JPH0648849A - Ceramic composite material - Google Patents

Abstract

PURPOSE:To improve properties of the material as a high-temp. structural material by forming alpha-sialon layer between an Si3N4 ceramic layer and a beta- sialon ceramic layer. CONSTITUTION:Powders of Si3N4, Al2O3 and AlN are mixed to obtain Si5Al1O1 N7 compsn. or the like to prepare the source powder of beta-sialon. On the other hand, an Si3N4-base powder is prepared by adding and mixing about 5wt.% Y2O5 and about 4theta Al2O3 to an Si3N4 powder. Then the beta-sialon source powder and Si3N4-base powder are successively supplied in a press-molding die and pressed to obtain a two-layer molded body consisting of beta-sialon and Si3N4. Then, this molded body is sintered at abut 1800 deg.C for 2 hours in an N2 atmosphere and further treated by heating to form an alpha-sialon layer of 5-1000mum thickness between the Si3N4 ceramic layer and beta-sialon ceramic layer. Thus, the ceramic composite material is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic composite material particularly suitable as a high temperature structural material.

[0002]

2. Description of the Related Art Fine ceramics materials have various properties that conventional materials such as metals do not have, such as excellent heat resistance and wear resistance, and light weight. Therefore, they are applied as various structural materials. Is being done.

For example, a silicon nitride sintered body, which is known as a typical structural ceramic material, has characteristics such as excellent room temperature strength and excellent fracture toughness. Therefore, it is used for ball bearings and automobile engines. It has been put to practical use as a turbo rotor and the like. However, such excellent characteristics strongly depend on the additive added to the silicon nitride sintered body as a sintering aid, and at high temperatures, the grain boundary phase formed by the sintering aid softens. Therefore, the high temperature characteristics of silicon nitride are not always satisfactory.

On the other hand, β-sialon has almost no grain boundary phase as described above, so that it has less strength lowering at high temperature than a silicon nitride sintered body and has excellent high temperature resistance such as oxidation resistance. It has characteristics. However,
Silicon nitride is superior to β-sialon in terms of absolute strength and fracture toughness.

As described above, silicon nitride and β-sialon each have excellent characteristics as structural materials, but they also have drawbacks. Therefore, when used alone, there is a natural limitation. Therefore, in order to make the best use of the advantages of both silicon nitride and β-sialon and to complement their respective disadvantages, it has been attempted to use them in combination. As a method for forming a composite of silicon nitride and β-sialon, for example, silicon nitride powder and β-sialon can be used at the powder molding stage.
A method has been considered in which sialon powder is sequentially pressure-molded and the composite compact is sintered.

[0006]

However, in the conventional compounding method of silicon nitride and β-sialon as described above, even if compounding is performed from the powder molding stage, the difference in the coefficient of thermal expansion and the sintering There is a problem that thermal strain occurs due to the difference in shrinkage ratio in the above, and the strength level of the whole is lowered by residual stress, and further cracks occur between layers, leading to destruction. Further, if the conventional composite material of silicon nitride and β-sialon as described above is exposed to a high temperature atmosphere for a long time, solid-phase diffusion of composition elements occurs between silicon nitride and β-sialon, and the creep characteristics deteriorate. There was a problem that it was easy.

The present invention has been made in order to cope with such a problem, and suppresses deterioration of strength, high temperature characteristics and the like due to the compounding of silicon nitride and β-sialon, and makes each characteristic sufficiently. The object is to provide a ceramic composite material that can be exhibited.

[0008]

The ceramic composite material of the present invention is a ceramic composite material comprising a silicon nitride ceramic layer and a β-sialon ceramic layer, wherein an α-sialon layer is provided between the both ceramic layers. It is characterized by

The silicon nitride ceramic layer in the present invention comprises a rare earth element oxide, an alkaline earth element oxide,
A normal sintering agent containing aluminum oxide etc.
It is a Si ₃ N ₄ sintered layer, and the β-sialon ceramic layer also has a β-sialon phase represented by Si _6-z Al _z O _z N _8-z (0 <z ≤ 4.2) as the main phase. And the sintered layer. In the present invention, M _x is formed between the silicon nitride ceramic layer and the β-sialon ceramic layer.
An α-sialon layer represented by (Si, Al) ₁₂ (O, N) ₁₆ (M represents a rare earth element or an alkaline earth element, and x is 0 <x ≦ 2) or the like is provided. The α-sialon layer functions as a stress / composition relaxation layer between the silicon nitride ceramic layer and the β-sialon ceramic layer, and its thickness is preferably about 5 to 1000 μm. If the thickness of the α-sialon layer is less than 5 μm, the thermal stress due to the difference in thermal expansion coefficient between silicon nitride and β-sialon cannot be relaxed sufficiently, and the solid phase diffusion between both ceramic layers is not enough. Cannot be suppressed. Also, α-
Even if the sialon layer is formed to have a thickness of more than 1000 μm, no further effect can be obtained and the original composite properties may be impaired.

The ceramic composite material of the present invention comprises, for example, (a) silicon nitride compound powder (including a sintering aid component),
Raw powder of β-sialon (Si ₃ N ₄ -Al ₂ O ₃ -AlN
System, Si ₃ N ₄ -AlN-SiO ₂ system, etc., to form a mixed powder that satisfies the β-sialon composition, and synthetic β-sialon powder) to form multiple layers. After heat treatment 1 is performed to sinter both ceramic layers, second heat treatment is performed to form an α-sialon layer between both ceramic layers by solid phase diffusion.

[0011] (b) silicon nitride formulated powder, alpha-sialon of the raw material powder _{(Si 3 N 4 - Al 2} O 3 -AlN-MO -based, Si ₃ N ₄ -
Mixed powder that satisfies α-sialon composition by AlN-SiO ₂ -MO system, etc., synthetic α-sialon powder), and β
-The raw powder of sialon is molded so that it is laminated in order, and this composite compact is sintered. And the like.

In the method shown in (a) above, the first heat treatment is performed under conditions such that the Si ₃ N ₄ layer and the β-sialon layer can be sufficiently sintered. For example, the heat treatment is performed at a temperature of about 1600 to 1900 ° C. in a non-pressurized or pressurized atmosphere of an inert gas. The second heat treatment for forming the α-sialon layer by solid phase diffusion is performed under the condition that grain growth of both ceramic layers does not occur. For example,
Heat treatment is performed at a temperature of about 1500 to 1800 ° C for about 1 to 20 hours to solid-phase diffuse the constituent elements to form an α-sialon layer.

Further, in any of the above methods (a) and (b), various known molding methods such as a press molding method, a slip cast molding method and an injection molding method can be applied. Further, the sintering is not limited to non-pressurizing sintering and atmospheric pressure sintering, and for example, a hot pressing method, a hot isostatic pressing method (HIP) or the like can be applied.

The ceramic composite material of the present invention is
As shown in (a) and (b) above, it is basically based on multilayering at least silicon nitride and β-sialon from the powder molding stage, but silicon nitride and β-sialon were separately sintered. The subsequent joining by brazing or solid phase diffusion joining is not necessarily excluded. In this case, the α-sialon layer may be formed on at least one surface in advance, or may be formed by solid phase diffusion after bonding.

[0015]

In the ceramic composite material of the present invention, the α-sialon layer is provided between the silicon nitride ceramic layer and the β-sialon ceramic layer. Here, since α-sialon has an intermediate coefficient of thermal expansion between silicon nitride and β-sialon, the residual stress due to the difference in thermal expansion coefficient between both ceramic layers is relaxed by the α-sialon layer, A good composite state is obtained. In addition, the generation of interlayer cracks due to thermal stress is also suppressed. Since these can prevent the strength level of the composite material from being lowered, a healthy ceramic composite material having the original characteristics of the silicon nitride ceramic layer and the β-sialon ceramic layer can be obtained. Further, even when it is held at a high temperature, the α-sialon layer functions as a composition relaxation layer of both ceramic layers, so that diffusion between both ceramic layers becomes extremely slow, and high temperature deformation resistance such as creep increases.

[0016]

EXAMPLES The present invention will be described below with reference to examples.

Example 1 First, Si ₃ N ₄ , Al ₂ O ₃ and AlN powders were replaced with Si ₅
Mix so that the composition of Al ₁ O ₁ N ₇ (z = 1) is satisfied, and β
-A raw powder of sialon was prepared. On the other hand, the Si ₃ N ₄ powder, Y ₂ O ₃ were mixed added 5 wt% and the Al ₂ O ₃ 4% by weight, to prepare a Si ₃ N ₄ Formulation powder.

Next, the above β-sialon raw material powder and
After filling the Si ₃ N ₄ compounded powder in the press mold in order, it was pressurized to prepare a two-layer compact of β-sialon and Si ₃ N ₄ . Then, the two-layer molded body was subjected to 1800 ° C in an N ₂ atmosphere.
The composite sintered body was produced by firing under the condition of 2 hours. After this, the composite sintered body was heated to 1750 ° C in N ₂ atmosphere ×
The heat treatment was performed for 2 hours.

When the crystal phase of the ceramic composite material thus obtained was identified by X-ray diffraction, as shown in FIG. 1, between the Si ₃ N ₄ ceramic layer 1 and the β-sialon ceramic layer 2, It was confirmed that the α-sialon layer 3 was formed. The α-sialon layer 3 was continuously formed with a thickness of about 20 μm.

The characteristics of the ceramic composite material were evaluated as follows. First, arrange so that only the β-sialon ceramic layer 2 is oxidized, and 1400 ° C ×
When the oxidation resistance test was carried out under the condition of 100 hours, the β-sialon ceramic layer 2 was hardly oxidized, and the Si ₃ N ₄ ceramic layer 1 on the back side was not changed at all. As shown in FIG. 2, the Si ₃ N ₄ ceramics layer 1 was placed on the 3-point bending jig so that it was on the lower side, and a load was applied from the β-sialon ceramics layer 2 side to conduct a 3-point bending test. When it was performed at room temperature, it showed a high strength of 1000 MPa, which was equivalent to the so-called silicon nitride sintered body.

Example 2 β-sialon raw material powder prepared in Example 1 and Si ₃ N ₄
Formulated powder and synthetic α-sialon powder (Y ₁ (Si, Al)
₁₂ (O, N) ₁₆ ) was used to prepare a molded body having a three-layer structure of β-sialon / α-sialon / Si ₃ N ₄ . Then, this three-layer molded body was subjected to 1800 ° C. in an N ₂ atmosphere.
Baking was performed for 2 hours to obtain a ceramic composite material.

The ceramic composite material thus obtained was analyzed and evaluated in the same manner as in Example 1. As in Example 1, β-sialon layer / α-sialon layer / Si ₃ N
It was confirmed that it had a three-layer structure of _four layers. Also, α
-The sialon layer was continuously formed with a thickness of about 500 μm.

The characteristics of the above ceramic composite material were measured in the same manner as in Example 1.
Only 0.05 mg / cm ^{2 of} β-sialon layer is oxidized,
The 3-point bending test showed high strength of 950 MPa.

Comparative Example 1 β-sialon raw material powder prepared in Example 1 and Si ₃ N ₄
A β-sialon / Si ₃ N ₄ two-layer compact was prepared using the blended powder, and then sintered in an N ₂ atmosphere at 1800 ° C. for 0.2 hours to obtain a composite sintered body. When this composite sintered body was analyzed and evaluated in the same manner as in Example 1, only two layers of the β-sialon layer and the Si ₃ N ₄ layer were formed, and no α-sialon layer was formed at the interface. When the 3-point bending strength of this composite sintered body was measured in the same manner as in Example 1, it was found to be 620 MPa, which was a strength deterioration. This is the β-sialon layer and Si
_It is considered that fine cracks were generated at the interface with the ₃ N ₄ layer due to thermal stress.

As described above, in the ceramic composite materials according to the respective examples, since the α-sialon layer is formed between the β-sialon layer and the Si ₃ N ₄ layer, the strength reduction due to the thermal stress can be suppressed. Therefore, the original strength of Si ₃ N ₄ can be stably obtained. This allows
It is possible to provide a ceramic composite material having excellent heat resistance and oxidation resistance and high strength with good reproducibility.

[0026]

As described above, according to the present invention, α
-Since the sialon layer is provided between the β-sialon ceramic layer and the silicon nitride ceramic layer as a stress / composition relaxation layer, it is possible to suppress the deterioration of strength and high temperature characteristics due to compounding. It is possible to provide a ceramic composite material capable of sufficiently exhibiting each property with good reproducibility. According to the present invention, it is possible to provide a ceramic composite material particularly suitable as a high temperature structural material.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing the structure of a ceramic composite material according to an embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement state in a three-point bending test carried out in an example of the present invention.

[Explanation of symbols]

1 …… Si ₃ N ₄ ceramics layer 2 …… β-sialon ceramics layer 3 …… α-sialon layer

Claims (1)

[Claims] 1. A ceramic composite material comprising a silicon nitride ceramic layer and a β-sialon ceramic layer, wherein an α-sialon layer is provided between the both ceramic layers.