitrogen content 37°2, silicon content 60.2%, oxygen content 2.1%, specific surface area 18.5)
ml g) 30 g of a mixture consisting of 94.5 parts and 5.5 parts of yttrium powder and 30 ml of benzene were charged into an alumina ball mill, and heated at room temperature under a nitrogen atmosphere for 16 g.
Pulverized time-wise.

The ground mixture was dried under nitrogen atmosphere to remove benzene and obtain a powder mixture.

This powder mixture was filled into a quartz boat, placed in a tubular electric furnace, and heated at 700° C. for 2 hours in a hydrogen atmosphere.

Subsequently, nitrogen gas was supplied and the mixture was heated at 900° C. for 5 hours to obtain a mixture of silicon nitride powder and yttrium nitride powder.

Using the powder mixture thus obtained, Example 3
A silicon nitride sintered body was obtained in the same manner as above.

The density of the sintered body is 3.10g/criL, and its bending strength is 80kg/m at 25℃72N11 72kg/m at 200℃
It was a.

Claims (1)

[Claims] 1 Silicon nitride material characterized by sintering silicon powder containing 2 to 15 weight coefficients of I-IJium nitride powder at a temperature in the range of 1500 to 1900° C. under a pressure of 200 ky/ff1 or more. Manufacturing method of sintered body.