JPH06100387A - Reinforcement of silicon nitride ceramic - Google Patents

Abstract

PURPOSE:To improve the high-temperature strength of sintered silicon nitride produced by using a sintering assistant in sintering. CONSTITUTION:A silicon nitride sintered by using a sintering assistant is heat- treated in an oxygen-containing atmosphere at 1300-1500 deg.C for 1-24hr and the surface layer is scraped off to the depth of 0.1-0.5mm. The surface-scraping of the sintered and heat-treated material remarkably improves the flexural strength at 1300 deg.C to expand the utilization field of the silicon nitride ceramic as a high-temperature structural material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for strengthening silicon nitride ceramics, and more particularly to a silicon nitride ceramics for improving the high temperature characteristics of a silicon nitride sintered body which is sintered by adding a sintering aid. It is about the method of strengthening.

Silicon nitride ceramics such as silicon nitride and sialon are regarded as promising as various high temperature structural materials because they have high mechanical strength and excellent heat resistance.

[0003]

2. Description of the Related Art Since these silicon nitride-based ceramics are difficult to sinter, and are difficult to densify by sintering, oxides such as Y ₂ O ₃ , Al ₂ O ₃ and MgO. Is added as a sintering aid, and the method of sintering is used.

[0004]

According to the above conventional method,
A liquid phase is generated by the added sintering aid, which promotes sintering to obtain a dense sintered body, but in the obtained sintered body, the liquid phase generated during sintering is low in softness. It remains as a dot phase. This causes the strength of the sintered body to decrease, and the strength of the silicon nitride ceramics sintered body at high temperature was not always sufficient.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present inventors have proposed a method for producing silicon nitride ceramics, especially a low softening point phase and a sintered body produced by a sintering aid. As a result of studying the relationship with the strength, a sintered body obtained by adding a sintering aid to the sintered body is heat-treated in an oxygen-containing atmosphere, and then the surface layer of the sintered body is ground and removed to remove silicon nitride ceramics. The present invention has been completed based on the finding that the high temperature strength of (1) significantly improves.

That is, according to the present invention, a silicon nitride-based sintered body obtained by adding a sintering aid and sintering it in an oxygen-containing atmosphere at 1300 to 15 is used.
A method for strengthening silicon nitride ceramics is characterized by heat-treating at a temperature of 00 ° C., and then grinding and removing the surface layer of the sintered body.

In the present invention, the method for adding a sintering aid to obtain a dense sintered body is not particularly limited, and a conventional method is used. That is, a commercially available silicon nitride powder or sialon powder is mixed with an oxide sintering aid such as Y ₂ O ₃ or Al ₂ O ₃ after molding, and then pressureless sintering or pressure sintering is performed. A silicon nitride-based sintered body containing a sintering aid is obtained.

In the method of the present invention, the above-mentioned sintered body is replaced with air,
Heat treatment is performed in an oxygen-containing gas atmosphere such as oxygen. The heat treatment temperature is 1300 ° C. to 1500 ° C. If the temperature is lower than the above range, it is not effective, and if it is higher than the above range, the sintered body is decomposed, which is not preferable.

Although the heat treatment time cannot be unambiguously defined depending on the relation with the treatment temperature, it is usually 1 to 24 hours, and within the above preferable heat treatment temperature range, the effect is extremely small when the treatment time is shorter than 1 hour. There is no problem even if a long time treatment exceeding the above range is performed, but the effect cannot be improved,
It will only be economically disadvantageous.

In the method of the present invention, the surface of the sintered body is removed by grinding the sintered body which has been subjected to the above heat treatment. The thickness of the surface layer to be removed is usually 0.1 to 0.5 mm. 0.1 mm
In the following grinding treatment, the strength improvement effect was not sufficient,
Grinding and removing over m can be done, but it has no further effect and is economically disadvantageous.

[0011]

The function of heat-treating a silicon nitride-based sintered body containing a sintering aid in an oxygen-containing atmosphere and then grinding and removing the surface layer of the sintered body in the present invention is as follows. Estimated to.

Usually, in a silicon nitride-based sintered body, the added sintering aid exists as a low softening point phase in a form that fills the gaps between silicon nitride or sialon crystal grains, and therefore silicon nitride is used. It is considered that the strength of the ceramics at high temperature decreases.

In the case of the present invention, the sintering aid component such as Y ₂ O ₃ diffuses to the surface of the sintered body during the heat treatment of the sintered body in the oxygen-containing atmosphere, and a glassy or crystalline silicate compound is obtained. As a result, it is considered that it is concentrated and deposited on the surface layer. That is, it is estimated that the concentration of the sintering aid component in the sintered body after the heat treatment is high in the surface layer and low in the inside. By removing this surface oxide layer by grinding, the concentration of the sintering aid component inside the sintered body becomes lower than the initial concentration, and the heat resistance of the grain boundary layer is improved. It is considered that the high temperature strength of the steel is improved.

[0014]

【Example】

Examples 1 to 9 A silicon nitride-based compound prepared by adding 6% by weight each of Y ₂ O ₃ and Al ₂ O ₃ to silicon nitride powder was press-formed into a disk-shaped compact having a diameter of 50 mm and a thickness of 10 mm. Molded, under nitrogen atmosphere, 1780
Pressureless sintering was performed at ℃ for 3 hours.

The obtained sintered body was processed into 3.5 mm × 4.5 mm × 40 mm rod-shaped test pieces, and the rod-shaped test pieces were subjected to air circulation in Table 1.
The heat treatment was performed under the conditions shown in.

The entire surface of the sample after the heat treatment was ground and removed by the amounts shown in Table 1, and then the three-point bending strength was measured in the atmosphere at 1300 ° C. The results obtained are shown in Table 1.

[0017]

[Table 1]

Comparative Examples 1 to 7 For comparison, a sintered body sintered under the same conditions as those of the examples was used, and the conditions of the heat treatment in air and the amount of subsequent surface grinding removal were changed. Was evaluated. The results are also shown in Table 1.

[0019]

Industrial Applicability According to the method of the present invention, it is possible to produce a silicon nitride-based ceramic whose strength at a high temperature is significantly improved, and to use the silicon nitride sintered body as a high temperature structural member for industrial use. Is greatly expanded.

Claims (1)

[Claims] 1. A method of heat-treating a silicon nitride-based sintered body, which has been sintered by adding a sintering aid, at a temperature of 1300 to 1500 ° C. in an oxygen-containing atmosphere, and thereafter grinding and removing the surface layer of the sintered body. A method for strengthening a characteristic silicon nitride ceramics.