JPS6230678A - Manufacture of high strength silicon nitride base ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing high-strength silicon nitride ceramics, and more specifically, the present invention relates to a method for producing high-strength silicon nitride ceramics, and more specifically, sintering a silicon nitride sintered body by high-temperature surface oxidation and rapid cooling. The present invention relates to a method for manufacturing high-strength silicon nitride ceramics strengthened by forming large compressive stress on the body surface.

[Conventional technology]

Silicon nitride ceramics have attracted attention as structural ceramic materials for automobile engine parts and other parts from the viewpoint of heat resistance, strength, and impact resistance, and some have already been put into practical use.

Conventionally, as a method for improving the strength of silicon nitride sintered materials, it has been proposed to select appropriate raw materials and use appropriate sintering aids (for example, Japanese Patent Application Laid-Open No. 59-19027
Publication No. 1, Publication No. 59-190272, Publication No. 59-19
No. 0273, Special Publication No. 4B-7486, No. 5
2-3647).

[Problem that the invention seeks to solve]

The bending strength of the (silicon nitride) ceramic according to the above proposal is less than 90 kg/Im2, and it cannot be said to be a material with sufficient reliability as an automobile part used under high stress.

Furthermore, since silicon nitride exists on the surface of these materials, there is a problem in that the materials are corroded by decomposition of 5iJ4 in a high-temperature steam atmosphere.

[Means and effects for solving the problems] In order to solve the above problems, the present invention provides silicon nitride as a main component, with the addition of a sintering aid containing an oxide, molded and sintered. Silicon ceramics are treated in a high-temperature oxidizing atmosphere to form a surface oxide film, and then rapidly cooled to strengthen them.

Here, silicon nitride ceramics are silicon nitride (Si)
Indicates a material containing 50% by weight or more of J4). Other than silicon nitride, various oxides such as zirconia and lanthania can be included. One type or two or more types of sintering aids can be added, and in addition to oxides such as aluminum oxide, magnesium oxide, yttrium oxide, and zirconium oxide, nitrides, oxynitrides, etc. may also be used in combination. .

Molding and sintering can be carried out by conventional methods.

When silicon nitride ceramic is treated in a high IIAL oxidation atmosphere to form a surface oxide film, silicon nitride (SizN4) is converted to silicon oxide (Si
z) and volumetric expansion occurs, compressive pressure is applied to the surface layer of the sintered body to improve its strength.

Further, since an oxide film exists on the surface, silicon nitride does not decompose and the material is not corroded even in an atmosphere of high temperature steam or oxygen. As a treatment condition, for example, in the atmosphere9
The temperature is 50 to 1500°C for 130 minutes to 10 hours. Through this process, the -e range is from submicron to 100μ.
A surface oxide film with a thickness of m is formed.

In the present invention, in order to improve the strength, the temperature range in which the viscosity of the grain boundary layer decreases and the creep phenomenon occurs, generally, is
Residual compressive stress is generated near the surface of the sintered body by rapidly cooling it from a temperature of 950° C. or higher. Moreover, by rapidly cooling from a high temperature, in addition to the above-mentioned effects, the high-temperature crystal phase is maintained as it is, and when used at a lower temperature, deterioration is reduced. Note that the rapid cooling is preferably performed by forced air cooling. The cooling rate is 4″/
min to 100@/min is preferable.

〔Example〕

±Upper comparison) SiJa 92″t%, Yz'034wt%, MgA1
After mixing zO44L% and press molding, 1750'CX
It was fired in an N2 atmosphere for 3 hours and processed with a 300mm diamond grindstone to create a 3 x 4 x 4 Q am test piece.

The strength of this test piece was determined by conducting a three-point bending test under the conditions of a span of 30 m and a loading rate of 0.5 van/min. Its strength was 71 kg/mm2.

Next, the test piece made in the same manner as above was
After heating in the air at 0°C for 3 hours, it was allowed to cool in the furnace to 100°C over about 10 hours.

This test piece was subjected to the same test as above to determine its strength, which was found to be 102 kg/am2.

Anal Si, N492″t%, Y2O34L%, M8A I□
044'''t% mixed and press molded at 1750°C.
Fired in N2 atmosphere for 3 hours, processed with a 300 diamond l° grindstone, 3 x 4 x 4 Q m+
A test piece of m was prepared.

This test piece was heated at 1300°C for 3 hours in the air, and then compressed air was applied to the test piece to cool it rapidly from 1300°C to 100°C in about 2 minutes.

Using this method, the reheating temperature and time after firing were performed under various conditions shown in Table 1 below, and the strengths were compared. The strength test was conducted under the same conditions as in Example 1.

The results are summarized in Table 1 below. Table 1 also shows the results of Example 1 for comparison.

Table 1 □ Flame Yu5i3N4904%, Y2O35't%, Al2O35
After mixing wL% and press molding, 1750°C x 3 hours N
It was fired in two atmospheres, processed with a 300mm diamond grindstone, and made into a 3X4X40mm test piece.

This processed test piece was heat treated in the same manner as in Example 2,
A strength test similar to Example 1 was conducted. Also, for comparison,
The strength of test pieces that were only fired and processed without being reheated or rapidly cooled was determined.

The results are shown in Table 2 below.

2nd table flame ↓ 5iJ4921'L%, Y2O:l4t%, MgA
1750℃ after press molding.
It was fired in an N2 atmosphere for 3 hours and processed with a 300mm diamond grindstone to create a 3 x 4 x 40 x* test piece.

After heating this test piece in an air atmosphere at 1300°C x 3 hours, the cooling rate from 1300°C was varied and the effects were compared. The results are shown in Table 3 below. The strength was measured under the same conditions as in Example 1.

Table 3 [Effects of the Invention] As is clear from the above explanation, according to the present invention, silicon nitride ceramics containing silicon nitride as a main component, adding a sintering aid, and sintered can be rapidly cooled after high-temperature oxidation treatment. This provides high-strength silicon nitride ceramics that have greatly improved strength, especially bending strength, and are resistant to water or oxygen corrosion.

Claims (1)

[Claims] 1. Silicon nitride ceramics whose main component is silicon nitride, with the addition of sintering aids containing oxides, molded, and sintered are treated in a high-temperature oxidizing atmosphere to form a surface oxide film, and then rapidly cooled. A method for producing high-strength silicon nitride ceramics characterized by: