JPH05194060A - Silicon nitride ceramic part - Google Patents

Abstract

PURPOSE:To obtain a Si3N4 ceramic part having an excellent mechanical strength at a low cost by cutting a Si3N4 ceramic sintered product produced by an ordinary pressure sintering method and thermally treating the cut product at the sintering temperature to a glass-softening temperature. CONSTITUTION:A Si3N4 ceramic sintered product obtained by an ordinary pressure sintering method is cut into a desired shape. The processed product is thermally treated at a temperature which is lower than the above-mentioned sintering temperature and which is higher than the softening temperature of the glass phase. The glass phase contains a sintering auxiliary preliminarily added, and the sintering auxiliary is preferably one kind or more of Y2O3, Al2O3 and AlN. The sintering temperature of the sintering auxiliary is preferably approximately 800 deg.C, and the above-mentioned thermal treatment temperature is preferably 800-1100 deg.C for preventing the proceeding of the oxidation of the sintered product. Thereby, an oxidation film-protecting layer comprising an extremely thin SiO2 is formed on the surface of the sintered product, and a Si3N4 ceramic part having an average flexure-resistant strength of >=105kg/mm<2> measured by bending 25 arbitrarily extracted test pieces at three points, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride ceramic part, and more particularly to a silicon nitride ceramic part obtained by pressureless sintering which is excellent in mechanical strength.

[0002]

2. Description of the Related Art Conventionally, for example, when a product such as a bearing or a ball bearing that requires high accuracy is manufactured by using a ceramics sintered body, a product larger than the final size is manufactured with relatively low accuracy. It has been performed that a ceramic sintered body obtained in this way is molded and fired, and is ground to a final shape.

[0003]

However, in the ceramic component manufactured by such a method, micro sharp-angled notches are generated in the grinding process, and therefore the mechanical strength is lowered and desired characteristics are obtained. There was a problem that I could not.

In particular, when a component made of a silicon nitride ceramics sintered body is used as such a ceramic component required to have high mechanical strength, a sintered structure having a dense structure and a density close to an ideal density is obtained. A hot press was used as a binding method.

However, although the silicon nitride ceramics sintered body sintered by hot pressing has high mechanical strength, it has been difficult to form it into a complicated shape. Further, the hot pressing performed under high temperature and high pressure requires a special furnace for exclusive use of equipment, the cost is high, and a better method has been desired.

On the other hand, a silicon nitride ceramics sintered body sintered by atmospheric pressure can easily be made into a complicated shape, but has a mechanical strength of less than 100 kg / mm ² .

The present invention has been made in view of the above-mentioned conventional drawbacks, and has a mechanical strength equivalent to that of a silicon nitride ceramics sintered body sintered by hot pressing, and easily formed into a complicated shape. It is an object of the present invention to provide a ceramic part made of a silicon nitride-based ceramics sintered body that is sintered by atmospheric pressure sintering and that can reduce the cost.

[0008]

The silicon nitride ceramic part of the present invention is at least 2 arbitrarily extracted from a silicon nitride ceramic sintered body obtained by pressureless sintering.
When the bending strength of five samples is measured by three-point bending, the average is 105 kg / mm ² or more.

Further, in the silicon nitride ceramics component of the present invention, a silicon nitride ceramics sintered body obtained by pressureless sintering is ground into a predetermined shape, Is a silicon nitride-based ceramic component obtained by heat treatment at a low temperature and at a temperature higher than the softening temperature of the glass phase.

The glass phase existing in the silicon nitride ceramics part in the present invention is selected from yttrium oxide, aluminum oxide and aluminum nitride, which are sintering aids added in advance when producing a silicon nitride ceramics sintered body. It is composed of one kind or two or more kinds.

The heat treatment temperature in the present invention needs to be 800 ° C. or higher which is the softening point of yttrium oxide, aluminum oxide and aluminum nitride, which are the glass phases of the silicon nitride ceramics sintered body. Further, the temperature at which the oxidation of the silicon nitride-based ceramics sintered body hardly proceeds even in the presence of oxygen such as in the air needs to be 1100 ° C. or less.

The heat treatment time is preferably 1 to 24 hours, but when the heat treatment temperature is low, the heat treatment time is long, and when the heat treatment temperature is high, the heat treatment time is short. There is. Generally, as for the quality of the product, the lower heat treatment temperature and longer heat treatment time are better than those having higher heat treatment temperature and shorter heat treatment time.

[0013]

According to the present invention, the microscopic acute-angled notch formed during the grinding process is rounded by the heat treatment. An extremely thin oxide film layer of submicron made of silicon dioxide is formed on the surface of the silicon nitride ceramics component obtained by pressureless sintering to protect the surface of the silicon nitride ceramics component. Due to these interactions, the mechanical strength of silicon nitride ceramic parts is further improved,
It is possible to obtain a silicon nitride ceramics component having mechanical strength equivalent to that of the conventional silicon nitride ceramics component obtained by hot pressing.

[0014]

EXAMPLES Examples of the present invention will be described below. Example 1 Si ₃ N ₄ 100 parts by weight Y ₂ O ₃ 5 parts by weight AlN 3 parts by weight Al ₂ O ₃ 3 parts by weight A binder was added to the above-mentioned mixed powder and pressure-molded into a flat plate, and the mixture was molded at 700 ° C. for 3 days. After degreasing for 1 hour, at normal pressure 1750 ° C
And sintered for 3 hours to obtain a flat plate-shaped silicon nitride ceramics sintered body of 100 mm × 100 mm × 12 mm.

Then, as a final finish of this flat plate-shaped silicon nitride ceramics sintered body, a diamond disk having a grain size of # 400 was used to cut into 3 mm × 4 mm × 40 mm to prepare a square rod-shaped test sample, 24 of which were sampled The bending strength was measured as it was by three-point bending at a gauge length of 20 mm (Comparative Example 1), and the remaining 25 samples were subjected to 100 in air.
After heat treatment at 0 ° C. for 2 hours, the bending strength was measured under the same conditions (Example 1). The results are shown in Table 1.

[0016]

[Table 1] Further, these Weibull distributions were as shown in FIG. 1 (Example 1) and FIG. 2 (Comparative Example 1). Example 2 Si ₃ N ₄ 100 parts by weight Y ₂ O ₃ 5 parts by weight Al ₂ O ₃ 2 parts by weight After adding a binder to the above mixed powder and press-molding it into a flat plate shape, and degreasing at 700 ° C. for 3 hours , 1750 ℃ at normal pressure
And sintered for 3 hours to obtain a flat plate-shaped silicon nitride ceramics sintered body of 100 mm × 100 mm × 12 mm.

Next, as a final finish of this flat plate-shaped silicon nitride ceramics sintered body, a diamond disk having a grain size of # 600 was used to cut into 3 mm × 4 mm × 40 mm to prepare square bar-shaped test samples, of which 6 samples were prepared. The bending strength was measured as it was by bending at three points with a gauge length of 20 mm (Comparative Example 2), and the remaining 25 samples were measured in air at 1000
After heat-treating at ℃ for 2 hours, the bending strength was measured under the same conditions (Example 2). The results are shown in Table 2.

[0018]

[Table 2] Moreover, these Weibull distributions were as shown in FIG. 3 (Example 2) and FIG. 4 (Comparative Example 2).

[0019]

As is apparent from the above, the silicon nitride ceramics component obtained by pressureless sintering according to the present invention has a very large mechanical strength, even though it is ground. It can be advantageously used for structural parts such as bearings and bearings.

Since it is not necessary to perform heat treatment in a non-oxidizing atmosphere (nitrogen atmosphere, inert atmosphere, etc.) as in the conventional case, the heat treatment is easy and the cost can be reduced because the atmosphere is used. .

Further, since the sintered body used for the silicon nitride ceramics part is sintered by pressureless sintering, equipment such as a furnace can be simplified and the cost can be reduced as compared with the case of sintering by hot pressing. This made it easier to maintain.

[Brief description of drawings]

FIG. 1 is a graph showing a Weibull distribution according to a first embodiment of the present invention.

FIG. 2 is a graph showing a Weibull distribution of Comparative Example 1 of the present invention.

FIG. 3 is a graph showing a Weibull distribution according to a second embodiment of the present invention.

FIG. 4 is a graph showing a Weibull distribution of Comparative Example 2 of the present invention.

Claims (6)

[Claims] 1. An average of 105 kg / mm ² or more when the bending strength of at least 25 samples arbitrarily extracted from a silicon nitride ceramics sintered body obtained by pressureless sintering is measured by three-point bending. A silicon nitride-based ceramic part characterized by the above. 2. A silicon nitride ceramics sintered body obtained by pressureless sintering is ground into a predetermined shape, and the glass phase thereof is lower than the sintering temperature of the silicon nitride ceramics sintered body. The silicon nitride ceramics component according to claim 1, which is heat-treated at a temperature higher than the softening temperature of. 3. The silicon nitride ceramics component according to claim 1 or 2, wherein the glass phase present in the silicon nitride ceramics component is a glass phase comprising a sintering additive added in advance. 4. The silicon nitride ceramic part according to claim 3, wherein the sintering aid is one or more selected from yttrium oxide, aluminum oxide and aluminum nitride. 5. The silicon nitride ceramics component according to claim 1, which has an oxide film layer made of extremely thin silicon dioxide on the surface. 6. The silicon nitride-based ceramic component according to claim 1, wherein the heat treatment temperature is 800 to 1100 ° C.